Complex motor dynamics and control in multilooped negative feedback systems

Experiments were performed in normal and Parkinsonian subjects who were asked to maintain a constant finger position using a time-delayed visual feedback. The finger position showed complex dynamics, with characteristic differences between normal subjects and persons suffering from Parkinson's disease. A discussion is presented of some of the theoretical issues that must be resolved in order to understand the mechanisms that underlie the generation of these complex signals.<<ETX>>