NEUROBIOLOGICAL PERSPECTIVE OF BEHAVIOUR

101 Chapter- 18 know as mind is closely related to certain aspects of the behavior of the brain, not to the heart, as An essay on Aristotle thought. Its most Consciousness mysterious aspect is consciousness or awareness, which can take many forms, from Scientists have long considered the experience of pain to self- the nature of consciousness consciousness. In the past the without producing a fully mind (or soul) was often regarded, satisfactory definition. In the early as it was by Descartes, as 20th century American something immaterial, separate philosopher and psychologist from the brain but interacting with William James suggested that it in some way. A few consciousness is a mental neuroscientists, such as Sir John process involving both attention to Eccles, still assert that the soul is external stimuli and short-term distinct from the body. But most memory. Later scientific neuroscientists now believe that explorations of consciousness all aspects of mind, including its mostly expanded upon James’s most puzzling attribute— work. In this article from a 1997 consciousness or awareness—are special issue of Scientific likely to be explainable in a more American, Nobel laureate Francis materialistic way as the behavior Crick, who helped determine the of large sets of interacting structure of DNA, and fellow neurons. As William James, the biophysicist Christof Koch explain father of American psychology, how experiments on vision might said a century ago, consciousness deepen our understanding of is not a thing but a process. consciousness. Exactly what the process is, however, has yet to be The Problem of Consciousness discovered. For many years after By Francis Crick and Christof James penned The Principles of Koch Psychology, consciousness was a taboo concept in American The overwhelming question in psychology because of the neurobiology today is the relation between the mind and the brain. dominance of the behaviorist Everyone agrees that what we movement. With the advent of cognitive science in the mid- 1950s, it became possible once

102 more for psychologists to consider psychologists feel that any satisfactory theory should try to mental processes as opposed to explain as many aspects of consciousness as possible, merely observing behavior. In including emotion, imagination, dreams, mystical experiences and spite of these changes, until so on. Although such an all- embracing theory will be recently most cognitive scientists necessary in the long run, we thought it wiser to begin with the ignored consciousness, as did particular aspect of consciousness that is likely to yield most easily. almost all neuroscientists. The What this aspect may be is a matter of personal judgment. We problem was felt to be either selected the mammalian visual system because humans are very purely \"philosophical\" or too visual animals and because so much experimental and theoretical elusive to study experimentally. It work has already been done on it. It is not easy to grasp exactly what would not have been easy for a we need to explain, and it will take many careful experiments before neuroscientist to get a grant just to visual consciousness can be described scientifically. We did not study consciousness. attempt to define consciousness itself because of the dangers of In our opinion, such timidity is premature definition. (If this seems like a copout, try defining the word ridiculous, so a few years ago we \"gene\"—you will not find it easy.) Yet the experimental evidence that began to think about how best to already exists provides enough of a glimpse of the nature of visual attack the problem scientifically. consciousness to guide research. In this article, we will attempt to How to explain mental events as show how this evidence opens the way to attack this profound and being caused by the firing of large intriguing problem. Visual theorists agree that the sets of neurons? Although there problem of visual consciousness is are those who believe such an approach is hopeless, we feel it is not productive to worry too much over aspects of the problem that cannot be solved scientifically or, more precisely, cannot be solved solely by using existing scientific ideas. Radically new concepts may indeed be needed—recall the modifications of scientific thinking forced on us by quantum mechanics. The only sensible approach is to press the experimental attack until we are confronted with dilemmas that call for new ways of thinking. There are many possible approaches to the problem of consciousness. Some

103 ill posed. The mathematical term cognitive scientists, that the \"ill posed\" means that additional computations carried out by the constraints are needed to solve brain are largely unconscious and the problem. Although the main that what we become aware of is function of the visual system is to the result of these computations. perceive objects and events in the But while the customary view is world around us, the information that this awareness occurs at the available to our eyes is not highest levels of the computational sufficient by itself to provide the system, Jackendoff has proposed brain with its unique interpretation an intermediate-level theory of of the visual world. The brain must consciousness. use past experience (either its What we see, Jackendoff own or that of our distant suggests, relates to a ancestors, which is embedded in representation of surfaces that are our genes) to help interpret the directly visible to us, together with information coming into our eyes. their outline, orientation, color, An example would be the texture and movement. (This idea derivation of the three-dimensional has similarities to what the late representation of the world from David C. Marr of the the two-dimensional signals falling Massachusetts Institute of onto the retinas of our two eyes or Technology called a \"2 1/2- even onto one of them. dimensional sketch.\" It is more Visual theorists also would agree than a two-dimensional sketch that seeing is a constructive because it conveys the orientation process, one in which the brain of the visible surfaces. It is less has to carry out complex activities than three-dimensional because (sometimes called computations) depth information is not explicitly in order to decide which represented.) In the next stage interpretation to adopt of the this sketch is processed by the ambiguous visual input. brain to produce a three- \"Computation\" implies that the dimensional representation. brain acts to form a symbolic Jackendoff argues that we are not representation of the visual world, visually aware of this three- with a mapping (in the dimensional representation. mathematical sense) of certain An example may make this aspects of that world onto process clearer. If you look at a elements in the brain. person whose back is turned to Ray Jackendoff of Brandeis you, you can see the back of the University postulates, as do most head but not the face.

104 Nevertheless, your brain infers see a face on the screen, there that the person has a face. We must be neurons in your brain can deduce as much because if whose firing, in some sense, that person turned around and had symbolizes that face. no face, you would be very We call this pattern of firing surprised. neurons an active representation. The viewer-centered A latent representation of a face representation that corresponds to must also be stored in the brain, the visible back of the head is probably as a special pattern of what you are vividly aware of. synaptic connections between What your brain infers about the neurons. For example, you front would come from some kind probably have a representation of of three-dimensional the Statue of Liberty in your brain, representation. This does not a representation that usually is mean that information flows only inactive. If you do think about the from the surface representation to Statue, the representation the three-dimensional one; it becomes active, with the relevant almost certainly flows in both neurons firing away. directions. When you imagine the An object, incidentally, may be front of the face, what you are represented in more than one aware of is a surface way—as a visual image, as a set representation generated by of words and their related sounds, information from the three- or even as a touch or a smell. dimensional model. These different representations It is important to distinguish are likely to interact with one between an explicit and an implicit another. The representation is representation. An explicit likely to be distributed over many representation is something that is neurons, both locally and more symbolized without further globally. Such a representation processing. An implicit may not be as simple and representation contains the same straightforward as uncritical information but requires further introspection might indicate. There processing to make it explicit. The is suggestive evidence, partly from pattern of colored dots on a studying how neurons fire in television screen, for example, various parts of a monkey's brain contains an implicit representation and partly from examining the of objects (say, a person's face), effects of certain types of brain but only the dots and their damage in humans, that different locations are explicit. When you aspects of a face—and of the

105 implications of a face—may be that does require attention. This in represented in different parts of the brain. turn probably leads to three- First, there is the representation of a face as a face: two eyes, a nose, dimensional object a mouth and so on. The neurons involved are usually not too fussy representations and thence to about the exact size or position of this face in the visual field, nor are more cognitive ones. they very sensitive to small changes in its orientation. In Representations corresponding to monkeys, there are neurons that respond best when the face is vivid consciousness are likely to turning in a particular direction, while others seem to be more have special properties. William concerned with the direction in which the eyes are gazing. James thought that consciousness Then there are representations of the parts of a face, as separate involved both attention and short- from those for the face as a whole. Further, the implications of seeing term memory. Most psychologists a face, such as that person's sex, the facial expression, the today would agree with this view. familiarity or unfamiliarity of the face, and in particular whose face Jackendoff writes that it is, may each be correlated with neurons firing in other places. consciousness is \"enriched\" by What we are aware of at any moment, in one sense or another, attention, implying that whereas is not a simple matter. We have suggested that there may be a attention may not be essential for very transient form of fleeting awareness that represents only certain limited types of rather simple features and does not require an attentional consciousness, it is necessary for mechanism. From this brief awareness the brain constructs a full consciousness. Yet it is not viewer-centered representation— what we see vividly and clearly— clear exactly which forms of memory are involved. Is long-term memory needed? Some forms of acquired knowledge are so embedded in the machinery of neural processing that they are almost certainly used in becoming aware of something. On the other hand, there is evidence from studies of brain-damaged patients that the ability to lay down new long-term episodic memories is not essential for consciousness to be experienced. It is difficult to imagine that anyone could be conscious if he or she had no memory whatsoever of what had just happened, even an extremely short one. Visual psychologists talk of iconic

