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EFFECTS OF EARLY EXPERIENCE ON BRAIN-BEHAVIORAL DEVELOPMENT, cont.

Timing of Maternal Separation in Rhesus Monkeys
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This study examines the different behavioral "profiles" of Rhesus monkeys whose mothers were removed at different times. Normally, a Rhesus monkey leaves its mother at 6 months. In this study, several groups of infant monkeys and their mothers were housed in pens with other monkeys, and then the mothers were removed when the infants were various ages: at 6 months of age, at 3 months, at 1 month and at 1 week. The monkeys whose mothers were removed when the infant was 6 months or 3 months old behaved like normal monkeys. The monkeys whose mothers were removed when they were 1 month old developed "clinging" behavior - they find a "surrogate" monkey to cling to, and continue to cling to that monkey long past the age when monkeys are usually independent. The monkeys whose mothers were removed at 1 week of age exhibit no social behavior - they play quite contentedly by themselves, but show no interest in interacting with other monkeys, and in fact become quite distressed when approached by another monkey. In addition, they appear to show little fear (compared to normal monkeys) when presented with novel objects.

Clearly, both of these groups of monkeys experienced some kind of disturbance in their social development when their mothers were prematurely removed. Additionally, it appears that the timing of this disturbance makes a great difference in the behavioral outcome - it is possible that different brain systems are maturing at those two different time points (1 week and 1 month) and are responsible for the two vastly different behavioral responses. We are currently experimenting with re-introducing a maternal female monkey at different times after the separation at 1 week to see if this group of monkeys can "re-learn" social behavior after having experienced a disturbance in this process.

Because this study is being performed in monkeys and not in humans it would be difficult, and perhaps scientifically irresponsible, to draw parallels between monkey and human experiences. By conducting other tests to identify the parts of the brain that may be affected by their early experience, we may be able to develop new hypotheses about how those parts of the brain may be involved in human social and emotional development.

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