Finger and nerve selectivity of an early somatic-motor interaction: a magnetoencephalogram study

Voluntary movements of individual or multiple body parts selectively modulate cortical responsiveness to sensory inputs depending on the task requirement. It remains unclear whether this selectivity of the somatic-motor interaction in the cerebral cortex is complete or gradient along the surface of the body part and varies with task characteristics. We herein used magnetoencephalograms to investigate the selectivity of the somatic-motor interactive modulation of somatosensory evoked cortical responses during self-paced movements of individual fingers (digits 1 to 5) or dynamic self-paced tapping or static pinching movements of two fingers (digits 1 and 2). The source strength of the cortical response at 35 ms post-stimulus contralateral to a stimulation, M35c, selectively decreased when the finger innervated by the stimulated nerve was individually moved. Furthermore, dynamic tapping and static pinching movements of two fingers exerted different effects on the strength of M35c. Therefore, the present study demonstrates the involvement of finger and nerve specificity in the somatic-motor functional interaction at the early cortical stage and its task-dependent flexibility.