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Abstract:
In the somatosensory domain it is still unclear at which processing stage information reaches the opposite hemispheres.
Due to dense transcallosal connections, the secondary somatosensory cortex (S2) has been proposed to be the key
candidate for interhemispheric information transfer. However, recent animal studies showed that the primary
somatosensory cortex (S1) might as well account for interhemispheric information transfer. Using paired median nerve
somatosensory evoked potential recordings in humans we tested the hypothesis that interhemispheric inhibitory
interactions in the somatosensory system occur already in an early cortical processing stage such as S1. Conditioning right
S1 by electrical median nerve (MN) stimulation of the left MN (CS) resulted in a significant reduction of the N20 response in
the target (left) S1 relative to a test stimulus (TS) to the right MN alone when the interstimulus interval between CS and TS
was between 20 and 25 ms. No such changes were observed for later cortical components such as the N20/P25, N30, P40
and N60 amplitude. Additionally, the subcortically generated P14 response in left S1 was also not affected. These results
document the existence of interhemispheric inhibitory interactions between S1 in human subjects in the critical time
interval of 20–25 ms after median nerve stimulation.
