We all have a personal bubble, an invisible zone of privacy around our bodies. When strangers cross this boundary, it makes us feel uncomfortable. But not all of us - Daniel Kennedy from the California Institute of Technology has been studying a woman known only as SM, who lacks any sense of personal space.
SM suffers from a rare genetic disorder called Urbach-Wiethe disease, that causes parts of the brain's temporal lobes to harden and waste away. This brain damage has completely destroyed SM's amygdalae, a pair of small, almond-shaped structures that help us to process emotions.
Kennedy asked her to say when she felt most comfortable as a female experimenter walked towards her. On average, she preferred a distance of around a foot, about half the usual two-foot gap that 20 other normal people demanded. SM's lack of boundaries remained whether she walked towards her partner or vice versa, whether they were looking away or at each other, and whether they started close by or far apart.
The fact that SM had a boundary at all was probably because at close distances, it's hard to see people. She said time and time again that she was actually comfortable at any distance, and during one trial, she actually walked all the way to her partner until they were actually touching. Even when they were making direct eye contact and touching nose-to-nose, she only rated the experience as 1 on a comfort scale of 1 to 10, where 1 is perfectly comfortable and 10 is a level of discomfort that only the British can survive. When a male stranger talked to her up close, she again rated the chat as a 1 (even though he gave it a 7).
SM has been working with this group of researchers, led by Ralph Adolphs, for over a decade but her comfort didn't stem from simply knowing her partner well. When Kennedy tested two other people who also knew the scientists equally well, but didn't have damaged amygdalae, they were much less accommodating with their personal space than SM was. Nor did SM simply put her discomfort to heel - she knew that Kennedy was "up to something", but so did the male stranger and that did nothing to allay his discomfort.
In fact, it was clear that SM understood the concept of personal space. She thought it was smaller than most people's, and she said that she didn't want to make other people too uncomfortable by standing too close to them. She estimated that people feel most comfortable about 1.5 feet apart - that's an underestimate but it's still larger than her own preference.
Kennedy's experiments suggest that our sense of personal space comes from the amydgala. Indeed, when he scanned the brains of a small group of volunteers, their amygdalae were more active when someone was standing close to the scanner than when they were keeping their distance.
Kennedy thinks that the amygdala, with its pivotal role in emotional processing, governs the emotional kick we feel when people enter our personal zone. Without it, we remain unfazed by close proximity. What's less clear is how this affect changes as we get to know people better. Why is it that friends and loved ones are allowed (or positively encouraged) to stay nearer than strangers are?
Other aspects of SM's ability to deal with emotions are off-kilter too. For a start, she knows no fear - not in a Batman way, but in the sense that she can't recognise the emotion in the eyes of others Way back in 1994, Adolphs' group showed that SM can reasonably recognise the emotions in most facial expressions, but she falters when the face in question is afraid. And even though she's a talented artist, she can't draw a scared face, once claiming that she didn't know what such a face would look like.
Now, Naotsugu Tsuchiya, working in Adolphs' team, has found that SM's knowledge of fear is a little more complicated. When asked to classify angry and fearful faces, or threatening and harmless scenes, SM did so completely normally when she had to do it quickly. Even though she felt that the scared faces were less intense than volunteers with intact amygdalae, she classified them correctly, with similar reaction times.
In a similar experiment, Tsuchiya showed SM faces that had been gradually morphed from fearful to neutral expressions. When she had unlimited time, it took much more severe expressions for her to recognise a face as fearful. But when she had to quickly pick scared faces from a set, her performances were indistinguishable from other people.
This means that the amygdala isn't always necessary to know fear. It's not needed for the earliest stages where our brain starts to process fearful images below the level of our consciousness. Instead, Tsuchiya suggests that after this first level of analysis is over, the amygdala helps us to use the results to make social judgments - to explicitly recognise fear for what it is and to assess the relevance of those first subconscious twinges.
Reference: Nature Neuroscience doi:10.1038/nn.2381 and 10.1038/nn.2380
More on the amygdala:
- Erasing a memory reveals the neurons that encode it
- Fearless mice are neglectful mothers but social butterflies
- Different neuron networks control fear of different threats
- Political attitudes linked to startle reflexes
- 9/11 memories reveal how flashbulb memories are made in the brain
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I'd say that 10 is a level of interpersonal discomfort that only the British can experience.
HAHAHAHAHAHAHA!!!!!!!!111
Yes, touche Nathan Myers.
Brilliant piece though, Ed :) If only I would have known about this research in middle school I would have had some epic insults for close-talking boys.
Do people with this disorder gravitate toward each other - they are going to be perfectly happy interacting at all times anyway?
Is there any confirmation of the old idea that there is a North-South gradient in Europe, i.e., that Southern Europeans perceive a shorter distance to be appropriate than the Northerners?
Does this patient experience fear herself? If not, it's a miracle she's alive.
The amygdala is a bit complicated. For one kind, it seems to be needed for learning new fears, but not expressing known ones. Disable the amgydalae in a rat and they can't learn new fear associations, but already learned associations are intact. So for fast evaluation she is probably simply recalling learned associations. Would be interesting to see how well she can learn new fearful associations.
Does she also have difficulty making decisions? I hae read recent reports that emotions play a pivotal role in decision-making.
Interesting. Nathan's brilliant comment "10 is a level of interpersonal discomfort that only the British can experience" made me think about something. I have witnessed different levels of discomfort in different cultures - South Americans and South East Asians can usually handle closer distances than North Americans. How would other countries' personal space sizes compare to each other?
I suspect this has a lot to do with the population density you experience everyday. People who commute on crowded subways are likely to have a smaller distance compared to residents of more rural areas. Perhaps submariners have the least ...
She estimated that people feel most comfortable about 1.5 feet apart - that's an underestimate but it's still larger than her own preference.
Social distance is strongly influenced by your culture, not just your amygdala. The preferred distance in WASPs of the USA is about twice the preferred distance of Latin Americans ... and watching a Mexican businessman backing his gringo counterpart around the room as each is trying to remain "comfortable" in a conversation is something that happens.
Edward T. Hall did quite a lot of research into how different cultures set personal boundaries, and how this interacted with cultural perceptions of both space and time, back in the 60s. There are very distinct cultural differences, seems to be a reasonably well-accepted conclusion! The Hidden Dimension (1966) makes interesting reading, and has become the basis for a great deal of the anthropology of space and sociological studies of spatial aspects of interpersonal relations.
Hey, I have that book! It's buried somewhere in the foothills of mount TBR.
So, SM was adamant she couldn't recognize fear, and claimed to be unable to draw faces that showed fear -- but when given no time to prepare a suitable non-response, she was, in fact, able to recognize fear -- but attempted to minimize the lapse from her usual 'inability' by claiming that she saw *less* fear than anyone else.
Bridge, anyone?
oregonbird: what bee crawled up YOUR butt this morning? ...Why do you have such an issue with believing that immediate, less "processed" responses draw on different cognitive systems? Neurologically that is entirely plausible. If you have reason to think she's faking responses, perhaps you should present evidence and devise tests, rather than snarking in the background.
For some reason the link to the Wikipedia article is not working for me. Gray Gaffer, according to Wikepedia, her condition does affect her decision making ability.
It might not be strictly scientific, and I shudder to think of the human-experimentation committee approval process that would be required, but I can't help but wonder how SM's responses might differ from those of a control group to an unexpected groping.
It's a good thing she lives in California, where everybody is so laid-back and cool that something of the sort could never happen outside the lab.