Brain activation during working memory 1 month after mild traumatic brain injury - A functional MRI study

Objective: To assess patterns of regional brain activation in response to v arying working memory loads shortly after mild traumatic brain injury (MTBI ). Background: Many individuals complain of memory difficulty shortly after MTBI. Memory performance in these individuals can be normal despite these complaints. Methods: Brain activation patterns in response to a working mem ory task (auditory n-back) were assessed with functional MRI in 12 MTBI pat ients within 1 month of their injury and in 11 healthy control subjects. Re sults: Brain activation patterns differed between MTBI patients and control subjects in response to increasing working memory processing loads. Maximu m intensity projections of statistical parametric maps in control subjects showed bifrontal and biparietal activation in response to a low processing load, with little additional increase in activation associated with the hig h load task. MTBI patients showed some activation during the low processing load task but significantly increased activation during the high load cond ition, particularly in the right parietal and right dorsolateral frontal re gions. Task performance did not differ significantly between groups. Conclu sion: MTBI patients differed from control subjects in activation pattern of working memory circuitry in response to different processing loads, despit e similar task performance. This suggests that injury-related changes in ab ility to activate or to modulate working memory processing resources may un derlie some of the memory complaints after MTBI.