reproductive system, causing the uterus to grow in preparation for nurturing an embryo. It enlarges the breasts to prepare them for nursing. It stimulates the brain to increase interest in sexual activity. And it stimulates the pituitary gland to release another hormone that causes a mature egg to be released by the ovary for fertilization. In males, sex organs called testes secrete testosterone, one of several sex hormones known as androgens. Androgens stimulate the maturation of sperm, increase a male’s motivation for sexual activity, and increase his aggressiveness THE ENDOCRINE SYSTEM The endocrine and nervous systems work together to act as a communication system for the human body. The endocrine system acts as a communication tool within the human body, working in tandem with the nervous system to communicate with the body’s other internal systems. Both the nervous and endocrine systems send messages everywhere inside the human body. These messages allow your heart to beat, your lungs to breathe in air, and your mind to make decisions. In the nervous system, signals travel very quickly, leading to instantaneous responses. However, within the endocrine system, signals move slowly but last longer. CHARCTERISTICS OF ENDOCRINE GLANDS The endocrine system is basically a group of glands called endocrine glands that secrete hormones into the internal environment of our body. Hormones diffuse from the interstitial fluid into the bloodstream, and act on target cells. There are other glands that secrete substances into the estrogen internal environment, they are not technically hormones but they function like messenger molecules that are often times referred to as \"local hormones\". These glands are paracrine secretions and autocrine secretions. The endocrine system is made up of glands that produce and secrete hormones, chemical substances produced in the body that regulate the activity of cells or organs. These hormones regulate the body's growth, metabolism (the physical and chemical processes of the body), and sexual development and function. The hormones are released into the bloodstream and may affect one or several organs throughout the body. Hormones are chemical messengers created by the body. They transfer information from one set of cells to another to coordinate the functions of different parts of the body. Paracrine secretions enter the interstitial fluid but affect only the neighboring cells, and autocrine secretions affect only the secreting cell itself. Exocrine glands secrete another category of substances. The substances enter tubes or ducts that lead to body surfaces. So, remember that exocrine glands secrete substances externally whereas endocrine glands secrete hormones internally. Examples of the substances that exocrine glands secrete are sweat being released at the skin's surface and stomach acid reaching the lumen of the digestive tract. 50 CU IDOL SELF LEARNING MATERIAL (SLM)
Endocrine glands and the hormones they secrete help to regulate metabolic processes. They help to regulate water balance, electrolyte balance, and blood pressure. Let's not forget that endocrine hormones are also vital roles in reproduction, development and growth. The largest and most vital endocrine glands that will be covered in this chapter are the pituitary gland, thyroid gland, parathyroid glands, adrenal glands and the pancreas. Figure 4.1.: Endocrine System TYPES OF ENDOCRINE GLANDS There are eight major endocrine glands, each with a different function. Hypothalamus The hypothalamus is a part of the brain that secretes hormones that regulate body temperature and metabolism. The hypothalamus is located in the lower central part of the brain. This part of the brain is important in regulation of satiety, metabolism, and body temperature. In a Hypothalamus releasing hormones signal secretion of stimulating hormones. The hypothalamus also secretes a hormone called somatostatin, which causes the pituitary gland to stop the release of growth hormone. Pituitary Gland The pituitary gland produces hormones that control many of the other endocrine organs. 51 CU IDOL SELF LEARNING MATERIAL (SLM)
The pituitary gland is located at the base of the brain beneath the hypothalamus and is no larger than a pea. It is often considered the most important part of the endocrine system because it produces hormones that control many functions of other endocrine glands. When the pituitary gland does not produce one or more of its hormones or not enough of them, it is called hypopituitarism. The pituitary gland is divided into two parts: the anterior lobe and the posterior lobe. The anterior lobe produces the following hormones, which are regulated by the hypothalamus: • Growth hormone: Stimulates growth of bone and tissue (Growth hormone deficiency results in growth failure. Growth hormone deficiency in adults results in problems in maintaining proper amounts of body fat and muscle and bone mass. It is also involved in emotional well-being.) • Thyroid-stimulating hormone (TSH): Stimulates the thyroid gland to produce thyroid hormones (A lack of thyroid hormones either because of a defect in the pituitary or the thyroid itself is called hypothyroidism.) • Adrenocorticotropin hormone (ACTH): Stimulates the adrenal gland to produce several related steroid hormones • Luteinizing hormone (LH) and follicle-stimulating hormone (FSH): Hormones that control sexual function and production of the sex steroids, estrogen and progesterone in females or testosterone in males • Prolactin: Hormone that stimulates milk production in females The posterior lobe produces the following hormones, which are not regulated by the hypothalamus: • Antidiuretic hormone (vasopressin): Controls water loss by the kidneys • Oxytocin: Contracts the uterus during childbirth and stimulates milk production The hormones secreted by the posterior pituitary are actually produced in the brain and carried to the pituitary gland through nerves. They are stored in the pituitary gland. Thyroid Gland The brain's growth and development is controlled by the thyroid gland. The thyroid gland is located in the lower front part of the neck. It produces thyroid hormones that regulate the body's metabolism. It also plays a role in bone growth and development of the brain and nervous system in children. The pituitary gland controls the release of thyroid hormones. Thyroid hormones also help maintain normal blood pressure, heart rate, digestion, muscle tone, and reproductive functions. Parathyroid Glands 52 CU IDOL SELF LEARNING MATERIAL (SLM)
The parathyroid glands are two pairs of small glands embedded in the surface of the thyroid gland, one pair on each side. They release parathyroid hormone, which plays a role in regulating calcium levels in the blood and bone metabolism. Adrenal Glands Adrenal glands regulate your body's metabolism, immune system, and sexual functions. The two adrenal glands are triangular-shaped glands located on top of each kidney. The adrenal glands are made up of two parts. The outer part is called the adrenal cortex, and the inner part is called the adrenal medulla. The outer part produces hormones called corticosteroids, which regulate the body's metabolism, the balance of salt and water in the body, the immune system, and sexual function. The inner part, or adrenal medulla, produces hormones called catecholamines (for example, adrenaline). These hormones help the body cope with physical and emotional stress by increasing the heart rate and blood pressure. Pineal Body The pineal body, or pineal gland, is located in the middle of the brain. It secretes a hormone called melatonin, which may help regulate the wake-sleep cycle of the body. Reproductive Glands The reproductive glands are the main source of sex hormones. In males, the testes, located in the scrotum, secrete hormones called androgens; the most important of which is testosterone. These hormones affect many male characteristics (for example, sexual development, growth of facial hair and pubic hair) as well as sperm production. In females, the ovaries, located on both sides of the uterus, produce estrogen and progesterone as well as eggs. These hormones control the development of female characteristics (for example, breast growth), and they are also involved in reproductive functions (for example, menstruation, pregnancy). Pancreas The pancreas is an elongated organ located toward the back of the abdomen behind the stomach. The pancreas has digestive and hormonal functions. One part of the pancreas, the exocrine pancreas, secretes digestive enzymes. The other part of the pancreas, the endocrine pancreas, secretes hormones called insulin and glucagon. These hormones regulate the level of glucose (sugar) in the blood. The HPA axis The hypothalamic-pituitary-adrenal axis (HPA or HTPA axis) is a complex set of direct influences and feedback interactions among the hypothalamus, the pituitary gland, and the adrenal glands. The interactions among these glands constitute the HPA axis, a major part of the neuroendocrine system that controls reactions to stress and regulates many body processes, including digestion, the immune system, mood and emotions, sexuality, and energy storage 53 CU IDOL SELF LEARNING MATERIAL (SLM)
and expenditure. While steroid hormones are produced mainly in vertebrates, the physiological role of the HPA axis and corticosteroids in stress response is so fundamental that analogous systems can be found in invertebrates and monocellular organisms as well. FUNCTIONS OF ENDOCRINE SYSTEM Endocrine System and Stress The hypothalamic-pituitary-adrenal axis regulates stress in vertebrates. Stress is the simple name for what happens when the body’s emergency response is activated; a stressful event is one that activates the sympathetic (fight-or-flight) nervous system. Because it elevates arousal, heart rate, and breathing, stress is useful for helping animals and humans escape dangerous situations; however, it can damage the body to be under stressful conditions for too long. The HPA and Stress Stressors can come in many forms, from immediate physical threats like an angry bear, to social threats like an angry friend. In experimental studies in rats, a distinction is often made between social stress and physical stress, but both types activate the HPA axis, albeit through different pathways. The hypothalamic-pituitary-adrenal (HPA or HTPA) axis is a complex set of direct influences and steroid-producing feedback interactions among the hypothalamus, the pituitary gland, and the adrenal glands. All vertebrates have an HPA, but the steroid- producing stress response is so important that even invertebrates and monocellular organisms have analogous systems. The HPA is important to psychology because it is intimately involved with many mood disorders involving stress, including anxiety disorder, bipolar disorder, insomnia, PTSD, borderline personality disorder, ADHD, depression, and many others. Antidepressants work by regulating the HPA axis. The Function of the HPA Axis The hypothalamus contains neurons that synthesize and secrete vasopressin and corticotropin-releasing hormone (CRH). These two hormones travel through blood to the anterior pituitary, where they cause the secretion of stored adrenocorticotropic hormone (ACTH). The ACTH acts on the adrenal cortex, which produces steroids—in humans, primarily the steroid cortisol. This causes a negative feedback cycle in which the steroids inhibit the hypothalamus and the pituitary gland, and it also causes the adrenal gland to produce the hormones epinephrine (also known as adrenaline) and norepinephrine. Cortisol, Stress, and Health In the process described above, the HPA axis ultimately produces cortisol. Studies on people show that the HPA axis is activated in different ways during chronic stress—depending on the type of stressor, the person’s response to the stressor, and other factors. Stressors that are 54 CU IDOL SELF LEARNING MATERIAL (SLM)
