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Home Explore Neuropsychology of Nonimpact Mild Traumatic Brain Injury

Neuropsychology of Nonimpact Mild Traumatic Brain Injury

Published by Karl Tombak, 2020-11-12 23:08:07

Description: Neuropsychology of Nonimpact Mild Traumatic Brain Injury


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Table of Contents Preface ………………………………………………………………… 1 Initial Studies …………………………………………………………. 2 Correlational Studies ………………………………………………… 6 Inferential Studies ……………………………………………………. 10 Spatial Performance Issues …………………………………………. 23 Further Research ……………………………………………………… 24 Research Summary …………………………………………………… 26 References ……………………………………………………………… 28

Preface It is not at all unusual for healthcare assessors to repeatedly observe in the course of clinical evaluation intriguing characteristics, behaviours, or test results for which there is no clear explanation in the professional literature. That was my experience in a medical-legal practice in neuropsychology focussing on the assessment of traumatic brain injury over a period of 31 years. I could have been described as a “closet neuroscientist”, quietly conducting research specifically designed to investigate the neuropsychological status of individuals claiming persistent cognitive difficulties following motor vehicle accidents. The current presentation provides a review of the findings and main conclusions of my published studies investigating a lesser-known form of Mild Traumatic Brain Injury (mTBI) that, decades ago, I called ​Nonimpact​ mTBI. The research showed that a significant minority of mTBI individuals presented with enduring brain-related cognitive deficiencies after being subjected to violent acceleration forces in motor vehicle accidents without sustaining direct impact to the head. Hopefully, this readable review will be helpful to healthcare professionals, research scientists and personal injury lawyers and, as well, introduce and educate the general public regarding the possible performance limitations related to this condition. James E. Sweeney, November 3, 2020. 1

Initial Studies Early in my practice that began in 1987, I noted that individuals referred for clinical neuropsychological evaluation following involvement in a single motor vehicle accident, experiencing ​no direct impact to the ​ head, s​ ometimes described symptoms immediately after the mishap that included cognitive confusion and/or amnesia regarding the accident itself or other accident-related events. Typically, complaints of attention and memory followed and, on occasion, observations suggested directional or spatial problems. Despite no direct impact to the head, the pattern of neuropsychological test results was sometimes consistent with mild traumatic brain injury and persistent neurocognitive deficiencies. By the 1990s, these observations compelled me to review the limited research in this area that involved mainly animal experimentation. Ommaya, Faas, and Yarnell (1968) studied the effects of acceleration forces on the brains of subhuman primates, primarily the rhesus monkey, by mimicking rear-end collisions. They found that high velocity rotational acceleration of the head involving “whiplash” hyperextension and hyperflexion of the neck consistently produced macroscopically visible lesions in the brain, but only when cerebral concussion (i.e., the sudden abolition of consciousness) occurred. There was therefore comparative experimental evidence of brain damage due to the imposition of extreme physical forces in the absence of direct impact to the head. 2

Another interesting result from Ommaya’s series of investigations was that concussion did not occur, and the extent of brain damage was less, when the head was fixed into position so that the neck could not hyperextend and hyperflex (Ommaya and Gennarelli, 1974). Given these comparative findings, there is a clear possibility that h​ yperextension and hyperflexion of the neck represent an important causal variable in understanding the neuropsychological condition of humans who suffer mild traumatic brain injury in motor vehicle accidents but do not sustain direct impact to the head.​ The finding of a correlation between the imposition of extreme physical forces and structural brain damage in the rhesus monkey rationalized my 1992 published review of studies that provided grounds for the clinical neuropsychological study of humans subjected to violent acceleration forces in motor vehicle accidents. Coincidentally, the definition of Mild Traumatic Brain Injury (mTBI) published by the American Congress of Rehabilitation Medicine in 1993 confirmed an association between intracranial brain movement due solely to external physical forces and brain injury. The clinical criteria for mTBI as set out in the definition include any loss of memory for events immediately before or after the accident, any alteration in mental state at the time of the accident, and focal neurological deficits that may or may not be transient. The aforementioned publications increased professional clinical interest and speculation regarding the phenomenon of traumatic brain injury without direct impact to the head. It was nonetheless unclear how the experimental findings of Ommaya and his collaborators might apply to Nonimpact mTBI in humans since uncomplicated Nonimpact mTBI, by definition, is not characterized by structural alterations of the brain, and loss of consciousness is a sufficient but unnecessary condition for a diagnosis of mTBI. It seemed 3

