We begin to develop our individual sense of personal space around age 3 or 4, and the sizes of our bubbles cement themselves by adolescence. Scientists have determined that the bubbles are constructed and monitored by the amygdala, the brain region involved in fear.
The amygdala is activated when you invade people’s personal space. This probably reflects the strong emotional response when somebody gets too close to us. Scientists confirmed this in a rare patient with lesions to her amygdala: she felt entirely comfortable no matter how close somebody got to her, and had no apparent personal space.
Futhermore, abnormal development of the amygdala may also explain why people with autism have difficulties maintaining a normal social distance to other people. Learn more here.