Temporal dynamics of early somatosensory processing in goal-directed actions

Tactile sensitivity is temporally modulated on a moving limb. Yet the neural mechanisms underlying this modulation remain unclear. Using electroencephalography, we examined the temporal dynamics of early somatosensory processing during goal-directed reaching. Participants (self-reported gender: 22 female, 16 male) reached for their unseen left hand while a brief standard vibration of a fixed intensity was applied to the moving right index finger in different movement phases. After each reach, participants compared this standard with a second comparison vibration of varying intensity applied to the sternum and judged which vibration felt stronger. The same task was performed at rest to account for individual differences. Psychophysical results revealed an overall reduction in tactile sensitivity during reaching compared to rest, with sensitivity transiently improving around maximum speed relative to the late movement phase. Consistent with the psychophysical data, the short-latency P45 component, originating in primary somatosensory cortex, was reduced during reaching but recovered around maximum speed. Lower P45 amplitudes were associated with lower tactile sensitivity measured behaviorally, suggesting that early somatosensory processing may contribute to the observed perceptual changes. This temporally specific modulation of tactile perception, together with corresponding changes at the early cortical stage, is consistent with the idea that the somatosensory system dynamically adapts its sensitivity to facilitate control of somatosensory-guided actions. Significance statement The perception of touch on a moving hand varies across movement phases, depending on the importance of somatosensory feedback for guiding the hand toward the movement target. Our results show that these changes in perception are associated with modulations in early brain activity. This indicates that the central nervous system adjusts touch processing in a time-sensitive manner at early processing stages, which may support goal-directed actions guided by somatosensory feedback.