Sustained arousal and attention after traumatic brain injury.

Clinicians report that patients with traumatic brain injury (TBI) often have difficulty with tasks requiring sustained attention, and there are neuroanatomical and neurophysiological reasons to expect such deficits. Nevertheless, laboratory measures of sustained attention or vigilance in TBI have produced conflicting results. These inconsistencies may be due to patient heterogeneity as well as the fact that vigilance performance is dependent on highly specific features of the task design. We developed a visual vigilance task in which the influence of non-attentional factors was minimized and task difficulty for patients and controls made comparable. Performance was characterized with respect to vigilance level as well as vigilance decrement, using measures of perceptual discrimination, response bias, reaction time and reaction time variability. Twenty-six patients with recent TBI and 18 control subjects were tested on this task. A MANOVA of ranked scores revealed significantly different patient and control performance overall. Initial level of performance (vigilance level) was slower and more variable for patients than controls, and patients showed more conservative response biases. Deterioration over time (vigilance decrement) was steeper for patients than controls for reaction time, reaction time variability, and response bias. Deterioration in accuracy (D') did not differ significantly between patients and controls. Performance was not related to available measures of injury severity. Hypotheses relating arousal mechanisms to vigilance performance are discussed.