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BackgroundCrossmodal interactions between relevant visual and tactile inputs can enhance attentional modulation at early stages in somatosensory cortices to achieve goal-oriented behaviors. However, the specific contribution of each sensory system during attentional processing remains unclear. We used EEG to investigate the effects of visual priming and attentional relevance in modulating somatosensory cortical responses.MethodsHealthy adults performed a sensory integration task that required scaled motor responses dependent on the amplitudes of tactile and visual stimuli. Participants completed an attentional paradigm comprised of 5 conditions that presented sequential or concurrent pairs of discrete stimuli with random amplitude variations: 1) tactile-tactile (TT), 2) visual-visual (VV), 3) visual-tactile simultaneous (SIM), 4) tactile-visual delay (TVd), and 5) visual-tactile delay (VTd), each with a 100 ms temporal delay between stimulus onsets. Attention was directed to crossmodal conditions and graded motor responses representing the summation of the 2 stimulus amplitudes were made.ResultsResults of somatosensory ERPs showed that the modality-specific components (P50, P100) were sensitive to i) the temporal dynamics of crossmodal interactions, and ii) the relevance of these sensory signals for behaviour.ConclusionNotably, the P50 amplitude was greatest in the VTd condition, suggesting that presentation of relevant visual information for upcoming movement modulates somatosensory processing in modality-specific cortical regions, as early as the primary somatosensory cortex (SI).

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Magnetoencephalography was used to investigate the effect of directed attention on changes in sensorimotor mu (8-12Hz) response (mu reactivity) to non-painful electrical stimulation of the median nerve in healthy adults. Results indicated attentionrelated sex differences in mu reactivity, with females showing i) prolonged mu suppression when attending to somatosensory stimuli indicating active processing of the sensory stimuli; ii) task-dependent attentional modulation of the mu response, which was absent in males, and iii) a trend for greater neuronal excitability of the primary somatosensory region suggesting greater physiological responsiveness to stimulation overall. Sex-related differences in attentional modulation of sensorimotor rhythms suggest that females and males use different top-down control strategies when processing somatosensory information. These sex differences in attention may underlie welldocumented sex-related biases in pain processing wherein females typically report greater sensitivity to experimental and clinical pain.iii ACKNOWLEDGEMENTS