Phasic arousal in response to auditory warnings after traumatic brain injury

Traumatic brain injury (TBI) is believed to have adverse effects on attention, but because of the multifaceted nature of the arousal and attentional network, the precise impact of TBI on various subcomponents of this network remains controversial. As part of a larger program of research on attention in TBI, we studied the effects of auditory warning signals on accuracy, reaction time, and response bias, as indices of phasic arousal in a visual go/no-go task. Warnings were presented randomly at various pre-stimulus intervals to a sample of recently injured patients and control subjects. For each subject and performance index, we examined the time interval required to reach maximal phasic arousal, the degree of performance change occurring at this maximal point, and the ability to maintain this state of increased arousal over longer warning intervals. After adjustment for baseline differences, there were no significant differences between patients and controls in any aspect of performance. Examination of effect sizes suggested that this was not due to limited statistical power, but that any differences between groups, if present, must have been small. In contrast, in our prior research on sustained attention and observable behaviors related to attention, large group differences have been found. These data suggest that mechanisms responsible for auditorily-induced phasic arousal responses are largely preserved in severe TBI.