highly likely that no confirmed brain lesions and, possibly, no loss of consciousness in Nonimpact mTBI related to much less severity of acceleration forces than in the Ommaya studies. The ultimate goal of my neuropsychology research program was identifying possible neurocognitive deficiencies underlying Nonimpact mTBI or mild traumatic brain injury due solely to exposure to violent acceleration forces in motor vehicle accidents. Clinical evaluation was in the Halstead-Reitan tradition, using tests assessing levels of performance by comparison with norms of central tendency and variability and revealing any atypical score patterns (psychological methods of assessment), and employing investigative techniques focussing on signs of pathology and aberrant right-left motor and sensory perceptual differences (traditionally used in neurology). The scientific use of Halstead-Reitan methods of clinical neuropsychological inference is reviewed in Sweeney et al. (2007). In 1994, I published a neuropsychological case study of WDR, a 53-year-old right-handed man whose small-sized stationary car was “rear-ended” by a large motor vehicle as he was sitting behind a line of traffic on a major highway in the white-out conditions of a snow storm. The impact was so forceful that the back of his bucket seat collapsed and he was thrown into the rear seat window area. There was no physical evidence of direct impact to the head. He reported post-traumatic amnesia of perhaps minutes including no memory for his car striking the car ahead. After exiting his vehicle, he apparently collapsed twice on the roadway and experienced severe nausea and vomiting. Nonetheless, he was able to exchange information with the other drivers involved, declined an offer of transport to hospital, and was able to drive his car to his home nearby. 4

WDR was selected as a write-up for publication because three formal clinical evaluations over five years reflected stable and dramatic changes consistently suggestive of severe neuropsychological impairment implicating primarily the right cerebral hemisphere, profound spatial judgment deficiencies, and severe motor and tactile perceptual difficulties with the left hand. While there was some suspicion in this medical-legal case that WDR was exaggerating symptoms and test performance difficulties, the use of performance validity measures was not standard procedure at that time, and there was an exceptional degree of consistency in the data profiles obtained in three evaluations over five years that reflected some credibility. The take-away here was that despite no direct impact to the head and some amplification of symptoms and test performance difficulty, t​ here was convincing neuropsychological evidence of bona fide brain-related problems in adaptation as a sole consequence of being subjected to extreme acceleration forces in a motor vehicle collision​. 5

Correlational Studies My initial group studies of Nonimpact mTBI were, by necessity, correlational since there were few opportunities earlier in my practice to obtain test results from “normal” or control subjects for comparison purposes. I therefore investigated the possibility of a relationship between Nonimpact mTBI sustained in a single motor vehicle accident and performances on neuropsychological tests, as compared with standard normative data. Inferential studies had to be deferred until test data became available permitting comparisons between groups of individuals who had been involved in motor vehicle accidents and sustained mTBI with and without direct impact to the head, and a normal group that had been in an accident but had no cognitive complaints and did not meet mTBI criteria. I conducted a group study of 33 right-handed Nonimpact mTBI adults that by definition met criteria for mTBI following involvement in a single motor vehicle accident but had not sustained external impact to the head (Sweeney, 1999). Comparing test results to Halstead-Reitan normative data and deficit classifications, frequency of overall mild impairment was quite high at 70%, with similar frequencies of deficiency noted for single-score tests requiring the formation of abstract visual-spatial concepts in problem-solving (e.g., the concept of proportion) and incidental memory for simple shapes in a specific spatial pattern perceived exclusively through the tactile modality. A comparable overall frequency percentage of atypical right-left performance differences was also exhibited on a challenging tactile-spatial test (associated with the aforementioned incidental memory test), with frequency of relatively 6