uncontrollable, threaten physical integrity, or involve trauma tend to have a high, flat profile of cortisol release (with lower-than-normal levels of cortisol in the morning and higher-than- normal levels in the evening) resulting in a high overall level of daily cortisol release. On the other hand, controllable stressors tend to produce higher-than-normal morning cortisol. Stress hormone release tends to decline gradually after a stressor occurs. In post-traumatic stress disorder there appears to be lower-than-normal cortisol release, and it is thought that a blunted hormonal response to stress may predispose a person to develop PTSD. There is growing evidence that prenatal stress can affect HPA regulation in humans. Children who were stressed prenatally may show altered cortisol rhythms. For example, several studies have found an association between maternal depression during pregnancy and childhood cortisol levels. Prenatal stress has also been implicated in a tendency toward depression and short attention span in childhood. However, there is no clear indication that HPA dis- regulation caused by prenatal stress can alter adult behavior. Endocrine System and Hunger Hunger is divided into long-term and short-term regulation, each stimulating different hormone responses from the hypothalamus. Hunger is the set of physical and psychological sensations that arise when food is needed by the body. It appears to increase activity and movement in many animals; this response may increase an animal’s chances of finding food. Food consumption (particularly overconsumption) can result in weight gain, whereas insufficient consumption, or malnutrition, will cause significant weight and motivational energy loss. Hunger is controlled by the hypothalamus and hormones. It is regulated over both the long term and the short term. Hormones The physical sensation of hunger comes from contractions of the stomach muscles. These contractions are believed to be triggered by high concentrations of the hormone ghrelin. Two other hormones, peptide YY and leptin, cause the physical sensations of being full. Ghrelin is released if blood sugar levels get low, a condition that can result from going long periods without eating. Hypothalamus The hypothalamus regulates the body’s physiological homeostasis. When you are dehydrated, freezing, or exhausted, the appropriate biological responses are activated automatically: body fat reserves are utilized, urine production is inhibited, and blood is shunted away from the surface of the body. The drive to eat, or drink water, or seek warmth is activated. In the 1940s, the “dual-center” model, which divided the hypothalamus into hunger (lateral hypothalamus) and satiety (ventromedial hypothalamus) centers, was popular. This theory developed from the findings that bilateral lesions of the lateral hypothalamus can cause anorexia, a severely diminished appetite for food, while bilateral lesions on the ventromedial 55 CU IDOL SELF LEARNING MATERIAL (SLM)
hypothalamus can cause overeating and obesity. Recently, further study has called the dual- center model into question, but the hypothalamus certainly does play a role in hunger. Figure 4.2.: Hypothalamus: The hypothalamus is the region of the forebrain below the thalamus that forms the basal portion of the diencephalon. It regulates body temperature and some metabolic processes, and governs the autonomic nervous system. Long-Term Hunger Regulation The long-term regulation of hunger prevents energy shortfalls and is concerned with the regulation of body fat. Leptin, a hormone secreted exclusively by adipose cells in response to an increase in body-fat mass, helps regulate long-term hunger and food intake. Leptin serves as the brain’s indicator of the body’s total energy stores. The function of leptin is to suppress the release of neuropeptide Y (NPY), which in turn prevents the release of appetite-enhancing orexins from the lateral hypothalamus. This decreases appetite and food intake, promoting weight loss. Though rising blood levels of leptin do promote weight loss to some extent, its main role is to protect the body against weight loss in times of nutritional deprivation. Short-Term Hunger Regulation The short-term regulation of hunger deals with appetite and satiety. It involves neural signals from the GI tract, blood levels of nutrients, and GI-tract hormones. Neural Signals from the GI Tract The brain can evaluate the contents of the gut through vagal nerve fibers that carry signals between the brain and the gastrointestinal (GI) tract. Studies have shown that the brain can sense differences between macronutrients through these vagal nerve fibers. Stretch receptors (mechanoreceptors that respond to an organ being stretched or distended) work to inhibit appetite when the GI tract becomes distended. They send signals along the vagus nerve afferent pathway and ultimately inhibit the hunger centers of the hypothalamus. Nutrient Signals Blood levels of glucose, amino acids, and fatty acids provide a constant flow of information to the brain that may be linked to regulating hunger and energy intake. Nutrient signals 56 CU IDOL SELF LEARNING MATERIAL (SLM)
indicate fullness. They inhibit hunger by raising blood glucose levels, elevating blood levels of amino acids, and affecting blood concentrations of fatty acids. Hormonal Signals Hormones can have a wide range of effects on hunger. The hormones insulin and cholecystokinin (CCK) are released from the GI tract during food absorption and act to suppress feelings of hunger. However, during fasting, glucagon and epinephrin levels rise and stimulate hunger. When blood sugar levels fall, the hypothalamus is stimulated. Ghrelin, a hormone produced by the stomach, triggers the release of orexin from the hypothalamus, signaling to the body that it is hungry. Starvation Starvation is a severe deficiency in caloric energy, nutrient, and vitamin intake. It is the most extreme form of malnutrition. Prolonged starvation can cause permanent organ damage and, untreated, leads to death. Individuals experiencing starvation lose substantial fat and muscle mass, called catabolysis, when the body breaks down its own fat and muscle for energy. Vitamin deficiency, diarrhea, skin rashes, edema, and heart failure are also common results of starvation. In a state of starvation, other motivators—such as the desire for sleep, sex, and social activities— decrease. Individuals suffering from starvation may experience irritability, lethargy, impulsivity, hyperactivity, and more apathy over time. SUMMARY 1. The endocrine system is a network of glands and organs located throughout the body. It’s similar to the nervous system in that it plays a vital role in controlling and regulating many of the body’s functions. 2. The endocrine system acts as a communication tool for the human body, working in tandem with the nervous system to communicate with the body’s other internalsystems. 3. The endocrine system is a chemical messenger system comprising feedback loops of the hormones released by internal glands of an organism directly into the circulatory system, regulating distant target organs. In humans, the major endocrine glands are the thyroid gland and the adrenal glands. 4. The endocrine system differs from the nervous system in that its chemical signals are slower-moving and longer-lasting. 5. Hormones act as chemical messengers within the body, telling it to perform specific physical and mental functions. 6. Some examples of bodily functions that are controlled by the endocrine system include: metabolism, growth and development, sexual function and reproduction, heart rate, blood pressure, appetite, sleeping and waking cycles and body temperature. 7. There are eight major endocrine glands, each performing a different function: the pituitary gland, the thyroid, the thymus gland, the adrenal gland, the ovaries (female) and testes (male), the pancreatic islets, and the pineal gland. 57 CU IDOL SELF LEARNING MATERIAL (SLM)
8. The hypothalamus produces multiple hormones that control the pituitary gland. It’s also involved in regulating many functions, including sleep-wake cycles, body temperature, and appetite. It can also regulate the function of other endocrine glands. 9. The pituitary gland is located below the hypothalamus. The hormones it produces affect growth and reproduction. They can also control the function of other endocrine glands. 10. This gland is found in the middle of your brain. It’s important for your sleep-wake cycles. 11. The thyroid gland is located in the front part of your neck. It’s very important for metabolism. 12. The Parathyroid gland isalso located in the front of your neck, the parathyroid gland is important for maintaining control of calcium levels in your bones and blood. 13. The Thymus gland is located in the upper torso, the thymus is active until puberty and produces hormones important for the development of a type of white blood cell called a T cell. 14. The Adrenal gland can be found on top of each kidney. These glands produce hormones important for regulating functions such as blood pressure, heart rate, and stress response. 15. The pancreas is located in your abdomen behind your stomach. Its endocrine function involves controlling blood sugar levels. 16. Some endocrine glands also have non-endocrine functions. For example, the ovaries and testes produce hormones, but they also have the non-endocrine function of producing eggs and sperm, respectively. 17. The HPA axis is a complex set of direct influences and feedback interactions among three organs crucial to endocrine function: the hypothalamus, the pituitary gland, and the adrenal glands. KEY WORDS/ ABBREVIATIONS • adrenal cortex- The external portion of the adrenal gland produces mineral corticosteroids, androgens, and glucocorticosteroids, all of which contribute to bodily homeostasis. • adrenal gland - Located atop (ad) the kidney (renal), the adrenal gland is composed of the adrenal cortex and the adrenal medulla. This gland produces hormones which regulate bodily homeostasis and energy expenditure. • Adrenaline- A hormone (C9H13NO3) and neurotransmitter created in the adrenal glands which acts primarily as an arousal agent. • endocrine system- Cells that form organs called glands and that communicate with one another by secreting hormones. • Epinephrine- A hormone (C9H13NO3) and neurotransmitter created in the adrenal glands which act primarily as an arousal agent. • Glands- Organs that secrete hormones into the bloodstream. • Hormones- Chemicals secreted by glands into the bloodstream, allowing stimulation of cells that are not directly connected. • Gland- Any organ whose function includes the secretion of a substance needed by the body. 58 CU IDOL SELF LEARNING MATERIAL (SLM)
• neuroendocrine system- Includes the hypothalamus, pituitary gland, and all endocrine glands, including the adrenal glands and the reproductive glands. LEARNING ACTIVITY 1. Make a table with the list of endocrine glands and their functions. 2. What are the different hormones secreted by our body? UNIT END QUESTIONS (MCQs AND DESCRIPTIVE) A. Descriptive Questions 1. The endocrine system is as important as the nervous system. Justify the statement 2. Outline the different endocrine glands present in our body. Elaborate the functions of these glands. 3. Explain the various characteristics of endocrine glands. 4. Describe in detail the role of endocrine system in stress management. 5. Certain medications are given to boast our energy. They are called steroids. Explain the detail how steroids are useful or harmful for our body. B. Multiple Choice Questions 1. At which site, the mind and body interact in the brain? [a] Pineal Gland [b] Thyroid Gland [c] Hypothalamus [d] Gonads 2. Melatonin is produced by which gland? 59 [a] Posterior Pituitary [b] Hypothalamus CU IDOL SELF LEARNING MATERIAL (SLM)
[c] Pineal Gland [d] Anterior Pituitary 3. are secreted by endocrine glands [a] Neurotransmitters [b] Hormones [c] Duct juice [d] All of the above 4. is chemicals within the endocrine system that affect physiological activity. [a] Neurotransmitters [b] Hormones [c] Duct juice [d] All of the above 5. There are endocrine glands. [a] 6 [b] 7 [c] 9 [d] 8 Answer 1 [a]2 [c]3 [b]4 [b]5 [d] REFERENCES • Martin, N. (2010). Psychology, (4th ed). Pearson Education Limited • Mangal, S.K. (1995). An Introduction to Psychology. Sterling Publishers Private Limited • Eynenck, M. (2014). Fundamentals of Psychology. Taylor & Francis. 60 CU IDOL SELF LEARNING MATERIAL (SLM)
• Woodworth, R. S. & Marquis, D. G. (2015). Psychology a study ofmental life. Taylor & Francis. • Bernstein D. (2018) Essentials of Psychology. Cengage Learning. • Feldman, R. S. (2012) Understanding Psychology (11th ed). McGraw-Hill Education – Europe • Pinel, J.P.J. (2007). Biopsychology. New Delhi: Pearson • Rosenzweig, M. R., Leiman, A. L. & Breedlove, S. M. (1996). Biological Psychology. Sunderland, Mass: Sinauer Associates. • Green, S. (1995). Principles of biopsychology. UK: Lawrence Erlbaum Associates Ltd. • Pinel, J. P. J. (2004). Biopsychology. Boston, MA: Allyn & Bacon. • Annett, M. (1984). Left, right, hand and brain: The right shift theory. London: Lawrence Erlbaum Associates Ltd. • Bannett, T.L. (1977). Brain and Behaviour. California: Brooks/ Cole. • Leukel, F. (1985). Introduction to Physiological Psychology. New Delhi: CBS Publishers 61 CU IDOL SELF LEARNING MATERIAL (SLM)
UNIT 5 METHODS OF STUDY Structure Learning Objectives Introduction Ablation Methods Histological Methods Psychophysiological Recording Methods Recording Electrical Activity Brain Stimulation Neuropsychological Assessment Summary Key Words/ Abbreviations Learning Activity Unit End Questions (MCQs and Descriptive) References LEARNING OBJECTIVES After this unit, you will be able to; • Outline the various research methods used in physiological psychology • Outline the variousways of studying the brain. • Identify commonly used methods to gather data about the brain INTRODUCTION He preceding sections introduced you to the nature, scope and major divisions of biopsychology. This section deals with the methods employed to study human brain. The structure of the brain (see Figure1.1) is quite complex and understanding its working is all the more challenging for the researchers. With the discovery of Broca's area, it was concluded that different brain areas had different functions. In 1861, Paul Broca, French neurologist, found that one of his patients who had lost the ability to speak, had damage in left frontal cortex. More patients with loss of speech showed damage in and around this area, which is now known as Broca's area. Thus, the research conducted in this area concludes that brain damage causes effects like increase or decrease in hunger, changes in emotional responses, to mention just a few. Let us see the main methods used in the study of brain. ABLATION AND LEISION METHODS Ablation means removal of a brain area, generally with a surgical knife.It is different from lesion. Both ablation and lesion methods are invasive and involve cutting a part of brain. Ablation method thus, involves the destruction of some tissue in the brain. This is followed 62 CU IDOL SELF LEARNING MATERIAL (SLM)
