A control-system perspective on parkinsonian tremor with implications on diagnosis and disease monitoring

Parkinson's disease, an idiopathic and degenerative disorder of the central nervous system, is characterized by increased reaction times (by as much as 0.1 sec) in voluntary movements and often results in among other symptoms unintended tremulous (oscillatory) motion of body parts not in action, termed as Parkinsonian tremor. There are however no definitive diagnostic test that can confirm the presence or severity of Parkinson's disease. This is a serious handicap especially since the drugs usually prescribed to control these symptoms have serious side effects and their dosages have to be tuned extensively. In the current work, we view an increased sensorimotor loop delay in Parkinson's Disease as a key distinguishing feature and hypothesize that this increased delay causes Parkinsonian tremor (as instability-induced oscillations). Through simulations and tests with two table-top experiments, we use this premise to gain further insight into the mechanism behind Parkinsonian tremor and draw qualitative observations about the features of tremors that could be used for diagnosis of Parkinson's disease and estimating its severity. We further discuss possibilities for a low-cost device or a smartphone app for diagnosis. We further explore ideas for detection of Parkinson's disease, before tremors develop.