inefficient performances being substantially higher with the left hand. Nonimpact mTBI appeared, in general, to be associated with a persistent, mild, neuropsychological impairment reflected most clearly by deficiencies of spatial reasoning and memory in visual and tactile modalities. Experience in my clinical practice led me to speculate that older age negatively affected the test performances of Nonimpact mTBI clients. I collaborated with Dr. Andrew M. Johnson, Associate Professor, School of Health Studies, Western University, an expert in statistical measurement, to investigate this possibility. The effect of age on the above sample of Nonimpact mTBI individuals was examined (Sweeney & Johnson, 2001). We found that ​almost all ​composite​ Halstead-Reitan measures​ (i.e., tests made up of multiple single-score tests) ​showed a significant decline in performance with older age.​ In contrast, most s​ ingle-score​ Halstead-Reitan tests did not yield a significant age effect. It was of some interest, however, that four of the five single-score measures in the study showing a notable negative age effect related to the two tests in the 1999 Sweeney study requiring visual- and tactile-spatial perception that yielded mildly impaired performances. My research activities were put on hold for about five years after the age study due to the increasing clinical demands of my practice but, in collaboration with six other neuropsychological practitioners throughout the United States and in Canada, we eventually found the time to publish a paper (noted above) addressing the scientific use of the Halstead-Reitan Neuropsychological Test Battery (Sweeney, et al., 2007). As the years went by, the number of potential subjects for Nonimpact mTBI clinical studies increased in conjunction with research questions to be addressed, but time for their completion was not available for about another eight years. Then, with relaxation of the clinical demands of my practice due to relocation to another 7

city, I had the welcome opportunity to conduct further studies of the Nonimpact mTBI population. Sweeney, Johnson, and Slade (2017) compared Halstead-Reitan level-of-performance deficit scores obtained from 62 right-handed Nonimpact mTBI adults utilizing two different classification systems developed by Reitan and Wolfson (1993) and Heaton and his collaborators (2005). (Incidentally, Ms. Anne M. Slade, the third author, was an exceptionally efficient and perceptive neuropsychometrist who provided testing services in my clinical practice.) The overall finding of this study was that ​the Reitan and Wolfson method generated deficit scores suggestive of a greater degree of impairment than did Heaton’s procedures​. On the basis of this result, we recommended an approach to interpretation that integrated the two systems of measurement. Responding to the complaint of a lack of information in the neuropsychological literature characterizing distinct clinical populations with relatively homogeneous demographic characteristics, Sweeney (2017) examined in detail 63 right-handed Nonimpact mTBI subjects. The four Halstead-Reitan inferential methods of interpretation were utilized to consider the possibility of neuropsychological deficiencies as demonstrated by below normal levels of performance; signs of pathology; irregular score patterns; and abnormal right-left motor and sensory perceptual performance relationships. Levels of performance for this sample reflected normal neurocognition generally, raising the possibility that in assessing group data, any clear expression of infrequent or subtle neuropsychological deficits might be “washed out” by averaging test results. Signs of pathology were very infrequent, although constructional dyspraxia (distortion in the perception and/or reproduction of spatial relationships) was fairly prominent in older 8

individuals. A score pattern thought to indicate general decline in neuropsychological status (involving a comparison of the Impairment Index and WAIS Full Scale IQ) was comparatively frequent, exhibited by almost 30% of the sample. Sensory suppressions were demonstrated minimally. Unusual right-left performance relationships were most frequently seen on motor tests bilaterally, especially grip strength, and performance on a fairly difficult tactile-spatial test with the left hand was significantly diminished relative to the right hand 41% of the time. All in all, these data, and the findings reported above, suggested that ​if some Nonimpact mTBI individuals were indeed suffering impairment neuropsychologically, the deficiencies were subtle and rather challenging to demonstrate clinically.​ The results of correlational studies of Nonimpact mTBI reviewed above raised the possibility that some individuals meeting criteria for this condition may be experiencing a mild decline in general neuropsychological status, minor diminishment in the ability to formulate and remember abstract spatial concepts and/or patterns, and aberrant right-left motor performance relationships. Alternatively, given the limitations of correlational studies, these data might have little bearing on neuropsychological status but, instead, reflect the effect of intervening variables. Consider, for example, the influence of psychological stress in litigation or the pursuit of financial compensation from an insurer as feasible hypothetical explanations of the above correlational data. The issue of cause is not addressed in correlational studies. 9

