California Institute of Technology researchers have uncovered the area of the brain responsible for perception of personal space.
The findings, to be reported August 30 in the journal Neuroscience, examine the brain’s amygdala, known to regulate fear and negative emotions, two critical elements of social interaction. NARSAD Distinguished Investigator Ralph Adolphs, Ph.D., Bren Professor of Psychology and Neuroscience and professor of biology, led the study.
Along with co-author Daniel P. Kennedy, professor of biology and postdoctoral scholar at CalTech, the team was 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.
The amygdala – a pair of almond-shaped regions located in the center of the brain – 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 researchers focused on a specific test subject, SM, "because she was 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," according to Kennedy.
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.
Previous studies of humans had not before 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.
Intrigued by SM's unusual social behavior, Adolphs, Kennedy, and their colleagues devised a simple experiment to quantify and compare her sense of personal space with that of healthy volunteers.
The experiment used what is known as the stop-distance technique.