Traumatic brain injury (TBI) is often associated with enduring
impairments in high-level cognitive functioning, including working
memory (WM). We examined WM function in predominantly chronic patients
with mild, moderate and severe TBI and healthy comparison subjects
behaviorally and, in a small subset of moderate-to-severe TBI patients,
with event-related functional magnetic resonance imaging (fMRI), using
a visual n-back task that parametrically varied WM load. TBI
patients showed severity-dependent and load-related WM deficits in
performance accuracy, but not reaction time. Performance of mild TBI
patients did not differ from controls; patients with moderate and
severe TBI were impaired, relative to controls and mild TBI patients,
but only at higher WM-load levels. fMRI results show that TBI patients
exhibit altered patterns of activation in a number of WM-related brain
regions, including the dorsolateral prefrontal cortex and Broca's
area. Examination of the pattern of behavioral responding and the
temporal course of activations suggests that WM deficits in
moderate-to-severe TBI are due to associative or strategic aspects of
WM, and not impairments in active maintenance of stimulus
representations. Overall, results demonstrate that individuals with
moderate-to-severe TBI exhibit WM deficits that are associated with
dysfunction within a distributed network of brain regions that support
verbally mediated WM. (JINS, 2004, 10,
724–741.)