Organization of somatosensory cortical areas in the naked mole-rat (Heterocephalus glaber).

ABSTRACT

Multiunit electrophysiology was combined with histological analysis of cortical sections to investigate the organization of somatosensory areas in the naked mole-rat. We provide new details for the organization of primary somatosensory cortex (S1) and identify cortical modules and barrels that correspond to the representations of different body parts. In addition, details of the location and organization of secondary somatosensory cortex (S2) are reported, and evidence for a third somatosensory representation, likely the parietal ventral area (PV), is provided and discussed. S1 contained a complete and systematic representation of the contralateral body surface and oral structures. The orientation of S1 was inverted, with the lower body represented medially and the face and oral structures located rostrolaterally. The S2 representation was found in caudolateral cortex forming a mirror image of S1. The two areas were joined at the representation of the vibrissae and snout, so that the orientation of S2 formed an upright representation of the body in cortex. Receptive fields for S2 were consistently larger than those in S1. Evidence for the presumptive parietal ventral area, lateral to S2, suggests that this area may be an inverted mirror image of S2. By aligning the electrophysiological maps of body representations with cytochrome oxidase-reacted cortical sections we were able to identify modules related to the buccal pad, chin, vibrissae, forelimb, hindlimb, trunk, tongue, lower incisor, and upper incisors. The orofacial modules in lateral cortex resemble similar modules reported to relate to oral structures previously described in the laboratory rat, owl monkey, and squirrel monkey.