Long-Term Transcranial Direct Current Stimulation in Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder and affects approximately 1 million people in the United States with total annual costs approaching 11 billion dollars. Current medical and surgical treatment approaches for PD are either only mildly effective, expensive, or associated with a variety of side effects. Therefore, the development of practical and effective therapeutic adjuncts to current treatment approaches would have significant benefits.

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that can modulate cortical excitability and improve motor function in healthy subjects, older adults, and in stroke. However, there are several crucial issues that currently prevents the determination of the viability of tDCS as an adjunct intervention in PD. For example, the magnitude to which tDCS may be able to improve long-term motor learning beyond what can be achieved by practice alone in PD is unknown. It is also unclear if short-term improvements in motor function induced by tDCS and measured in the OFF state in PD can be attained over the long-term in the ON state, which is necessary for real world application. In addition, it is uncertain if the effects of tDCS generalize to non-practiced tasks and to the ipsilateral, non-tDCS stimulated hand. Finally, the physiological mechanisms underlying any of these issues have not been identified because no long-term motor learning tDCS studies in PD to date have concurrently quantified behavioral, clinical, and physiological measures.

The project will be a single-center, double-blind, randomized, sham-controlled, experimental design. PD patients will practice 2 motor tasks (practice tasks) with their right (primarily affected) hand in 9 practice sessions over a 2 week period in association with either tDCS or SHAM stimulation of the left (contralateral) motor cortex. In addition, 4 testing sessions will be performed and will include a Baseline test, an end of training test (EOT), a follow up test 2 weeks after the end of training (EOT+14), and a follow up test 4 weeks after the end of training (EOT+28). The primary outcome variables will be the force error in the first practice task (precision grip task; PGT) and the stroke amplitude, stroke variability, and writing speed in the second practice task (handwriting task; HWT). The secondary outcome variables the Unified Parkinson's Disease Rating Scale (UPDRS) Part 3, the Purdue Pegboard Test (PT), and the Jebsen Taylor Hand Function Test (JTT).