Social environment and nocturnal sleep: studies in peer-reared monkeys

Nocturnal sleep was recorded for a total of 40 nights by means of totally implantable, multichannel biotelemetry from 11 peer-reared pigtail (Macaca nemestrina) monkey infants (aged 221 +/- 28 days). Fourteen sleep variables were compared to values previously obtained from similar-aged, mother-reared infants living in social groups. Sleep in peer-reared monkeys was more fragmented, contained less drowsy, more stage 2, less REM, fewer REM periods, and longer interREM intervals than sleep in mother-reared infants. It would appear that these effects are not due to a relatively impoverished environment that may accompany peer rearing, as has been reported to be true for rodents, but rather to the disruptive influence of sleeping with a peer in the absence of the organization and control effected by a monkey mother and a social group.