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Title: Modulations of cerebellar predictive language function through continuous theta burst stimulation
Author: Allen-Walker, Louise
ISNI:       0000 0004 6498 8345
Awarding Body: Prifysgol Bangor University
Current Institution: Bangor University
Date of Award: 2017
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Although the role of the cerebellum has historically been associated with motoric function, more recently it has become clear that the cerebellum also has a role in many cognitive functions, such as learning, perception, verbal working memory and emotion. Of particular interest to this thesis is how the cerebellum is involved in predictive language processing. Studies employing transcranial magnetic stimulation to examine the role of the cerebellum in language have primarily indicated that it is in some way associative or predictive, and have used methodologies that principally rely upon associative priming. The aims of this thesis are to: a) replicate previous findings as regards the role of the cerebellum in associative as compared to categorical priming, but with stimuli where the categorical relationship is controlled for across both types (namely, opposite pairs as compared to categorical pairs), and to determine whether these behavioural modulations are reflected in language specific event-related potentials that index language prediction, b) examine whether the role of the cerebellum in associative priming extends to backward priming, whose models imply a differing process as compared to forward priming, and c) examine whether the predictive or associative role of the cerebellum in language can be extended to more complex sentences and how modulation of this function affects later language specific event-related potentials that index language prediction. In Chapter 4, the opposite stimuli, and not the categorical, displayed a priming effect. This was reflected by the phonological mismatch negativity wave, implying that this task required only phonological access to be completed. There was no effect of the cTBS, possibly because this task did not require semantic access. This indirectly supports the literature that suggests the cerebellum plays a role in semantic prediction. In Chapter 5 I show for the first time, beyond fMRI activation, that the left cerebellar hemisphere is actively involved in backward priming. Modulation of the left cerebellar hemisphere through cTBS selectively enhanced backward as compared to forward priming, indicating that the cerebellum has a role in backward priming that is localized to the left cerebellar hemisphere. Additionally, this finding provides a potential explanation for the presence and mechanism of short stimulus onset asynchrony backward priming. Finally, Chapter 6 shows that modulation of right cerebellar function through cTBS results in easier processing of incongruent endings of highly predictable sentences, as indexed by the N400 event-related potential. I hypothesise that the effect of cTBS exhibited here is caused by modulation of the process through which errors are fed back in order to update cerebellar internal models. For the first time, we have shown that modulation of cerebellar predictive language function impacts upon later electrophysiological measures, and that this method might be an effective way to further elucidate the role of the cerebellum in language. Overall, this thesis supports the evidence that the cerebellum is involved in predictive language function, and that it applies a similar set of computations or internal models here as it does in motoric function and other cognitive functions. Additionally, we have proposed mechanisms through which cTBS may be affecting these internal models attributed to the cerebellum.
Supervisor: Bracewell, Robert Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available