Parkinson's disease tremor explained by reflex loop changes.

Many Parkinson's Disease tremor behaviors that were considered hard to interpret can be explained by control systems modeling of mid-level motor control. The model in this paper includes stretch reflex loop with feedback delay and tonically controlled antagonist muscles. It also includes Basal Ganglia circuit that commands (schedules) gain changes in the reflex feedback loop. Computational analysis of the control systems model shows how the gain changes might turn the tremor on and off between pose maintenance and voluntary motion in the disease and normal state. The results might be useful for interpreting and tuning the effects of Parkinson's Disease treatments. They also provide new control systems engineering insight into mid-level motor control.