This month's issue of Nature Neuroscience features a report from researchers at California Institute of Technology, showing that an individual with "complete amygdala lesions lacked any sense of personal space." Someone with this type of damage to the amygdala region of the brain had an "abnormally small interpersonal distance preference." In other words, you might feel more than a tad uncomfortable while the other person leans in, seemingly unaware of the invisible personal boundary we erect between ourselves and others. [See earlier reports on this study at NPR Topics]
We manage to overcome the desire for personal space pretty quickly, at least for unavoidable and relatively brief periods of time (that sardine feeling in a crowded bus, say). Earlier studies documented the negative outcomes of persistent crowding stress (try a subject search on "crowding stress" in OBIS).
We do not subscribe to Nature Neuroscience online, so stop by the library and read the print issue. Learn more about the amygdala in The Human amygdala, edited by Paul J. Whalen and Elizabeth A. Phelps (on order for Oberlin's science library; request it through OhioLINK).
Two relevant, older books are available in our library: The Amygdala : a functional analysis and The Amygdala : neurobiological aspects of emotion, memory, and mental dysfunction.