Cortical contributions to sensory gating in the ipsilateral somatosensory cortex during voluntary activity

Abstract

An important principle in the organization of the somatosensory cortex is that it processes afferent information from the contralateral side of the body. The role of the ipsilateral somatosensory cortex (iS1) in sensory gating in humans remains largely unknown. Using electroencephalographic recordings over the iS1 and electrical stimulation of the ulnar nerve at the wrist we examined somatosensory evoked potentials (SSEPs; P14/N20, N20/P25, and P25/N33 components) and paired-pulse SSEPs between (interhemispheric inhibition) and within (intracortical inhibition) the iS1 at rest and during tonic index finger voluntary activity. We found that the amplitude of the P25/N33, but not other SSEP components, was reduced during voluntary activity compared with rest. Interhemispheric inhibition increased the amplitude of the P25/N33 and intracortical inhibition reduced the amplitude of the P25/N33, suggesting a cortical origin for this effect. The P25/N33 receives inputs from the motor cortex, therefore, we also examined the contribution of distinct sets of cortical interneurons by testing the effect of ulnar nerve stimulation on motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation over the ipsilateral motor cortex with the coil in the posterior-anterior (PA) and anterior-posterior (AP) orientation. Afferent input attenuated PA, but not AP, MEPs during voluntary activity compared with rest. Notably, changes in interhemispheric inhibition correlated with changes in PA MEPs. Our novel findings suggest that interhemispheric projections between S1s and intracortical circuits, likely from somatosensory and motor cortex, contribute to sensory gating in the iS1 during voluntary activity in humans.

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