Microelectrode delineation of fine grain somatotopic organization of SmI cerebral neocortex in albino rat

Microelectrode recording, systematic mapping, and cytoarchitectural techniques were combined in the present study to determine fine details in the patterns of somatic sensory projections from mystacial vibrissae, and other body regions, to SmI of the rat.

Abstract

Microelectrode recording, systematic mapping, and cytoarchitectural techniques were combined in the present study to determine fine details in the patterns of somatic sensory projections from mystacial vibrissae, and other body regions, to SmI of the rat. Single unit and unit-cluster responses to delicate mechanical stimuli were recorded in as many as 27 penetrations per sq.mm in animals anesthetized with pentobarbital sodium. Somatic sensory afferents from one half of the body were found to project contralaterally to a 45 sq.mm cortical area. About two-thirds of this area received projections from very small receptive fields on the head which usually consisted of either single large vibrissae on the lateral face or smaller sinus hairs on the rostral face. The relative spatial relationships of the cortical projections from all the vibrissae were identical to their spatial relationships on the body surface. There was no overlap between projections from any vibrissae. The physiological boundaries of SmI coincided with a cytoarchitectural area which exhibited a prominent granular IVth layer. Distinct multicellular aggregates were found within layer IV of the facial sinus hair area. The location of these aggregates, their number (which was similar to the number of facial sinus hairs), and their somatotopic arrangement suggested the hypothesis that each aggregate is a functional unit which receives somatic sensory information from a single, specific sinus hair.