| Author: | Simpson, Michael William |
| Title: | The effect of transcranial direct current stimulation on upper limb motor performance in Parkinson’s disease |
| Advisors: | Mak, Margaret (RS) |
| Degree: | Ph.D. |
| Year: | 2022 |
| Subject: | Magnetic brain stimulation Motor ability Parkinson's disease -- Treatment Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Rehabilitation Sciences |
| Pages: | xxviii, 262 pages : color illustrations |
| Language: | English |
| Abstract: | General introduction Parkinson's disease (PD) is characterised by a pathology that not only manifests motor symptoms such as bradykinesia, but subtle deficits of motor learning. Overcoming such deficits is the primary aim of rehabilitative therapy. Pharmacologic treatment and surgical intervention offer considerable clinical benefit, yet prolonged treatment efficacy and safety concerns cast a shadow over the long-term treatment of PD. Transcranial direct current stimulation (tDCS), a non-invasive brain stimulation technique with the capacity to modulate neural excitability, may offer clinical benefit as an adjunctive therapy to combat PD. Little is known about the effects of tDCS on upper limb motor performance or explicit motor sequence learning (MSL) in PD. In this thesis, we aimed to examine the effects of tDCS on upper limb motor performance in PD, focusing on the capacity of tDCS to modulate explicit MSL. This aim was pursued through two systematic reviews, and three experimental studies. Systematic review one Aim: To systematically appraise the literature to establish explicit MSL capacity of people with PD compared to healthy. Methods: Databases MEDLINE, PsycINFO, EMBASE, CINAHL, PubMed, and Web of Science were systematically searched for articles that examined explicit MSL with the upper limbs in PD and healthy. Results: The findings of thirteen studies were synthesised into three categories regarding the explicit MSL capacity of (1) PD ON-medication compared with healthy, (2) PD OFF-medication compared with healthy, and (3) PD ON-medication compared to PD OFF-medication. Explicit MSL was evaluated according sequential task speed, accuracy, and skill index. As a function of practice, the change of sequential task speed among PD is comparable to healthy, but task accuracy is less consistent, particularly when ON-medication. Conclusions: The speed of sequential task performance is preserved in PD. During the OFF-medication phase, task accuracy appears preserved, although longer practice time is required. Task accuracy ON-medication is inconsistent, possibly due to suboptimal dopamine levels in the striatum. Systematic review two Aim: To systematically appraise available evidence to establish the effects of tDCS on upper limb motor performance in PD. Methods: Databases Medline, Cochrane, PsycINFO, EMBASE, CINAHL, and Web of Science were searched for articles that applied tDCS to PD and examined the effects on upper limb motor performance. Results: The findings of fourteen studies were synthesised into five categories regarding the effect of tDCS on: (1) Unified Parkinson's disease rating scale motor section (UPDRS III), (2) upper limb motor tasks, (3) manual dexterity, (4) reaction time, and (5) neurophysiology. Conclusions: UPDRS III, and the speed and force of movement may improve with tDCS applied to the motor cortex. High variation exists among tDCS parameters, and the long-term effects of tDCS on both simple and complex motor tasks requires clarification. Additional neurophysiological evidence is required to better guide the utility of tDCS. Experimental study one Aim(s): (1) To examine haemodynamic response of the motor cortex to tDCS applied at rest in PD and healthy. (2) To examine the change of task related motor cortical haemodynamic activity following tDCS in PD and healthy. Methods: In a randomised crossover experiment with 14 PD and 12 heathy, the haemodynamic response of the motor cortex to a regulated finger tapping task (right index finger, 3 Hz) was examined before and after anodal, cathodal, and sham tDCS applied over the primary motor cortex (M1). Three visits were separated by ≥ five days. M1 haemodynamic activity was quantified using functional near-infrared spectroscopy (fNIRS). Results: Task related activity was observed in M1 and inferior parietal lobe in PD and healthy (p < 0.05), but PD additionally recruited the dorsal premotor cortex. Anodal and cathodal tDCS significantly increased M1 oxygenated haemoglobin compared to sham during tDCS, (t62 = 4.09 and t62 = 4.25, respectively). Task related haemodynamic activity was unchanged following tDCS (p > 0.05). Conclusions: Task related hemodynamic response of M1 is not modulated by tDCS. Anodal and cathodal tDCS significantly increase M1 oxygenation during stimulation, the clinical significance of which remains to be clarified. Experimental study two Aim: Evaluate the effects of single-session tDCS when coapplied over the motor cortex during task practice on explicit MSL in PD. Methods: Thirty-three mild to moderate PD patients were randomised to receive either anodal, cathodal, or sham tDCS and learnt a short and long finger tapping sequence with their right hand. During task practice, tDCS was applied over M1. Single- and dual-task finger tapping performance was assessed before and after task practice and fNIRS was used to measure task related changes of oxygenated haemoglobin. Results: Short and long sequence single-task performance significantly improved with practice (p = 0.010 and p < 0.001, respectively). A condition-by-time interaction approached significance for single-task performance of the long sequence p = 0.069) driven by improved performance in the cathodal (p = 0.001) and sham (p < 0.001) tDCS conditions, but not anodal tDCS (p = 0.198). M1, premotor cortex, and supplementary motor area were active in all tasks. No interaction or main effects were observed for task related changes of oxygenated haemoglobin. Conclusions: PD retain capacity for explicit MSL, but single-session tDCS does not improve the rate of learning. Moreover, anodal tDCS may suppress learning. Experimental study three Aim: To evaluate the effects of multiple sessions of tDCS when coapplied over the motor cortex during task practice on explicit MSL and retention in PD. Methods: Forty-eight mild to moderate PD patients to learn a long finger tapping sequence with their right hand. Participants received five sessions of either anodal, cathodal, or sham tDCS applied over M1 during task practice and performance was assessed under single- and dual-task conditions over a 30-day follow-up period. Task related changes of oxygenated haemoglobin captured using fNIRS. Results: Single- and dual-task speed, error, and skill index improved with practice (p < 0.05). Greater offline reduction of single-task error was observed under anodal tDCS compared to sham (p = 0.03). A condition-by-time interaction for dual-task skill index (p = 0.037) was driven by a faster rate of improvement under anodal tDCS when compared to cathodal tDCS (p = 0.085) during post intervention and three-day follow-up assessment. No interaction or main effects were observed for task related changes of oxygenated haemoglobin. Conclusions: Anodal tDCS may improve offline single-task learning, but does not mediated a superior behavioural improvement against the sham tDCS protocol. General conclusions Components of explicit MSL, including sequential task speed, are retained in PD, yet the accuracy of task performance is less consistent and may be affected dopaminergic medication. The application of tDCS over M1 modifies resting cortical haemodynamic activity, but not subsequent task related activity. When coapplied with MSL task practice, anodal tDCS improves single-task offline learning and may improve overall dual-task performance. Improvements appear reliant on multiple sessions, as single-session tDCS did not improve learning, suggesting that improvements are driven by greater motor memory consolidation. |
| Rights: | All rights reserved |
| Access: | open access |
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