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Title: Cerebellar contributions to nonmotor behaviour
Author: Tomlinson, Simon P.
ISNI:       0000 0004 5350 0551
Awarding Body: Prifysgol Bangor University
Current Institution: Bangor University
Date of Award: 2014
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The cerebellum's role in the co-ordination of motor behaviours is well-established. Evidence has been gathered that suggests that the cerebellum plays a role in a wider range of behaviours, but the nature and scope of this role remains controversial. Given the largely homogenous nature of the cerebellum's cytoarchitecture and the existence of discrete pathways linking motor and non-motor cerebral areas with the cerebellum the suggestion has been made that any cerebellar non-motor role is likely to be analogous to that played within motor behaviour. This thesis presents a series of experiments that sought to examine whether a cerebellar non-motor role can be placed within this explanatory framework. Previous attempts to elucidate the cerebellum's role in non-motor behaviour have relied on clinical investigations or neuroimaging. Both of these methods present issues with either the limited availability of suitable subjects or the strength of the inferences that can be drawn from correlations. The experiments within this thesis instead used brain stimulation techniques to investigate the living, healthy cerebellum in a range of non-motor behaviours. The experiments described in chapter 3 employed a Sternberg paradigm and transcranial direct current stimulation (tDCS) to investigate the cerebellar role in verbal and visual working memory (WM). No clear evidence for a cerebellar role in WM was obtained. These experiments highlighted the difficulties entailed in the use of a non-focal stimulation technique for cerebellar stimulation. From this point a rationale is advanced for the use of more-focal stimulation techniques for further research. An experiment is presented in Chapter 4 that used continuous theta burst stimulation (cTBS) targeting the posterolateral cerebellum (lobule VI/Crus I) to determine whether a lateralised cerebellar contribution to WM processes could be detected during the performance of visual and verbal Sternberg tasks. An impairment in the percentage of correct responses after cTBS to the right cerebellar hemisphere was noted. Chapter 5 presents two experiments that used cTBS targeting mid-hemispheric and lateral areas of the posterior cerebellum to determine whether a lateralised cerebellar role could be demonstrated in visuospatial WM. An impairment in the recall of the order of presented targets was seen after stimulation of the left cerebellar mid-hemisphere. An impairment in the speed of participants' responses was seen after stimulation of the more lateral areas of the left cerebellar hemisphere. The results were taken to indicate a preferential role for the cerebellar left hemisphere in spatial WM. Chapter 6 describes an experiment that examined the cerebellum's role in processing emotional stimuli in contrast to the proposed cerebellar function in verbal cognition. This experiment sought a dissociation between the effects of vermal and lateral cTBS in the performance of a 'masked emotional faces' colour-naming task, which incorporated emotionally-salient distractors, and a lexical decision task. Increased reaction times were seen on the emotional faces task after stimulation to both areas. No changes were indicated in participants' reported mood and post-stimulation differences were not specific to a single valence of emotional stimulus. These results were taken to indicate a cerebellar role in the orientation and shifting of attention, with particular emphasis on emotionally-salient stimuli. The WM results lent support to the proposed cerebellar hemispheric specialisation that is similar, but opposite to that observed in the cerebral hemispheres. The results, as a whole, are discussed in the context of the wider literature and an argument is made that the cerebellum does indeed play a role in the efficient implementation of non-motor behaviours that is somewhat analogous to its role within motor activity.
Supervisor: Bracewell, Robert Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available