106 memory, which lasts for a fraction handed person) appears not to be of a second, and working memory aware of visual information (such as that used to remember a received exclusively by the right new telephone number) that lasts side. This shows that none of the for only a few seconds unless it is information required for visual rehearsed. It is not clear whether awareness can reach the other both of these are essential for side of the brain by traveling down consciousness. In any case, the to the brain stem and, from there, division of short-term memory into back up. In a normal person, such these two categories may be too information can get to the other crude. side only by using the axons in the If these complex processes of corpus callosum. visual awareness are localized in A different part of the brain—the parts of the brain, which hippocampal system—is involved processes are likely to be where? in one-shot, or episodic, memories Many regions of the brain may be that, over weeks and months, it involved, but it is almost certain passes on to the neocortex. This that the cerebral neocortex plays a system is so placed that it dominant role. Visual information receives inputs from, and projects from the retina reaches the to, many parts of the brain. Thus, neocortex mainly by way of a part one might suspect that the of the thalamus (the lateral hippocampal system is the geniculate nucleus); another essential seat of consciousness. significant visual pathway from the This is not the case: evidence retina is to the superior colliculus, from studies of patients with at the top of the brain stem. damaged brains shows that this The cortex in humans consists of system is not essential for visual two intricately folded sheets of awareness, although naturally a nerve tissue, one on each side of patient lacking one is severely the head. These sheets are handicapped in everyday life connected by a large tract of about because he cannot remember half a billion axons called the anything that took place more than corpus callosum. It is well known a minute or so in the past. that if the corpus callosum is cut, In broad terms, the neocortex of as is done for certain cases of alert animals probably acts in two intractable epilepsy, one side of ways. By building on crude and the brain is not aware of what the somewhat redundant wiring, other side is seeing. In particular, produced by our genes and by the left side of the brain (in a right- embryonic processes, the

107 neocortex draws on visual and otherwise, no animal could other experience to slowly \"rewire\" survive. The brain is handicapped itself to create categories (or in forming neuronal coalitions \"features\") it can respond to. A rapidly because, by computer new category is not fully created in standards, neurons act very the neocortex after exposure to slowly. The brain compensates for only one example of it, although this relative slowness partly by some small modifications of the using very many neurons, neural connections may be made. simultaneously and in parallel, and The second function of the partly by arranging the system in a neocortex (at least of the visual roughly hierarchical manner. part of it) is to respond extremely If visual awareness at any moment rapidly to incoming signals. To do corresponds to sets of neurons so, it uses the categories it has firing, then the obvious question is: learned and tries to find the Where are these neurons located combinations of active neurons in the brain, and in what way are that, on the basis of its past they firing? Visual awareness is experience, are most likely to highly unlikely to occupy all the represent the relevant objects and neurons in the neocortex that are events in the visual world at that firing above their background rate moment. The formation of such at a particular moment. We would coalitions of active neurons may expect that, theoretically, at least also be influenced by biases some of these neurons would be coming from other parts of the involved in doing computations— brain: for example, signals telling it trying to arrive at the best what best to attend to or high-level coalitions—whereas others would expectations about the nature of express the results of these the stimulus. computations, in other words, Consciousness, as James noted, what we see. is always changing. These rapidly Fortunately, some experimental formed coalitions occur at different evidence can be found to back up levels and interact to form even this theoretical conclusion. A broader coalitions. They are phenomenon called binocular transient, lasting usually for only a rivalry may help identify the fraction of a second. Because neurons whose firing symbolizes coalitions in the visual system are awareness. This phenomenon can the basis of what we see, be seen in dramatic form in an evolution has seen to it that they exhibit prepared by Sally form as fast as possible;

108 Duensing and Bob Miller at the In some cases, only part of the Exploratorium in San Francisco. face disappears. Sometimes, for example, one eye, or both eyes, Conflicting Inputs will remain. If the viewer looks at the smile on the person's face, the Binocular rivalry occurs when face may disappear, leaving only each eye has a different visual the smile. For this reason, the input relating to the same part of effect has been called the the visual field. The early visual Cheshire Cat effect, after the cat system on the left side of the brain in Lewis Carroll's Alice's receives an input from both eyes Adventures in Wonderland. but sees only the part of the visual Although it is very difficult to field to the right of the fixation record activity in individual point. The converse is true for the neurons in a human brain, such right side. If these two conflicting studies can be done in monkeys. inputs are rivalrous, one sees not A simple example of binocular the two inputs superimposed but rivalry has been studied in a first one input, then the other, and monkey by Nikos K. Logothetis so on in alternation. and Jeffrey D. Schall, both then at In the exhibit, called \"The M.I.T. They trained a macaque to Cheshire Cat,\" viewers put their keep its eyes still and to signal heads in a fixed place and are told whether it is seeing upward or to keep the gaze fixed. By means downward movement of a of a suitably placed mirror, one of horizontal grating. To produce the eyes can look at another rivalry, upward movement is person's face, directly in front, projected into one of the monkey's while the other eye sees a blank eyes and downward movement white screen to the side. If the into the other, so that the two viewer waves a hand in front of images overlap in the visual field. this plain screen at the same The monkey signals that it sees up location in his or her visual field and down movements occupied by the face, the face is alternatively, just as humans wiped out. The movement of the would. Even though the motion hand, being visually very salient, stimulus coming into the monkey's has captured the brain's attention. eyes is always the same, the Without attention the face cannot monkey's percept changes every be seen. If the viewer moves the second or so. eyes, the face reappears. Cortical area MT (which some researchers prefer to label V5) is

109 an area mainly concerned with retina where the optic nerve leaves the retina and projects to movement. What do the neurons the brain. Its location is about 15 degrees from the fovea (the visual in MT do when the monkey's center of the eye). Yet if you close one eye, you do not see a hole in percept is sometimes up and your visual field. Philosopher Daniel C. Dennett of sometimes down? (The Tufts University is unusual among philosophers in that he is researchers studied only the interested both in psychology and in the brain. This interest is much monkey's first response.) The to be welcomed. In a recent book, Consciousness Explained, he has simplified answer—the actual data argued that it is wrong to talk are rather more messy—is that about filling in. He concludes, correctly, that \"an absence of whereas the firing of some of the information is not the same as information about an absence.\" neurons correlates with the From this general principle he argues that the brain does not fill changes in the percept, for others in the blind spot but rather ignores it. the average firing rate is relatively Dennett's argument by itself, however, does not establish that unchanged and independent of filling in does not occur; it only suggests that it might not. Dennett which direction of movement the also states that \"your brain has no machinery for [filling in] at this monkey is seeing at that moment. location.\" This statement is incorrect. The primary visual Thus, it is unlikely that the firing of cortex lacks a direct input from one eye, but normal \"machinery\" all the neurons in the visual is there to deal with the input from the other eye. Ricardo Gattass neocortex at one particular and his colleagues at the Federal University of Rio de Janeiro have moment corresponds to the shown that in the macaque some of the neurons in the blind-spot monkey's visual awareness. Exactly which neurons do correspond to awareness remains to be discovered. We have postulated that when we clearly see something, there must be neurons actively firing that stand for what we see. This might be called the activity principle. Here, too, there is some experimental evidence. One example is the firing of neurons in a specific cortical visual area in response to illusory contours. Another and perhaps more striking case is the filling in of the blind spot. The blind spot in each eye is caused by the lack of photoreceptors in the area of the