by assessing the changes that occur in behaviour due to the removal or destruction of the tissue. Scientists sometimes create lesions by cutting or destroying part of an animal’s brain. If the animal behaves differently after the operation, they assume that the destroyed brain area is involved with that type of behaviour. For example, in one classic lesion study, two researchers removed a certain area of the temporal lobe from rhesus monkeys. Normally, these animals are fearful, aggressive, and vicious, but after the operation, they became less fearful and at the same time less violent (Klüver & Bucy, 1937). The implication was that this area of the brain controlled aggression. The relations revealed by this type of research are far more subtle and complex than people first believed. Any wound or injury thereby, is known as a lesion. But one has to be very careful as different parts of the brain are all connected to one another and work in conjunction with another. So if a lesion is created in one area, it may exert an influence on the neighbouring areas as well. Sometimes the animal also recovers from the brain damage either partially or the functions of the damaged part of the brain are covered up by another part of the brain. There are different ways to cause lesions. The main techniques discussed here are aspiration, radio frequency, knife cuts, cryogenic blockades and nerve poison Aspiration: A fine thin needle is placed on the tissue (which can be seen by the surgeon and accessible by the instruments) that needs to be examined and it is aspirated and the contents are then placed on the slide and examined for any diagnostic analysis. This is generally the preferred technique when a part of the cortical tissue has to be sucked to reveal the area that is under it for further investigation. Radio-Frequency: Radio frequency (RF) current is used to produce sub-cortical lesions. The wire is placed on the tissue which needs to be examined. Radiofrequency devices produce a high frequency current, that is alternating current. The heat that results from this current destroys the tissue in that area. The duration and intensity of the current will determine the size and shape of the lesion. Knife Cuts: Sectioning (Cutting) is used to make a cut on any area of the nerves or the brain. There is a special device that is used to make sub-cortical knife cuts very carefully by placing the brain using a stereotaxic apparatus. By using such a technique, extensive damage to the surrounding area is decreased. Cryogenic Blockade: 63 CU IDOL SELF LEARNING MATERIAL (SLM)
This is a temporary way of inducing lesions. A cryoprobe is placed in the brain. Through this tube a coolant is sent to the area under study. The coolant reduces the temperatures at its tip to such an extent that the neurons stop sending impulses. Since the temperature is maintained at above freezing point there is no structural damage. Once the temperature is restored to the normal level, the neurons start functioning again. Nerve poison: Certain chemicals such askainic acid or ibotenic acid are used as nerve poisons to create lesions in a particular area in the brain. These chemicals are inserted through a glass tube known as cannula. The destruction is only partial, that is only the cell bodies are destroyed. So, if there is any change in behaviour, then that can be attributed to the cell bodies. HISTOLOGICAL METHODS With the advent of technology in the present times, there are many techniques and methods to study anatomy and functioning of human brain. For studying minute details of tissue (microscopic investigation), histological methods are used for the purpose. In this method, the sample of the brain that is under investigation, needs to be prepared so that it can be mounted on a slide and observed under a light microscope. The neural tissue is very fragile and under normal conditions it may just disintegrate. Hence, the tissue needs to be fixed and stained in order to be viewed on the slide. When it is taken out, the bacteria or moulds tend to decompose the neural tissue. Let us now look at the procedures in histological methods. Fixation: In this method, a fixative is used to fix the tissue. The tissue is cleaned and dipped in a fixative solution. The most commonly used fixative is formalin. This fixative prevents autolysis and makes the tissue hard. But still, the tissue is not so hard to be cut using a microtome (automatic slicing machine used in microscopy to produce thin sections of the fixed and embedded tissue for microscopic observations). Hence, the brain tissue is freeze so that the tissue becomes harder. It is also used to stabilize neural tissue. Freezing: In freezing, the tissue needs to be frozen, in order to be sliced. To freeze the tissue, it is dipped in a sugar solution and then put in a freezer. The temperature is regulated in a way so that the tissue is maintained at an appropriate temperature. Once the tissue is hard enough, it is to be placed on the microtome to be sliced. Embedding: Another way to make the brain tissue hard is by embedding and covering it by paraffin or nitrocellulose. Once the tissue is hard then it is cut using a microtome. These slices are then placed on a slide and mounted on it using albumin which is taken from the egg. The slide is dried, it is then dyed using different chemical solutions. 64 CU IDOL SELF LEARNING MATERIAL (SLM)
Staining: It is done so that the structural details of the tissue become apparent under the microscope.This is done by darkening or colouring particular features of the tissue. Nissil stains or cell-body stains are most frequently used to dye the cell bodies. Myelin stains colour the myelin sheath to study the nerve pathways. Membrane stains like Golgi-cox stain, helps to colour the cell body, dendrites and axon. PSYCHOPHYSIOLOGICAL RECORDING METHODS There are different psychophysiological methods that help to examine human participants in a non-invasive way. Such methods record from outside the skull (and other parts of the body) without inserting anything. The most widely used methods in this category are as follows: X-rays X-rays (radiographs) are the most common and widely available diagnostic imaging technique. Even if you also need more sophisticated tests, you will probably get an x-ray first. The part of your body being pictured is positioned between the x-ray machine and photographic film or digital x-ray sensor. You have to hold still while the machine briefly sends electromagnetic waves (radiation) through your body, exposing the film to reflect your internal structure. Electroencephalography: The electrical activity of the brain is recorded using Electroencephalograph (EEG) machine and the technique is known as electroencephalography. Electrodes are placed on the scalp of the patient and recording is done on the computer. Earlier a rolling paper was used where the readings were displayed, now a computer printout is taken. The EEG signals help in the diagnosis of various disorders of the brain, mild head injury, cerebral pathology, epilepsy, and speed of processing information or how the memory functions with an increase in age. Computed Tomography (CT) Computed tomography (CT) is an imaging tool that combines x-rays with computer technology to produce a more detailed, cross-sectional image of your body. A CT scan lets your doctor see the size, shape, and position of structures that are deep inside your body, such as organs, tissues, or tumors. Tell your doctor if you are pregnant before undergoing a CT scan. You lie as motionless as possible on a table that slides into the center of the cylinder-like CT scanner. The process is painless. An x-ray tube slowly rotates around you, taking many pictures from all directions. A computer combines the images to produce a clear, two- dimensional view on a television screen. 65 CU IDOL SELF LEARNING MATERIAL (SLM)
You may need a CT scan if you have a problem with a small, bony structure or if you have severe trauma to the brain, spinal cord, chest, abdomen, or pelvis. Sometimes, you may be given a dye or contrast material to make certain parts of your body show up better. A CT scan costs more and takes more time than a regular x-ray. It can be done in either a hospital setting or an outpatient imaging center. RECORDING ELECTRICAL ACTIVITY Magnetic Resonance Imaging (MRI) Magnetic resonance imaging (MRI) is another diagnostic imaging technique that produces cross-sectional images of your body. Unlike CT scans, MRI works without radiation. The MRI tool uses magnetic fields and a sophisticated computer to take high-resolution pictures of your bones and soft tissues. Tell your doctor if you have a pacemaker, implants, metal clips, or other metal objects in your body before you undergo an MRI scan. You lie as motionless as possible on a table that slides into the tube-shaped MRI scanner. The MRI creates a magnetic field around you and then pulses radio waves to the area of your body to be pictured. The radio waves cause your tissues to resonate. A computer records the rate at which your body's various parts (tendons, ligaments, nerves, etc.) give off these vibrations, and translates the data into a detailed, two-dimensional picture. You will not feel any pain while undergoing an MRI, but the machine may be noisy. An MRI may be used to help diagnose torn knee ligaments and cartilage, torn rotator cuffs, herniated disks, osteonecrosis, bone tumors, and other problems. It may take from 30 to 60 minutes to do the study. Like a CT scan, an MRI scan may be done in a hospital or at an outpatient imaging center. Positron Emission Tomography (PET) Positron Emission Tomography (PET) uses trace amounts of short-lived radioactive material to map functional processes in the brain. When the material undergoes radioactive decay a positron is emitted, which can be picked up by the detector. Areas of high radioactivity are associated with brain activity. Magnetoencephalography (MEG) Magnetoencephalography (MEG) is an imaging technique used to measure the magnetic fields produced by electrical activity in the brain via extremely sensitive devices known as SQUIDs. These measurements are commonly used in both research and clinical settings. There are many uses for the MEG, including assisting surgeons in localizing a pathology, assisting researchers in determining the function of various parts of the brain, neurofeedback, and others. Near infrared spectroscopy (NIRS) 66 CU IDOL SELF LEARNING MATERIAL (SLM)
Near infrared spectroscopy is an optical technique for measuring blood oxygenation in the brain. It works by shining light in the near infrared part of the spectrum (700-900nm) through the skull and detecting how much the remerging light is attenuated. How much the light is attenuated depends on blood oxygenation and thus NIRS can provide an indirect measure of brain activity. BRAIN STIMULATION Electrodes may be used to set off the firing of neurons as well as to record it. Brain surgeon Wilder Penfield stimulated the brains of his patients during surgery to determine what functions the various parts of the brain perform. In this way he could localize the malfunctioning part for which surgery was required, for example, for epilepsy. When Penfield applied a tiny electric current to points on the temporal lobe of the brain, he could trigger whole memory sequences. During surgery, one woman heard a familiar song so clearly that she thought a record was being played in the operating room (Penfield & Rasmussen, 1950). Stimulation techniques have aroused great medical interest. They have been used with terminal cancer patients to relieve them of intolerable pain without using drugs. A current delivered through electrodes implanted in certain areas of the brain may provide a sudden temporary relief (Delgado, 1969). Furthermore, some psychiatrists have experimented with similar methods to control violent emotional behavior in otherwise uncontrollable patients. Brain stimulation therapies can play a role in treating certain mental disorders. Brain stimulation therapies involve activating or inhibiting the brain directly with electricity. The electricity can be given directly by electrodes implanted in the brain, or noninvasively through electrodes placed on the scalp. The electricity can also be induced by using magnetic fields applied to the head. While these types of therapies are less frequently used than medication and psychotherapies, they hold promise for treating certain mental disorders that do not respond to other treatments. Electroconvulsive therapy is the best studied brain stimulation therapy and has the longest history of use. Other stimulation therapies discussed here are newer, and in some cases still experimental methods. These include: • vagus nerve stimulation (VNS) • repetitive transcranial magnetic stimulation (rTMS) • magnetic seizure therapy (MST) • deep brain stimulation (DBS) A treatment plan may also include medication and psychotherapy. Choosing the right treatment plan should be based on a person's individual needs and medical situation, and under a doctor's care. Electroconvulsive Therapy 67 CU IDOL SELF LEARNING MATERIAL (SLM)
