A 42-year-old woman with a rare genetic condition has given scientists insight into the brain areas that underpin the discomfort we feel when a stranger stands too close. The woman is a patient with Urbach-Wiethe disease—a very rare disorder that causes a hardening of brain tissue in the temporal lobes and wreaks havoc on the amygdala, the region involved in controlling fear and processing emotion. During years of studying this individual, California Institute of Technology neuroscientist Ralph Adolphs, PhD, noticed that she was very outgoing, occasionally violating others' personal space.

"She is extremely friendly and wants to approach people more than normal," Adolphs says.

Collaborating with postdoctoral scholar Daniel P. Kennedy, PhD, Adolphs compared the woman's sense of personal space with that of 20 healthy volunteers. The researchers instructed study participants to stand at a predetermined distance from an experimenter and to walk toward the researcher, stopping where they felt most comfortable. Their findings, published online in August in Nature Neuroscience, show that the woman preferred to stand twice as close to the experimenter—about one foot away—as the control participants.

The researchers suspected that the woman's lack of anxiety while standing near others might be the result of her damaged amygdala. So, to see how that part of the brain reacted to personal space violations, they used fMRI to examine amygdala activation among control group members as they heard that an experimenter stood nearby or far away. The normal participants' amygdala activity increased when they believed a researcher stood nearby, even though they could not see, feel or hear him.

The results, Kennedy says, suggest that "the amygdala is involved in regulating social distance, independent of specific sensory cues that are typically present when someone is standing close." The findings, he adds, may offer insight into autism and other disorders that affect the development of social and communication skills.

—A. Novotney