- Title
- Transcranial direct current stimulation: a potential modality for stroke rehabilitation
- Creator
- Marquez, Jodie
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2018
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Transcranial Direct Current Stimulation (tDCS) is a form of non-invasive brain stimulation which has been investigated in a broad range of neuropsychiatric conditions and as a method to modulate cognitive performance in healthy individuals. It is generally accepted that the main mechanism by which tDCS modulates brain function is via a neural membrane polarization shift which can, in turn, lead to diverse changes in single neuron, synaptic and network activity (Peterchev, Wagner et al. 2012). However, the direction of polarization shift is sensitive to the stimulation dose, the state of brain activity at the time of stimulation and individual anatomy (Bikson and Rahman 2013). This results in a large inter individual variability to the neurophysiological and behavioural response to tDCs. Given the simplicity of tDCS and the complexity of brain function, we sought to unveil some of the physiological mechanisms underpinning the effects of tDCS in order to better our understanding of the variability in response to tDCS and to allow us to predict those most likely to respond. Ultimately our objective was to direct the translation of the research evidence into therapeutic applications of tDCS for stroke patients. The aim of this research was to determine the potential application of tDCS in the stroke population. At the commencement of this PhD research project, keen interest in the use of tDCS as a potential therapeutic tool in neuromotor conditions, such as stroke, was emerging. As tDCS is portable, relatively inexpensive, free from major adverse effects, and easily applied concurrently with other interventions, it is ideally suited for use in stroke rehabilitation therapy. The goal of tDCS in stroke is to increase cortical excitability of the lesioned hemisphere and/or reduce excitability on the non-lesioned hemisphere to restore interhemispheric balance (Mordillo-Mateos, Turpin-Fenoll et al. 2012). The vast majority of literature investigating tDCS has been conducted in young, healthy subject. As stroke patients are typically more senior and have age related changes in cortical structure, function and excitability, we began our investigation into the functional and physiological effects of tDCS in a healthy, aged population. We found that the hemispheres responded differently to tDCS and the response appeared to be task specific, but it was not mediated by age. However, a subsequent multimodal imaging study did not support these findings and failed to reveal a difference when tDCS was applied to the dominant or non-dominant hemisphere but showed that the effects were diffuse and determined by the type of stimulation. In a systematic review of the stroke literature we synthesised the evidence from 15 studies and confirmed the safety and acceptability of this modality in the stroke population. We concluded that tDCS may be effective in enhancing motor performance, atleast in the short term. Those most likely to benefit were patients with chronic stroke and/or mild to moderate impairments. However these positive findings were not consistent across all studies and the size of the treatment effect was at best modest and may not translate to clinically meaningful change for some or all patients. We used this evidence to conduct a randomised controlled trial in chronic stroke patients and found that neither anodal nor cathodal stimulation resulted in statistically significant improvement in upper limb performance. A secondary analysis was performed and identified that those with moderate or severe disability responded positively to cathodal stimulation with improved gross motor function. This thesis, in conjunction with the rapidly growing body of evidence in this field, highlights the inconsistency in the effects of tDCS at both an intraindividual level and between subjects, and the transient nature of these effects which limits the clinical value of this intervention. Further scrutiny of the mechanisms underpinning the effects of tDCS is required for the rational advancement of tDCS as a clinical modality in stroke rehabilitation.
- Subject
- tDCS; brain stimulation; stroke; rehabilitation; upper limb; aging
- Identifier
- http://hdl.handle.net/1959.13/1383654
- Identifier
- uon:31972
- Rights
- Copyright 2018 Jodie Marquez
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 4 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 217 KB | Adobe Acrobat PDF | View Details Download |