Somatic sensory transmission to the cortex during movement: Gating of single cell responses to touch

Abstract

We recently showed that the responsiveness of single somatosensory (SI) cortical units in rats to electrical stimulation of cutaneous receptive field areas was markedly decreased during motor behaviors. The present study was conducted to determine if the responses of such cells to natural touch stimulation occurring as a result of movement were also suppressed relative to their responses to passive touch of the same area. We recorded cells in the forepaw area of the SI cortex of awake, freely moving rats. Perievent histograms of the units' sensory responses to passive touch stimulation of the palmar skin area with a flat probe were compared with histograms of the responses of the same cells to contact of the same paw on the ground during running. Thirty-two of 61 cells responded similarly to both “active” and “passive” touch. Twenty-nine of the 61 SI cells, however, responded only weakly or not at all to foot contact during forced treadmill locomotion. Thorough analysis of the nature of the receptive fields of those cells indicated that their lack of response to footfall could not be explained by simple differences in the passive skin stimulation and thus may have been caused by a suppression of sensory transmission without the central nervous system. Most cells which did not respond to footfall in “regular” locomotion did respond to contacts of the foot on various surfaces during certain types of “irregular” locomotor behaviors, especially those in which the paw was used to explore the environment. These data suggest that, during movements in which the paw touches various objects, transmission of the resulting sensory input to various cortical cells may depend on the motor or behavioral context in which the movements are made.