Neuronal activity in monkey primary somatosensory cortex is related to expectation of somatosensory and visual go-cues.

The present study was to investigate whether neuronal activity in primary somatosensory cortical areas (SI) differs when monkeys expect go-cues of different sensory modalities. Two monkeys made wrist extensions and flexions after steadily holding wrist at a center position. Movements were guided by increases in vibration to the monkey's palm (VIB), visual targets (VIS), or both in combination (COM). Neuronal activity recorded in SI during the early and late phases (i.e., the first and last 250 ms) of the instructed delay periods (IDP) were analyzed. Of 406 neurons recorded during all three paradigms, 263 (64.8%) showed significant changes in firing rates (FR) between the early and late IDP phases during either VIB or VIS trials and were selected for further analyses. The selected neurons were classified as VIB- or VIS-biased, depending on the paradigm (VIB or VIS) in which the greater FR changes occurred. Both increases and decreases in FRs were observed during the analyzed epochs. Most VIB-biased neurons showed the biggest FR changes during VIB trials and the least during VIS trials. Conversely, most VIS-biased neurons had the biggest FR changes during VIS trials and the least during VIB trials. For both VIB- and VIS-biased neurons, however, the FR changes were intermediate during COM trials. These results suggest that SI neurons play an important role in initiating/executing wrist movements. Neurons involved in wrist movements showed biases to the modality of cueing signals. Most SI neurons were biased to only one sensory modality. The expectation-related FR changes suggest different involvement by SI in movement initiation when tasks are guided by vibratory and visual signals.