Inferential Studies With the limitations of correlational studies in mind, a series of five preliminary experimental or inferential studies was implemented to investigate the neuropsychological status of Nonimpact mTBI as compared to other groups of individuals who had been involved in motor vehicle accidents. All subjects were right-handed. From the perspective of the above correlational studies, a fundamental question was whether Nonimpact mTBI clients were indeed experiencing mild decline involving spatial neurocognitive deficiencies. Since the validity of test results is obviously an important consideration in the neuropsychological evaluation of individuals involved in litigation and/or the pursuit of financial compensation, participants in these investigations successfully underwent the scrutiny of embedded and free-standing performance validity tests. Study 1.​ S​ weeney and Johnson (2019a) conducted an inferential neuropsychological study comparing the Halstead-Reitan neuropsychological characteristics of 60 Nonimpact mTBI individuals with the same number of Impact mTBI subjects who had sustained direct impact to the head, and with a No mTBI control group of 29 individuals that had not sustained mTBI. The three groups were statistically comparable in terms of age, years of education, and time in years since the accident. Unexpectedly given previous correlational results, statistical analysis revealed that the three groups performed similarly on almost all tests administered. We were intrigued, 10

however, that N​ onimpact subjects generated significantly more abnormal Impairment Index vs. Full Scale IQ patterns​ than the other two groups (suggesting greater decline in neuropsychological status), and ​produced significantly longer response times on the Tactile Form Recognition Test (requiring the speeded visual recognition of simple shapes perceived through the tactile modality). The Impact mTBI and No Impact groups showed no significant differences on any test performances, suggesting full neuropsychological recovery on the part of Impact mTBI individuals. In conclusion, we felt that i​ ssues of neuropsychological decline and slower perceptual reaction to tactile/visual stimuli warranted more attention in our investigation of underlying neurocognitive deficiencies being encountered by Nonimpact mTBI clients.​ Study 2.​ The Impairment Index vs. Full Scale IQ score pattern represents a comparison of premorbid and current neuropsychological status as a measure of neuropsychological decline. However, upon examining the components of this composite measure, Sweeney and Johnson (2019b) determined that Full Scale IQ was suboptimal as an index of premorbid ability since some of its constituent elements were known to be sensitive to cerebral damage. To improve upon this composite measure as an index of decline, we developed an algorithm called “C-Voc” made up of a comparison of the WAIS Vocabulary subtest score (known to be a relatively good indicator of premorbid cognitive ability) and the Category Test score (considered very sensitive to brain dysfunction). The C-Voc scores for the Nonimpact mTBI, Impact mTBI, and No mTBI groups were then compared statistically. The findings were dramatic and are presented in Figure 1. Neuropsychological decline was statistically similar for Impact mTBI and No 11

mTBI individuals, thereby supporting complete or almost complete recovery by Impact mTBI subjects after a post-accident period of about two years. Nonimpact mTBI subjects, in contrast, seem to continue to be burdened with diminished higher-level neurocognitive skills after the same period of time. Figure1. C-Voc Index means for Nonimpact and Impact mTBI and the No mTBI control. Taken from Sweeney and Johnson (2019b). The results of this inferential study support the hypothesis that Nonimpact mTBI individuals may suffer persistent neuropsychological loss as a consequence of exposure to violent acceleration forces in motor vehicle accidents in the absence of direct impact to the head​. Study 3.​ In the Sweeney and Johnson (2019a) study, speed of response to the requirements of the Tactile Form Recognition Test (TFR) was significantly slower for Nonimpact mTBI individuals as compared to the Impact mTBI and 12

No mTBI groups that showed no notable difference in response time. The TFR is a bi-sensory perceptual test measuring the total time required to immediately perceive simple shapes by touch and identify their visual representations. Administration of the TFR is shown in Figure 2. The speeded requirement to integrate tactile- and visual-spatial stimuli would seem, intuitively, to be an effective method of revealing subtle sensory-spatial perceptual deficiencies. Given that TFR response time requires immediate Figure 2. Tactile Form Recognition Test. Stimuli not shown to protect test content. integration of tactile- and visual-spatial sensory information, Sweeney and Slade (2020) thought that an exploratory study of Nonimpact mTBI subjects who performed at different response levels might begin to capture the essence of apparent neurocognitive problems experienced by some Nonimpact participants. (Parenthetically, Ms. Heather P. Slade, the second author of this study, was a very helpful and insightful neuropsychometrist in my practice who later became a registered Psychological Associate practising 13

