Observations on peripheral servo mechanisms in Parkinsonian rigidity

Abstract

The activity of the muscle spindles was studied indirectly in eight patients afflicted with the rigidity of Parkinsonism and in normal subjects. Electromyographic and ergographic recordings were made from the thumb adductor by means of concentric needle electrodes. In order to silence the opponens pollicis in some cases, the median nerve was blocked at the wirst with local anesthesia. A study of the silent period revealed that the greatest defect in Parkinsonism was lack of suppression of motor discharge. Experi-ments involving the Jendrassik manoeuvre, performed by comparing the amplitude of the knee jerk before and during the classical hand manoeuvre, showed augmentation in all afflicted patients . This suggested that the lower motor unit and its peripheral length sensor are accessible to some facilitatory impulses influencing the annulospiral endings. Increasing peripheral proprioceptive input was capable of driving the anterior horn cell in a patient with severe rigidity and slight tremor. Interpretation of the data proposes that defective muscle spindle bias may underlie the rigidity of Parkinsonism.