Distinguishing the Relative Impact of Post-Traumatic Stress Disorder and Traumatic Brain Injury on iPad-Measured Cognitive Function

Traumatic brain injury (TBI) and post-traumatic stress disorder (PTSD) are highly prevalent, and frequently comorbid, among active and retired military service members. Both TBI and PTSD may contribute to impaired cognitive function, but it remains insufficiently clear what the relative impact of each is on overall cognition and whether multiple TBIs may further impair cognitive function. To understand the relative impact of TBI and symptoms of PTSD on cognitive function we examined data from 326 active or retired military service members, or dependents, either with or without a history of TBI, using questionnaires and the NIH Toolbox Cognitive Battery (NIH-TB), a brief iPad-based assessment that measures the cognitive domains most important to daily functioning. The NIH-TB was developed for use as a "common currency" among research studies, and was more recently adapted to the iPad for ease of use. To our knowledge, this is the first report of its application to evaluate the relative impact of TBI and PTSD. Our results indicate that cognitive function remains largely intact after multiple TBIs if symptoms of PTSD are not evident, and that measures of literacy and overall intelligence are relatively impervious to both TBI and PTSD. When cognitive impairment is observed after TBI, it is predominantly associated with the presence of significant symptoms of PTSD in most domains. However, TBI alone may impair some aspects of executive function. These findings need to be validated in other populations.