Recent investigations indicate that language abilities in people with chronic stroke aphasia may continue to evolve spontaneously. However, it is not clear to what extent this linguistic change occurs, and how it relates to neural structures. Behavioural speech and language therapy can improve performance of chronic aphasic participants, and it would be clinically useful to understand the neuropsychological and neural predictors of successful outcomes. This thesis, therefore, comprised four longitudinal studies to explore and predict the trajectory of linguistic symptoms in chronic stroke aphasia. The first two studies concentrated on spontaneous change, whilst the two later focused on therapy-induced change. Chapter 2 demonstrated that an amount of sentence comprehension change, both positive and negative, occurred in 34 chronic ( > 12 months) participants over a course of 26 months (mean time interval = 26.18 months, SD = 11.32). Decline in sentence comprehension was mapped using voxel-based correlational methodology (VBCM) to a neural cluster centred in the left posterior superior temporal gyrus. This finding is in line with previous research showing that this area is involved in sentence comprehension processes. Chapter 3 extended this work by (prospectively) examining chronic change in a detailed neuropsychological battery (n = 11 tests). This project was a progression from my work in Chapter 2, and it included 26 participants (mean time interval = 28.37 months, SD = 12.66). The majority of these individuals (n = 25/26) had previously participated in the study described in Chapter 2. Behavioural analyses indicated a degree of individual variability (recovery as well as decline) in performance. At the group-level, participants significantly declined in sentence comprehension and marginally improved in non-word repetition. VBCM revealed two neural clusters associated with behavioural change: decline in naming abilities was related to the right anterior temporal lobe and frontal cortex (and the uncinate fasciculus connecting them); and recovery in non-word repetition was related to the white matter underlying the right caudate and surrounding tissue. These results are consistent with the current knowledge of the role of anterior temporal lobes/frontal cortex in naming functions, and the caudate in speech motor processes. Chapter 4 included a therapy study in 26 chronic aphasic participants ( > 12 months post-stroke) who underwent a range of repetition-based treatments. The participants were recruited for this study and had not participated in the spontaneous change studies (Chapters 2 and 3). The treatments included an existing one, repetition in the presence of a picture, as well as two novel variants: repetition in the presence of articulation, and repetition in the presence of a picture and articulation. Each therapy cycle lasted two weeks, and patients were assessed at 7-days post treatment (i.e., immediate testing) 8 and at a 12-day follow-up (i.e., delayed testing). All therapies induced a significant improvement in naming performance. Participantsâ pre-therapy phonological abilities correlated with the therapeutic gains. The right precentral gyrus and superior parietal lobule were further associated with gains. These results indicated that key neuropsychological functions and right hemisphere structures can be used as predictors of therapeutic outcomes. Finally, Chapter 5 constitutes an analysis of an additional outcome measure from the study in Chapter 4, namely therapy-induced changes in phonological error-profiles. This final exploratory study examined the evolution of error-profiles as a result of the therapies described in Chapter 4. Importantly, the same individuals participated in the studies reported in Chapters 4 and 5. Post-therapy, there was a reduction in the proportion of errors farthest from the target (i.e., omissions and distant phonological), and an increase in the proportion of errors closer to the target (i.e., eventually correct responses). Overall, these empirical studies advance the current understanding of the trajectory of performance observed amongst people with chronic stroke aphasia. These findings may lead to more targeted interventions for people with aphasia, which may enhance their quality of life.
|Date of Award||31 Dec 2022|
- The University of Manchester
|Supervisor||Anna Woollams (Supervisor) & Ajay Halai (Supervisor)|