The neuroscientific basis of speech therapy for aphasic word-finding difficulties

Abstract

A wide range of different behavioural treatments for post-stroke aphasia have been developed and studied in depth over the course of modern aphasia research. Recent work involving neuroimaging has also developed our understanding of how these treatments function in relation to the functional and structural changes in the brain experienced by people with aphasia (PWA). However, understanding of the intricate relationships between different treatment effects and PWA lesion, language and demographic profile is not yet fully developed. This thesis focused on progressing our understanding in this area via investigation of a range of treatments and their effects across various PWA exhibiting differences across these three areas. Chapter 2 sought to summarise existing research in this area via a systematic literature review. It discussed the research into a range of different neuroscientifically-based treatments for post-stroke aphasia that has occurred since 1997. In addition, it helped to highlight areas in this field which are currently more sparsely researched and could benefit from greater examination. These areas - namely, the relationships between white matter damage and PWA language profile and response to treatment, direct comparison between differing behavioural treatments, the effects of treatments on functional communication, and how and to what extent treatment effects are affected by inter-participant variation, were then explored in greater detail in subsequent chapters. Chapter 3 investigated the relationships between language deficits and lesion location using analyses of both structural Magnetic Resonance Imaging (MRI) and Diffusion Tensor Imaging (DTI) imaging in 18 participants. The results showed some support for a dual pathway model of language processing, as well as support for the roles of the fornix, frontal aslant tract, and corticospinal tract in language. Tract-Based Spatial Statistics analyses also found differences in integrity between controls and semantically improved PWA in several right hemisphere tracts. Chapter 4 discussed the methodology developed in order to perform a standardised, direct comparison of three different approaches to aphasia treatment, divided into six individual treatments, for 18 PWA. This includes details of the overall structure and timepoints of the study, as well as the methodology for each treatment, and details of the assessments performed at each timepoint. Chapter 5 covers the results and discussion from this comparison, including cumulative link mixed models (CLMM) analyses in addition to more standard analyses, in order to try to capture some of the nuances in the interactions between treatment effect and inter-participant factors. The two executive function focused treatments, Speeded and Interfered naming, were found to outperform the others in terms of the primary outcome measure. While this success was modulated by inter-participant factors to some degree, they were generally the strongest treatments regardless of the inter-participant factors accounted for, although Interfered naming was found to be more resilient to the effects of these factors than Speeded naming. Some evidence supporting length of treatment as an important factor in generalisation to untrained naming was also found.

Date of Award	1 Aug 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Andrew Stewart (Supervisor) & Paul Conroy (Supervisor)