Behavioral and electrophysiological investigation of attention and executive functions with and without minor head injury

The existence of lasting cognitive effects following a minor head injury (MHI) is subject to considerable debate. Frequently persons with MHI complain of difficulties with attention and concentration whereas standard objective measures such as neuropsychological testing and neuroimaging do not reveal any behavioral deficits or underlying structural damage. In Experiment 1, a group of high-functioning students with MHI had difficulty with tasks that required them to divide their attention and allocate attentional resources during a dual-task despite normal performance on most behavioral tasks associated with frontal-lobe function. In Experiment 2, we collected event-related potential (ERP) and electroencephalographic (EEG) coherence measures while participants with head injury and controls performed tasks that increased in difficulty and in demands on cognitive resources. Even though, in this sample, participants with head injury and controls performed similarly on all behavioral measures, those with head injury demonstrated an increased cortical-activation cost associated with increased demands on attentional allocation.;Data from Experiment 2 also revealed theoretically relevant relations between electrophysiological. activity and task requirements. Early components of information-processing (N1, P2, N2) were found to be enhanced with increased cognitive demands, suggesting that these components are affected by increased focused attention as demands on attentional abilities increase. Speed of information-processing increased and processing capacity decreased with increased demands on attentional allocation as evidenced by task effects on P3 ERP component latency and amplitude. Increasing focused attention led to a decrease in EEG coherence between frontal and posterior regions and an increase in local, short connection EEG coherence in posterior brain regions. Divided attention, on the other hand: increased EEG coherence between frontal and parietal sites. In all, tasks requiring divided, relative to focused, attention elicited different patterns of brain activation and these were captured through subtle variation in electrophysiological activity.