Suomi – nurturing foster mothers: foster mothers

Well, we have two sets of findings. One that was done some years ago before we knew specific genes that might be involved, taking monkeys that were genetically shy and fearful, and these are monkeys that under normal circumstances develop patterns of behavior that look very much like the behaviorally inhibited children that Jerome Kagan has been studying for the last two decades. These are individuals who, under challenging, under normal circumstances or familiar circumstances show perfectly normal behavioral and physiological patterns, but when they are exposed to model or moderately stressful circumstances, they show excessive amounts of fearful and anxious-like behavior; they show heightened arousal of a variety of physiological systems including the hypothalamic-pituitary-adrenal axis, evidenced by higher levels of cortisol, ACTH and CRF, a high unstable heart rate; greater norepephrine turnover;  and some compromising of the immune system. These monkeys, who make up about 20 percent of the population in the wild and in our colony, also are at risk for developing depressive behaviors if the challenge they are exposed to is more extreme, and later in life they show excessive consumption of alcohol.  

When we carried out a cross-fostering study, we took these monkeys whose genetic backgrounds suggested that they were going to develop into this bio-behavior phenotype, and we put them with unusually nurturant foster mothers that we call super moms. These were females, multiparous females, whose care of their own previous offspring indicated that they had very, established very firm and secure attachment relationships, they were very supportive of their infants’ exploration, they showed very low patterns of punishment, and when we cross-fostered our high-reactive, as we called them, infant monkeys to these foster mothers, we were quite surprised because the up-tight monkeys, as we characterized them, actually showed supernormal development. They were behaviorally precocious, they actually explored more than their counterparts. During the weaning process they showed lower levels of disturbance and distress behavior in reaction to their mother’s punishment and they became unusually adept in social situations of seeking out help when they needed it. So they were, became very good at establishing functional social relationships with others in their social group. And ultimately they rose to the top of their group’s social dominance hierarchy, whereas high-reactive infants reared with normal mothers or cross-fostered to normal mothers usually end up at the bottom of their group’s social dominance hierarchy. And most interesting to us, when the females, high-reactive females who were cross-fostered by the super moms, grew up and started having kids of their own, they showed the same patterns of maternal care that they received when they were infants. Thus they were capable of passing on the advantages that they had accrued from their own foster mothers onto their own offspring.