COMPARISON OF PRIMARY AND SECONDARY SOMATOSENSORY CORTICAL RESPONSES TO FOREPAW STIMULATION

Two cortical regions, primary somatosensory (S1) and secondary somatosensory cortex (S2), are engaged in coding somatosensory information in all mammals. Although the role of S1 has been extensively reported, the anatomical and functional knowledge for S2 remained to be determined. Our aim was to investigate how S2 participates in information processing by comparing with corresponding S1 region. Ensemble neuronal activities of S1 and S2 forepaw regions were obtained by multiple-channel multiple single-unit recording method, and electrical stimulations of various intensities were applied to the forepaw. Several similarities between stimulation-evoked S2 and S1 neuronal responses were found. First, S2 neurons' activations were with similar onset and peak latencies in comparison with those of the S1 neurons at all intensities tested. Second, S2 and S1 neurons showed statistically indistinguishable half maximum duration. In addition, neurons in both areas responded to electrical stimulation with similar response magnitude. Finally, the response magnitude of S2 and S1 neurons showed comparable variation with increasing stimulation intensity. This similarity in response patterns between S1 and S2 neurons to peripheral stimulation suggested that S2 and S1 shared comparable hierarchy in anatomical and functional aspects in the somatosensory system.