SUMMARY The influence of 10 days of maternal separation on behavior and physiology was studied in 8 social group living pigtailed macaque (M. nemestrina)monkey infants. Maternal separation was accompanied by behavioral changes' included slowing of movement, decreases in play, increases in oral behaviors, and assumption of a characteristic slouched posture and sad facial expression. Physiological changes included decreases in heart rate and body temperature, sleep disturbances that were most pronounced in the Awake and REM sleep systems, and changes in EEG alpha power‐spectra. Individual variability in the behavioral and physiological response to maternal separation was marked, and showed only a minimal correlation with measures of early behavioral development and the early mother‐infant interaction. Some physiological changes appeared to lie relatively long lasting. The data demonstrate that the disruption of an attachment bond may be accompanied by pronounced physiological changes suggestive of d general impairment of autonomic homeostatic regulatory processes. The findings have important implications for our understanding of the Pathophysiology of grief, and the physiological concomitants of. separation, loss, and depression in children.

Three pigtail infant monkeys (Macaca nemestrina) were separated from their mothers shortly after birth and raised in social isolation on cloth surrogates. At about 24 weeks of age they were surgically implanted with multichannel biotelemetry systems. Following the collection of baseline behavioral and physiological data, the cloth surrogates were removed for 4 days, then returned. The behavioral and physiological (heart rate, body temperature, sleep patterns) reaction to separation from the surrogate was much less intense than is the case in group-living pigtail infants that are separated from their mothers, suggesting that the attachment bond to a cloth surrogate may be different than the bond to a living mother in a social group. Heart rate mean values and variability were similar in surrogate-reared and mother-reared infants, suggesting a degree of environmental independence in heart rate regulation.

The occurrence of nocturnal cardiac arrhythmias was determined in 9 infant pigtail (M. nemestrina) monkeys during 3 baseline normal nights, 3 nights following maternal separation, and 3 nights following reunion with the mother. All infants lived in social groups where they had been raised by their natural mothers; heart rate data were collected by means of totally implantable biotelemetry systems. Marked individual differences were found in the mean frequency of cardiac arrhythmias in the baseline condition, and infants with lower heart rates had a greater mean number of arrhythmias. Maternal separation was accompanied by both increases in arrhythmias and decreases in heart rate. The relationship (slope of the regression line) between arrhythmias and heart rate changed in 8 of the 9 infants during separation, suggesting that the increase in arrhythmias was greater than could be accounted for by the decreases in heart rate alone. While both heart rate and arrhythmia values tended to return to baseline values following reunion with the mother, some infants exhibited prolonged separation‐induced alterations.