Autonomic activity during task performance in adults with closed head injury.

Skin conductance (SC) and heart rate (HR) were recorded in two experiments in persons who had suffered a closed head injury (CHI) at least 2 years previously and in control subjects. Experiment 1 consisted of a rest period, a series of innocuous tones, and a short simple reaction time (RT) task. Experiment 2 consisted of initial and final rest periods and a longer RT task with constant and variable preparatory intervals. The results from both protocols showed no group differences in HR, SC levels, or SC fluctuations during rest periods, but the SC variables increased less to the task instructions in the CHI group. There were no differences in SC response frequency or magnitude to innocuous tones, but the CHI subjects had fewer SC responses to the RT stimuli in both experiments. SC responses to both innocuous tones and RT stimuli had longer latencies in the CHI group. The results show that selective deficits in tonic and phasic autonomic responding to meaningful, significant, or demanding situations and stimuli are long-term sequelae to CHI. These attenuated activation increases may be related to inadequate mobilization of processing resources and to behavioral deficits shown by these patients.