In a finding that sheds new light on the neural mechanisms involved in social behavior, neuroscientists at the California Institute of Technology (Caltech) have pinpointed the brain structure responsible for our sense of personal space.
The discovery, described in the August 30 issue of the journal Nature Neuroscience, could offer insight into autism and other disorders where social distance is an issue.
The structure, the amygdala—a pair of almond-shaped regions located in the medial temporal lobes—was previously known to process strong negative emotions, such as anger and fear, and is considered the seat of emotion in the brain. However, it had never been linked rigorously to real-life human social interaction.
The scientists, led by Ralph Adolphs, Bren Professor of Psychology and Neuroscience and professor of biology and postdoctoral scholar Daniel P. Kennedy, were able to make this link with the help of a unique patient, a 42-year-old woman known as SM, who has extensive damage to the amygdala on both sides of her brain.
“SM is unique, because she is one of only a handful of individuals in the world with such a clear bilateral lesion of the amygdala, which gives us an opportunity to study the role of the amygdala in humans,” says Kennedy, the lead author of the new report.
SM has difficulty recognizing fear in the faces of others, and in judging the trustworthiness of someone, two consequences of amygdala lesions that Adolphs and colleagues published in prior studies.
During his years of studying her, Adolphs also noticed that the very outgoing SM is almost too friendly, to the point of “violating” what others might perceive as their own personal space. “She is extremely friendly, and she wants to approach people more than normal. It’s something that immediately becomes apparent as you interact with her,” says Kennedy.
Previous studies of humans never had revealed an association between the amygdala and personal space. From their knowledge of the literature, however, the researchers knew that monkeys with amygdala lesions preferred to stay in closer proximity to other monkeys and humans than did healthy monkeys.