The effects of transcranial direct current stimulation on dual-task walking in Parkinson's disease
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BACKGROUND: Parkinson’s disease (PD) is a common debilitating disorder that largely effects the aging population. It is associated with a loss of dopamine-producing brain cells, which leads to abnormal brain activity and ultimately, a loss of locomotor control. Transcranial direct current stimulation (tDCS) is a technology that effectively modulates brain excitability by sending low electric current through the scalp. It has been demonstrated to improve working memory, intelligence, learning ability, as well as relieving symptoms of depression, Alzheimer’s and schizophrenia (Kekic, Boysen, Campbell, & Schmidt, 2015; Khedr et al., 2014; Manor et al., 2015). tDCS may thus serve as an effective therapeutic strategy for this vulnerable PD population. OBJECTIVE: The primary purpose of this study was to examine the acute effects of single sessions of tDCS targeting different brain networks on locomotor control metrics and other outcomes in patients with PD. DESIGN: A pilot, double-blinded, sham-controlled study. METHODS: A total of 15 older adults between the ages of 40-85 with a physician diagnosis of PD will be recruited. Participants are screened with questionnaires to determine eligibility. If eligible, participants will undergo a dual task assessment and a freezing of gait (FOG) provoking protocol prior to, as well as immediately after, a 20-minute session of tDCS. The acute effects of each stimulation session will be observed. There will be three different stimulation conditions that each target different areas of the brain: the motor cortex (M1), the motor cortex and the dorsolateral prefrontal cortex (DLPFC), and a sham (i.e., control) condition. Multiple aspects of locomotion (i.e., FOG, gait speed, stride time variability, percent of each walking stride spent with both feet on the ground) and cognition are assessed. RESULTS: This study began enrolling participants on March 3rd, 2016. To date, one participant has been enrolled and completed baseline testing as well as all three tDCS visits. This 42-year-old participant was diagnosed with PD two years ago and symptoms are mild. No side effects were observed during tDCS and the participant was unable to decipher between the M1 and the sham stimulation, but was able to tell the difference between sessions when receiving multi-focal stimulation. DISCUSSION: In this case study, tDCS was well tolerated by the patient and double-blinding procedures were effective. Thus, while tDCS did not induce significant improvements in gait or cognition in this relatively high functioning patient, the developed study protocol and tDCS intervention are highly feasible in the PD population.