STUDY OF CONTRIBUTION OF PROPRIOSEPTIVE SENSATION'S INPUT TO VOLUNTARY MOVEMENT MEASURED BY MAGNETOENCEPHALOGRAPHY

In order to investigate the contribution of the proprioceptive sensation to the central control of the voluntary movements, we performed the following three studies by recording brain responses by whole-head magnetometer. 1. Kinesthetic sensation during passive movement We recorded evoked magnetic field by whole-head magnetometer following the passive movement of the right wrist joint produced by the specially designed device made of non-magnetic materials. We observed responses in the primary somatosensory area at 57 ms after the initiation of the passive movement, another activity 27 ms later over the posterior parietal cortex, which is thought to be an association cortex. Although the magnitude of the activities in the primary somatosensory area showed clear correlation with the velocity of the movement, that in the posterior parietal cortex did not show significant change. 2. Change of the excitability of the somatosensory cortex during the voluntary movement We recorded the evoked magnetic field following the electric shock deliver to the right median nerve at the wrist with random interval of 3-5 s while subjects were performing self-paced movement with 3-5 s interval. The activities of N20m in the primary somatosensory area reduced in magnitude while the electric shock was given within 600 ms after the initiation of the movement. The activity in the secondary somatosensory cortex increased in the same period and that in the parietal cortex was suppressed during 600-ms period after the initiation of the movement and enhanced in the following 300-ms period. 3. Movement-related magnetic field and the change of the background brain magnetic field associated with the initiation and termination of the movement We recorded brain magnetic field accompanying self-paced brisk extension of the right index finger and that with the brisk movement followed by the sustain of isometric contraction for two seconds. 20-Hz background magnetic field showed decrement 1 sec prior to the movement for both initiation and termination. This suppression was not observed during the sustained muscle contraction. We recorded the background magnetic field accompanied by the unilateral extension of the wrist joint from a patient suffering from the disturbance of the deep sensation, and found the same findings as that in the normal subjects. Deep proprioceptive sensation which is making a important role for the movement by responding quickly to the movement. It affects the transient response of the brain and has little effect on the background steady state.