Plasticity of the cortical dentition representation after tooth extraction in naked mole-rats

Naked mole-rats (Heterocephalus glaber) have a large cortical representation of their behaviorally important front teeth, accounting for 30% of primary somatosensory cortex (SI). Here we investigated the plasticity of this dental representation after the extraction of a single lower tooth. The representation of the contralateral lower incisor normally accounts for approximately 15% of somatosensory cortex in mole-rats. In five mole-rats the lower right incisor was extracted on either postnatal day 7 or 21. After 5-8 months the deprived tooth zone in S1 was investigated with multiunit microelectrode recordings. The results revealed a dramatic reorganization of the orofacial representation in SI. Neurons in the cortical lower tooth representation were responsive to tactile inputs from surrounding orofacial structures, including the contralateral upper incisor, ipsilateral lower incisor, tongue, chin, gums, and buccal pad. Neurons in the former lower tooth zone had complex receptive fields that often encompassed multiple sensory surfaces surrounding the extracted tooth in the periphery. These results suggest that the representation of the dentition in mammals is capable of significant reorganization after the loss of sensory inputs from the teeth. These data parallel findings in the somatosensory hand area of primates after deafferentation where cortex can become activated by a mixture of widely spaced surrounding sensory surfaces (e.g., chin and upper arm).