artist depiction of electroconvulsive therapy Electroconvulsive therapy (ECT) uses an electric current to treat serious mental disorders. This type of therapy is usually considered only if a patient's illness has not improved after other treatments (such as antidepressant medication or psychotherapy) are tried, or in cases where rapid response is needed (as in the case of suicide risk and catatonia, for example). Figure 5.1.: Person undergoing Electroconvulsive Therapy ECT is most often used to treat severe, treatment-resistant depression, but it may also be medically indicated in other mental disorders, such as bipolar disorder or schizophrenia. It also may be used in life-threatening circumstances, such as when a patient is unable to move or respond to the outside world (e.g., catatonia), is suicidal, or is malnourished as a result of severe depression. ECT can be effective in reducing the chances of relapse when patients undergo follow-up treatments. Two major advantages of ECT over medication are that ECT begins to work quicker, often starting within the first week, and older individuals respond especially quickly. Before ECT is administered, a person is sedated with general anesthesia and given a medication called a muscle relaxant to prevent movement during the procedure. An anesthesiologist monitors breathing, heart rate and blood pressure during the entire procedure, which is conducted by a trained medical team, including physicians and nurses. During the procedure: Electrodes are placed at precise locations on the head. Through the electrodes, an electric current passes through the brain, causing a seizure that lasts generally less than one minute. Because the patient is under anesthesia and has taken a muscle relaxant, it is not painful and the patient cannot feel the electrical impulses. Five to ten minutes after the procedure ends, the patient awakens. He or she may feel groggy at first as the anesthesia wears off. But after about an hour, the patient usually is alert and can resume normal activities. A typical course of ECT is administered about three times a week until the patient's depression improves (usually within 6 to 12 treatments). After that, maintenance ECT treatment is sometimes needed to reduce the chances that symptoms will return. ECT maintenance treatment varies depending on the needs of the individual, and may range from 68 CU IDOL SELF LEARNING MATERIAL (SLM)
one session per week to one session every few months. Frequently, a person who undergoes ECT also takes antidepressant medication or a mood stabilizing medication. Vagus Nerve Stimulation Figure 5.2.: Person undergoingVagus nerve stimulation (VNS) Vagus nerve stimulation (VNS) works through a device implanted under the skin that sends electrical pulses through the left vagus nerve, half of a prominent pair of nerves that run from the brainstem through the neck and down to each side of the chest and abdomen. The vagus nerves carry messages from the brain to the body's major organs (e.g. heart, lungs and intestines) and to areas of the brain that control mood, sleep, and other functions. Repetitive Transcranial Magnetic Stimulation Figure 5.3.: Person undergoingRepetitive Transcranial Magnetic Stimulation Repetitive transcranial magnetic stimulation (rTMS) uses a magnet to activate the brain. First developed in 1985, rTMS has been studied as a treatment for depression, psychosis, anxiety, and other disorders. Unlike ECT, in which electrical stimulation is more generalized, rTMS can be targeted to a specific site in the brain. Scientists believe that focusing on a specific site in the brain reduces the chance for the types of side effects associated with ECT. But opinions vary as to what site is best. Magnetic Seizure Therapy 69 CU IDOL SELF LEARNING MATERIAL (SLM)
Magnetic seizure therapy (MST) borrows certain aspects from both ECT and rTMS. Like rTMS, MST uses magnetic pulses instead of electricity to stimulate a precise target in the brain. However, unlike rTMS, MST aims to induce a seizure like ECT. So the pulses are given at a higher frequency than that used in rTMS. Therefore, like ECT, the patient must be anesthetized and given a muscle relaxant to prevent movement. The goal of MST is to retain the effectiveness of ECT while reducing its cognitive side effects. MST is in the early stages of testing for mental disorders, but initial results are promising. A recent review article that examined the evidence from eight clinical studies found that MST triggered remission from major depression or bipolar disorder in 30-40% of individuals. Deep Brain Stimulation Figure 5.4.: Person undergoingDeep Brain Stimulation Deep brain stimulation (DBS) was first developed as a treatment for Parkinson's disease to reduce tremor, stiffness, walking problems and uncontrollable movements. In DBS, a pair of electrodes is implanted in the brain and controlled by a generator that is implanted in the chest. Stimulation is continuous and its frequency and level are customized to the individual. DBS has been studied as a treatment for depression or obsessive compulsive disorder (OCD). Currently, there is a Humanitarian Device Exemption for the use of DBS to treat OCD, but its use in depression remains only on an experimental basis. A review of all 22 published studies testing DBS for depression found that only three of them were of high quality because they not only had a treatment group but also a control group which did not receive DBS. The review found that across the studies, 40-50% of people showed receiving DBS greater than 50% improvement. DBS: How it works DBS requires brain surgery. The head is shaved and then attached with screws to a sturdy frame that prevents the head from moving during the surgery. Scans of the head and brain using MRI are taken. The surgeon uses these images as guides during the surgery. Patients are awake during the procedure to provide the surgeon with feedback, but they feel no pain because the head is numbed with a local anesthetic and the brain itself does not register pain. 70 CU IDOL SELF LEARNING MATERIAL (SLM)
Once ready for surgery, two holes are drilled into the head. From there, the surgeon threads a slender tube down into the brain to place electrodes on each side of a specific area of the brain. In the case of depression, the first area of the brain targeted by DBS is called Area 25, or the subgenual cingulate cortex. This area has been found to be overactive in depression and other mood disorders. But later research targeted several other areas of the brain affected by depression. So DBS is now targeting several areas of the brain for treating depression. In the case of OCD, the electrodes are placed in an area of the brain (the ventral capsule/ventral striatum) believed to be associated with the disorder. After the electrodes are implanted and the patient provides feedback about their placement, the patient is put under general anesthesia. The electrodes are then attached to wires that are run inside the body from the head down to the chest, where a pair of battery-operated generators are implanted. From here, electrical pulses are continuously delivered over the wires to the electrodes in the brain. Although it is unclear exactly how the device works to reduce depression or OCD, scientists believe that the pulses help to \"reset\" the area of the brain that is malfunctioning so that it works normally again. NEUROPSYCHOLOGICAL ASSESSMENT The branch of medicine that focuses on the nervous system and its disorders is neurology. The branch of psychology that focuses on the relationship between brain functioning and behaviour is neuropsychology. Formerly a specialty area within clinical psychology, neuropsychology has evolved into a specialty, with its own training regimens and certifying bodies. Neuropsychologists study the nervous system as it relates to behaviour by using various tools, including neuropsychological assessment. Neuropsychological assessment may be defined as the evaluation of brain and nervous system functioning as it relates to behaviour. Subspecialty areas within neuropsychology include paediatric neuropsychology (Baron, 2004; Yeates et al., 2000), geriatric neuropsychology (Attix & Welsh-Bohmer, 2006), forensic neuropsychology (Larrabee, 2005), and school neuropsychology (Hale & Fiorello, 2004)—an area well known to our guest test user. A subspecialty within the medical specialty of neurology that also focuses on brain–behaviour relationships (with more biochemical and less behavioural emphasis) is behavioural neurology (Feinberg & Farah, 2003; Rizzo & Eslinger, 2004). There are even subspecialty areas within behavioural neurology. For example, the assessment professional featured in Chapter 7, Rd. Erik Vireo, is a physician who specializes in neurotology, a branch of medicine that focuses on problems related to hearing, balance, and facial nerves. In what follows, we survey some of the tools and procedures used by clinicians and neuropsychologists to screen for and diagnose neuropsychological disorders. We begin with a brief introduction to brain–behaviour relationships. This material is presented to lay a foundation for understanding how test taking, as well as other behaviour, can be evaluated to form hypotheses about levels of brain intactness and functioning. 71 CU IDOL SELF LEARNING MATERIAL (SLM)
Neuropsychological assessments are frequently completed to provide additional information about a variety of developmental disorders. The most common referral questions con•cern medical disorders including genetic disorders, concussion/traumatic brain injury, recovery from cancer/brain tumours, and other neurologic concerns such as epilepsy and movement disorders. In addition, children who have acquired disorders such as those resulting from exposure to lead or other teratogenic substances are also frequently referred for an evaluation. Disorders such as dyslexia, ADHD, autism spectrum disorder, and fatal alcohol spectrum disorder are common reasons for referral for assessment, particularly when typical interventions have not been successful. Psychiatric disorders such as obsessive-compulsive disorder, anxiety and depression, and behavioural dysregulation are referred for evaluation to more fully understand the child's difficulty and to provide recommendations for intervention in the home and at school. Child clinical neuropsychology is best viewed within an integrative perspective for the study and treatment of child and adolescent disorders. By addressing brain functions and the environmental influences inherent in complex human behaviours, such as thinking, feeling, reasoning, planning, and executive functioning, clinicians can assist neurologists and paediatricians in providing the most appropriate service to children with severe learning, psychiatric, developmental, and acquired disorders (Chapters 50 and 58 and chapters in part XIX). Although clinical psychologists and neuropsychologists use similar measures, the interpretation differs. A neuropsychologist views test findings through the lens of neurodevelopment. With our burgeoning knowledge of neural development from studies of serial magnetic resonance imaging, we are able to more fully understand how the environment, genetics, age, gender, and experience can alter brain activity and brain development (Shaywitz et al., 2004). Attention to the scope and sequence of development of cortical structures and related behaviours that emerge during childhood allows further understanding of the effect of interventions, instructional opportunities, and enrichment on the neurodevelopmental process. Due to the complexity of the brain, and in particular the developing brain, it is most appropriate to utilize a transactional approach to the study and treatment of childhood and adolescent disorders. A description of a transactional approach is that it takes into consideration how abnormalities or developmental complications interact with the environment, how development itself affects the nature and severity of impairment, how to most efficiently assess these difficulties, and how to determine the most appropriate interventions. In this model, neuropsychological assessment—correctly completed—is therapeutic. In this view, the child's performance on appropriate measures plus the feedback to the medical professional, parent, and school provide a basis for understanding the child's strengths and weaknesses and for participating in the development of appropriate interventions. A transactional approach stresses consultation and collaboration with the caregivers of the child (as well as assisting the child in adjusting to his/her areas of challenge) but also with medical practitioners. In summary, child clinical neuropsychology is best viewed within an integrated framework, incorporating behavioural, psychosocial, cognitive, 72 CU IDOL SELF LEARNING MATERIAL (SLM)
