The Network has conducted several related studies in Rhesus monkeys that address how early social deprivation affects brain and behavioral development. Monkeys who were removed from their mothers at either 1 week of age or 4 weeks of age developed strikingly abnormal behaviors compared both to each other and to normal monkeys who left their mothers at 6 months, the usual time for maternal separation. Neuroanatomical studies of these monkeys have shown distinct differences in some areas related to social functioning. Other studies involve introducing monkeys separated at 1 week of age (who appear to lack any social drive after the separation) to a supermom (a female monkey known to adopt infants). These studies are showing that, while the behavioral abnormalities seen in these separated monkeys can be remediated by the introduction of a substitute mother, there appears to be a narrow window of opportunity for the reintroduction of maternal care. After this window of opportunity, it is highly unlikely that either the infant or the mother will be amenable to adoption.
The behavioral abnormalities seen in the 1-week and 4-week separated monkeys appear to have long-lasting consequences. The first separated monkeys are now of reproductive age, and several have had infants of their own. Those monkeys separated from their mothers at one week of age display highly abnormal parenting behaviors. We are watching the infants of these mothers closely to see if there is any intergenerational transmission of the abnormal behavioral profile.
Another study that involved re-organizing separated monkeys into unfamiliar social groups has just been concluded, and behavioral data show striking behavioral abnormalities among the one-week- and four-week-separated monkeys. This suggests that there may be some further brain and behavioral abnormalities caused by the early deprivation that do not manifest themselves until later in life, or until the introduction of some social stress (perhaps akin to the social stress undergone by adolescents entering a new school setting).