110 area of the primary visual cortex having to do with motion. A neuron, for instance, might fire do respond to input from both strongly in response to the movement of a bar in a particular eyes, probably assisted by inputs place in the visual field, but only when the bar is oriented at a from other parts of the cortex. certain angle, moving in one of the two directions perpendicular to its Moreover, in the case of simple length within a certain range of speed. filling in, some of the neurons in It is technically difficult to excite just a single neuron, but it is that region respond as if they were known that neurons that respond to roughly the same position, actively filling in. orientation and direction of movement of a bar tend to be Thus, Dennett's claim about blind located near one another in the cortical sheet. The experimenters spots is incorrect. In addition, taught the monkey a simple task in movement discrimination using a psychological experiments by mixture of dots, some moving randomly, the rest all in one Vilayanur S. Ramachandran [see direction. They showed that electrical stimulation of a small \"Blind Spots,\" SCIENTIFIC region in the right place in cortical area MT would bias the monkey's AMERICAN, May 1992] have shown motion discrimination, almost always in the expected direction. that what is filled in can be quite Thus, the stimulation of these neurons can influence the complex depending on the overall monkey's behavior and probably its visual percept. Such context of the visual scene. How, experiments do not, however, show decisively that the firing of he argues, can your brain be such neurons is the exact neural correlate of the percept. The ignoring something that is in fact correlate could be only a subset of the neurons being activated. Or commanding attention? perhaps the real correlate is the Filling in, therefore, is not to be dismissed as nonexistent or unusual. It probably represents a basic interpolation process that can occur at many levels in the neocortex. It is, incidentally, a good example of what is meant by a constructive process. How can we discover the neurons whose firing symbolizes a particular percept? William T. Newsome and his colleagues at Stanford University have done a series of brilliant experiments on neurons in cortical area MT of the macaque's brain. By studying a neuron in area MT, we may discover that it responds best to very specific visual features

111 firing of neurons in another part of sight patients have some ability to the visual hierarchy that are respond to wavelength, orientation strongly influenced by the neurons and motion, yet they cannot activated in area MT. distinguish a triangle from a These same reservations apply square. also to cases of binocular rivalry. It is naturally of great interest to Clearly, the problem of finding the know which neural pathways are neurons whose firing symbolizes a being used in these patients. particular percept is not going to Investigators originally suspected be easy. It will take many careful that the pathway ran through the experiments to track them down superior colliculus. Recent even for one kind of percept. experiments suggest that a direct It seems obvious that the purpose albeit weak connection may be of vivid visual awareness is to feed involved between the lateral into the cortical areas concerned geniculate nucleus and other with the implications of what we visual areas in the cortex. It is see; from there the information unclear whether an intact primary shuttles on the one hand to the visual cortex region is essential for hippocampal system, to be immediate visual awareness. encoded (temporarily) into long- Conceivably the visual signal in term episodic memory, and on the blindsight is so weak that the other to the planning levels of the neural activity cannot produce motor system. But is it possible to awareness, although it remains go from a visual input to a strong enough to get through to behavioral output without any the motor system. relevant visual awareness? Normal-seeing people regularly That such a process can happen respond to visual signals without is demonstrated by the remarkable being fully aware of them. In class of patients with \"blindsight.\" automatic actions, such as These patients, all of whom have swimming or driving a car, suffered damage to their visual complex but stereotypical actions cortex, can point with fair accuracy occur with little, if any, associated at visual targets or track them with visual awareness. In other cases, their eyes while vigorously the information conveyed is either denying seeing anything. In fact, very limited or very attenuated. these patients are as surprised as Thus, while we can function their doctors by their abilities. The without visual awareness, our amount of information that \"gets behavior without it is rather through,\" however, is limited: blind restricted.

112 Clearly, it takes a certain amount hierarchy and in other parts of the of time to experience a conscious percept. It is difficult to determine brain. Processing is also more just how much time is needed for an episode of visual awareness, rapid in trained, compared with but one aspect of the problem that can be demonstrated naive, observers. experimentally is that signals received close together in time are Because it appears to be involved treated by the brain as simultaneous. in some forms of visual A disk of red light is flashed for, say, 20 milliseconds, followed awareness, it would help if we immediately by a 20-millisecond flash of green light in the same could discover the neural basis of place. The subject reports that he did not see a red light followed by attention. Eye movement is a form a green light. Instead he saw a yellow light, just as he would have of attention, since the area of the if the red and the green light had been flashed simultaneously. Yet visual field in which we see with the subject could not have experienced yellow until after the high resolution is remarkably information from the green flash had been processed and small, roughly the area of the integrated with the preceding red one. thumbnail at arm's length. Thus, Experiments of this type led psychologist Robert Efron, now at we move our eyes to gaze directly the University of California at Davis, to conclude that the at an object in order to see it more processing period for perception is about 60 to 70 milliseconds. clearly. Our eyes usually move Similar periods are found in experiments with tones in the three or four times a second. auditory system. It is always possible, however, that the Psychologists have shown, processing times may be different in higher parts of the visual however, that there appears to be a faster form of attention that moves around, in some sense, when our eyes are stationary. The exact psychological nature of this faster attentional mechanism is at present controversial. Several neuroscientists, however, including Robert Desimone and his colleagues at the National Institute of Mental Health, have shown that the rate of firing of certain neurons in the macaque's visual system depends on what the monkey is attending to in the visual field. Thus, attention is not solely a psychological concept; it also has neural correlates that can be observed. A number of researchers have found that the

113 pulvinar, a region of the thalamus, example, be associated with only appears to be involved in visual those areas that connect back attention. We would like to believe directly to the primary visual cortex that the thalamus deserves to be or alternatively with those areas called \"the organ of attention,\" but that project into one another's this status has yet to be layer 4. (The latter areas are established. always at the same level in the visual hierarchy.) Attention and Awareness The key issue, then, is how the brain forms its global The major problem is to find what representations from visual activity in the brain corresponds signals. If attention is indeed directly to visual awareness. It has crucial for visual awareness, the been speculated that each cortical brain could form representations area produces awareness of only by attending to just one object at a those visual features that are time, rapidly moving from one \"columnar,\" or arranged in the object to the next. For example, stack or column of neurons the neurons representing all the perpendicular to the cortical different aspects of the attended surface. Thus, the primary visual object could all fire together very cortex could code for orientation rapidly for a short period, possibly and area MT for motion. So far in rapid bursts. experimentalists have not found This fast, simultaneous firing might one particular region in the brain not only excite those neurons that where all the information needed symbolized the implications of that for visual awareness appears to object but also temporarily come together. Dennett has strengthen the relevant synapses dubbed such a hypothetical place so that this particular pattern of \"The Cartesian Theater.\" He firing could be quickly recalled—a argues on theoretical grounds that form of short-term memory. If only it does not exist. one representation needs to be Awareness seems to be held in short-term memory, as in distributed not just on a local remembering a single task, the scale, but more widely over the neurons involved may continue to neocortex. Vivid visual awareness fire for a period. is unlikely to be distributed over A problem arises if it is necessary every cortical area because some to be aware of more than one areas show no response to visual object at exactly the same time. If signals. Awareness might, for all the attributes of two or more

114 objects were represented by figure from ground or assist the neurons firing rapidly, their mechanism of attention. attributes might be confused. The color of one might become Correlates of Consciousness attached to the shape of another. This happens sometimes in very Are there some particular types of brief presentations. Some time ago Christoph von der neurons, distributed over the Malsburg, now at the Ruhr- Universität Bochum, suggested visual neocortex, whose firing that this difficulty would be circumvented if the neurons directly symbolizes the content of associated with any one object all fired in synchrony (that is, if their visual awareness? One very times of firing were correlated) but out of synchrony with those simplistic hypothesis is that the representing other objects. Recently two groups in Germany activities in the upper layers of the reported that there does appear to be correlated firing between cortex are largely unconscious neurons in the visual cortex of the cat, often in a rhythmic manner, ones, whereas the activities in the with a frequency in the 35- to 75- hertz range, sometimes called 40- lower layers (layers 5 and 6) hertz, or g, oscillation. Von der Malsburg's proposal mostly correlate with prompted us to suggest that this rhythmic and synchronized firing consciousness. We have might be the neural correlate of awareness and that it might serve wondered whether the pyramidal to bind together activity concerning the same object in neurons in layer 5 of the different cortical areas. The matter is still undecided, but at present neocortex, especially the larger the fragmentary experimental evidence does rather little to ones, might play this latter role. support such an idea. Another possibility is that the 40-hertz These are the only cortical oscillations may help distinguish neurons that project right out of the cortical system (that is, not to the neocortex, the thalamus or the claustrum). If visual awareness represents the results of neural computations in the cortex, one might expect that what the cortex sends elsewhere would symbolize those results. Moreover, the neurons in layer 5 show a rather unusual propensity to fire in bursts. The idea that layer 5 neurons may directly symbolize visual awareness is attractive, but it still is too early to tell whether there is anything in it.

