You know that uncomfortable feeling when someone is encroaching on your personal space? Caltech scientists haven't found a way to alleviate that anxiety but they have discovered the spot in the brain where such feelings originate.

The researchers studied an unusual patient, a woman, 42, called SM, who had extensive damage to a part of the brain called the amygdala, which is known to process strong negative emotions. In prior studies, the researchers showed that this brain damage was responsible for SM's difficulty recognizing fear in the faces of others as well as judging trustworthiness. But the lead researcher, Ralph Adolphs, noticed that SM tended to "violate" what others perceived as personal space.

"She is extremely friendly, and she wants to approach people more than normal," another researcher, Daniel P. Kennedy, said in a news release.

The researchers compared SM with 20 volunteers in an experiment. The subjects were asked to walk toward a researcher and stop at the point where they feel most comfortable. The average preferred distance was about 2 feet. SM, however, preferred about 1 foot, and her preferred distance didn't change based on who the researcher was or how well she knew them. The volunteer subjects' brains were also examined using functional MRI. They could not see anyone present in the room, but the mere belief that someone was nearby caused their amygdalas to light up.

"It was just the idea of another person being there, or not, that triggered the amygdala," Kennedy said. The study shows that "the amygdala is involved in regulating social distance, independent of the specific sensory cues that are typically present when someone is standing close, like sounds, sights and smells."

People who live in crowded societies, such as Japan, appear to be more tolerant of close contact with others, the researchers note. Such customs can train the brain to respond to situations that are uncomfortable. "If you violate the accepted cultural distance, it will make people uncomfortable, and the amygdala will drive that feeling," Kennedy said.

The study could provide some insight into conditions, like autism, in which social distance is an issue. The research was published today in the journal Nature Neuroscience.

-- Shari Roan

Image credit: Caltech