Contralateral voluntary hand movement inhibits human parkinsonian tremor and variably influences essential tremor.

While voluntary movement blocks Parkinsonian rest tremor (PT), essential tremor (ET) is enforced by postural and/or kinetic action. We studied the effect of contralateral externally- and internally triggered hand movement on PT and ET to investigate the transhemispheric influences on tremor genesis. We measured the changes of tremor peak frequency power after flash signal (F), flash triggered (FM) and self-paced (SPM) movement of the contralateral hand in nine PT and seven ET patients using accelerometer. PT significantly decreased both during FM and SPM tasks, suggesting that it is generated by a constant subcortico-cortical network, which includes higher order motor areas. Intensity of ET showed a remarkable intra- and interindividual variability both during FM and SPM reflecting a different generator circuitry with variable functional connections.