How the brain distinguishes friends from strangers

David L. Ryan

Researchers at Harvard Medical School have become the first group to demonstrate how the brain processes social memories, allowing us to recognize our friends.

Amar Sahay, an associate professor at Harvard Medical School and a senior author of a study published in the journal Nature Communications, said he and his team discovered the role of the region of the brain known as the hippocampus in distinguishing between social memories.

“The hippocampus is like a fantastic librarian,” he said, storing and retrieving information and using it to tell other parts of the brain what to do.

It’s been well-studied, including in Sahay’s lab, but he said its role in social memory was poorly understood until now.

“The behavioral significance was not known, and certainly not implicated in making the distinction in social stimuli,” he said.

The team found that the hormone oxytocin is the catalyst that allows the hippocampus to handle social memories and make distinctions between social stimuli, Sahay said.

They tested their theory on mice, “deleting” oxytocin receptors in the hippocampus of a mouse, which is similar in structure and function to that of a human, he said.

When the receptors were removed, the mice were able to distinguish between similar objects, Sahay said, but they could no longer tell the difference between friends and strangers.

“It’s telling us that these receptors are required for the distinction of social stimuli, but not non-social stimuli,” he said.

This discovery could be used to explain the connection between certain psychiatric and neurological conditions and anomalies in social behavior, Sahay said.

Sahay said he hopes to use the new information about oxytocin receptors as he investigates the hippocampus’s role in behavioral anomalies in people with autism spectrum disorders.

The research is important because social behavior dictates many aspects of human life. “Social behavior is the cornerstone of human society and behavior as we know it,” he said.