BME PhD Defense Seminar: Vivek J. Khandwala

Effects of Aging, Parkinson’s Disease and Deep Brain Stimulation on Voluntary Upper Limb Movements

Co-Supervised by Professors Martha Johnson Gdowski and Greg Gdowski

Abstract

Voluntary movements depend heavily on coordinated motor patterning that necessitates simultaneous motion at multiple joints and sensorimotor integration. Parkinson’s disease (PD), a chronic neurodegenerative movement disorder, is typically characterized by impairments in voluntary movement observed clinically as akinesia/bradykinesia, rigidity, tremor, and postural instability. Clinical observations and experimental studies report impairments in sensorimotor integration and coordinated multijoint movements in PD. The therapeutic efficacy of deep brain stimulation (DBS) of the subthalamic nucleus (STN) to ameliorate PD motor symptoms has been well documented. However, both the effects of STN DBS at the level of individual joints and the mechanisms that underlie such motor improvements remain poorly characterized. We quantified the effects of healthy aging, PD, and PD treatment using STN DBS and medication on end-point and joint kinematics of upper limb movements during a set of visually guided button-pressing tasks. The movement kinematics of study participants were evaluated by analyzing index finger and joint kinematics.

Participants included healthy age-matched subjects (baseline), untreated PD patients without STN DBS and medication (patient baseline), patients treated with DBS only and patients receiving both STN DBS and medication (optimal therapeutic state). Results revealed improved upper limb motor function in PD patients as a consequence of STN DBS, predominantly due to a change in the temporal profile of movement, especially during the deceleration phase. STN DBS has little to no effect on peak velocity, which only improves significantly in the presence of STN DBS and medication. These trends were representative of simple movements requiring movement of only one joint and complex movements that required simultaneous motion at multiple joints. To assess sensorimotor integration, the performance of tasks with and without visual precue were evaluated, resulting in the prolongation of deceleration times for patients in the untreated condition, which was not observed in control subjects and appeared to be a consequence of the disease process and was ameliorated with stimulation therapy. STN DBS normalized the sensorimotor integration such that deceleration times were similar during both tasks.