115 Visual awareness is clearly a use for many different actions or difficult problem. More work is thoughts. Exactly how all these needed on the psychological and pathways work and how they neural basis of both attention and interact is far from clear. very short-term memory. Studying There have been more the neurons when a percept experiments on the behavior of changes, even though the visual neurons that respond to bistable input is constant, should be a visual percepts, such as binocular powerful experimental paradigm. rivalry, but it is probably too early We need to construct to draw firm conclusions from neurobiological theories of visual them about the exact neural awareness and test them using a correlates of visual combination of molecular, consciousness. We have neurobiological and clinical suggested on theoretical grounds imaging studies. based on the neuroanatomy of the We believe that once we have macaque monkey that primates mastered the secret of this simple are not directly aware of what is form of awareness, we may be happening in the primary visual close to understanding a central cortex, even though most of the mystery of human life: how the visual information flows through it. physical events occurring in our This hypothesis is supported by brains while we think and act in some experimental evidence, but the world relate to our subjective it is still controversial. sensations—that is, how the brain About the authors: Francis Crick relates to the mind. and Christof Koch share an Postscript: There have been interest in the experimental study several relevant developments of consciousness. Crick is the co- since this article was first discoverer, with James Watson, of published. It now seems likely that the double helical structure of there are rapid \"on-line\" systems DNA. While at the Medical for stereotyped motor responses Research Council Laboratory of such as hand or eye movement. Molecular Biology in Cambridge, These systems are unconscious he worked on the genetic code and lack memory. Conscious and on developmental biology. seeing, on the other hand, seems Since 1976, he has been at the to be slower and more subject to Salk Institute for Biological Studies visual illusions. The brain needs to in San Diego. His main interest form a conscious representation of lies in understanding the visual the visual scene that it then can system of mammals. Koch was

116 awarded his Ph.D. in biophysics by the University of Tübingen. After spending four years at the Massachusetts Institute of Technology, he joined the California Institute of Technology, where he is now professor of computation and neural systems. He is studying how single brain cells process information and the neural basis of motion perception, visual attention and awareness. He also designs analog VLSI vision chips for intelligent systems.

117 Chapter- 19 sexual growth and development of an individual but also his entire behaviour DUCTLESS GLANDS OR ENDOCRINE and developmental process. A slight GLANDS imbalance of these glands causes There are several glands in our body, restlessness, anxiety and weakness. which secrete several bodily chemicals Our physical strength, morale thinking both internally as well as externally. and reasoning power and decision- They can be grouped into two distinct making ability – all depend upon the categories namely duct glands and health of the glands. In short, these ductless glands r endocrine glands. glands are found to play a dominant role The glands like salivary glands that pour in the life of a person. Without their their secretion through ducts to the body proper functioning a man or woman surface directly are called duct glands. finds difficulty in leading a happy normal On the other hand ductless glands do life. not need ducts to pour the secretion. Eg. During emotional current the Their secretions are known as adrenal gland is observed to perform a hormones and are poured straight into useful function. In such a situation more the blood stream. The locations are as adrenaline is secreted that prepares an given below. individuals organs for the particular emotional state. Their over activity The under activity or over activity of makes an individual highly active and these glands caused by the deficiency energetic. or excess of the hormones secreted by These hormones may also cause sexual them as well as well as by the co acting maturity at an earlier age. A little boy or influence of other glands like Thyroid, girl may acquire secondary sex Pituitary and Adrenal affects not only the characteristics of a mature man or woman. In some cases over development of adrenal glands results in increased masculine characteristics like the growth of moustache and bearded in woman. All endocrine or ductless glands discussed above exercise a great influence various aspects of growth and development. These glands affect the behaviour of an individual by controlling

118 his emotional behaviour and our nervous system particularly by our physiological activities. In this way they brain apparatus. The proper growth and have a direct bearing upon the total development of nervous tissue and personality of an individual. Actually nervous system as whole, helps in the these are the hormones, secreted by task of proper intellectual development . these glands, which are responsible for Any defect in spinal cord or brain developing the typical personality apparatus seriously affects the characteristics in an individual. These intellectual growth. Similarly physical as hormones are circulated throughout the well as emotional development is also body and influence all those tissues on influenced by our nervous system. Our which functioning of body system, autonomic nervous system plays a emotional actions and even thoughts leading role in this direction. It controls depend.. Thus the hormones secreted the activity of involuntary processes like by deferent endocrine glands control the circulation of blood , digestion behaviour as well as the overall respiration and action of the glands. . personality development of an individual. And in a way the knowledge These processes not only control of the secretion of these hormones and the physical or emotional activity of an functioning of the respective glands is a individual but also exercise a great deal matter of vital importance for the learner of influence over the physical and of psychology and counseling. emotional development of an individual. Nerve tissues also cause the change in NERVOUS SYSTEM AND PERSONALITY the secretion of hormones by some DEVELOPMENT glands and consequently influence the emotional behaviour of an individual. Our behaviour to a great extend is More over the nervous system acts as a controlled by our nervous system. How coordinating agency for the many we will behave in a particular situation operations going on inside the body and depends upon the judgment of our harmonizes the activities and functions brain. the sense impression which we of the body parts – internal as well as receive through our sense organs are external. In this way nervous system meaning less unless they are given should be considered as one of the meaning by our nervous system. There important components of the body fore our observation and perceptions machine that plays an important role in are controlled by nervous system. How the growth and development of the intelligently we would react or make use personality of an individual. of our mental power is again decided by

119 Major Hormones Hormone Gland Origin Target Tissue Function Adrenocorticotropic Pituitary gland Adrenal cortex Triggers secretion of hydrocortisone from the (anterior) adrenal gland Growth hormone Pituitary gland Throughout body Stimulates growth and development (anterior) Follicle-stimulating Pituitary gland Sex glands Stimulates female egg maturation and male hormone (anterior) Sex glands sperm production Luteinizing hormone Mammary glands Pituitary gland Thyroid gland Stimulates female ovulation and male secretion Prolactin (anterior) of testosterone Thyroid-stimulating Pituitary gland Stimulates milk production in the breasts after hormone (anterior) childbirth Pituitary gland Triggers secretion of thyroid hormones (anterior) Melanocyte-stimulating Pituitary gland Melanin-producing cells Controls skin pigmentation hormone (anterior) Antidiuretic hormone Pituitary gland Kidneys Regulates water retention and blood pressure (posterior) Oxytocin Pituitary gland Uterus Triggers contraction of the uterus during labor (posterior) Mammary glands Stimulates milk letdown for breast-feeding after childbirth Melatonin Pineal gland Unclear, although possible May affect skin pigmentation; may regulate target sites are pigment biorhythms (awake/sleep patterns) and cells and sex organs prevent jet lag Calcitonin Thyroid gland Bones Controls the level of calcium in the blood by depositing it in the bones Thyroid hormone Thyroid gland Throughout body Increases the body's metabolic rate; promotes normal growth and development Parathyroid hormone Parathyroid glands Bones, intestines, and Regulates calcium level in blood Thymosin kidneys Promotes the growth and development of white Thymus White blood cells blood cells, helping the body fight infection Aldosterone Adrenal gland Kidneys Regulates sodium and potassium levels in the Hydrocortisone Adrenal gland blood to control blood pressure Epinephrine Adrenal gland Norepinephrine Adrenal gland Throughout body Plays key role in stress response; increases Glucagon Pancreas blood glucose levels and mobilizes fat stores; Insulin Pancreas reduces inflammatation Estrogen Ovaries Progesterone Ovaries Muscles and blood vessels Increases blood pressure, heart and metabolic Testosterone Testes rate, and blood sugar levels; dilates blood Erythropoietin Kidney vessels. Also released during exercise Muscles and blood vessels Increases blood pressure and heart rate; constricts blood vessels Liver Stimulates the breakdown of glycogen (stored carbohydrate) into glucose (blood sugar); regulates glucose blood level Throughout body Regulates blood glucose levels; increases storage of glycogen; facilitates glucose intake by body cells Female reproductive Causes sexual development and growth; system maintains proper functioning of female reproductive system Mammary glands Prepares uterus for pregnancy Uterus Causes sexual development and growth spurt; Throughout body maintains proper functioning of male reproductive system Bone Marrow Produces red blood cells

