Digit somatotopy within cortical areas of the postcentral gyrus in humans.

Characterizing the cortical representation of the body surface is fundamental to understanding the neural basis of human somatic sensation. Monkey studies benefited from the detailed somatotopic maps obtained from electrophysiology methods. Advances in noninvasive neuroimaging techniques now permit such questions to be probed in humans. The present study characterizes the detailed somatotopic representation of individual digits within subregions of the postcentral gyrus in humans using high-spatial resolution functional magnetic resonance imaging and surface-based mapping. Four areas of consistent activation included area 3b, area 2, and 2 discrete foci within area 1. Area 3b and the superior area 1 foci demonstrated an orderly somatotopic distribution for all digits of the hand, whereby the thumb was represented most lateral, anterior, and inferior and the fifth digit was most medial, posterior, and superior. Compared with area 3b, somatotopic variability was greater in area 1 and the digits spanned less cortical territory. This study additionally identified the specific digit pairs that are separable in areas 3b and 1 using current imaging methods. Somatotopy was not resolved in area 2 or in the inferior area 1 foci.