Somatosensory Cortex in Owl Monkeys

1. Several features of the two complete and separate representations of the contralateral body surface in cortical areas 3b and 1 of somatosensory cortex in owl monkeys were quantitatively studied. 2. Area1 magnification factors for different body regions in the two representations were obtained. The glabrous hand and foot regions were found to occupy nearly 100 times more cortical tissue per unit body-surface area than the trunk or upper arm. 3. In the representations of the hand digits, inverse magnification was linearly related to distance from the digit tips. 4. Receptive-field size was found to be proportional to inverse magnification over the entire body-surface representation as well as over the local region of the glabrous hand digits. The relation between receptive-field size and inverse magnification appears to be linear; specification of one would specify the other over the representation in one area. 5. By relating receptive-field overlap to distance separating recording sites, the area of cortex presumed to receive all fibers from any given receptive field was obtained and found to be independent of the body surface represented. Such an area of somatosensory cortex, about l1.5 mm in diameter, may be akin to the “hypercolumn” proposed for primary visual cortex (6).