independently in clinical psychology.) Ms. Heather Slade is the daughter of Ms. Anne Slade, the third author of the Sweeney et al. (2017) study). The subjects of the TFR sensory-spatial study (Study 3) were composed of 55 right-handed Nonimpact participants selected from the 2019a Sweeney and Johnson investigation. We divided the subjects into three groups according to Halstead-Reitan norms for TFR response speeds: Deficient (n=16), Perfectly Normal (n=15), and Normal (n=24) and analyzed the tactile- and visual-spatial test performances of the three groups. Fingertip Number Writing Perception with the right hand was the most sensitive measure exhibited by the TFR Deficient group, showing significantly inferior performance in comparison to both Perfectly Normal and Normal individuals. The Fingertip Number Writing Perception Test requires the subject to identify numbers traced on the inner surface of the fingertips of each hand without the benefit of vision. Figure 3. Tactual Performance Test. Stimuli not shown to protect test content. 14

The nonverbal tactile-spatial demands of the Tactual Performance Test were also particularly sensitive to TFR Deficiency. Similar to the Fingertip Number Writing Perception measure, TFR Deficient individuals fell significantly below those of Perfectly Normal and Normal TFR subjects. Administration of the Tactual Performance Test is shown in Figure 3. Before the Tactual Performance Test begins, the subject is seated at a table and blindfolded. A formboard is then placed on the table in front of the subject with spaces of various sizes and shapes. Ten wooden blocks are arranged on the table between the formboard and the subject that fit into the spaces. The subject is not permitted to see the formboard or blocks at any time. The task is to fit the blocks into the spaces on the formboard as fast as possible, first with the dominant hand, then with the nondominant hand, and finally with both hands together, recording the performance time for each trial. The main score is the total time required to complete all three trials. The time difference between performances with the two hands is also noted. After completion of the third trial with both hands, the formboard and blocks are taken from the subject’s field of vision and the blindfold is removed. The subject is then asked to draw a picture of the formboard with the blocks in their proper spaces. The Memory score is the number of shapes correctly remembered. The Localization score is the number of blocks correctly identified by both shape and position on the formboard. The demands of the Tactual Performance Test are rather unusual and may be considered particularly challenging because of the need to adapt to unfamiliar requirements. One of the most salient outcomes of Study 3 was that ​the tests most sensitive to Deficient TFR response times​ r​ equired spatial perception and problem-solving exclusively within the tactile modality.​ The six tests showing 15

statistical significance reflecting the spatial perceptual deficiencies of the TFR Deficient group, in order of statistical sensitivity, are as follows: Fingertip Number Writing Perception – Right Hand; Tactual Performance Test – Left Hand; Category Test – Memory; Fingertip Number Writing Perception – Total; Tactual Performance Test – Memory; and the WAIS Digit Span Subtest. Visual-spatial tests requiring memory for abstract concepts formulated previously (Category Test – Memory) and the speeded matching of numbers and geometric configurations (WAIS Digit Span Subtest) appear less sensitive than tactile-spatial tests, rendering performances inferior to just the Perfectly Normal subjects. The Nonimpact mTBI correlational studies reviewed above, comparing test results and normative data, also showed mild sensory-spatial cognitive difficulties, clearly supporting our inferential findings. The sensory-spatial performance deficiencies exhibited by the Deficient group would, according to the literature, raise the possibility of functional compromise of post-central cerebral regions.​ It would be reasonable to hypothesize that (a) speeded sensory-spatial performance deficiencies exhibited by 29% of our Nonimpact mTBI sample reflect some diminished functional integrity of posterior cerebral regions, and (b) the lateralization of inefficient tactile-spatial performances under the constraint of time depends upon whether a spatial task is language-related or nonverbal, adversely influenced by dysfunction of the contralateral post-central cerebral region specializing in the type of spatial processing required. Study 4.​ The relatively frequent atypical right-left motor performance relationships exhibited by Nonimpact mTBI subjects in the aforementioned descriptive study (Sweeney, 2017) motivated Sweeney and Johnson (2020) to investigate the frequency of Halstead-Reitan correlates of brain injury for the 16

