Conscious Tactile Perception Depends on Early Processing in Primary Somatosensory Cortex.

The primary somatosensory cortex (S1) has long been implicated in tactile perception, yet its precise role in conscious tactile detection remains uncertain. The current study investigated the causal and time-specific involvement of S1 in tactile detection using single-pulse transcranial magnetic stimulation (spTMS). In two experiments, spTMS was applied over contralateral S1, an active control site (inferior parietal lobe; IPL), or under a sham condition at short (25 and 75 ms; Experiment 1) or longer (130 ms; Experiment 2) intervals following electrotactile stimulation of the finger. Participants performed a go/no-go detection task at sensory threshold. In Experiment 1, tactile sensitivity was significantly reduced following early S1 stimulation compared with both active control and sham conditions. In contrast, no such effect was observed at a later timepoint in Experiment 2. Self-reported TMS-related distraction ratings did not account for the observed sensitivity differences, suggesting sensitivity-specific modulation by early TMS rather than general task disruption. Together, these findings support a causal role for early S1 activity in conscious tactile detection. We propose that disruption at this early stage impairs initial encoding of tactile input, thereby attenuating subsequent perceptual awareness. Overall, the results underscore the critical contribution of S1 in conscious tactile detection and are compatible with recent accounts in which conscious tactile perception emerges from processing within a distributed neural network.