Studies on induced exacerbation of Parkinsonian rigidity: The effect of contralateral voluntary activity

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Abstract
A clinical and electromyographic study of Parkinsonian rigidity augmented by active movement of the contralateral limbs is presented. This exaggeration was observed clinically in 82% of 197 patients with Parkinsonism. In 20 normal controls no stretch discharge is elicited the passive wrist motion with or without contralateral reinforcement. Investigation of 49 patients with Parkinson''s disease showed stretch-evoked dis-charges exaggerated markedly by contralateral movements pre-operatively and post-operatively no stretch response in cases of completely alleviated rigidity. The mechanism of this phenomenon is probably related to activity of the gamma system. The exact role, however, of the gamma system in reinforcement of rigidity by contralateral movement is not established.