TFR groups. The clinical characteristics of interest were signs of pathology, abnormal score patterns, and aberrant right-left performance differences on motor and sensory perceptual tests. We were curious as to whether TFR Deficient Nonimpact mTBI individuals would show significantly greater frequency of these neurodiagnostic features as compared to TFR Perfectly Normal and Normal subjects. After an exhaustive analysis of the aforementioned variables, the only frequency measure that showed significantly inferior performance associated with the right-handed TFR Deficient group was Fingertip Number Writing Perception lateralized to the right hand. TFR Deficient performance on Fingertip Number Writing Perception with the right hand was about five times more likely to show errors t​ han right-sided TFR Perfectly Normal and Normal performance. T​ his result is consistent with the parametric data of the Sweeney and Slade (2020) study that found that Fingertip Number Writing Perception errors with the right hand was the most sensitive test in differentiating the TFR Deficient group from the other two groups. Inaccurate identification of fingertip number writing or graphesthesia of the right hand has been associated traditionally with left-sided posterior cerebral lesions. The professional literature clearly states that a single concussion meeting the criteria for mTBI following direct impact to the head almost always results in complete recovery from neurocognitive dysfunction within days or weeks of injury. The true incidence of persistent brain-related cognitive difficulties after Impact mTBI may be as low as one to five percent. Considering, (a) cognitive deficiency in association with posterior cerebral dysfunction is, in general, uncommon in traumatic brain injury; (b) our preliminary findings of a relationship between Nonimpact mTBI and a 17

continuing spatial neurocognitive deficiency about 29% of the time may implicate post-central cerebral regions, and (c) the failure of most “especially sensitive” and atypical right-left performance relationship measures of the Halstead-Reitan Battery, and virtually all signs of pathology and unusual score patterns to characterize TFR Deficient participants, m​ any persistent neuropsychological deficiencies associated with Nonimpact mTBI may be qualitatively different from those commonly related to Impact mTBI, perhaps requiring less known, newly developed, or relatively novel tests for optimal identification​. Neuropsychologists assessing right-handed clients reporting symptoms following a motor vehicle accident that meet criteria for mTBI in the absence of direct impact to the head, and using Halstead-Reitan tests or other tests that might be considered comparable, may benefit from the following list of tentative clinical markers of persistent sensory-spatial changes, in order of sensitivity, as a consequence of Nonimpact mTBI: 1. A summary response time on the Tactile Form Recognition Test of 24 seconds or more; 2. Four or more errors on Fingertip Number Writing Perception with the right hand; 3. At least 60% of total Fingertip Number Writing Perception errors with the right hand; 4. Seven or more minutes required to complete the Tactual Performance Test with the left hand; 5. Six or less correct responses on the Memory component of the Tactual Performance Test; 6. Six or more errors on the Memory subtest of the Category Test (inferior to just the Perfectly Normal group); 18

7. 51 or less correct responses on the WAIS Digit Symbol Subtest (inferior to just the Perfectly Normal group). Study 5.​ ​The issue of cause is, quite naturally, of great interest when reviewing neuropsychological profiles that deviate markedly from normative expectations. The frequency percentages for rear-end motor vehicle vehicle collisions as reported in Study 1 was 40% for Nonimpact mTBI and 18% for Impact mTBI. The difference between these percentages prompted Sweeney and Johnson (2019c) to investigate the possibility that neck injury was significantly more prevalent in Nonimpact mTBI found to be associated with sensory-spatial perceptual deficiencies. We considered the following in our decision to carry out the study: (a) High velocity of arc-like back and forth motions of the head and neck producing hyperextension and hyperflexion of the neck in subhuman primates caused concussion (i.e., abolition of consciousness) whereas restricting head movement did not; (b) Whiplash injury due to ​hyperextension and hyperflexion of the neck is commonly caused by rear-end vehicular collisions; (c) Vertebral arteries running up through the neck are part of the vertebrobasilar vascular system maintaining posterior cerebral regions; and (d) Disruption of vertebral artery blood flow as a consequence of neck injury can produce vertebrobasilar 19

