There is no simple temporal relationship between the initiation of rapid reactive hand movements and the phase of an enhanced physiological tremor inman

A postural hand tremor of enhanced size was induced in eleven subjects. The re was rhythmic activity in the posturally active extensor muscles synchron ised to the tremor oscillation, which implied an oscillatory modulation of motor neurones. The subjects executed single rapid wrist flexion movements in response to a flash of light. The light flash was presented at an instant when the wrist was spontaneously moving in the flexion direction, extension direction or at random. The time taken to generate a movement was not significantly diff erent or more consistent in any of the conditions. Inspection of individual and averaged acceleration and EMG records strongly suggests that the movement is made at a time that is independent of the tr emor cycle at the time of stimulus presentation or at the moment of movemen t initiation. These observations suggest that the central or spinal mechanism generating tremor does not gate the central mechanism that produces voluntary movement .