Luck struck a group of scientists from California recently. They came across patient S.M., a 42 year-old woman missing her entire amygdala, a part of your brain not very far from the hippocampus. Studying this woman confirmed a lot of things we already knew about the amygdala, for example that it’s important for fear. However, S.M. thought us something new: the amygdala is the part of your brain that controls your perception of an elusive concept: personal space.
The study of S.M. consisted of having her indicate to the experimenter at which point she felt uncomfortable while a person would approach her from across the room. The chin-to-chin preferred distance was then compared with that of healthy, age-matched controls. S.M.’s preferred distance was significantly smaller than the preferred distance of the control subjects. To make sure this wasn’t due to some random fluke, quite a few factors that may influence personal space were controlled for, including presence or absence of eye-contact, familiarity with the person approaching, etc. All in all, there was really no situation that could make S.M. uncomfortable, even when the person would move towards her all the way to the point of touching. The weird thing is that S.M. knew she should feel uncomfortable, and she understood the concept of personal space, but she just wasn’t experiencing it.
It always amazes me to find out that something so vague, so variable (people who live in densely populated places typically have smaller personal spaces), and so elusive is actually regulated by a huge chunk of your brain. It leads me to wonder: is there a part of us, of our mind, of our personality, that isn’t already hardwired in our brain?
While S.M. gave us great insight into the biological basis of personal space, the greatest contribution of this study is possibly the ugliest journal cover image of all times:
Reference: Personal space regulation by the human amygdala. (2009) Kennedy D.P., Glascher J., Tyszka J.M., Adolphs R. Nature Neuroscience, 12(10):1226-7.