Those unfortunate babies no one immediately adopts and so spend months, even years, in institutions often grow up to be children who behave inappropriately, in particular showing a lack of wariness toward strangers. Now, UCLA researchers have found evidence that suggests such indiscriminate friendliness is rooted in the amygdala, where the brain has apparently adapted to their early-life experiences.

"This can be a very frightening behavior for parents," Nim Tottenham, an associate professor of psychology at UCLA and the study's senior author, stated in a press release. "The stranger anxiety or wariness that young children typically show is a sign that they understand their parents are very special people who are their source of security." The research appears online in Biological Psychiatry.

Brain Imaging

For the study, the team from UCLA used functional magnetic resonance imaging (fMRI) to explore their hypothesis that children who experienced early maternal deprivation show changes in the brain structure known as the amygdala. As part of the study, the parents of participating children answered questions designed to gauge how trusting the child was with new adults as well as the likelihood of their child wandering away with a stranger. During the experiment, 67 children between the ages of four and 17 underwent fMRI while they were shown pictures of their adoptive mother and of an unfamiliar female. Approximately half (33) the children had spent time in institutions, ranging from five months to about five-and-a-half years, before they were adopted.

The UCLA researchers discovered that while the typically-raised children exhibited higher amygdala signals for their mothers compared to strangers, the previously institutionalized children showed amygdala responses to strangers that were similar to those they showed toward their adoptive mothers. Additionally, the children who had lived in an institution showed greater amygdala reactivity to strangers than did the typically-raised children. In turn, the parents more frequently reported indiscriminate friendliness in the cases of reduced amygdala differentiation. Finally, after fully analyzing the data, the team concluded that children who had been adopted later displayed the least discrimination on the scans and the greatest degree of indiscriminate behavior.

"The early relationship between children and their parents or primary caregivers has implications for their social interaction later in life, and we believe the amygdala is involved in this process," Aviva Olsavsky, Semel Institute for Neuroscience and Human Behavior at UCLA and the study's first author, stated. "Our findings suggest that even for children who have formed attachments to their adoptive parents, this early period of deprivation has led to changes in the brain that were likely adaptations and that may persist over time."

The amygdala is an almond-shape set of neurons located deep in the brain's medial temporal lobe. Part of the limbic system of the brain, the amygdala has been shown to play a role in the processsing of emotions and is often linked to fear responses as well as emotional response to other people. Past research offers some evidence that aggression, anxiety, depression, post-traumatic stress disorder, and phobias may be linked to abnormal functioning of the amygdala. Experiments with rodents have found that the process of forming a maternal bond early in life has powerful effects on amygdala development and attachment-related behaviors. In a recent study conducted by a team of researchers in the Netherlands and the U.S., rat pups exposed to maternal separation displayed deficits in social play and more contextual fear memory, as compared to controls, when they became adults. And these behaviors were echoed by changes in the amygdala related to the level of expression of c-Fos, a protein related to cellular function. In fact, over-expression of c-Fos has been linked to several cancers.

Sources: Olsavsky AK, Telzer EH, Shapiro M, et al. Indiscriminate Amygdala Response to Mothers and Strangers After Early Maternal Deprivation. Biological Psychiatry. 2013.

Daskalakis NP, Diamantopoulou A, Claessens SE, et al. Early experience of a novel-environment in isolation primes a fearful phenotype characterized by persistent amygdala activation. Psychoneuroendocrinology. 2014.