Brain structure invests us with sense of personal space

Washington, Aug 31 ( Neuro scientists have pinpointed the brain structure regulating our sense of personal space, possibly opening the way to a better understanding of autism and other disorders.

The structure, the amygdala – a pair of almond-shaped regions located in 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 scientists, led by Ralph Adolphs, psychology and neuroscience professor and post-doctoral scholar Daniel P. Kennedy, at the California Institute of Technology (Caltech), 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, who led the study.

SM has difficulty recognising 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 closer to other monkeys and humans than did healthy monkeys.

Intrigued by SM’s unusual social behaviour, 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. Among the other subjects, the average preferred distance was .64 metres-roughly two feet.

SM’s preferred distance was just .34 meters, or about one foot. Unlike other subjects, who reported feelings of discomfort when the experimenter went closer than their preferred distance, there was no point at which SM became uncomfortable; even nose-to-nose, she was at ease.

Furthermore, her preferred distance didn’t change based on who the experimenter was and how well she knew them.

“Respecting someone’s space is a critical aspect of human social interaction, and something we do automatically and effortlessly,” Kennedy says.

The discovery appeared in the Sunday issue of Nature Neuroscience.