120 Chapter 20 are the hormones responsible for such blissful romantic feelings? Psychoneuroendocrinology of hormonal changes when falling in love DESIRE AND LUST: THE ROLE OF ESTROGEN AND TESTOSTERONE ARTICLE 1: Desire or lust is the first stage of love. CAN HORMONES BE Both genders experience this stage. The RESPONSIBLE FOR PEOPLE two hormones responsible for desire are estrogen and testosterone. The human FALLING IN LOVE? body’s immediate reaction to a potential mate is the urge to procreate. The Love is a many-splendored thing, logical part of our brains would say indeed. It is often the subject of art, otherwise. But perhaps Sigmund Freud literature and music but no matter how was right in his theory that sexual urges complex and unearthly the magical in the unconscious constitute the main feeling of falling in love seems, science human drives. The body is unconscious can perfectly explain the butterflies in about all these bodily processes and yet your stomach and why people feel they for thousands of years, people do crazy are destined for each other. It can even things for someone they have just met. partly explain why you got left behind or Why is that? why someone cheated. But they say it is abstract so let us try to translate and Hormonal changes of a woman’s compare it into its closest quantifiable monthly cycle may be more significant in elements such as attraction, desire, and the arena of attraction and mating. commitment. Certain forms of estrogen make women more attractive to men while Our hormones have been associated testosterone also makes men more with behavior, depression, stress, attractive by helping them achieve more anxiety, manliness, forgetfulness, masculinity. Studies suggest that daintiness, social bonding, reliability, women may dress more provocatively, generosity, honesty, risk tolerance and flirt more, and have a higher probability guess what? It is also highly responsible of becoming more sexually inclined for for romance and sexual behavior. Going approximately six days mid-cycle, back to prehistoric times, the first Homo before and after ovulation. Slight shifts sapiens perhaps never thought of this in their scent, skin tone and voice pitch thing called love. But they felt attraction also occur comparable to how certain or an urge to procreate, and they species in the animal kingdom show off propagated, and later on, became a way their flamboyant colors to attract their more evolved species creating mates. technologies and giant buildings today. If you’ve been thinking all along that all Both testosterone and estrogen are also the love stories are controlled by fate, at their peak during the follicular phase science wouldn’t agree so much as hormones tell a different story. So what

121 of a woman’s cycle. The testosterone and make people drug users feel an level in a woman’s body is directly elated pleasure. Aside from using drugs, related to the length of the follicular winning and other pleasurable events, phase. Yes, women have testosterone high levels of dopamine get released as well, albeit in smaller amounts when someone is thinking about or near compared to men. And unsurprisingly, his or her potential partner or love men with higher testosterone levels interest. The feeling of pleasure can be have higher sex drives and are addictive. Who does not want to feel somewhat perceives as attractive. Not pleasure? The mere act of thinking all men are equally born physically about a potential partner can give attractive. However, some women tend butterflies in the stomach. But then to gravitate to certain men despite the again, those aren’t butterflies. It’s fact that they are not exceedingly dopamine. physically attractive. One explanation could be his hormones. He may have Adrenaline higher testosterone that makes him appear more masculine and that tends Adrenaline, also known as epinephrine, to attract women particularly during their is a hormone that makes your heart ovulation period. Testosterone and race, makes you feel nervous and estrogen also regulate the reproductive sweaty. You breathe faster as if you system, which is why birth control pills were being chased by dogs but instead, can affect libido. you just saw your crush. This hormone is produced in some parts of the ATTRACTION nervous system and chromaffin cells. When you are attracted to a person, the Attraction is the next stage of love. It is body’s initial response is stress, causing more complicated than just mere desire. you to sweat, have a dry mouth, and This is the period when a person have a raced heartbeat. becomes spell-bound to someone and spends most of their time thinking about Serotonin the other person. Three hormones are responsible for turning The third hormone responsible for rational people head-over-heels into attraction is serotonin. Serotonin is someone. These powerful hormones are highly responsible for several process dopamine, adrenaline, and serotonin. and reactions in the body. This includes mood, appetite, and perception of Dopamine situations. In the case of attraction, serotonin makes a person obsessive- Dopamine is the feel-good hormone. It compulsive, which is why a person can gets activated when something good or go on for several days and months pleasurable happens. Have you ever thinking about the person they are heard people say, “Love is like a drug?” attracted to. Sometimes people wonder Well, literally it can act that way. The why they are so obsessed over reason why people are addicted to someone even if it seems illogical. certain drugs is because of dopamine. Hormones don’t really work in such a Drugs stimulate dopamine production conscious way. Thus, one can trust that

122 as long as the body is able to produce procreation. Males those who received a this hormone, there is always a chance suppressant drug with their levels of of attraction. vasopressin stopped showing devotions and no longer cared to protect them During the phase of attraction, all these against new potential mates. hormones and chemicals work together with several other neurotransmitters to Oxytocin give feelings of excitement, pleasure, obsession, and even anxiety. It is Oxytocin is known as the hormone of understandable why people cannot seem to understand what they feel when love. This hormone is produced in the they are in love because it is all these contrasting feelings from these three hypothalamus and released into the different hormones happening all at once. I However, the pleasure somehow blood by the pituitary gland. It increases dissipates in the third stage causing people to go in separate ways and do social bonding, strengthens that same routine all over again. remembering of positive things and interactions, enhances the development of positive relationships. This hormone is present during childbirth and breastfeeding. High levels of oxytocin have been associated with increased ATTACHMENT generosity and trust. Aside from childbirth and breastfeeding, oxytocin is The third stage of love is attachment. also released when people hug, kiss or This is the test if such feelings of love will make a relationship between two during an orgasm. It promotes long term people last. After all the excitement, obsession, and pleasure, adrenaline, bonding and stops men in monogamous dopamine and serotonin will go back to normal levels. At this point two other relationships from being physically close hormones may be released, oxytocin and vasopressin. These hormones to other women. initially determine whether a couple will stay together. In theory, vasopressin and oxytocin are recognized by social science, evolutionary psychology, and neuroscience to be hormones that ensure the togetherness and longevity of a couple to raise a family. Physical Vasopressin intimacy and regular sexual activity keep Vasopressin, a neurohypophysial these hormones at their ideal levels. hormone found in most mammals SUBCONSCIOUS HORMONAL PRODUCTION VS. CONSCIOUS including humans, is responsible for CHOICES feelings of bonding. This hormone stimulates a rewarding feeling for forming lasting bonds with a mate. Although hormones are produced subconsciously, awareness to how we Studies about vasopressin have been can regulate these hormones is entirely up to us. Being devoted to a partner mostly limited to studying animals, after the attraction stage can be caused by the hormones eventually causing the specifically prairie vole. Prairie vole is an animal that forms life-long bonds and has intercourse beyond the needs of

123 ideal levels of vasopressin and oxytocin testosterone levels. All hormonal in the body. It may also be the mere differences were eliminated when the instinct or decision to stop. subjects were re-tested from 12 to 24 months later. The increased cortisol and We can blame hormones why certain low FSH levels are suggestive of the things might have felt so magical and \"stressful\" and arousing conditions ended up so dramatically tragic. But associated with the initiation of a social now that you know how hormones affect contact. The changes of testosterone love, you can put this knowledge in your concentrations, which varied in opposite favor and consciously decide from there. directions in the two sexes, may reflect changes in behavioural and/or Psychoneuroendocrinology of hormonal temperamental traits which have yet to changes when falling in love. be clarified. In conclusion, the findings of the present study would indicate that . To fall in love is the first step in pair to fall in love provokes transient hormonal changes some of which seem formation in humans and is a complex to be specific to each sex. process which only recently has become Article 2: the object of neuroscientific The science behind lust, attraction, and companionship. investigation. The little information Scientists in fields ranging from available in this field prompted us to anthropology to neuroscience have been asking this same question (albeit measure the levels of some pituitary, less eloquently) for decades. It turns out the science behind love is both simpler adrenal and gonadal hormones in a and more complex than we might think. group of 24 subjects of both sexes who Google the phrase “biology of love” and you’ll get answers that run the gamut of had recently (within the previous six accuracy. Needless to say, the scientific basis of love is often sensationalized, months) fallen in love, and to compare and as with most science, we don’t know enough to draw firm conclusions them with those of 24 subjects who about every piece of the puzzle. What we do know, however, is that much of were single or were part of a long- love can be explained by chemistry. So, if there’s really a “formula” for love, what lasting relationship. The following is it, and what does it mean? hormones were evaluated by means of Scientists in fields ranging from anthropology to neuroscience have standard techniques: FSH, LH, estradiol, progesterone, dehydroepiandrosterone sulphate (DHEAS), cortisol, testosterone and androstenedione. The results showed that estradiol, progesterone, DHEAS and androstenedione levels did not differ between the groups and were within the normal ranges. Cortisol levels were significantly higher amongst those subjects who had recently fallen in love, as compared with those who had not. FSH and testosterone levels were lower in men in love, while women of the same group presented higher

