Detection of feedback in the central nervous system of Parkinsonian patients

Closed-loop system identification techniques are applied to signals obtained from the central nervous system of human Parkinsonian patients. The question is posed as to whether feedback exists from tremor, via sensory inputs, to thalamic "tremor cells" which are thought to drive Parkinsonian tremor. Linear multivariable models are fitted to the data and it is found that, in general, the relationship between tremor and cell activity is best described by a closed-loop system. The results are consistent with the hypothesis that Parkinsonian tremor is the result of an unstable reflex loop in the central nervous system.