Body representation in ventrobasal thalamus of macaque: a single-unit analysis

Abstract

Recordings were obtained from 1439 single neurons in the ventrobasal nuclear complex (VB) and in adjacent regions of the thalamus of rhesus monkeys (Macaca mulatta), in the absence of general anesthesia. Each neuron was classified as either cutaneous or deep on the basis of its responsiveness to light tactile stimulation, limb movement or pressure on deep tissues. The location and extent of each neuron''s receptive field (RF) was determined, using stimuli of uniform intensity. On the basis of qualitative criteria, each neuron was assigned to either the lemniscal or nonlemniscal category. The locations of all neurons in the sample were reconstructed histologically, thus relating a neuron''s position in VB to the location of its RF. VB neurons were segregated according to submodality class along the anteroposterior dimension of VB. At levels near the anterior and posterior ends of VB, neurons with deep RFs predominated, whereas neurons with cutaneous RF predominated at intermediate levels. The body representation in VB can be viewed as a series of nearly identical horizontal 2-dimensional maps stacked on top of one another. In any of these maps, over a rather wide vertical range, all body regions and submodalities were represented. There were striking similarities between the characteristic organizational plan evident in reconstructions of horizontal cross sections of VB and the organizational plan of its projection field in the postcentral gyrus.