Changes in premovement activity in primary somatosensory cortex differ when monkeys make hand movements in response to visual vs vibratory cues

Rhesus monkeys were taught to make identical wrist flexion and extension movements in response to either a visual cue or to vibratory cues. Changes in firing rates that were not stimulus-associated but preceded the movements were measured for each primary somatosensory cortical neuron recorded under the two stimulus cued conditions. The onset of the premovement activity changes and the magnitude of these changes differed when visually cued trials were compared with vibratory cued trials that resulted in the same behavioral response. In general, the magnitudes of premovement activity changes were less and the onset of these changes occurred earlier for vibratory cued trials than for the corresponding trials triggered by the visual stimulus. These findings support the hypothesis that centrally generated modulatory influences arriving at primary somatosensory cortical neurons prior to movement onset may differ, depending upon the modality of the stimulus which signals that a movement may be initiated.