Genetic Variation Cues Social Anxiety In Monkeys And Humans
A genetic variation involving the brain chemical serotonin has been found to shape the social behavior of rhesus macaque monkeys, which could provide researchers with a new model for studying autism, social anxiety and schizophrenia. Humans and macaques are the only members of the primate family to have this particular genetic trait.
“We have found very similar gene-based disruptions in social rewards shared by monkeys and by humans,” said Michael Platt, Ph.D., associate professor of neurobiology at Duke University Medical Center and an expert in neuroeconomics.
Platt’s research group at Duke studied behavior and social anxiety in two groups of monkeys with variations in the serotonin transporter gene, crucial to regulating emotion. Based on earlier observations in humans, the scientists knew that humans carry two versions of the gene, long and short. Some people have two long versions (L/L), but the people with one of each (S/L) are known to experience a higher incidence of social anxiety and other behaviors.
In a series of experiments, the S version of the gene in monkeys was found to influence their risk-taking when faced with particular social stimuli.
“Based on work in humans, we interpreted this to reflect an induction of a fearful emotional state, which often leads people to become risk averse,” said Karli Watson, Ph.D., of the Duke Department of Neurobiology, lead author on the paper.
In human populations of European ancestry, 48% are S/L and 36% are L/L. The rest are S/S. The S allele is more common in Asian populations, Watson noted.
The authors conducted three experiments with male monkeys that had been genotyped for the S/L or L/L variants to learn how genetic variation might influence their responses to social rewards and punishments. They found that monkeys with one copy of the short gene spent less time gazing at images of the face and eyes of other monkeys, were less likely to engage in risk-taking behavior, and less likely to want to view a picture of a high-status male.
“For both human and non-human primates, faces and eyes are a rich source of social information, and it’s well established that both humans and macaques tend to direct visual attention to faces, especially the eye region,” Platt said. “Rhesus monkeys live in highly despotic societies, and convey social rank information by making threats and showing dominant and submissive behaviors.”
In the eye imaging experiment, the monkeys were observed while being shown images of the faces or scrambled faces of familiar monkeys. In addition to spending less time looking at faces and eyes, the S/L monkeys also had larger pupil diameters when gazing at photos of high-status male macaques, indicating higher arousal.