124 been asking this same question (albeit have stammered, your palms may have less eloquently) for decades. It turns out sweated; you may have said something the science behind love is both simpler incredibly asinine and tripped and more complex than we might think. spectacularly while trying to saunter away (or is that just me?). And chances Google the phrase “biology of love” and are, your heart was thudding in your you’ll get answers that run the gamut of chest. It’s no surprise that, for centuries, accuracy. Needless to say, the scientific people thought love (and most other basis of love is often sensationalized, emotions, for that matter) arose from the and as with most science, we don’t heart. As it turns out, love is all about know enough to draw firm conclusions the brain – which, in turn, makes the about every piece of the puzzle. What rest of your body go haywire. we do know, however, is that much of love can be explained by chemistry. So, According to a team of scientists led by if there’s really a “formula” for love, what Dr. Helen Fisher at Rutgers, romantic is it, and what does it mean? love can be broken down into three categories: lust, attraction, and Total Eclipse of the Brain attachment. Each category is characterized by its own set of Think of the last time you ran into hormones stemming from the brain someone you find attractive. You may (Table 1). Table 1: Love can be distilled into three hormones. Testosterone and estrogen categories: lust, attraction, and drive lust; dopamine, norepinephrine, attachment. Though there are overlaps and serotonin create attraction; and and subtleties to each, each type is oxytocin and vasopressin mediate characterized by its own set of attachment.

125 Let’s Get Chemical hormones testosterone and estrogen f Lust is driven by the desire for sexual rom the testes and ovaries (Figure 1). gratification. The evolutionary basis for While these chemicals are often this stems from our need to reproduce, stereotyped as being “male” and a need shared among all living things. “female,” respectively, both play a role in Through reproduction, organisms pass men and women. As it turns out, on their genes, and thus contribute to testosterone increases libido in just the perpetuation of their species. about everyone. The effects are less pronounced with estrogen, but some The hypothalamus of the brain plays a women report being more sexually big role in this, stimulating the motivated around the time they ovulate, production of the sex when estrogen levels are highest. Figure 1: A: The testes and ovaries Love is its Own Reward secrete the sex hormones testosterone and estrogen, driving sexual desire. B Meanwhile, attraction seems to be a and C: Dopamine, oxytocin, and distinct, though closely related, vasopressin are all made in the phenomenon. While we can certainly hypothalamus, a region of the brain that lust for someone we are attracted to, controls many vital functions as well as and vice versa, one can happen without emotion. D: Several of the regions of the the other. Attraction involves the brain brain that affect love. Lust and attraction pathways that control “reward” behavior shut off the prefrontal cortex of the (Figure 1), which partly explains why the brain, which includes rational behavior. first few weeks or months of a

126 relationship can be so exhilarating and Last but not least, attachment is the even all-consuming. predominant factor in long-term relationships. While lust and attraction Dopamine, produced by the are pretty much exclusive to romantic hypothalamus, is a particularly well- entanglements, attachment mediates publicized player in the brain’s reward pathway – it’s released when we do friendships, parent-infant bonding, social things that feel good to us. In this case, cordiality, and many other intimacies as these things include spending time with well. The two primary hormones here loved ones and having sex. High levels appear to of dopamine and a related be oxytocin and vasopressin (Figure hormone, norepinephrine, are released 1). during attraction. These chemicals make Oxytocin is often nicknamed “cuddle us giddy, energetic, and euphoric, even hormone” for this reason. Like leading to decreased appetite and dopamine, oxytocin is produced by the insomnia – which means you actually can be so “in love” that you can’t eat hypothalamus and released in large and can’t sleep. In fact, norepinephrine, quantities during sex, breastfeeding, also known as noradrenalin, may sound and childbirth. This may seem like a familiar because it plays a large role in very strange assortment of activities – the fight or flight response, which kicks not all of which are necessarily into high gear when we’re stressed and enjoyable – but the common factor here keeps us alert. Brain scans of people in is that all of these events are precursors love have actually shown that the to bonding. It also makes it pretty clear primary “reward” centers of the brain, why having separate areas for including the and the caudate nucleus attachment, lust, and attraction is (Figure 1), fire like crazy when people important: we are attached to our are shown a photo of someone they are immediate family, but those other intensely attracted to, compared to emotions have no business there (and when they are shown someone they feel let’s just say people who have muddled neutral towards (like an old high school this up don’t have the best track record). acquaintance). Love Hurts Finally, attraction seems to lead to a This all paints quite the rosy picture of love: hormones are released, making us reduction in serotonin, a hormone feel good, rewarded, and close to our that’s known to be involved in appetite romantic partners. But that can’t be the whole story: love is often accompanied and mood. Interestingly, people who by jealousy, erratic behavior, and irrationality, along with a host of other suffer from obsessive-compulsive less-than-positive emotions and moods. It seems that our friendly cohort of disorder also have low levels of hormones is also responsible for the downsides of love. serotonin, leading scientists to speculate that this is what underlies the overpowering infatuation that characterizes the beginning stages of love. The Friend Zone

127 Dopamine, for instance, is the hormone cocaine maintains dopamine responsible for the vast majority of the brain’s reward pathway – and that signaling for much longer than usual, means controlling both the good and the leading to a temporary “high.” In a way, bad. We experience surges of dopamine for our virtues and our vices. In fact, the attraction is much like an addiction to dopamine pathway is particularly well another human being. Similarly, the studied when it comes to addiction. The same regions that light up when we’re same brain regions light up when we feeling attraction light up when drug addicts take cocaine and when we binge become addicted to material goods as eat sweets. For example, when we become emotionally dependent on our partners. And addicts going into withdrawal are not unlike love-struck people craving the company of someone they cannot see. Figure 2: Dopamine, which runs the companions, elevated oxytocin can also fuel prejudice. reward pathways in our brain, is great in The story is somewhat similar for moderate doses, helping us enjoy food, oxytocin: too much of a good thing can be bad. Recent studies on party drugs exciting events, and relationships. such as MDMA and GHB shows that oxytocin may be the hormone behind However, we can push the dopamine the feel-good, sociable effects these chemicals produce. These positive pathway too far when we become feelings are taken to an extreme in this case, causing the user to dissociate addicted to food or drugs. Similarly, too from his or her environment and act much dopamine in a relationship can underlie unhealthy emotional dependence on our partners. And while healthy levels of oxytocin help us bond and feel warm and fuzzy towards our

128 wildly and recklessly. Furthermore, could define “love” for you if I kept you oxytocin’s role as a “bonding” hormone here for another ten thousand pages. appears to help reinforce the positive feelings we already feel towards the In the end, everyone is capable of people we love. That is, as we become defining love for themselves. And, for more attached to our families, friends, better or for worse, if it’s all hormones, and significant others, oxytocin is maybe each of us can have “chemistry” working in the background, reminding us with just about anyone. But whether or why we like these people and increasing not it goes further is still up to the rest of our affection for them. While this may be you. a good things for monogamy, such associations are not always positive. For example, oxytocin has also been suggested to play a role in ethnocentrism, increasing our love for people in our already-established cultural groups and making those unlike us seem more foreign (Figure 2). Thus, like dopamine, oxytocin can be a bit of a double-edged sword. And finally, what would love be without embarrassment? Sexual arousal (but not necessarily attachment) appears to turn off regions in our brain that regulate critical thinking, self- awareness, and rational behavior, including parts of the prefrontal cortex (Figure 2). In short, love makes us dumb. Have you ever done something when you were in love that you later regretted? Maybe not. I’d ask a certain star-crossed Shakespearean couple, but it’s a little late for them. So, in short, there is sort of a “formula” for love. However, it’s a work in progress, and there are many questions left unanswered. And, as we’ve realized by now, it’s not just the hormone side of the equation that’s complicated. Love can be both the best and worst thing for you – it can be the thing that gets us up in the morning, or what makes us never want to wake up again. I’m not sure I

129 Article 3: purposes’ – it makes reproduction more likely. If judgment is suspended, the THE BRAIN IN LOVE most unlikely pair can get together and reproduce. Someone in love will still be The frontal cortex, vital to judgment, capable of making other major decisions shuts down when we fall in love. MRI in their lives, from striking a business scans show this de-activation occurs deal to choosing a new mortgage. only when someone is shown a photo of the person they adore, causing them to And this sanity makes it harder for suspend all criticism or doubt. friends to convince them ‘they have taken leave of their senses’ when it Semir Zeki, professor of neuro- comes to an ill-advised affair. aesthetics at University College London, says: ‘When you look at someone you Brain scans have also shown the area are passionate about, some areas of the of the brain that controls fear, and brain become active,’ he says. ‘But a another region involved in negative large part is de-activated, the part that emotions, close down, explaining why plays a role in judgment.’ people feel so happy with the world – and unafraid of what might go wrong – Prof Zeki believes the brain may behave when they fall head over heels. in this way for ‘higher biological

