Dynamics of neuronal processing in rat somatosensory cortex

Recently, the study of sensory cortex has focused on the context-dependent evolution of receptive fields and cortical maps over millisecond to second timescales,This article reviews advances in our understanding of these proc esses in the rat primary somatosensory cortex (SI), Subthreshold input to i ndividual rat SI neurons is extensive, spanning several vibrissae from the center of the receptive field, and arrives within 25 ms of vibrissa deflect ion, These large subthreshold receptive fields provide a broad substrate fo r rapid excitatory and inhibitory multi-vibrissa interactions,The 'whisking ' behavior, an similar to 8 Hz ellipsoid movement of the vibrissae, introdu ces a context-dependent change in the pattern of vibrissa movement during t actile exploration. Stimulation of vibrissae over this frequency range modu lates the pattern of activity in thalamic and cortical neurons, and, at the level of the cortical map, focuses the extent of the vibrissa representati on relative to lower frequency stimulation (I Hz). These findings suggest t hat one function of whisking is to reset cortical organization to improve t actile discrimination. Recent discoveries in primary visual cortex (VI) dem onstrate parallel non-linearities in center-surround interactions in rat SI and VI, and provide a model for the rapid integration of multi-vibrissa in put,The studies discussed in this article suggest that, despite its origina l conception as a uniquely segregated cortex, rat SI has a wide array of dy namic interactions, and that the study of this region will provide insight into the general mechanisms of cortical dynamics engaged by sensory systems .