Muscle-afferent projection to the sensorimotor cortex after voluntary movement and motor-point stimulation: an MEG study.

Objective: To investigate the projection of muscle afferents to the sensorimotor cortex after voluntary finger movement by using magnetoencephalography (MEG).

Methods: The movement-evoked magnetic fields (MEFs) after voluntary index-finger extension were recorded by a 204-channel whole-head MEG system. Somatosensory-evoked magnetic fields (SEFs) were recorded after motor-point stimulation was applied to the right extensor indicis muscle by using a pair of wire electrodes.

Results: The MEF waveforms were observed at 35.8±9.7 ms after movement onset (MEF1). The most concentrated SEFs were identified at 78.7±5.6 ms (M70), and the onset latency of M70 was 39.0±5.5 ms after motor-point stimulation. The mean locations of the equivalent current dipoles (ECDs) of MEF1 and M70 were significantly medial and superior to that of N20m elicited by median-nerve stimulation. The ECD locations and directions of both MEF1 and M70 were concordant in the axial, coronal and sagittal planes.

Conclusions: MEF1 and M70 might be elicited by muscle-afferent feedback following muscle contraction. In addition, these ECDs may be located in area 4.

Significance: Motor-point stimulation is a useful tool for confirming the projection of muscle-afferent feedback to the sensorimotor cortex after voluntary movement.