Somatosensory Cortical Maps: Reorganization Following Post-Ontogenetic Plasticity — Experiments and Theory

Abstract

The adult mammalian cortex maintains a substantial post- ontogenetic plasticity even after the critical developmental period. A few hours of Intra Cortical Micro Stimulation (ICMS) or of Paired Peripheral Tactile Stimulation (PPTS) leads to an overall reorganization of cortical representational maps within a region of up to 1 mm cortex. These changes are paralleled by alterations of geometric-topologic related parameters such as receptive field (RF) size, RF location, RF overlap and response latencies and of functional aspects such as tuning and transfer characteristics. This functional plasticity is interpreted as the modulation of fast plastic, probably Hebbian types of synapses in interactive and overlapping cortical and subcortical networks, serving as a part of dynamic lifelong adaptational mechanism of sensory processing. Based on a multi-level network, we propose a model which is composed of skin, thalamus and somatosensory area. The model is built upon the following hypothesis: (1) an inhibition of cortical layer VI by ICMS which improves latency responses of thalamic cells, (2) a lateral extension of stellate cells in layer IV in association with inhibitory basket cells to form a DOG operator modified by Hebbian rules during ICMS, and (3) a maxicolumnar organization of SI which mediates the modulation of tuning responses.