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137 Glossary (GABA), which also have inhibitory actions on nerve cells. ACETYLCHOLINE A neurotransmitter AMYGDALA A structure in the forebrain active both in the brain, where it regulates that is an important component of the limbic memory, and in the peripheral nervous system and plays a central role in emotional system, where it controls the actions of learning, particularly within the context of skeletal and smooth muscle. fear. ANDROGENS Sex steroid hormones, ACTION POTENTIAL An electrical charge including testosterone, found in higher travels along the axon to the neuron’s levels in males than females. They are terminal, where it triggers the release of a responsible for male sexual maturation. neurotransmitter. This occurs when a neuron ANTAGONIST A drug or other molecule is activated and temporarily reverses the that blocks receptors. Antagonists inhibit the electrical state of its interior membrane from effects of agonists. negative to positive. APHASIA Disturbance in language comprehension or production, often as a ADRENAL CORTEX An endocrine organ result of a stroke. that secretes corticosteroids for metabolic functions; for example, in response to stress. APOPTOSIS Programmed cell death in duced by specialized biochemical pathways, ADRENAL MEDULLA An endocrine organ often serving a specific purpose in the that secretes epinephrine and nor development of the animal. epinephrine in concert with the activation of the sympathetic nervous system; for AUDITORY NERVE A bundle of nerve example, in response to stress. fibers extending from the cochlea of the ear to the brain that contains two branches: the AGONIST A neurotransmitter, drug, or other cochlear nerve, which transmits sound molecule that stimulates receptors to information, and the vestibular nerve, which produce a desired reaction. relays information related to balance. ALZHEIMER’S DISEASE The major cause of dementia most prevalent in the elderly, it AUTONOMIC NERVOUS SYSTEM A part inflicts enormous human financial cost on of the peripheral nervous system responsible society. The disease is characterized by for regulating the activity of internal organs. death of neurons in the hippocampus, It includes the sympathetic and cerebral cortex, and other brain regions. parasympathetic nervous systems. AXON The fiber like extension of a neuron AMINO ACID TRANSMITTERS The most by which it sends information to target cells. prevalent neurotransmitters in the brain, BASAL GANGLIA Clusters of neurons, these include glutamate and aspartate, which have excitatory actions on nerve cells, and glycine and gamma-amino butyric acid

138 which include the caudate nucleus, putamen, example, in right-handed people, the left globus pallidus, and substantia nigra, hemisphere is specialized for speech, located deep in the brain that play an writing, language, and calculation; the right important role in the initiation of movements. Cell death in the substantia nigra contributes Hemisphere is specialized for spatial to Parkinson’s disease. abilities, visual face recognition, and some aspects of music perception and production. BRAINSTEM The major route by which the CEREBROSPINAL FLUID A liquid found fore brain sends information to and receives within the ventricles of the brain and the information from the spinal cord and central canal of the spinal cord. peripheral nerves. The brainstem controls, among other things, respiration and the CHOLECYSTOKININ A hormone released regulation of heart rhythms. from the lining of the stomach during the BROCA’S AREA The brain region located early stages of digestion that acts as a in the frontal lobe of the left hemisphere that powerful suppressant of normal eating. It is important for the production of speech. also is found in the brain. CIRCADIAN RHYTHM A cycle of behavior CATECHOLAMINES The neurotransmitters or physiological change lasting dopamine, epinephrine, and norepinephrine, approximately 24 hours. which are active in both the brain and the CLASSICAL CONDITIONING Learning in peripheral sympathetic nervous system. which a stimulus that naturally produces a These three molecules have certain specific response (unconditioned stimulus) structural similarities and are part of a larger is repeatedly paired with a neutral stimulus class of neurotransmitters known as (conditioned stimulus). As a result, the monoamines. conditioned stimulus can come to evoke a response similar to that of the unconditioned CEREBELLUM A large structure located at stimulus. the roof of the hindbrain that helps control the coordination of movement by making COCHLEA A snail-shaped, fluid-filled organ connections to the pons, medulla, spinal of the inner ear responsible for transducing cord, and thalamus. It also may be involved motion into neurotransmission to produce in aspects of motor learning. an auditory sensation. CEREBRAL CORTEX The outermost layer of the cerebral hemispheres of the brain. It is COGNITION The process or processes by largely responsible for all forms of con- which an organism gains knowledge or scious experience, including perception, becomes aware of events or objects in its emotion, thought, and planning. environment and uses that knowledge for comprehension and problem-solving. CEREBRAL HEMISPHERES The two specialized halves of the brain. For CONE A primary receptor cell for vision located in the retina. It is sensitive to color

139 and is used primarily for daytime vision. drug intake or compulsive seeking and CONTUSIONS An injury to the body in which taking of drugs, despite adverse skin and bone are not broken but damage is consequences. done to tissues under the skin, causing a bruise ENDOCRINE ORGAN An organ that CORPUS CALLOSUM The large bundle of secretes a hormone directly into the nerve fibers linking the left and right cerebral bloodstream to regulate cellular activity of hemispheres. certain other organs. NDORPHINS Neurotransmitters produced CORTISOL A hormone manufactured by in the brain that generate cellular and the adrenal cortex. In humans, cortisol is behavioral effects like those of morphine. secreted in the greatest quantities before dawn, readying the body for the activities of EPILEPSY A disorder characterized by the coming day. repeated seizures, which are caused by abnormal excitation of large groups of DEPRESSION A mental disorder neurons in various brain regions. Epilepsy characterized by depressed mood and can be treated with many types of abnormalities in sleep, appetite, and energy anticonvulsant medications. level. EPINEPHRINE A hormone, released by the DENDRITE A tree-like extension of the neuron cell body. The dendrite is the primary adrenal medulla and specialized sites in the site for receiving and integrating information from other neurons. brain, that acts with norepinephrine to affect DOPAMINE A catecholamine the sympathetic division of the autonomic neurotransmitter known to have varied functions depending on where it acts. nervous system. Sometimes called Dopamine-containing neurons in the substantia nigra of the brainstem project to adrenaline. the caudate nucleus and are destroyed in Parkinson’s victims. Dopamine is thought to ESTROGENS A group of sex hormones regulate key emotional responses such as found more abundantly in females than reward and plays a role in schizophrenia and males. They are responsible for female drug abuse. sexual maturation and other functions. DORSAL HORN An area of the spinal cord EVOKED POTENTIALS A measure of the where many nerve fibers from peripheral brain’s electrical activity in response to pain receptors meet other ascending and sensory stimuli. This is obtained by placing descending nerve fibers. electrodes on the surface of the scalp (or more rarely, inside the head), repeatedly DRUG ADDICTION Loss of control over administering a stimulus, and then using a computer to average the results. EXCITATION A change in the electrical state of a neuron that is associated with an enhanced probability of action potentials.

