Somatosensory representation of the climbing fiber system in the rostral intermediate cerebellum

Abstract

The fine grain organization of the climbing fiber (CF) representation for the intermediate cortex of lobules III, IV, and Va was examined. Data were obtained from cats anesthetized with sodium pentobarbital. Through extracellular recording techniques, CF responses were identified in 814 Purkinje cells; 74% were elicited by mechanical stimulation of various body surfaces. Of the CF responses elicited by stimulation, 60% involved the ipsilateral hindlimb, 36% represented parts of the forelimb, and only 4% represented areas of the face, tail, or abdomen. Hindlimb representation predominated in lobules III and IV, and forelimb representation was mainly confined to lobule Va. No distinct parasagittal zones that involved all three lobules were identified. In general, the organization for most sublobules could be best described as a mixture of patches of forelimb or hindlimb representations. Within the patches there was considerable diversity of receptive field types, particularly for the extremities. The receptive fields involving the distal phalanges were generally smaller than those for the proximal areas, but a range in field sizes was evident for both distal and proximal regions. More than half of either the forelimb or the hindlimb representation was limited to the distal paw areas; the two middle toes received the most frequent representation. Representations of the proximal limb areas were generally centered around either the wrist or the heel, or around the elbow or knee, but many of these receptive fields also extended to the phalanges. The multiple representation of various areas of forelimb and hindlimb throughout the rostral intermediate cortex was consistent with the type of organization that had been identified in other regions of the anterior lobe, although each cortical area contained a unique proportional CF representation of various body areas.