Year of Publication

2020

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Health Sciences

Department

Rehabilitation Sciences

First Advisor

Dr. Richard Andreatta

Second Advisor

Dr. Isabel Hubbard

Abstract

Introduction. Aphasia is a devastating acquired language disorder that affects about one third of stroke survivors. Aphasia can severely affect quality of life and can be associated with economic burdens due to the need for long-term communication rehabilitation. Traditional aphasia therapies are known to be effective; however, progress is often slow and limited in severe cases – full restoration of communication abilities is rarely achieved. Thus, there is a critical need for therapeutic solutions that can reduce the associated burden of aphasia. Transcranial direct current stimulation (tDCS) is a non-invasive and inexpensive neuromodulation technique that has the potential to boost language recovery in post-stroke aphasia, as well as reduce rehabilitation duration compared to traditional therapies alone. However, despite over a decade of research on tDCS for post-stroke aphasia, this method has yet to be approved for clinical use. In addition, there are many methodological challenges that must be addressed in order to produce stronger evidence.

Purpose. This dissertation comprises three projects that investigate the use of tDCS to improve language functions in people with post-stroke aphasia. The aim of the first project is to conduct a review to critically analyze the methodological rigor of current evidence, regarding the use of tDCS for post-stroke anomia. The second project investigates the effect of tDCS on improving reaction time in healthy participants, and tests the timing factor of stimulation (i.e., comparing offline and online stimulation). The aim of the third project is to test an individualized tDCS approach and find the optimal tDCS montage, based on three stroke recovery patterns, to improve naming in people with post-stroke aphasia.

Methods. Several methodologies were used to conduct the three projects. A critical review method was used to answer the first project’s objective. For the second project, a cross-over within-subject randomized control design was used. For the third project, a within subject experimental design was used to test three active stimulation conditions and define the optimal condition for each participant.

Results. The findings of the first study show that the current level of evidence for using tDCS for anomia is at the pre-efficacy level, with emerging evidence at the efficacy level. In addition, several methodological issues in tDCS literature were identified. The second study did not show significant effects of tDCS on naming latency in healthy participants, suggesting that a single session with a short stimulation period may not be sufficient to induce behavioral changes in naming performance. In contrast, the third study paired multiple sessions of stimulation with efficacious anomia treatments in individuals with post-stroke aphasia, resulting in gains in single word retrieval. This finding occurred regardless of the stimulation montage. Bilateral stimulation was the optimal condition for four out of six participants. Upregulating the left hemisphere with A-tDCS was the second most optimal condition. Upregulating the right hemisphere with A-tDCS was not an optimal condition for any participant.

Conclusion. tDCS is a promising technique to boost language recovery in aphasia, when combined with evidence-based language treatment. People with aphasia may benefit from more than one tDCS montage, and factors such as aphasia severity and lesion location and size may determine the amount of gain. Further studies on individualized tDCS approach are needed.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2020.513

Funding Information

This study was supported by a scholarship from Taibah University, Saudi Arabia awarded September 2015.

Available for download on Friday, December 16, 2022

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