Cortical neuromagnetic activation accompanying two types of voluntary finger extension.

We examined the amplitude and latency of movement-related cerebral field (MRCF) waveforms, the generator and afferent feedback of movement-evoked field 1 (MEF1), and the relationship between motor field neuromagnetic activity and electromyographic activity during performance of two types of voluntary index extension. Eight healthy, right-handed male volunteers participated in this study. Experiments for each subject consisted of recording of MRCFs following two types of finger movement. One (Task 1) involved voluntary extension of the right index finger to about 40 degrees . In the second (Task 2), an elastic band was placed on the right index fingertip, producing a resistance of about 1.5 times the electromyographic activity associated with the voluntary movement yielding extension to approximately 40 degrees . Peak amplitude and the ECD moment of the motor field differed significantly between the two tasks. In Task 2, the electromechanical delay from EMG onset to movement onset (77.8+/-16.2) was longer than in Task 1 (44.4+/-10.4). However, the latency from EMG onset to MEF1 peak was 87.6+/-8.5 ms in Task 2, and did not differ significantly from that in Task 1 (88.6+/-8.5). The ECDs of MEF1 were located significantly medial to N20 m and lateral and posterior to the motor field. These findings suggest that the ECD of MEF1 is located in area 3b, but is slightly different from N20 m, and that this MEF1 component activation is due not to the onset of joint movement but to that of muscular contraction.