Habituation and dishabituation of the heart rate component of the orienting response in brain-damaged patients

Measures of the heart rate (HR) orienting response (OR), its habituation, and its dishabituation were tested in brain-damaged (BD) and nonbrain-damaged (NBD) middle-aged males. The habituation stimulus was an 80-dB pure tone, the dishabituation stimulus was a change in frequency, and a return to the original stimulus provided a test for dishabituation. A “blank” trial was scored 20 sec after the task to provide a special dishabituation stimulus. Another “blank” trial 20 sec before the task provided a measure of natural HR variability during rest. Both the NBD and BD exhibited ORs on Trials 1 and 2 and habituation on later trials. Change in stimulus resulted in dishabituation in the NBD but not in the BD. It is concluded that the response “model” for the OR is less elaborated and more diffuse in the BD than in the NBD S.