Temporal dynamics of somatosensory gating and facilitation in the primary somatosensory cortex during finger movements.

Dexterous manual movements require accurate sensorimotor integration; however, understanding how the primary somatosensory cortex (SI) dynamically processes incoming afferent information during such tasks remains limited. Using magnetoencephalography, we investigated somatosensory evoked magnetic fields during two types of finger movement, varying in speed and force exertion. We focused on three SI components-M20, M30, and M38-occurring within 20 to 40 ms post-stimulation. Across all movement conditions, the M20 and M30 amplitudes were significantly reduced when compared with the stationary condition, reflecting sensory gating, whereas M38 was significantly enhanced during both the rotation and pinch tasks. Further analyses revealed that the reduction in M20 was sensitive to movement speed, and that of M30 was influenced by both speed and force. In contrast, the enhancement of M38 was modulated by the finger movement type. These findings suggest that SI activity is not uniformly inhibited during movement, but selectively modulated in a context-dependent manner. The initial components in the SI may reflect the filtering of predictable inputs, whereas M38 could represent the more complex integration associated with skillful finger movement. Thus, our results suggest a dynamic somatosensory processing mechanism that underpins fine motor control.