Cognitive fatigue is a subjective lack of mental energy that interferes with daily activities. Researchers at Kessler Foundation and Dartmouth College Medical School looked for more clarity as to its cause as an after effect of traumatic brain injury (TBI). The researchers compared brain activation patterns in 22 individuals with moderate to severe TBI and 20 healthy controls. Both groups performed tasks of working memory during functional MRI imaging of the brain; the TBI group reported more fatigue, although performance was comparable between the groups. The results showed that the experience of self-reported fatigue is associated with activation changes in the caudate nucleus of the basal ganglia. The findings are similar to research in multiple sclerosis (MS) and imply that this area of the brain is a likely target for interventions to alleviate fatigue.