Bilateral activation of the human somatomotor cortex by distal hand movements.
We recorded cortical magnetic signals, simultaneously over the whole scalp, from 6 healthy subjects during 3 motor tasks to track the varying proportion of contra- vs. ipsilateral activation. The subjects performed self-paced index finger flexions, simultaneous flexion of 4 fingers, and a sequence of rapid digit movements in different sessions. Index finger and 4-finger movements were associated with phasic bilateral dampening of spontaneous 10 and 20 Hz rhythms along the central sulcus, starting approximately 1 sec before the movement in the contralateral hemisphere. A rebound occurred within 1 sec after the index finger and 4-finger flexions; the rapid finger movements resulted in a persistent blocking of the rhythms. Averaging with respect to movement onset showed a slow bilateral frontal readiness field starting about 0.5 sec prior to motion onset. It was followed, within 200 msec after movement onset, by phasic movement-evoked fields (MEFs) which were bilateral during the tasks involving several fingers. The contra- vs. ipsilateral MEF amplitude ratio C/I decreased from 4.0 during index finger movements to 0.6 during rapid finger flexions, reflecting the enhanced activation of the ipsilateral primary somatomotor cortex with increasing complexity of movement.
Low Temperature Laboratory, Helsinki University of Technology, Espoo, Finland.
R
R
Salmelin
N
N
Forss
J
J
Knuutila
R
R
Hari
D000328:Adult; D001931:Brain Mapping; D005071:Evoked Potentials / Q000502:physiology; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006225:Hand / Q000502:physiology; D006801:Humans; D015225:Magnetoencephalography; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009068:Movement / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D013003:Somatosensory Cortex / Q000502:physiology*