Spatiotemporal properties of layer V neurons of the rat primary somatosensory cortex

Animals in their natural environments actively process spatiotemporally com plex sensory signals in order to guide adaptive behavior. It therefore seem s likely that the properties of both single neurons and neural ensembles sh ould reflect the dynamic nature of such interactions. During exploratory be haviors, rats move their whiskers to actively discriminate between differen t tactile features. We investigated whether this dynamic sensory processing was reflected in the spatial and temporal properties of neurons in layer V of the 'whisker area' in the rat primary somatosensory cortex. We found th at the majority of layer V neurons had large (8.5 +/- 4.9 whiskers) spatiot emporal receptive fields (i.e. individual cells responded best to different whiskers as a function of post-stimulus time), and that the excitatory res ponses of surround whiskers formed a spatial gradient of excitation that se emed to reflect the greater use of the ventral and caudal whiskers during n atural behaviors. Analyses of ensembles of layer V neurons revealed that si ngle whisker stimuli activated a portion of layer V that extends well beyon d a single cortical column (average of 5.6 barrel cortical columns). Based on these results, we conclude that the rat primary somatosensory cortex doe s not appear to operate as a static decoder of tactile information. On the contrary, our data suggest that tactile processing in rats is likely to inv olve the on-going interactions between populations of broadly tuned neurons in the thalamocortical pathway.