and environmental factors into a comprehensive model for the assessment and treatment of brain-related disorders in children and adolescents. Current theory posits that regions of the brain have a bidirectional influence on various neural functional systems, which in turn affect the intellectual and perceptual capacity of the child. The child's behavioural, psychological, and cognitive manifestation of a childhood disorder is likely influenced by the interaction of these functional systems. In addition, the child's neurologic functioning also interacts with his/her social, family, and school environments that facilitate compensatory or coping skills in the individual child, which are either helpful or problematic. SUMMARY 1. The methods used in behavioural neuroscience today are much advanced over those available in earlier time, but the use to which these methods are put remains the same: to better understand the biology of behaviour and of our selves. 2. Behavioural neuroscience focuses on the study of living organisms, both humans and other species. The overriding objective of this research is to deepen our knowledge of the biology of behaviour and to use that knowledge in battering the lives and relieving suffering of both humans and animals. 3. Laboratory rats, for example, have been extremely useful in learning about the biology of aging, since rats have a natural life span of two to three years. Thus, behavioural neuroscience is continually enriched by progress in physics, chemistry, and engineering. 4. The study of the biological basis of behaviour depends critically upon the integrity of the experimental methods by which theoretical ideas are tested. Fortunately, the physical, chemical, and engineering sciences over the past several decades have provided increasingly powerful and precise tools for the study of the nervous system and its functions. 5. Perhaps the most spectacular of these new methods are the brain-imaging technologies. Computerized tomography utilizes multi-pass X-ray data to construct images of horizontal slices though the human brain. 6. Magnetic resonance imaging, a more recent development, provides images with higher resolution, in any arbitrary plane, without the use of ionizing radiation. Positron emission tomography permits the imaging of the functional and chemical activity of the nervous system in addition to providing data about brain structure. 7. Microscopic methods and histological procedures clarify the structure and functions of the nervous system at the cellular level. Staining methods are now routinely available to visualize many specific properties of individual neurons, including their metabolic demands and chemical properties. 8. Recording the electrical activity of the brain and its cells also has contributed greatly to understanding nervous system functions, since neurons process information by altering their electrical potential. The electroencephalogram recorded from the scalp has been particularly useful in the study of sleep and certain neurological disorders, such as epilepsy. 73 CU IDOL SELF LEARNING MATERIAL (SLM)
9. Magnetoencephalography may provide a way of obtaining more information concerning the sources of EEG signals. Brain responses to specific sensory stimuli may be extracted from the ongoing EEG by event-related signal averaging. Recording may also be performed to study the electrical activity of single nerve cells by using microelectrodes or even portions of a cell by using patch clamp methods. 10. Yet another approach to analysing brain functions is to study the behavioural effects of either brain stimulation or brain damage. Electrical or chemical methods may be employed to stimulate the brain. Similarly, a variety of procedures are useful in producing restricted brain lesions. In either case, careful behavioural analysis is required to understand the precise effects of the experimental treatment. KEY WORDS/ ABBREVIATIONS • Biopsychology - The biological approach to the study of human and animal behaviour is known as biopsychology. • Ablation- Ablation is a method to study the destruction of tissue in the brain and examining its effect on behaviour due to the removal or destruction of tissue. • Histological methods- It is the method of scientifically examining the tissue for its structure, function, or pathology. • Brain imaging- Also known as neuroimaging, it involves various techniques analysing (such as EEG, PET, MRI, and fMRI scan) to study the structure, function, or pharmacology of the brain. • Embedding- t is a procedure to make the brain tissue hard by covering it with paraffin or nitrocellulose LEARNING ACTIVITY 1. What are the ways in which we can study the brain of a deseeded person? 2. How can we study the impact of human brain? UNIT END QUESTIONS (MCQS AND DESCRIPTIVE) A. Descriptive Questions 1. Doctors use different methods to collect data from our brain. Describe any of the four methods used to do so. 74 CU IDOL SELF LEARNING MATERIAL (SLM)
2. Psychologists conduct tests known as neuro-psychological assessment to understand the cognitive functioning. Elaborate. 3. Elaborate the specific situations wherein psychologists use neuro-psychological assessment? 4. Outline the different types of lesion carried out on brain and the reason for doing so. 5. Explain the purpose of stimulating the brain. Identify the different methods in which the process is done and the situations in which it is performed. B. Multiple Choice Questions 1. When is aspiration a method of choice of lesion? [a] in a deeper brain area [b] in an area of cerebral cortex [c] an irreversible lesion [d] in underlying white matter 2. is used to produce sub-cortical lesions. [a] Ablation [b]Aspiration [c] Radio frequency (RF) current [d] Cryogenic Blockade 3. removal of a brain area. [a] Ablation [b]Aspiration [c] Radio frequency (RF) current [d] Cryogenic Blockade 4. a temporary way of inducing lesions [a] Ablation CU IDOL SELF LEARNING MATERIAL (SLM) 75
[b]Aspiration [c] Radio frequency (RF) current [d] Cryogenic Blockade 5. is done by darkening or colouring particular features of the tissue. [a] Ablation [b]Aspiration [c] Staining [d] Cryogenic Blockade Answer 1 [b]2 [c]3 [a]4 [d]5 [c] REFERENCES • Martin, N. (2010). Psychology, (4th ed). Pearson Education Limited • Mangal, S.K. (1995). An Introduction to Psychology. Sterling Publishers Private Limited • Eynenck, M. (2014). Fundamentals of Psychology. Taylor & Francis. • Woodworth, R. S. & Marquis, D. G. (2015). Psychology a study ofmental life. Taylor & Francis. • Bernstein D. (2018) Essentials of Psychology. Cengage Learning. • Feldman, R. S. (2012) Understanding Psychology (11th ed). McGraw-Hill Education - Europe • Pinel, J.P.J. (2007). Biopsychology. New Delhi: Pearson • Rosenzweig, M. R., Leiman, A. L. & Breedlove, S. M. (1996). Biological Psychology. Sunderland, Mass: Sinauer Associates. • Green, S. (1995). Principles of biopsychology. UK: Lawrence Erlbaum Associates Ltd. • Pinel, J. P. J. (2004). Biopsychology. Boston, MA: Allyn & Bacon. • Annett, M. (1984). Left, right, hand and brain: The right shift theory. London: Lawrence Erlbaum Associates Ltd. • Bannett, T.L. (1977). Brain and Behaviour. California: Brooks/ Cole. • Leukel, F. (1985). Introduction to Physiological Psychology. New Delhi: CBS Publishers 76 CU IDOL SELF LEARNING MATERIAL (SLM)
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UNIT 6 RECORDING BRAIN ACTIVITY Structure Learning Objectives Introduction Electrical and Chemical Imaging Techniques Electroencephalography (EEG) Magnetic Resonance Imaging Physiological and Molecular Imaging Functional MRI Summary Key Words/ Abbreviations Learning Activity Unit End Questions (MCQs and Descriptive) 6.11.References LEARNING OBJECTIVES After this unit you will be able to, • Explain the ways in which data collection in physiological psychology • Identify the different ways in which data from the brain is gathered • Describe the various ways used for mapping brain activity INTRODUCTION Neuroimaging is an increasingly important tool for studying brain structure and function in both research and clinical care. Neuroimaging methods currently provide unprecedented sensitivity to visualizations of brain structure and function from the level of individual molecules to the whole brain; and technological advances continue to expand the range of structural, physiological, and molecular processes that can be assessed in vivo (in living humans, animals, organisms, and cells). Human brain imaging methods must be non-invasive, though they may include exposure to ionizing radiation or contrast agents. These methods can be equally used to noninvasively study brain structure and function in preclinical laboratory models, and the ability to derive identical metrics of brain structure and function from the bench to the bedside is a key benefit of neuroimaging methods for translational research. Analogous neuroimaging methods are also increasingly being applied to ex vivo studies (of autopsied brain tissue) so that the three- dimensional structure of the brain can be assessed at microscopic resolution without the disruption and distortion caused by sectioning for staining and analysis by standard microscopy. Finally, over the past decade, there have been remarkable advances in optical microscopic methods that allow cellular structure and function to be visualized in vivo. 78 CU IDOL SELF LEARNING MATERIAL (SLM)
Neuroimaging methods are enabling researchers to identify neural networks involved in cognitive processes, understand disease pathways, recognize and diagnose diseases early when they are most effectively treated, and determine how therapies work. As in other areas of biomedical research, these opportunities are closely intertwined. As an example, imaging can provide a better understanding about a disease process that leads to discovery of potential therapies that intervene in that process. Thereafter, imaging can help provide a better understanding about how that drug or therapy works at the physiological-molecular level, leading to a more precise understanding of the disease process and then to the development of a more highly specific drug to treat it. A range of imaging methods are used to reveal brain structure (anatomy), physiology (functions), and biochemical actions of individual cells or molecules. The three main categories, therefore, are often referred to as structural, functional, and molecular imaging. More recently, cellular imaging methods have emerged for use in preclinical models, and a key goal of the NIH BRAIN Initiative is to extend these methods to imaging brain cells and circuits in the human brain. While most imaging techniques have applications throughout the body, the descriptions provided in this monograph focus on their use in the nervous system, primarily the brain. Alone and in combination, these imaging techniques are transforming our understanding of how the brain functions, how immune cells function, and how immune cells interact with the brain in health and disease. ELECTRICAL AND CHEMICAL IMAGING TECHNIQUES Using Early Structural Imaging Techniques: X-ray, Angiography, Computer Assisted Tomography and Ultrasound While many structural and functional imaging techniques are relatively recent, the origin of structural imaging was the x-ray, developed in 1895. X-rays measure the density of tissues. X-rays use photons, a quantum of visible light that possesses energy; the photons are passed through the body and deflected and absorbed to different degrees by the person’s tissues. The photons were initially recorded onto a silver halide film as they passed out of the body. Dense structures such as bone, which block most of the photons, appear white; structures containing air appear black; and muscle, fat, and fluids appear in various shades of Gray. This technology was the clinician’s main imaging tool for more than half of the 20th century. X-rays of the head provided limited information about the brain, however, since brain parenchyma (the functional tissue) is far less radio dense than the skull. Locations of calcified structures such as the choroid plexae and pineal gland, though, might be visible and seen to be displaced by a putative mass lesion. The pneumoencephalogram examined x-rays of the head after replacing the spinal fluid with air or another gas which allowed the ventricular outlines to be detected, again as a way of assessing for symmetry or its disruption. Angiography, a related early technique, uses radio dense dye injected through a catheter into a blood vessel to detect a blockage or narrowing of downstream vessels, or other vascular 79 CU IDOL SELF LEARNING MATERIAL (SLM)
