Tremor: Is Parkinson's disease a dynamical disease?

Experimental evidence has shown a plethora of short-term fluctuations in patients with Parkinson's disease. We investigate these transitory events using the concept of dynamical disease. Several examples of short-term fluctuations in tremor are analyzed, and in two cases, other systemic variables (i.e., respiration and blood pressure) are examined as well. A model for tremor, based on negative feedback with delays is proposed, and the transient events are simulated. The theoretical implications of the model suggest that interactions between the central and peripheral loops, as well as interactions between the control loops and other systemic signals, can give rise to transitory events in tremor, both in the pathological and in the normal case. (c) 1995 American Institute of Physics.