Heart rate (HR) responses evoked by I sec of 85-dB white noise were studied in 12 1-year-old pigtailed macaques, 6 of which were raised in social isolation and 6 with mothers and peers. Tests were given for 5 days, with 25 trials each day. Although baseline HR did not differ between groups, the pattern of change from baseline was not the same. Isolates showed only HR acceleration, returning to baseline within 10-1 1 sec of stimulus onset. Socially reared monkeys had a 10-to I I-sec biphasic response of acceleration followed by deceleration, with subsequent return to baseline. The same group difference in HR pattern occurred when subjects were tested with a less intense 65-dB stimulus. These findings were discussed in terms of activity, emotionality, and autonomic regulatory functions. It was concluded that early rearing experiences may affect later physiological processes involving autonomic nervous system balance. This conclusion was related to observations of persistent individual differences in HR by human children classified as inhibited.
Many studies of nonhuman primates have assessed effects of varied types and durations of social and perceptual deprivation on subsequent behavior. Total isolation from species members in an unchanging perceptual environment has produced the most severe and long-lasting deficits . Rhesus macaques (Macaca rnulatta) raised from birth to 9 or more months in total isolation show species-deviant social, emotional, sexual, maternal, and exploratory behavior . Their behavioral repertoires include high levels of self-directed and stereotyped motor patterns and inappropriate responses to noxious stimuli. In the absence of post-isolation ther-