lesions such as aneurysms or arteriovenous malformations. The vessels are outlined on x-ray as white. Angiography is used to visualize arteries anywhere in the body, including the neck and brain. Although angiographic data are now digitized and analysed using algorithms that subtract pre-contrast and post-contrast images (termed “digital subtraction angiography”), this method still provides the highest resolution images of vascular structures in the brain and remains in wide clinical use. CT imaging was the first technique to show clear evidence during life of decreases in the amount of brain tissue when comparing scans of older and younger people. CT can be used with or without contrast agents. Such agents (typically containing radio dense iodine) make it easier to see blood vessels or lesions with blood-brain barrier breakdown and enables CT to show bone, soft tissues, and blood vessels in the same images. Because CT can be done quickly and has few contraindications, it is especially useful in emergency situations to identify any abnormalities in brain structure including swelling, or bleeding that arises from ruptured aneurysms, haemorrhagic stroke (a ruptured blood vessel) and head injury. In most clinical circumstances, the ease and utility of CT scanning outweighs the risk of associated exposure to ionizing radiation, but cumulative radiation remains a concern for patients who require frequent imaging. At the same time, technological advances are reducing the amount of radiation needed for CT scanning. CT angiography acquires dynamic CT scans during injection of intravenous contrast to provide visualization of the extracranial and intracranial vessels and has become a key clinical test when evaluating patients with acute stroke for possible thrombectomy (interventional removal of a blood clot). Of course, dynamic CT scanning typically entails a greater exposure to ionizing radiation than a static study since repeated images are acquired. Further signal processing of CT images during contrast passage through the brain can also create maps of blood flow and blood volume that are used in clinical decision-making. Additional tomographic techniques are discussed in later sections. Ultrasound, another early technique developed in the 1930s-40s, was primarily used neurologically until the 1960s to try to identify brain tumours. Ultrasound uses sound waves to determine the locations of surfaces within tissues and differentiates surfaces from fluids. It does so by measuring the time that passes between the production of an ultrasonic pulse and the echo created when the surface reflects the pulse. But, when scientists determined that the skull significantly distorts the signals, its use for this purpose stopped while its use in obstetrics and gynaecology—to image the foetus in utero and to detect ovarian tumours— became widespread. Ultrasound remains a valuable brain imaging technique in neonates where signals can be reliably obtained through the fontanelle. Transcranial ultrasound is still used clinically to monitor flow in the major intracranial arteries through thinner areas in the skull (so-called “bone windows”) that are variably available, and ultrasound methods are widely used to evaluate the carotid arteries in the neck region where there is no bony interference. Ultrasound evaluation of arteries includes both imaging of vessel walls and plaque and methods leveraging the Doppler effect (flow induced shifts in frequency) to evaluate flow velocities. 80 CU IDOL SELF LEARNING MATERIAL (SLM)
ELECTROENCEPHALOGRAPHY (EEG) Electroencephalography (EEG) is used to show brain activity in certain psychological states, such as alertness or drowsiness. It is useful in the diagnosis of seizures and other medical problems that involve an overabundance or lack of activity in certain parts of the brain. To prepare for an EEG, electrodes are placed on the face and scalp. After placing each electrode in the right position, the electrical potential of each electrode can be measured. According to a person’s state (waking, sleeping, etc.), both the frequency and the form of the EEG signal differ. Patients who suffer from epilepsy show an increase of the amplitude of firing visible on the EEG record. The disadvantage of EEG is that the electric conductivity — and therefore the measured electrical potentials—may vary widely from person to person and also over time, due to the natural conductivities of other tissues such as brain matter, blood, and bones. Because of this, it is sometimes unclear exactly which region of the brain is emitting a signal. Figure 6.3.: EEG recording MAGNETIC RESONANCE IMAGING Magnetic Resonance Imaging (MRI) is based on the principle of nuclear magnetic resonance (NMR) and uses radiofrequency waves to probe tissue structure and function without requiring exposure to ionizing radiation. MRI was originally called nuclear magnetic resonance imaging because it was an extension of NMR, but the name was changed to magnetic resonance imaging to avoid erroneous associations with nuclear radiation. The two researchers (Paul Lauterbur and Sir Peter Mansfield) who made MRI clinically feasible in the 1980s by building on initial discoveries of the 1930s won the Nobel Prize in Physiology or Medicine in 2003. Several biologically relevant nuclei can provide magnetic resonance 81 CU IDOL SELF LEARNING MATERIAL (SLM)
signals. Most MRI uses signals from water, which constitutes about two-thirds of human body weight, to develop information on brain structures and functions. The high concentration of water in living tissues offsets the generally low sensitivity of NMR signals. Figure 6.2.: Brain MRI results Structural MRI measures the nuclear magnetic resonance of water protons to create a computerized three-dimensional image of tissues. More specifically, protons in the nuclei of hydrogen atoms in water move (oscillate) between two points and vibrate when they are exposed to a strong magnetic field. They absorb energy in the frequency of radio waves, and then they remit this energy in the same radiofrequency (a process called resonance) when they return to their original state. Small differences in the protons’ oscillations are mathematically analysed by computer to build a three-dimensional image of tissues. Variations that occur in the molecular environment of water located in different brain structures and compartments provide contrast and the ability to see the spatial orientation of various brain structures. The contrast differentiates, for example, the brain’s Gray matter (primarily nerve cell bodies) from white matter (primarily axons and their myelin sheaths) which are the nerve cell communication cables that connect brain regions. Structural MRI undertaken serially over a two-year period, for instance, shows that the brain’s hippocampus (primarily Gray matter) becomes progressively smaller (degenerates) in adults with dementing illnesses compared to adults who are cognitively healthy. The molecular environment of water is also affected by disease processes. Additionally, variations in exactly how the water signals are excited and measured in MRI can produce a range of different contrast mechanisms with varying sensitivity to structure, pathology, and physiological effects. PHYSIOLOGICAL AND MOLECULAR IMAGING: Positron Emission Tomography and Single Photon Emission Computed Tomography 82 CU IDOL SELF LEARNING MATERIAL (SLM)
While studies intended to identify structural lesions in the brain are the mainstay of clinical neuroimaging, imaging methods can also be used to study brain physiology. Indeed, much of the field of neuroimaging research is focused on expanding the types of information about the brain that can be spatially resolved noninvasively. Positron emission tomography (PET) was the first major technology to measure physiological functioning in the brain. PET scanning was introduced in 1977-78. In PET scanning, the regional distribution of exogenously administered positron-emitting tracers in the brain is measured using tomographic imaging. This technology is comprised of sensitive detector arrays and image reconstruction algorithms analogous to those used in CT scanning. A similar technique that is conceptually related to PET is single photon emission computed tomography (SPECT), but SPECT provides lower spacial resolution. Figure 6.3.: A PET scanner Both PET and SPECT detect gamma rays that are emitted from an exogenously administered gamma-emitting radioisotope attached to a molecule of interest. Radioisotope tracers used in PET and SPECT imaging also differ in that PET tracers tend to have much shorter half-lives and, in many cases, need to be synthesized within minutes or hours of administration. Thus, both methods require exposure to a low dose of ionizing radiation that is injected intravenously. Because of this, PET and SPECT studies are generally not carried out in children. SPECT detects single rays directly. PET uses “coincidence detection” to identify two gamma rays with opposing trajectories that are created from a positron-emitting tracer. This provides improved spatial localization of the gamma ray origin and hence better spatial resolution. The sensitivity of PET scanning is also extremely high. PET is the only imaging modality capable of detecting picomolar concentrations of tracer in the brain, and therefore has a unique role in molecular imaging. PET tracers designed with affinity for specific neurotransmitter receptors can be used to map out their distribution in the brain, and to explore how the receptor distribution may be altered by disease. For example, a reduction in striatal dopamine receptors can be measured using tracers that bind to receptors on cells that use the neurotransmitter dopamine to communicate, and a SPECT tracer with these properties is in clinical use for the diagnosis of Parkinson’s disease. 83 CU IDOL SELF LEARNING MATERIAL (SLM)
Similarly, PET tracers binding to amyloid or tau proteins that build up in neurodegenerative conditions have been used to detect neuropathological changes associated with Alzheimer’s disease, and amyloid imaging has also been translated to clinical care. PET radiochemistry is currently an active area of research with the goals of visualizing a diverse range of cellular and molecular processes in the human brain, and how these are altered in neurological and psychiatric diseases. PET analogues of novel therapeutic agents are also used in the pharmaceutical industry to verify target engagement of novel compounds. FUNCTIONAL MRI The discovery of blood oxygenation level dependent (BOLD) contrast and advances in MRI hardware that provided dramatically increased imaging speed combined to launch the field of functional MRI (fMRI) in the 1990s. BOLD contrast reflects a complex interaction between cerebral blood flow, cerebral blood volume, cerebral metabolic rate, and biophysical interactions between the brain and the local magnetic field that in 2019 still remain incompletely understood. Nonetheless, BOLD MRI scans are sensitive to changes in regional brain function. Figure 6.4.: An fMRI of the brain The ability to localize regional brain activity associated with cognitive or sensorimotor tasks was a major stimulus to the field of cognitive neuroscience. This ability facilitated the direct testing in the human brain of hypotheses about the organization of regional brain function derived from behavioural testing and from studies in patients with focal lesions. Like functional imaging with PET, fMRI is based on the principle that changes in regional cerebral blood flow and metabolism are coupled to changes in regional neural activity involved in brain functioning, such as memorizing a phrase or remembering a name. Compared to using PET scanning, though, fMRI was and continues to be much less costly, more widely available, and does not require exposure to ionizing radiation. Furthermore, fMRI has improved spatial and temporal resolution. 84 CU IDOL SELF LEARNING MATERIAL (SLM)
SUMMARY 1. Advanced non-invasive neuroimaging techniques such as EEG and fMRI allow researchers to directly observe brain activities while subjects perform various perceptual, motor, and/or cognitive tasks. 2. By combining functional brain imaging with sophisticated experimental designs and data analysis methods, functions of brain regions and their interactions can be examined. 3. Current neuroimaging techniques reveal both form and function. They reveal the brain's anatomy, including the integrity of brain structures and their interconnections. They elucidate its chemistry, physiology and electrical and metabolic activity. 4. The newest tools show how different regions of the brain connect and communicate. They can even show with split-second timing the sequence of events during a specific process, such as reading or remembering. 5. Psychologists employ these tools across the range of the discipline. Social cognitive neuroscientists, for instance, are capturing the psychological and neural processes involved in emotion, pain, self-regulation, self-perception and perception of others. P 6. psychologists have used neuroimaging technology to demonstrate how white Americans, even those who report themselves free of prejudice, show differences in brain activity in the amygdala — a structure involved in emotional learning – when they look at pictures representing people of different racial groups. 7. Positive emotions are also studied. Psychologists have compared functional images taken when students looked at pictures of their romantic partner versus pictures of an acquaintance. 8. When students gazed at their beloved, two deep-brain areas that communicate as part of a circuit showed increased levels of activity. Those areas help to regulate the neurotransmitter dopamine, which floods the brain when people anticipate a reward. 9. Neuroimaging is also helping us understand how the brain develops from infancy through adulthood. Developmental neuroscientists study the neurobiological underpinnings of cognitive development. 10. Combining functional measures of brain activity with behavioral measures, they explore how subtle early insults to the nervous system affect cognitive and emotional function later in life – for example, the effects of maternal illness or early childhood neglect on learning, memory and attention later in life. 11. Imaging tools can pay off in the classroom, too: Using such tools, literacy experts have shown that a year of intensive, methodical reading instruction makes the brains of high- risk kindergarteners look and function like those of more skilled young readers. 12. To aid clinical treatments, psychologists are using functional imaging to get at the neural mechanisms involved in such difficult problems as post-traumatic stress disorder, phobias and panic disorder. 13. For example, scans reveal that schizophrenia's diverse symptoms may result not from faults in single neural components but rather from differences in webs of neural connections. 14. Scans similarly help researchers follow brain activity to assess whether various treatments change the underlying brain dysfunction. 85 CU IDOL SELF LEARNING MATERIAL (SLM)