ischemia compromising posterior cerebral functions that mediate sensory-spatial skills. If neck injury is indeed a correlate of sensory-spatial perceptual difficulties due to posterior cerebral ischemia, we would expect, as stated in the first hypothesis of the study, that Nonimpact mTBI would generate significantly more frequency of neck injury than Impact mTBI individuals. Nonimpact and Impact mTBI participants were compared on both frequency of complaints of neck injury and/or pain and healthcare diagnostic conclusions of neck injury and/or pain. Our second hypothesis was that there would be higher frequency of concordance between neck injury complaints and diagnoses for the Nonimpact group vs. Impact subjects, again reflecting greater neck injury for Nonimpact mTBI. Table 1 Frequency Percentages of Neck Complaints and Diagnostic Conclusions of Neck Injury, and their Concordance, for Nonimpact and Impact mTBI ____________________________________________________ ​Neck Injury ​mTBI %Complaints %Diagnosis Nonimpact (n=60) 70 68 Impact (n=60) 53 50 ____________________________________________________ Neck Injury Nonimpact Impact %Concordance 55 37 ____________________________________________________ 20

Frequencies converted to percentages for the two dependent neck injury variables are presented in Table 1. Frequencies of neck injury complaints and diagnostic conclusions of neck injury for the Nonimpact and Im​ pact mTBI groups were non-significant at a probability level of 0.06 when adjusted for multiple comparison bias, falling just short of an experiment-wise alpha of 0.05. Despite statistical non-support for the first hypothesis, there is no clear justification in completely dismissing the possibility of significantly more symptoms of neck injury for the Nonimpact mTBI group statistically since, considering the results obtained, additional subjects may very well have resulted in statistical significance. There was, nonetheless, a statistically significant higher frequency of concordance between neck injury complaints and diagnosis for Nonimpact mTBI relative to Impact mTBI. This outcome supports the second hypothesis that agreement between complaints of neck injury and diagnosis occurs significantly more often for Nonimpact mTBI participants. It is therefore warranted to conclude that ​neck injury represents a relatively frequent condition experienced by individuals meeting criteria for Nonimpact mTBI after a motor vehicle accident​. Given the following: ● Impact mTBI​ individuals achieve complete neuropsychological recovery but Nonimpact mTBI subjects do not; and ● Whiplash neck injury in rear-end collisions relates causally to brain-related sensory-spatial difficulties of N​ onimpact mTBI​ clients; 21

Direct impact to the head in mTBI may actually play a protective role in a rear-end collision by disrupting or preventing the neck of Impact mTBI individuals from entering into high velocity arc-like back-and-forth movements of hyperextension and hyperflexion. Comparatively frequent neck injury sustained by Nonimpact mTBI individuals supports the possibility that vertebral artery dysfunction due to whiplash may bring about ischemia of posterior cerebral regions, culminating in sensory-spatial perceptual deficiencies. Numerous articles and studies in the professional literature report that disruption of blood flow of the vertebral artery can compromise function of numerous post-central regions of the brain including occipital association cortex, the parietal lobe, and posterior portions of the temporal lobe. The most frequent cause of traumatic vertebrobasilar ischemia is neck injury in motor vehicle accidents. 22

Spatial Performance Issues Practical examples of “everyday” problems possibly experienced by Nonimpact mTBI clients in situations requiring immediate appreciation of visual-spatial information could include: generalized slowing of visual-spatial perceptual processing; interference with judgment of distance or size; difficulty negotiating the movements of your car when driving relative to other traffic; problems learning new travel routes; inability to respect the “personal space” of others; discomfort walking in large open spaces without visual cues nearby to provide points of reference to your physical location; and slow or hesitant reading due to difficulty spontaneously recognizing the visual-spatial features of letters and word configurations. Although visual-spatial deficiencies are usually more observable, it might be helpful in the clinical evaluation of Nonimpact mTBI for neuropsychologists to be particularly attentive to tactile-spatial issues that seem most prominent on the basis of the research. For example, tactile-spatial perceptual problems may result in feelings of disorientation when trying to navigate around objects in the dark, and shifting gears of a manual transmission while driving by using touch alone may be challenging. Commonplace tactile-spatial problems could also be relevant to diagnosis such as difficulty finding the right key on the key chain in your pocket using only touch, or taking an unusually lengthy period of time to dress in the dark. 23

