Neuroscientists find brain region responsible for our sense of personal space

Neuroscientists find brain region responsible for our sense of personal space
Patient SM, a woman with complete bilateral amygdala lesions (red), preferred to stand close to the experimenter (black). On average, control participants (blue) preferred to stand nearly twice as far away from the same experimenter. Images drawn to scale. Credit: Nature Neuroscience/Dan Kennedy (Caltech)

In a finding that sheds new light on the neural mechanisms involved in social behavior, neuroscientists at the California Institute of Technology 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 .

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 preferred to stay in closer proximity to other monkeys and humans than did healthy monkeys.

Intrigued by SM's unusual , 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. Briefly, the subject (SM or one of 20 other volunteers, representing a cross-section of ages, ethnicities, educations, and genders) stands a predetermined distance from an experimenter, then walks toward the experimenter and stops at the point where they feel most comfortable. The chin-to-chin distance between the subject and the experimenter is determined with a digital laser measurer.

Among the 20 other subjects, the average preferred distance was .64 meters—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. "These findings suggest that the amygdala, because it is necessary for the strong feelings of discomfort that help to repel people from one another, plays a central role in this process. They also help to expand our understanding of the role of the amygdala in real-world social interactions."

Adolphs and colleagues then used a functional magnetic resonance imaging (fMRI) scanner to examine the activation of the amygdala in a separate group of healthy subjects who were told when an experimenter was either in close proximity or far away from them. When in the fMRI scanner, subjects could not see, feel, or hear the experimenter; nevertheless, their amygdalae lit up when they believed the experimenter to be close by. No activity was detected when subjects thought the experimenter was on the other side of the room.

"It was just the idea of another person being there, or not, that triggered the amygdala," Kennedy says. The study shows, he says, 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."

The researchers believe that interpersonal distance is not something we consciously think about, although, unlike SM, we become acutely aware when our space is violated. Kennedy recounts his own experience with having his personal space violated during a wedding: "I felt really uncomfortable, and almost fell over a chair while backing up to get some space."

Across cultures, accepted interpersonal distances can vary dramatically, with individuals who live in cultures where space is at a premium (say, China or Japan) seemingly tolerant of much closer distances than individuals in, say, the United States. (Meanwhile, our preferred personal distance can vary depending on our situation, making us far more willing to accept less space in a crowded subway car than we would be at the office.)

One explanation for this variation, Kennedy says, is that cultural preferences and experiences affect the brain over time and how it responds in particular situations. "If you're in a culture where standing close to someone is the norm, you'd learn that was acceptable and your personal space would vary accordingly," he says. "Even then, if you violate the accepted cultural distance, it will make people uncomfortable, and the amygdala will drive that feeling."

The findings may have relevance to studies of autism, a complex neurodevelopmental disorder that affects an individual's ability to interact socially and communicate with others. "We are really interested in looking at personal space in people with autism, especially given findings of amygdala dysfunction in autism. We know that some people with autism do have problems with personal space and have to be taught what it is and why it's important," Kennedy says.

He also adds a word of caution: "It's clear that amygdala dysfunction cannot account for all the social impairments in autism, but likely contributes to some of them and is definitely something that needs to be studied further."

More information: "Personal Space Regulation by the Human ," , August 30, 2009.

Source: California Institute of Technology (news : web)

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Aug 30, 2009
This is utter nonesense. Cultures have unique perceptions of personal space. The caucasians, for example, love hugging and touching each other, even in between strangers. Some other cultures find it polite to stand close to the person you are talking to, and, yes these things are habitual, but why assume that humans prefer to have personal space naturally, and not the other way round? Perhaps it's western culture that shapes its youth to demand personal space, while other cultures follow natural behavior?

And to boot, they had a testing sample of 20 people! Nineteen, furthermore, were used as a baseline, and the entire study is based off the fact the the last one hapenned to have a brain disfunction. I think this is more correlation than causation.

Aug 31, 2009
I think, that this radius might have something to do with the length of hand. You don't feel so secure if somebody is in the reach, unless the other person is someone to whom you are 'close'.

Aug 31, 2009
Great, I'm going to get a 'stop-distance' beeper on me set to my preferred spatial distance to keep close-talkers at bay.

Aug 31, 2009
Title is a little misleading, would be better like this:
Neuroscientists find brain region partaking in our sense of personal space.

From what I've learning the amygdala is mainly a switching board.

Aug 31, 2009
That was pretty stunning. A woman with brain lesions (damage) used to explain behavior is defined if autism is diagnosed as dysfunction, instead? Is there a vocabulary problem here? anyone examine the intended subjects of research for lesions or is it just assumed their brain is whole, undamaged, and skewed in response because someone saw a set of symptoms that match a page in the DSM?

Isn't it pretty ridiculous to attribute abnormal proximity to assumed brain dysfunction when the individual doesn't have a clue what social proximity even is? (See DSM for details on social development).

How about NOT assuming the person with autism is whole, healthy, completely aware of social norms and expectations before setting up a study that makes those assumptions? It's really, REALLY hard to come up with good stats when the bias screams out like a banshee.

Sep 23, 2009
"The caucasians, for example, love hugging and touching each other, even in between strangers."

Caucasians is too general. I hate to argue, but while I have seen your suggestion to be true in most of Europe, Americans tend to distrust strangers as a rule. I have travelled most of the country, and my experiance as a young female on the road (on business, not road-tripping) refutes your statement. In the north-eastern part of the country at least, you don't see people saying "hi" to someone they don't know just to be neighborly or friendly. And normally "Excuse me" or "Sorry" don't include eye contact. Alot of people are even reluctant to shake hands when being introduced; they suffice with a nod and, at times, a reluctant smile.

Sep 23, 2009
Sorry, IE froze....

This includes both caucasians and people of other ethnicities. Environment and experiance are key in relation to the test sample as opposed to race or ethnicity. We learn from those around us and adapt to cope. (See third to last paragraph "One explaination for this...")

IE: The article is Not about the normal person's preference, but about how the brain damage affects SM's conduct. Its point is to present findings that "suggest that the amygdala, because it is necessary for... strong feelings of discomfort..., plays a central role" in some of our social interaction.

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