A comparative approach to the study of early experience and development is ubiquitous throughout the research initiatives of this network. Of particular relevance to the goals of this initiative are selective rearing studies with animals (rats and monkeys) that parallel the conditions under which young children are raised.
An example of such an undertaking can be found in recent pilot work conducted with Rhesus monkeys by Dr. Judy Cameron (a core group member). Dr. Cameron has separated monkeys from their mothers at four different ages: one week, one month, three months, and six months (this last age is when separation would occur normally). The behavioral repertoire of animals separated at three and six months is normal.
However, animals separated from their mothers at one month show profound behavioral (particularly emotional) deficits. For example, these animals quickly seek out an adult to adopt them, and latch onto this adult. Once adopted, they spend as much time as they can clinging to “mother.” They do not interact with peers at all. When alone they show a range of behavioral stereotypies (e.g., rocking, chewing on their feet) and, in more general terms, seem very disturbed, perhaps even depressed. Finally, these animals do not learn to bottle feed, and unless given extensive instruction in feeding, will waste away and die.
The animals separated at one week differ quite dramatically than those separated at one month. These animals are happy and carefree when left by themselves; by all accounts, their solitary behavior is perfectly normal and they show no urge to be adopted. In addition, unlike the animals separated at one month, these animals quickly learn to bottle feed, and indeed, eat frequently and heartily. Finally and most dramatically, the moment these animals are approached by another animal (adult or peer) they engage in freezing behavior, essentially stopping whatever they are doing, slinking to the floor, and becoming immobile, behavior that is maintained until the animal that approached them finally leaves.
The differential effects of being separated from caretakers at different ages are dramatic, and in some instances, bear an uncanny resemblance to the behavior of children reared in institutionalized orphanages. This points up the need to conduct more formal comparative studies. Unfortunately, the behaviors of Dr. Cameron’s animals have thus far not been extensively characterized, and there have been no neurobiological or neuropsychological studies conducted. Clearly much work remains to be done.
For purposes of this module, it would seem important to attempt to further mimic (in the rodent and the monkey) the conditions the child adopted from Romania experiences the first year of life while living in an institution. And having done this, can we conduct in-depth studies of these animals’ behavior, and of course, their brains? Similarly, can we create animal models of human conditions such as autism by performing selective lesions or by rearing animals in such a way as to imitate the human condition? Naturally, our success in this endeavor will to a great degree be determined by our success in developing the tools necessary to assess brain-behavior relations (see Study Area B).