A histologically visible representation of the fingers and palm in primate area 3b and its immutability following long-term deafferentations

An isomorph of the glabrous hand is visible in primary somato-sensorycortex (area 3b) of owl monkeys in brain sections cut parallel to thesurface and stained for myelin. A mediolateral row of five ovals, separatedby myelin-light septa, represents digits and corresponds precisely withcortical sites activated by light touch on individual digits inmicroelectrode recordings. A number of caudal ovals relate to pads of thepalm. A more distinct septum separates the hand from the more lateral facerepresentation. Within the face representation, two large myelin-denseovals can be identified that are activated by the upper or lower face in acaudo-rostral sequence. Accidental finger loss or dorsal column section,deafferentations that result in reorganization of the physiological map inarea 3b, do not alter the morphological map. The proportions for each digitand palm in the morphological map do not vary across normal anddeafferented animals. Similar isomorphs were also seen in area 3b ofsquirrel and macaque monkeys. We conclude that the anatomical isomorph forthe body surface representation in area 3b is a reliable reflection ofnormal cortical organization and may be a common feature of the primatearea 3b. The isomorph can provide a reference in studies of somatotopicreorganization.