Spatiotemporal properties modulate intermodal influences on early somatosenory processing during sensory-guided movement

OBJECTIVES: Somatosensory evoked potentials (SEPs) were used to (1) investigate intermodal influences upon somatosensory processing in primary somatosensory cortex (S1), (2) determine the influence of spatiotemporal relationships between bimodal stimuli in S1 and (3) observe behavioral changes associated with intermodal modulation. METHODS: Median nerve SEPs were elicited from electrical stimulation and recorded from scalp electrodes during continuous tracking of one of two simultaneously presented stimuli (vibrotactile/visual). In Experiment 1, spatial relationship was manipulated by placing the visual stimulus in the same/opposite hemi-field as the vibrotactile stimulus. In Experiment 2, temporal synchrony was manipulated by altering the pattern of intensity changes such that they followed identical/different patterns. RESULTS: For Experiment 1, greater spatial relationship reduced the amplitude of the P27 SEP component whereas in Experiment 2 greater temporal synchrony increased the amplitude of the P27 SEP component. Temporal synchrony increased P50 amplitude only during vibrotactile tracking. Tracking performance mirrored early SEP amplitude changes. In Experiment 2, task-relevance was associated with increased N140 amplitude. CONCLUSIONS: The changes in P27 amplitude observed in Experiments 1 and 2 reflect an intermodal mechanism of somatosensory gating dependent upon spatiotemporal properties of bimodal stimulation whereas the P50 reflects multisensory aspects of somatosensory processing. Changes in behavior may reflect the importance of these early influences to sensorimotor transformations. SIGNIFICANCE: Modulation of the P27 component reflects an intermodal sensory gating in somatosensory processing.