THE FORMATION OF A CORTICAL SOMATOTOPIC MAP

The primary somatosensory cortex of small rodents is an isomorphic rep resentation of the body surface. Similar representations are character istic of the subcortical pathways, leading from the periphery to the c ortex, and these representations develop in a sequence that begins at the periphery, and that ends in the cortex. Furthermore, central repre sentations at all levels of the neural axis are altered by perinatal p erturbations of the peripheral surface. This has led to the hypothesis that the periphery plays an instructional role in the formation of ce ntral neuronal structures. The morphology of this discrete organizatio n has been examined thoroughly during the development of the thalamoco rtical projections. The mechanism(s) that underlies the formation of t hese representations remains unclear although some recent evidence sug gests the involvement of activity-dependent processes that are modulat ed by 5-HT.