KEY WORDS/ ABBREVIATIONS • ECT- Electroconvulsive therapy: the intentional induction of convulsions through sending low-voltage electrical current through the head, which is used to treat severe depression and occasionally other disorders. Also called electroconvulsive shock treatment or electroconvulsive shock therapy. • EEG- The EEG (or electroencephalogram) is the graph of an electrical signal produced by large groups of neurons in the brain that can be picked up by scalp electrodes. • electroencephalogram(EEG) A graph made by recording the electrical current passing through different portions of the brain over time by means of a set of electrodes attached to the skin of the head in a standard pattern. • Electroencephalography- The process of making graphs of the electrical current passing through different portions of the brain over time by means of a set of electrodes attached to the skin of the head in a standard pattern. • Electromyogram- (EMG) A graphic representation of the electrical activity of a muscle or group of muscles over time recorded by electrodes attached to the skin over the muscles. • MRI- Magnetic resonance imaging, which uses a medical device for creating three- dimensional images of the body by measuring the reactivity of the hydrogen atoms in tissues to intense magnetic fields. The MRI is more accurate than computed tomography (CT) scanning and shows more tissue differences than do X-ray images. • PET scan- Positron emission tomography. A method of creating images of the insides of bodies including the brain by means of computer analysis of the absorption of positron emitting radioactive chemicals ingested by or injected into subjects and then differentially absorbed by different tissues. LEARNING ACTIVITY 1. With the help of a time line show the evolution of the brain imaging techniques. 1. With the help of a time line show the evolution of the brain imaging techniques. UNIT END QUESTIONS (MCQS AND DESCRIPTIVE) A. Descriptive Questions 1. Certain test study the structure of the brain. Elaborate on some of these tests. 86 CU IDOL SELF LEARNING MATERIAL (SLM)
2. Specialized test are used to study the function of the brain. Elaborate on some of the tests used for the same. 3. Explain the MRI machine. Elaborate the process and data gathered from an MRI. 4. Outline and explain how fMRI is different from MRI. 5. Identify the test used to understand the physiological and molecular imaging in the brain and explain how it works. B. Multiple Choice Questions (MCQs) 1. is a graph made by recording the electrical current passing through different portions of the brain over time by means of a set of electrodes attached to the skin of the head in a standard pattern. [a] ECG [b] EEG [c] MRI [d] fMRI 2. uses a medical device for creating three-dimensional images of the body by measuring the reactivity of the hydrogen atoms in tissues to intense magnetic fields. [a] ECG [b] EEG [c] MRI [d] fMRI 3 is a method of creating images of the insides of bodies including the brain by means of computer analysis of the absorption of positron emitting radioactive chemicals [a] PET Scan [b] EEG [c] MRI [d] fMRI 87 CU IDOL SELF LEARNING MATERIAL (SLM)
4. is based on the principle that changes in regional cerebral blood flow and metabolism are coupled to changes in regional neural activity involved in brain functioning [a] ECG [b] EEG [c] MRI [d] fMRI 5. is a form of therapy. [a] ECT [b] EEG [c] MRI [d] fMRI Answer 1 [b]2 [c]3 [a]4 [d]5 [a] REFERENCES • Brain Imaging technology: Clinical and Neuroscience Application by analogues Carolyn H. Asbury, and John A. Detre • Martin, N. (2010). Psychology, (4th ed). Pearson Education Limited • Mangal, S.K. (1995). An Introduction to Psychology. Sterling Publishers Private Limited • Eynenck, M. (2014). Fundamentals of Psychology. Taylor & Francis. • Woodworth, R. S. & Marquis, D. G. (2015). Psychology a study ofmental life. Taylor & Francis. • Bernstein D. (2018) Essentials of Psychology. Cengage Learning. • Feldman, R. S. (2012) Understanding Psychology (11th ed). McGraw-Hill Education - EuropePinel, J.P.J. (2007). Biopsychology. New Delhi: Pearson • Rosenzweig, M. R., Leiman, A. L. & Breedlove, S. M. (1996). Biological Psychology. Sunderland, Mass: Sinauer Associates. • Green, S. (1995). Principles of biopsychology. UK: Lawrence Erlbaum Associates Ltd. • Pinel, J. P. J. (2004). Biopsychology. Boston, MA: Allyn & Bacon. 88 CU IDOL SELF LEARNING MATERIAL (SLM)
• Annett, M. (1984). Left, right, hand and brain: The right shift theory. London: Lawrence Erlbaum Associates Ltd. • Bannett, T.L. (1977). Brain and Behaviour. California: Brooks/ Cole. • Leukel, F. (1985). Introduction to Physiological Psychology. New Delhi: CBS Publishers 89 CU IDOL SELF LEARNING MATERIAL (SLM)
UNIT 7 PHYSIOLOGICAL BASIS: SENSES Structure Learning Objectives Introduction What is Sensation? Threshold Vision Hearing Pain Summary Key Words/ Abbreviations Learning Activity Unit End Questions (MCQs and Descriptive) 7.11.References LEARNING OBJECTIVES After this unit, you will be able to; • Describe the concept of sensation and threshold • Explain the various physiological process involved in perception of light • Explain the various physiological process involved in perception of sound • Explain the various physiological process involved in perception of taste • Explain the various physiological process involved in perception of pain • Physiological basis of pain INTRODUCTION Why did you see your hand moving even though it was totally dark while doing the experiment above? You have just experienced kinesthesis—one of the senses. Although people are thought to have five senses, there are actually more. In addition to vision, hearing, taste, smell, and touch, there are several skin senses and two internal senses: vestibular and kinesthetics. Each type of sensory receptor takes some sort of external stimulus— light, chemical molecules, sound waves, and pressure—and converts it into a chemical-electrical message that can be transmitted by the nervous system and interpreted by the brain. So far, we know most about these processes in vision and hearing. The other senses have received less attention and are more mysterious in their functioning. 90 CU IDOL SELF LEARNING MATERIAL (SLM)
WHAT IS SENSATION? The world is filled with physical changes—an alarm clock sounds; the flip of a switch fills a room with light; you stumble against a door; steam from a hot shower billows out into the bathroom, changing the temperature and clouding the mirror. Any aspect of or change in the environment to which an organism responds is called a stimulus. An alarm, an electric light, and an aching muscle are all stimuli for human beings. A stimulus can be measured in many physical ways, including its size, duration, intensity, or wavelength. A sensation occurs anytime a stimulus activates one of your receptors. The sense organs detect physical changes in energy such as heat, light, sound, and physical pressure. The skin notes changes in heat and pressure, the eyes note changes in light, and the ears note changes in sound. Other sensory systems note the location and position of your body. A sensation may be combined with other sensations and your past experience to yield a perception. A perception is the organization of sensory information into meaningful experiences. Psychologists are interested in the relationship between physical stimuli and sensory experiences. In vision, for example, the perception of colour corresponds to the wavelength of the light, whereas brightness corresponds to the intensity of this stimulus. What is the relationship between colour and wavelength? How does changing a light’s intensity affect your perception of its brightness? The psychological study of such questions is called psychophysics. The goal of psychophysics is to understand how stimuli from the world (such as frequency and intensity) affect the sensory experiences (such as pitch and loudness) produced by them. THRESHOLD In order to establish laws about how people sense the external world, psychologists first try to determine how much of a stimulus is necessary for a person to sense it at all. How much energy is required for someone to hear a sound or to see a light? How much of a scent must be in the room before one can smell it? How much pressure must be applied to the skin before a person will feel it? To answer such questions, a psychologist might set up the following experiment. First, a person (the participant) is placed in a dark room and is instructed to look at the wall. He is asked to say “I see it” when he is able to detect a light. The psychologist then uses an extremely precise machine that can project a low-intensity beam of light against the wall. The experimenter turns on the machine to its lowest light projection. The participant says nothing. The experimenter increases the light until finally the participant responds, “I see it.” Then the experimenter begins another test in the opposite direction. He starts with a visible but faint light and decreases its intensity until the light seems to disappear. Many trials are completed and averaged. This procedure detects the absolute threshold—the weakest amount of a stimulus required to produce a sensation. The absolute threshold is the level of stimulus that produces a positive response of detection 50 percent of the time. 91 CU IDOL SELF LEARNING MATERIAL (SLM)
The absolute thresholds for the five senses in humans are the following: in vision—seeing a candle flame 30 miles away on a clear night; for hearing—hearing a watch ticking 20 feet away; for taste—tasting 1 teaspoon of sugar dissolved in 2 gallons of water; for smell— smelling 1 drop of perfume in a 3-room house; for touch—feeling a bee’s wing falling a distance of 1 centimetre onto your cheek. VISION The visual system allows us to do many activities that we take for granted: in a quick glance we can recognise what there is to see – people, objects and landscapes – in depth and full colour. Because of the dominance of visual information in our lives, it is perhaps not surprising that vision is our dominant sense. Light The eye is sensitive to light. Light consists of radiant energy similar to radio waves. As the radiant energy is transmitted from its source, it oscillates. For example, the antenna that broadcasts the programmes of your favourite FM station may transmit radio waves that oscillate at 88.5 MHz (megahertz, or million times per second). Because radiant energy travels at 297,600 km/s, the waves transmitted by this antenna are approximately 3.3 m apart (297,600 km divided by 88.5 million equals approximately 3.3 m). Thus, the wavelength of the signal from the station – the distance between the waves of radiant energy – is 3.3 m. The wavelength of visible light is much shorter, ranging from 380 to 760 nanometres (a nanometre, nm, is one-billionth of a metre). When viewed by a human eye, different wavelengths of visible light have different colours: for instance, 380 nm light looks violet and 760 nm light looks red. All other radiant energy is invisible to our eyes. Ultraviolet radiation, X-rays and gamma rays have shorter wavelengths than visible light has, whereas infrared radiation, radar and radio waves have longer wavelengths. The entire range of wavelengths is known as the electromagnetic spectrum; the part our eyes can detect – the part we see as light – is referred to as the visible spectrum, as seen in. 92 CU IDOL SELF LEARNING MATERIAL (SLM)
Figure 7.1.: Wavelength versus vibration. Because the speed of light is constant, faster vibrations produce shorter wavelengths. Figure 7.2.: The electromagnetic spectrum. The definition of the visible spectrum is based on the human visual system. Some other species of animals would define the visible spectrum differently. Bees, for example, can see ultraviolet radiation that is invisible to us. Some plants have taken advantage of this fact and produce flowers that contain dyes that reflect ultraviolet radiation, presenting patterns that attract bees to them. Some snakes (notably, pit vipers such as the rattlesnake) have special organs that detect infrared radiation. This ability enables them to find their prey in the dark by detecting the heat emitted by small mammals in the form of infrared radiation. The eye and its functions The eyes are important and delicate sense organs – and they are well protected. Each eye is housed in a bony socket and can be covered by the eyelid to keep out dust and dirt. The eyelids are edged by eyelashes, which help keep foreign matter from falling into the open eye. The eyebrows prevent sweat on the forehead from dripping into the eyes. Reflex mechanisms provide additional protection: the sudden approach of an object towards the face 93 CU IDOL SELF LEARNING MATERIAL (SLM)
