Traumatic brain injuries represent the leading cause of death and disability in young adults in industrialized countries. Recently, it has been suggested that dysfunctions of the frontomedian cortex, which enables social cognition, are responsible for clinical deficits in the long-term. To validate this hypothesis, we examined brain activation in seven young adults suffering from diffuse axonal injury during a cognitive task that specifically depends on frontomedian structures, namely evaluative judgments, contrasted with semantic memory retrieval. Brain activation in patients was compared with healthy age and gender matched control subjects using event-related functional magnetic resonance imaging. Evaluative judgments were related to a neural network discussed in the context of self-referential processing and theory of mind. More precisely, the neural network consisted of frontomedian regions, the temporal pole, and the posterior superior temporal gyrus and sulcus/angular gyrus. Patients showed higher activations in this network and the inferior frontal gyrus, whereas healthy control subjects activated more dopaminergic structures, namely the ventral tegmental area, during evaluative judgments. One possible interpretation of the data is that deficits in the ventral tegmental area, and consequently the mesocorticolimbic projection system, have to be compensated for by higher brain activations in the frontomedian and anterior cingulate cortex in patients with diffuse axonal injury. In conclusion, our study supports the hypothesis that traumatic brain injury is characterized by frontomedian dysfunctions, which may be responsible for clinical deficits in the long-term and which might be modified by rehabilitative strategies in the future.

It is well known that traumatic brain injury particularly affects the frontal lobes. Consequently, patients often suffer from executive dysfunction and behavioral disturbances. Accordingly, our study aimed at investigating patients after traumatic brain injury with two tasks involving different functional processes and structural networks supported by the frontal lobes. Two paradigms were applied: the Stroop color-word task and a task in which subjects had to inhibit imitative response tendencies. We selected a patient group solely with diffuse axonal injury, as this type of injury is homogenous and is correlated with cognitive dysfunction more than focal contusions. To evaluate long-term effects most relevant for rehabilitation, we selected a patient group whose brain injuries dated back several years. Our results show that patients with diffuse axonal injury inhibited imitative responses more successfully than control subjects, whereas executive processes examined with the Stroop task were unaltered. Interestingly, impairments were tightly correlated both with the length of the post-traumatic amnesia predicting outcome in traumatic brain injury and with behavioral disturbances. Impairments in the imitation-inhibition task may indicate alterations in an anterior frontomedian neural network even years after traumatic brain injury.