Distinct directional patterns of somatosensory interhemispheric interactions in expert pianists and nonmusicians.

Skilled bimanual actions require the nervous system to process sensory information from both hands while preserving hand-specific information. How interhemispheric somatosensory interactions are organized during bimanual hand movements, and whether their directional patterns differ in individuals with extensive bimanual expertise, remains unclear. Here, we compared bidirectional somatosensory interactions between pianists and nonmusicians using paired-pulse nerve stimulation combined with passive robotic finger movement. In nonmusicians, movement-evoked responses to nondominant-hand movements were reduced when the dominant hand moved simultaneously. Paired-pulse stimulation revealed direction-dependent modulation of early somatosensory evoked responses. Behaviorally, dominant-hand movement selectively impaired perceptual discrimination in the nondominant hand, with interference magnitude correlating with early interhemispheric interactions. In pianists, early responses did not provide evidence for a group-consistent directional asymmetry, whereas perceptual interference occurred for both hands. These findings suggest that expert pianists show reduced group-level directional bias at early somatosensory processing stages, with bilateral interactions emerging at the perceptual level.