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On Fri 16 May, James F. Slattery wrote: > Hi Phil, > > > Question for Gray Miller or any of you other techies. Have any of > > you come across a feedback control system model of the sensing > > and muscle control elements affected by Parkinsons disease? > For Jim Slattery; You were asking about models of the PD system: I have for a long time considered the shakines to be an example of a feed-back system which has become unstable. The demand or control loop starts at the brain, takes in the Substantia nigra, and follows the relevant nerves to the appropriate muscles of the body.The feedback loop uses different nerves to carry a position signal back to the brain - a route which takes it by the Globus Pallidus. The PD symptoms begin because the output signal from the Substantia Nigra has faded to such a low level that the control loop becomes unstable. The Pallidotomy operation consists of partially severing the nerve bundle in the feedback loop, so that the output strength of the feedback loop signal more closely matches the signal strength from the Substantia Nigra.. It works as a concept: Whether it really is like that I have no way of knowing. Does anyone else know? Regards -- Brian Collins <[log in to unmask]>