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Chimpanzees' brains reflect their early childhood experiences

Proper socialization could make up, in part, for separation of a child from their mother

Lauren Granata


Northeastern University

In the 1980s, the NIH began a chimpanzee breeding program. The initiative was meant to produce animals that could be used for future research. While some chimp moms gave their infants the appropriate care needed to support brain development, others struggled to deliver the same parenting. In those instances, the babies were placed in a nursery under human care. Separating the chimps from their mothers was not an intentional experimental design, but it was necessary at the time because of the inadequate treatment their mothers were giving them.

Although the nursery was not explicitly harmful, raising these chimps without a primary caregiver remarkably resembled the conditions human children are sometimes subjected to under institutional care. In a recent study led by University of Wisconsin-Madison biological psychologist Allyson Bennett, researchers took advantage of these circumstances to uncover how nursery care affected these chimps over 15 years later.

Starting from birth, the complex interplay between our genome and influences from the environment shapes connections in our brains that will help us function throughout life. Infants learn how to interact with the world through stable, nurturing interactions with their caregivers, but without proper parental support, children may struggle to build the skills necessary for social and emotional functioning. By following up with people who were surrendered to institutional care facilities as children, studies have revealed a link between adverse childhood experiences and mental health disorders.

Since there is a window of vulnerability when children can be most impacted by their experiences, researchers have directed their attention to uncovering how brain development is affected by the environment. Adverse childhood experiences are often modeled in laboratory animals by separating infants from their caregiver, the primary source of nutrition, warmth, and comfort. Without regular caregiving, infants struggle to form secure attachment, the foundation of socioemotional development. Studies in rodents have shown that separating infants from their parents can lead to abnormal functioning in brain areas controlling learning, anxiety, social behavior, and risk-taking.

While the evidence suggests that adversity is overall damaging to mental health, this one-track expectation can lead to biased investigations of individual brain regions or circuits expected to be deficient in mental disorders. Thus, researchers can sometimes overlook areas of resilience and fail to recognize opportunities that would support more positive outcomes, such as interventions and preventative strategies.

The researchers behind this new study examined the chimps' brains holistically. Instead of testing for differences between chimpanzees raised by their mothers and those raised in nurseries on a particular measure in the brain, they used machine learning as a tool to ask whether different early life environments cause alterations in the brain that are distinct enough for an algorithm to recognize them.

A chimpanzee and her baby

A mother chimpanzee and her baby

Becker1999 on Wikimedia Commons

When they were 15 years old, the mother-raised and nursery-raised chimps were scanned using MRI, which detects differences in water content to reveal structures inside the body. The investigators were interested in the brain’s gray matter. With thousands of iterations of machine learning training, they created an algorithm that learned how the brains from chimps raised in each environment differed from one another. Mother-raised and nursery-raised chimps had different gray matter volumes in the somatosensory cortex, parietal cortex, and precuneus, brain areas important for higher order cognitive functions.

For the most part, the algorithm could accurately predict the childhood histories of the chimps, but the investigators also wondered why some brains were incorrectly classified. Some of the chimps that were misidentified were labeled as mother-raised when they were in fact raised in the nursery.

Looking back at their histories, it turned out that many of the misidentified nursery-reared chimps were part of a smaller social intervention program meant to help support their development in the nursery. Chimps in the intervention were prescribed a regimen of extra social stimulation from humans and other chimps their age, and we can now see that they grew to develop brains that were very similar to chimps raised by their natural mothers.

Despite being raised in the nursery, consistent social experiences provided a buffer to protect these chimps from the derailment that other chimps in the nursery showed in their brain development. Social experiences are the foundation for forming healthy relationships and being able to respond to challenges, and this study shows just how impactful social interactions can be even when faced with environmental stressors.

“It is the power of being with others that shapes our brains”, says clinical psychologist Louis Cozolino in his book, The Neuroscience of Human Relationships: Attachment and the Developing Social Brain. As the primary source of interaction early in life, caregivers exert major influence on childhood development. When children are separated from their parents or face other forms of childhood adversity, interventions can still prevent and reverse some of the mental health consequences that may come later in life. When it comes to institutionalized children, intervention programs have already shown that better social relationships lead to better outcomes for these children. The best outcomes come when interventions are applied as early as possible. With more research pointing to the effects of social relationships on mental health, it is clear that social interactions with peers are a powerful supplement to shaping a healthy brain.