Neonatal whisker removal in rats stabilizes a transient projection from the auditory thalamus to the primary somatosensory cortex.

A normally transient cross-modal thalamocortical projection from the magnocellular subdivision of the medial geniculate nucleus (MGm) to the primary somatosensory (SI) cortex of rats was found to remain unchanged throughout adulthood following unilateral removal of whiskers in newborn animals. The normal MGm projection to the auditory cortex is not lost in these neonatally whisker-deprived adults rats but some of the MGm neurons send collaterals to both primary auditory and SI cortices. Parallel electrophysiological experiments demonstrated the multimodal character of some MGm neurons, since they responded to both auditory and cutaneous stimulation. These results suggest that the areal distribution in the cortex of thalamocortical projections arising from a multimodal thalamic nucleus, such as the MGm, may be determined during early postnatal development by the normal flow of sensory information from the periphery to the thalamus and that an early postnatal somatosensory deprivation may prevent the normal withdrawal of a cross-modal projection from the MGm to the SI.