Abstract
Personal space (PS) is the distance that people prefer to maintain between themselves and unfamiliar others. Intrusion into the PS evokes discomfort, and an urge to move further apart. Behavioral aspects of PS regulation have been well studied, but the brain mechanisms underlying PS have not. Here we hypothesized that PS processing involves a known body-defensive circuit including inferior parietal cortex. We examined this hypothesis at high spatial resolution, demonstrating two categories of space-sensitive cortical columns in inferior parietal cortex, using 7T fMRI (1.1 mm isotropic).
First, personal space was measured in each subject, both outside and inside the scanner. During subsequent scanning, one category of columns responded when faces were presented at virtual distances that were within (but not beyond) each subject’s personal space boundary. In the majority of columns in this category, BOLD response amplitudes increased with increasing face proximity; in remaining columns, the responses decreased. These fMRI response variations appeared related to previously-described variations in subjective discomfort levels, and physiologic arousal, during intrusion into (but not beyond) personal space.
The second category of columns responded strongly to either ‘near’ or ‘far’ binocular disparity in visual space, in random dot stereograms. These disparity columns in parietal cortex were functionally similar to disparity columns described previously in occipital cortex.
Topographically, the disparity-selective columns were found to be systematically interdigitated with the personal space-sensitive columns. Thus, the transformation of visual to higher-order information may be computed in multiple discrete sites, rather than in a graded fashion, across parietal cortex.