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ArticlesMild Traumatic Brain Injury and Working Memory Author: Richard H. Adler It is common for researchers and practitioners to encounter mild traumatic brain injury (MTBI) patients with normal CT or MRI scans, who experience a number of post-concussive complaints and cognitive deficits. A recent study (McAlister TW, Saykin AJ, et al. "Brain Activation During Working Memory One Month After Mild Traumatic Brain Injury" Neurology 1999; 531:1300-1308) deals with the concepts of "working memory" and "processing load." The authors define working memory as, "the online storage of information necessary for performing cognitive operation," and processing load as, "the amount of information that must be held online to solve a particular problem." They hypothesize that individuals with mild traumatic brain injury have a physiologic basis to their memory and attentional complaints. The researchers used a functional MRI within one month of injury. Twelve mild traumatic brain injury patients and 11 healthy individuals had their brains scanned while performing memory tasks. Eleven of the patients had a normal CT and MRI scan. Both groups completed a "symptom checklist." The mild traumatic brain injury patients reported more symptoms, including poor memory of recent events, difficulty in doing their job, and trouble concentrating. The control group showed no decline in performance when moving from the low processing demand tasks to the high processing demand tasks. Both the control and the patient groups had similar areas of brain activation and similar task performance. However, there were differences in how the memory worked in the brain injury patients vs those in the control group. Patients with brain injuries showed increased activity in the right lateral parietal regions and the right dorsolateral frontal regions. The authors claim it is unlikely the differences in activation are related to attentional difference, distress, or depression, since both groups scored similarly on the symptom checklist. The authors also concluded it was unlikely that the brain injury patients suffered neural loss since they showed performance similar to the controls in memory tasks. They concluded: "the ability to activate, modulate, or allocate processing resources in response to gradations of processing load may be impaired in the post-acute period after MTBI." This means mild traumatic brain injury patients do not have decreases in brain resources, (the information is all there) but do have limitations in the circuitry, i.e., difficulty moving, timing, and regulating access to the information. To explain all the incongruities between the traumatic brain injury patient's experience of difficulties and what test results imply, the authors write: "One possible explanation is that the MTBI patients perceive the change
in their ability to engage working memory easily and efficiently, and experience
this change as 'having to work harder' to maintain accurate task performance.
Perhaps this is then labeled as 'problems with memory.' If true, this might
account for the discrepancy between the severity of complaints voiced by
many MTBI patients and the relatively minor performance deficits often found
in these individuals." The mild traumatic brain injury patient then, is not malingering or experiencing depression or anxiety which is causing their symptoms as some researchers posit when grappling with the chasm between test results and brain injury patient complaints. The authors noted the discrepancy between patient complaints and actual task performance: "is at the heart of the controversy about the etiology of the post-concussive
syndrome, and frequently reported results in attributing mild traumatic brain
injury patient complaints to malingering orpsychopathology such as depression,
anxiety, post-traumatic stress disorder, or other mechanisms.” Rather the results here suggest that cognitive complaints of mild traumatic brain injury patients are related to differences in brain activation and the condition of brain circuitry. The authors also point out that "this study describes significant differences in patterns of brain activation in response to working memory tasks and suggests that an alteration in the ability to activate or to allocate processing resources in response to a moderate working memory task may be associated with cognitive complaints after very mild TBI." Complaints of post-concussion symptoms are common among auto accident and other trauma victims, particularly during the first weeks following injury. Reports of memory and attention deficit are frequently heard. Symptoms seem to lessen and resolve within several months in many cases. However, the degree of perceived dysfunction, coupled with a presumption for improvement, may have deterred more rigorous inquiry into the nature of the phenomenon. This study lends support for the proposition that head injury symptoms are real and ongoing sequella of mild traumatic brain injury in these cases, even when not detected by CT or MRI scans. Brain injury survivors are particularly vulnerable to insurance company machinations. In cases of mild traumatic brain injury a referral for consultation with experienced personal injury attorneys with advanced knowledge in traumatic brain injury is warranted. |