Further Research The results of Study 3 were crucial to our conclusion of a relationship between Nonimpact mTBI and sensory-spatial perceptual deficiencies. Since the relatively small number of individuals composing the three clinical groups in the study limits generalization of our findings, the inclusion of many more participants in further similar research regarding the neuropsychological features of Nonimpact mTBI is necessary. Moreover, control of numerous extraneous variables that could influence test performance such as, for example, inadequate sleep, physical pain, medication side effects, the use of recreational drugs and abnormal psychological states, not controlled in our studies, is very much warranted. Finally, the use of a computerized testing format to measure the time required to immediately respond in tactile/visual spatial recognition paradigms would improve accuracy, and manipulation of the difficulty level of stimuli might enhance the diagnostic potential of tactile/visual spatial integration. The number of individuals referred for neuropsychological evaluation in my practice that met criteria for Nonimpact mTBI was relatively low, perhaps at 5-10% per annum, taking decades to collect the subjects suitable for the Nonimpact mTBI group studies currently reported. Hence, in the interests of time, further group studies of Nonimpact mTBI could be conducted by a number of neuropsychologists collaborating simultaneously. Single case studies could, of course, be readily completed by a single practitioner in a timely fashion. In conjunction with continuing neuropsychological studies of Nonimpact mTBI, functional neuroimagery measures of the brain such as fMRI, PET, and SPECT, and CT or MR angiography to assess the integrity of vertebral arteries, could be undertaken. In all of this, risk factors for 24

vertebrobasilar ischemia as a consequence of atherosclerosis should be given due consideration including smoking, hypertension, hyperlipidemia, gender, older age, and family history. 25

Research Summary W​e conducted preliminary neuropsychology investigations of people subjected to violent acceleration forces in motor vehicle accidents with no direct impact to the head who met criteria for Mild Traumatic Brain Injury. Our results suggest that a​ significant minority of these individuals experience persistent visual- and tactile-spatial perceptual, conceptual and integrative cognitive deficiencies specifically w​ hen speeded or immediate responses are required​. Such difficulties appear neurocognitive in nature involving dysfunction of post-central sensory cerebral regions. Since whiplash neck injury is a prominent diagnosis associated with this condition, disruption of vertebral artery function, culminating in ischemia of these regions, would be a parsimonious explanation. Our findings may underlie notable day-to-day and occupational liabilities in coping spontaneously with sensory-spatial environmental demands. 26

Please be advised that I am now retired from both clinical practice and actively conducting research. However, I remain available for consultation with other neuroscientists on a complimentary basis regarding Nonimpact mTBI research. I can be reached at j​ [email protected] 27

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Sweeney, J. E., & Johnson, A. M. (2001). Age and neuropsychological status following exposure to violent nonimpact acceleration forces in MVAs. Journal of Forensic Neuropsychology, 2,​ 31-40. Sweeney, J. E., & Johnson, A. M. (2019a). Halstead-Reitan characteristics of nonimpact and impact mild traumatic brain injury. A​ pplied Neuropsychology: Adult, 26,​ 65-75. Sweeney, J. E., & Johnson, A. M. (2019b). An index of decline or recovery following nonimpact and impact mTBI. ​Applied Neuropsychology: Adult, 26,​ 181-185. Sweeney, J. E., & Johnson, A. M. (2020). Exploratory study of HRB signs, patterns, and right-left differences relating to spatial cognition following nonimpact mild traumatic brain injury. ​Applied Neuropsychology: Adult, 27, 532-539. Sweeney, J. E., & Johnson, A. M. (2019c). Neck injury following nonimpact mild traumatic brain injury in motor vehicle collisions. ​Applied Neuropsychology: Adult.​ Article ID 1654478.​. Sweeney, J. E., Johnson, A. M., & Slade, A. M. (2017). Halstead-Reitan deficit scores in assessment of nonimpact head injury. Applied Neuropsychology: Adult, 24​, 169-175. Sweeney, J. E., & Slade, H. P. (2020). Preliminary study of spatial cognition relating to nonimpact mTBI. A​ pplied Neuropsychology: Adult, 27, 35-43. Sweeney, J. E., Slade, H. P., Ivins, R. G., Nemeth, D. G., Ranks, D. M., & Sica, R. B. (2007). Scientific investigation of brain-behavior relationships using the Halstead-Reitan Battery. ​Applied Neuropsychology, 2,​ 65-72. 29

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