or a touch on the surface of the eye causes automatic eyelid closure and withdrawal of the head. The transparent cornea forms a bulge at the front of the eye and admits light. The rest of the eye is coated by a tough white membrane called the sclera (from the Greek skleros, ‘hard’). The iris consists of two bands of muscle that control the amount of light admitted into the eye. The brain controls these muscles and thus regulates the size of the pupil, constricting it in bright light and dilating it in dim light. The space immediately behind the cornea is filled with aqueous humour, which simply means ‘watery fluid’. This fluid is constantly produced by tissue behind the cornea that filters the fluid from the blood. In place of blood vessels, the aqueous humour nourishes the cornea and other portions of the front of the eye; this fluid must circulate and be renewed. If aqueous humour is produced too quickly or if the passage that returns it to the blood becomes blocked, the pressure within the eye can increase and cause damage to vision – a disorder known as glaucoma. Because of its transparency, the cornea must be nourished in this unusual manner. Our vision would be less clear if we had a set of blood vessels across the front of our eyes. The curvature of the cornea and of the lens, which lies immediately behind the iris, causes images to be focused on the inner surface of the back of the eye. Although this image is upside-down and reversed from left to right, the brain interprets this information appropriately. The shape of the cornea is fixed, but the lens is flexible; a special set of muscles can alter its shape so that the eye can obtain focused images of either nearby or distant objects. This change in the shape of the lens to adjust for distance is called accommodation. People experience light as having three features: colour, brightness, and saturation. These three types of experiences come from three corresponding characteristics of light waves: 5. The colour or hue of light depends on its wavelength, the distance between the peaks of its waves. 6. The brightness of light is related to intensity or the amount of light an object emits or reflects. Brightness depends on light wave amplitude, the height of light waves. Brightness is also somewhat influenced by wavelength. Yellow light tends to look brighter than reds or blues. 7. Saturation or colourfulness depends on light complexity, the range of wavelengths in light. The colour of a single wavelength is pure spectral colour. Such lights are called fully saturated. Outside a laboratory, light is rarely pure or of a single wavelength. Light is usually a mixture of several different wavelengths. The greater number of spectral colours in a light, the lower the saturation. Light of mixed wavelengths looks duller or paler than pure light. 94 CU IDOL SELF LEARNING MATERIAL (SLM)
Wavelength ——>Colour Amplitude ——> Brightness Complexity ——> Saturation Rainbows and Lights White light: Completely unsaturated. It is a mixture of all wavelengths of light. The visible spectrum: Includes the colours of the rainbow, which are red, orange, yellow, green, blue, indigo, and violet. Ultraviolet light: The kind of light that causes sunburns. It has a wavelength somewhat shorter than the violet light at the end of the visible spectrum. Infrared radiation: Has a wavelength somewhat longer than the red light at the other end of the visible spectrum. Vision is different from all the other senses. The neurons in this case are sensitive to light. Light enters through the pupil and lens of the eye and is projected onto the back surface of the eye called the retina. There are two types of receptors present in the retina. They are called rods and cones. The process of vision cannot be understood without some knowledge about the structure of the eye: 8. The cornea is the transparent, protective outer membrane of the eye. 9. The iris, the coloured part of the eye, is a ring of muscle. 10. The iris surrounds an opening called the pupil, which can get bigger or smaller to allow different amounts of light through the lens to the back of the eye. In bright light, the pupil contracts to restrict light intake; in dim light, the pupil expands to increase light intake. 11. The lens, which lies behind the pupil and iris, can adjust its shape to focus light from objects that are near or far away. This process is called accommodation. 12. Light passing through the cornea, pupil, and lens falls onto the retina at the back of the eye. The retina is a thin layer of neural tissue. The image that falls on the retina is always upside down. 13. The centre of the retina, the fovea, is where vision is sharpest. This explains why people look directly at an object they want to inspect. This causes the image to fall onto the fovea, where vision is clearest. 95 CU IDOL SELF LEARNING MATERIAL (SLM)
Figure 7.3.: The Human Eye The retina has millions of photoreceptors called rods and cones. Photoreceptors are specialized cells that respond to light stimuli. There are many more rods than cones. The long, narrow cells, called rods, are highly sensitive to light and allow vision even in dim conditions. There are no rods in the fovea, which is why vision becomes hazy in dim light. However, the area just outside the fovea contains many rods, and these allow peripheral vision. The rod cells are sensitive to light. They contain a chemical called rhodopsin or visual purple which is sensitive to light. Cones function similarly but they have a chemical called iodipin. This chemical is more sensitive to specific wavelengths of light depending on the pigments associated with the chemical. Normally, the length of the eye matches the refractive power of the cornea and the lens so that the image of the visual scene is sharply focused on the retina. However, for some people these two factors are not matched, and the image on the retina is therefore out of focus. There is a problem with sensing objects at various distances: some have difficulty in focusing on objects in the distance; others have difficulty in focusing on near objects. These people need an extra lens in front of their eyes (in the form of spectacles or contact lenses) to correct the discrepancy and bring the image into focus. 96 CU IDOL SELF LEARNING MATERIAL (SLM)
People whose eyes are too long (front to back) are said to be near-sighted; they need a concave lens to correct the focus. The image on the right of Figure 5.10 shows what a near- sighted person would see. People whose eyes are too short are said to be farsighted; they need a convex lens. As people get older, not only does the cornea of the eye begin to yellow and the sensitivity of the rods to decline (Sturr et al., 1997), but the lenses of their them to focus on objects close to them. These people need reading glasses with convex lenses (or varifocals, if they already wear glasses). The retina, which lines the inner surface of the back of the eye, performs the sensory functions of the eye. Embedded in the retina are over 130 million photoreceptors – specialised neurons that transduce light into neural activity. The information from the photoreceptors is transmitted to neurons that send axons towards one point at the back of the eye – the optic disc. All axons leave the eye at this point and join the optic nerve, which travels to the brain Figure 7.4.: Lenses used to correct near-sightedness and farsightedness. The human retina contains two general types of photoreceptors: 125 million rods and 6 million cones, so called because of their shapes. Rods function mainly in dim light; they are very sensitive to light. Cones function when the level of illumination is bright enough to see things clearly. They are also responsible for colour vision. The fovea, a small pit in the back of the retina approximately 1 mm in diameter, contains only cones and is responsible for our most detailed vision. When we look at a point in our visual field, we move our eyes so that the image of that point falls directly on the cone-packed fovea. Farther away from the fovea, the number of cones 97 CU IDOL SELF LEARNING MATERIAL (SLM)
decreases and the number of rods increases. Up to 100 rods may converge on a single ganglion cell. A ganglion cell that receives information from so many rods is sensitive to very low levels of light. Rods are therefore responsible for our sensitivity to very dim light, but they provide poor acuity. HEARING Hearing depends on vibrations of the air, called sound waves. Sound waves from the air pass through various bones until they reach the inner ear, which contains tiny hairlike cells that move back and forth (much like a field of wheat waving in the wind). These hair cells change sound vibrations into neuronal signals that travel through the auditory nerve to the brain. Loudness of sound is determined by the amplitude, or height, of sound waves. The higher the amplitude, the louder the sound. This strength, or sound-pressure energy, is measured in decibels. The sounds humans hear range upward from 0 decibels, the softest sound the human ear can detect, to about 140 decibels, which is roughly as loud as a jet plane taking off. Any sound over 110 decibels can damage hearing as can persistent sounds as low as 80 decibels. Any sound that is painful when you first hear it will damage your hearing if you hear it often enough. Pitch depends on sound-wave frequency, or the rate of the vibration of the medium through which the sound wave is transmitted. Low frequencies produce deep bass sounds, and high frequencies produce shrill squeaks. If you hear a sound composed of a combination of different frequencies, you can hear the separate pitches even though they occur simultaneously. For example, if you strike two keys of a piano at the same time, your ear can detect two distinct pitches. The ear and its functioning When people refer to the ear, they usually mean what anatomists call the pinna – the flesh- covered cartilage attached to the side of the head (pinna means ‘wing’ in Latin). But the pinna performs only a small role in audition: it helps us to determine the direction of sound. The real business of hearing is done in the inner ear The ear is designed to capture sound waves. The outer ear receives sound waves, and the earflap directs the sounds down a short tube called the auditory canal. The vibration of air (the sound wave) causes air in the auditory canal to vibrate, which in turn causes the eardrum to vibrate. The middle ear is an air-filled cavity. Its main structures are three tiny bones— the hammer, anvil, and stirrup. These bones are linked to the eardrum at one end and to the cochlea at the other end. When sound waves cause the eardrum to vibrate, these bones vibrate and push against the cochlea. The cochlea makes up the inner ear. The cochlea is a bony tube that contains fluids and neurons. The pressure against the cochlea makes the liquid inside the cochlea move. Tiny hairs inside the cochlea pick up the motion. These hairs are attached to sensory cells. The 98 CU IDOL SELF LEARNING MATERIAL (SLM)
sensory cells turn the sound vibrations into neuronal impulses. The auditory nerve carries these impulses to the brain. This neuronal input goes to the hearing areas of the cerebral cortex of the brain. Figure 7.5.: Human Ear The eardrum is a thin, flexible membrane that vibrates back and forth in response to sound waves. It passes these vibrations, via the bones of the middle ear, to the inner ear, a 2 cm cavity which separates the outer and middle ear. The eardrum is attached to the first of three middle ear bones called the ossicles (literally, ‘little bones’). The three ossicles are known as the malleus, incus and stapes (from Latin: hammer, anvil and stirrup) because of their shapes. These bones act together, in lever fashion, to transmit the vibrations of the eardrum to the fluid-filled structure of the inner ear that contains the receptive organ. The part of the ear that contains the receptive organ of hearing is called the cochlea (kokhlos means ‘snail’, which also describes its shape). Uncoiled, this would reach 35 mm and is 2 mm in diameter (Goldstein, 2007). It is filled with liquid and a bony chamber attached to the cochlea (the vestibule) contains two openings, the oval window and the round window. The last of the three ossicles (the stapes) presses against a membrane behind an opening in the bone surrounding the cochlea called the oval window, thus transmitting sound waves into the liquid inside the cochlea, where it can reach the receptive organ of hearing. The cochlea is divided along its length into three cavities by the basilar membrane and Reisner’s membrane. The auditory receptor cells sit on the surface of the basilar membrane. As the footplate of the stapes presses back and forth against the membrane behind the oval window, pressure changes in the fluid above the basilar membrane cause the basilar membrane to vibrate up and down. Because the basilar membrane varies in width and flexibility along its length, different frequencies of sound cause different parts of the basilar membrane to vibrate. High-frequency sounds cause the end near the oval window to vibrate, medium-frequency sounds cause the middle to vibrate, and low- frequency sounds cause the tip to vibrate. 99 CU IDOL SELF LEARNING MATERIAL (SLM)
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