Observations on peripheral servo mechanisms in Parkinsonian rigidity

traction. The length and intensity of alpha motoneurone 'shutdown' in response to a twitch was compared in normal and afflicted subjects. The second group of observations was designed to study the effects of central modification of proprioceptive feedback. In these tests the Jendrassik manoeuvre was used in both normal and afflicted subjects, and the results were measured in terms of visible and palpable facilitation of the quadriceps reflex. The last group of experiments was designed to evaluate the availability of the peripheral feedback mechanism in paralysis agitans. Resting bias could, perhaps, be estimated from the silent period experiments, but passive elongation of the peripheral sensor would show whether it could fire in response to peripheral events. Here, the thumb adductor was simply stretched passively by the