Independent control of voluntary movements and associated anticipatory postural responses in a bimanual task.
OBJECTIVE
When one hand loads the other arm, EMG responses in the stationary arm anticipate the load. This study used transcranial magnetic stimulation over each hemisphere to clarify the relationship between a voluntary movement on one side and the anticipatory postural response on the other.


METHODS
Subjects (n = 7) performed elbow flexion movements of one arm as a reaction-time task. Because subjects' arms were linked, flexion about one elbow resulted in extension force about the other, and an anticipatory response occurred in those elbow flexor muscles. After the 'go' signal and before the predicted onset of EMG, transcranial magnetic stimuli were delivered over one or other motor cortex.


RESULTS
Stimulation contralateral to the reaction-time movement delayed the onset of voluntary EMG (46 ms in right biceps, 77 ms left) but did not alter the onset of EMG in the postural arm. Stimulation contralateral to the anticipatory postural response delayed only the postural EMG (left 96 ms, right 52 ms).


CONCLUSIONS
Thus, the associated voluntary and postural responses were delayed independently by stimuli over their respective contralateral motor cortex.


CONCLUSIONS
This suggests that, although timing of responses may be linked by an initial signal, the response from each motor cortex develops independently.
Taylor
Janet L
JL
Prince of Wales Medical Research Institute and University of New South Wales, Barker Street 2031, Randwick, NSW, Australia. jl.taylor@unsw.edu.au
D000328:Adult; D001132:Arm / Q000502:physiology; D004574:Electromagnetic Fields; D004576:Electromyography; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009068:Movement / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D011187:Posture / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology; D011930:Reaction Time / Q000502:physiology