RELATIONSHIP BETWEEN REPRESENTATION OF HINDPAW AND HINDPAW BARREL SUBFIELD (HBS) IN LAYER-IV OF RAT SOMATOSENSORY CORTEX

WE describe the organization of the hindpaw barrel subfield (HBS) in l ayer IV of rat somatosensory cortex (SI) and relate this organization to the representation of the hindpaw. The ovoid-shaped, HBS is oriente d anterior to posterior and comprises barrels and barrel-like structur es, the most prominent of which consist of at least five anteriorly-lo cated elongated barrel bands. Posterior to these elongated bands is a cluster of four barrels. Two additional barrels are found, one lateral , the other medial. The lateral border is formed by a nearly continuou s band that overlaps portions of the anterior elongated bands and post erior barrels. The HBS shows considerable variability in size and shap e; nevertheless, the overall pattern reflects a common plan of organiz ation. Electrophysiological mapping confirmed that hindpaw representat ion is somatotopically organized. The glabrous toes are represented an teriorly, the pads posteriorly, and the dorsal hairy skin of the toes and hindpaw laterally. By aligning physiological and morphological (HB S) maps according to lesion sites, our data suggest that the elongated anteriorly-located barrel bands represent the hindpaw toes, the four toe pads are represented immediately posterior followed by barrels rep resenting the plantar pads. The representations of dorsal hairy skin o f toe and dorsal hindpaw form the lateral border; the heel and ankle a re represented most posterior. We interpret our findings as support th at individual barrels in the HBS are associated with discrete regions of the hindpaw; however, the precise relationship of structure and fun ction reported between the vibrissae and posteromedial barrel subfield (PMBSF) and between the forepaw and the forepaw barrel subfield (FBS) were not observed.