140 FOLLICLE-STIMULATING HORMONE A GLUTAMATE An amino acid hormone released by the pituitary gland that stimulates the production of sperm in neurotransmitter that acts to excite the male and growth of the follicle (which produces the egg) in the female. neurons. Glutamate stimulates N-methyl-d- FOREBRAIN The largest part of the brain, aspartate (NMDA) andalpha-amino-3- which includes the cerebral cortex and basal ganglia. The forebrain is credited with hydroxy-5-methylisoxazole-4-propionicacid the highest intellectual functions. (AMPA). AMPA receptors have been FRONTAL LOBE One of the four divisions (the other lobes are the parietal, temporal, implicated in activities ranging from and occipital) of each hemisphere of the cerebral cortex. The frontal lobe has a role learning and memory to development and in controlling movement and in the planning and coordinating of behavior. specification of nerve contacts in GAMMA-AMINO BUTYRIC ACID developing animals. Stimulation of NMDA (GABA) An amino acid transmitter in the brain whose primary function is to inhibit receptors may promote beneficial changes, the firing of nerve cells. whereas overstimulation may be a cause of GLIA Specialized cells that nourish and support neurons. nerve cell damage or death in neurological trauma and stroke. GONAD Primary sex gland: testis in the male and ovary in the female. GROWTH CONE A distinctive structure at the growing end of most axons. It is the site where new material is added to the axon. HIPPOCAMPUS A sea horse shaped is characterized by abnormal movements structure located within the brain and called chorea— sudden, jerky movements considered an important part of the limbic without purpose. system. One of the most studied areas of the brain, it functions in learning, memory, HYPOTHALAMUS A complex brain and emotion. structure composed of many nuclei with various functions, including regulating the HORMONES Chemical messengers activities of internal organs, monitoring information from the autonomic nervous secreted by endocrine glands to regulate system, controlling the pituitary gland, and the activity of target cells. They play a role in sexual development, calcium and bone regulating sleep and appetite. metabolism, growth, and many other INHIBITION A synaptic message that activities. prevents a recipient neuron from firing. HUNTINGTON’S DISEASE A movement IONS Electrically charged atoms or disorder caused by the death of neurons in molecules. the basal ganglia and other brain regions. It LIMBIC SYSTEM A group of brain

141 structures—including the amygdala, hippocampus, septum, basal ganglia, and others—that help regulate the expression MONOAMINE OXIDASE (MAO) The brain of emotion and emotional memory. and liver enzyme that normally breaks down the catecholamines norepinephrine, LONG-TERM MEMORY The final phase of dopamine, and epinephrine, as well as other memory, in which information storage may monoamines such as serotonin. last from hours to a lifetime. MOTOR NEURON A neuron that carries MANIA A mental disorder characterized by information from the central nervous excessive excitement, exalted feelings, system to muscle. elevated mood, psychomotor over activity, and overproduction of ideas. It may be MYASTHENIA GRAVIS A disease in which associated with psychosis, for example, acetylcholine receptors on muscle cells are delusions of grandeur. destroyed so that muscles can no longer respond to the acetylcholine signal to MELATONIN Produced from serotonin, contract. Symptoms include muscular melatonin is released by the pineal gland weakness and progressively more common into the bloodstream. Melatonin affects physiological changes related to time and bouts of fatigue. The disease’s cause is lighting cycles. unknown but is more common in females MEMORY CONSOLIDATION The physical than in males; it usually strikes between the and psychological changes that take place ages of 20and 50. as the brain organizes and restructures information to make it a permanent part of MYELIN Compact fatty material that memory. surrounds and insulates the axons of some METABOLISM The sum of all physical and neurons. chemical changes that take place within an NECROSIS Cell death due to external organism and all energy transformations factors, such as lack of oxygen or physical that occur within living cells. damage, that disrupt the normal biochemical MIDBRAIN The most anterior segment of processes in the cell. the brainstem. With the pons and medulla, NERVE GROWTH FACTOR A substance the mid brain is involved in many functions, whose role is to guide neuronal growth including regulation of heart rate, during embryonic development, especially in respiration, pain perception, and the peripheral nervous system. Nerve movement. growth factor also probably helps sustain MITOCHONDRIA Small cylindrical neurons in the adult. organelles inside cells that provide energy NEURON A nerve cell specialized for the for the cell by converting sugar and oxygen transmission of information and into special energy molecules, called ATP. characterized by long, fibrous projections

142 called axons and shorter, branchlike PARKINSON’S DISEASE A movement projections called dendrites. disorder caused by death of dopamine neurons in the substantia nigra, located in NEUROPLASTICITY A general term used the midbrain. Symptoms include tremor, to describe the adaptive changes in the shuffling gait, and general paucity of structure or function of nerve cells or groups movement. of nerve cells in response to injuries to the nervous system or alterations in patterns of PEPTIDES Chains of amino acids that can their use and disuse. function as neurotransmitters or hormones. NEUROTRANSMITTER A chemical PERIPHERAL NERVOUS SYSTEM A division of the nervous system consisting of released by neurons at a synapse for the all nerves that are not part of the brain or spinal cord. purpose of relaying information to other neurons via receptors. NOCICEPTORS In animals, nerve endings PHOSPHORYLATION A process that that signal the sensation of pain. In humans, modifies the properties of neurons by acting they are called pain receptors. on an ion channel, neurotransmitter receptor, or other regulatory protein. During NOREPINEPHRINE A catecholamine phosphorylation, a phosphate molecule is neurotransmitter, produced both in the brain placed on a protein and results in the and in the peripheral nervous system. activation or inactivation of the protein. Norepinephrine is involved in arousal and in Phosphorylation is believed to be a regulation of sleep, mood, and blood necessary step in allowing some pressure. neurotransmitters to act and is often the result of second-messenger activity. OCCIPITAL LOBE One of the four subdivisions of the cerebral cortex. The PINEAL GLAND An endocrine organ occipital lobe plays a role in processing found in the brain. In some animals, the visual information. ORGANELLES Small structures within a pineal gland serves as a light-influenced cell that maintain the cell and do the cell’s biological clock. work. PITUITARY GLAND An endocrine organ PARASYMPATHETIC NERVOUS SYSTEM closely linked with the hypothalamus. In A branch of the autonomic nervous system humans, the pituitary gland is composed of concerned with the conservation of the two lobes and secretes several different body’s energy and resources during relaxed hormones that regulate the activity of other states. endocrine organs throughout the body. PARIETAL LOBE One of the four PONS A part of the hind brain that, with subdivisions of the cerebral cortex. The other brain structures, controls respiration parietal lobe plays a role in sensory and regulates heart rhythms. The pons is a processes, attention, and language.

143 major route by which the forebrain sends growth and development. The messengers’ information to and receives information direct effects on the genetic material of cells from the spinal cord and peripheral nervous may lead to long-term alterations of system. behavior, such as memory and drug addiction. PSYCHOSIS A severe symptom of mental disorders characterized by an inability to SEROTONIN A monoamine perceive reality. Psychosis can occur in many conditions, including schizophrenia, neurotransmitter believed to play many mania, depression, and drug-induced states. roles, including, but not limited to, RECEPTOR CELL A specialized sensory temperature regulation, sensory perception, cell, designed to pick up and transmit sensory information. and the onset of sleep. Neurons using RECEPTOR MOLECULE A specific protein serotonin as a transmitter are found in the on the surface of or inside a cell with a characteristic chemical and physical brain and gut. Several antidepressant drugs structure. Many neurotransmitters and hormones exert their effects by binding to are targeted to brain serotonin systems. receptors on cells. SHORT-TERM MEMORY A phase of REUPTAKE A process by which released memory in which a limited amount of neurotransmitters are absorbed for later information may be held for several seconds reuse. or minutes. ROD A sensory neuron located in the STIMULUS An environmental event periphery of the retina. The rod is sensitive capable of being detected by sensory to light of low intensity and is specialized for receptors. night time vision. STROKE The third-largest cause of death SCHIZOPHRENIA A chronic mental in the United States, stroke is an impeded disorder characterized by psychosis (e.g., blood supply to the brain. Stroke can be hallucinations and delusions), flattened caused by a rupture of a blood vessel wall, emotions, and impaired cognitive function. an obstruction of blood flow caused by a clot or other material, or pressure on a SECOND MESSENGERS Substances that blood vessel (as by a tumor). Deprived of oxygen, which is carried by blood, nerve trigger communications among different cells in the affected area cannot function and die. Thus, the part of the body parts of a neuron. These chemicals play a controlled by those cells cannot function either. Stroke can result in loss of role in the manufacture and release of consciousness and death. neurotransmitters, intracellular movements, SYMPATHETIC NERVOUS SYSTEM A carbohydrate metabolism, and processes of branch of the autonomic nervous system

144 responsible for mobilizing the body’s energy information flowing into the brain, the and resources during times of stress and thalamus filters out information of particular arousal. importance from the mass of signals SYNAPSE A physical gap between two entering the brain. neurons that functions as the site of VENTRICLES Comparatively large information transfer from one neuron to spaces filled with cerebrospinal fluid. Of another. the four ventricles, three are located in the TEMPORAL LOBE One of the four major fore brain and one in the brain stem. The subdivisions of each hemisphere of the lateral ventricles, the two largest, are cerebral cortex. The temporal lobe functions symmetrically placed above the brainstem, in auditory perception, speech, and complex one in each hemisphere. visual perceptions. WERNICKE’S AREA A brain region THALAMUS A structure consisting of two responsible for the comprehension of egg-shaped masses of nerve tissue, each language and the production of meaningful about the size of a walnut, deep within the speech. brain. The key relay station for sensory