Zeni, Silvia
(2020)
Function of the human cerebellum in timing and auditory-motor synchronisation.
PhD thesis, University of Nottingham.
Abstract
This thesis is divided into two main parts: introduction and experimental research. Chapter 1 and Chapter 2 in the introduction provide a theoretical background for the experimental research presented in Chapters 4–6. Chapter 3 includes a description of the general methods, set-up and measures used in the experimental research.
Chapter 1 opens with some general considerations on the concept of time in cognitive psychology, followed by a classification of timing abilities. Timing processing is conceptualized as the ability of the brain to track the passage of time and to process temporal properties of exogenous sensory stimuli. Timing ability is thought to be fundamental to both perception and action. After a general introduction on timing, the topic moves onto auditory-motor synchronisation, a behaviour that is thought to rely on temporal processing. This section includes an account of auditorymotor synchronization both in human and in other species, and a discussion of the clinical relevance of auditory-motor synchronization. Chapter 2 is dedicated to the cerebellum, a structure at the back of the brain that is the focus of the work presented in this thesis. The chapter includes a description of cerebellar anatomy, function and dysfunction.
The second part of the thesis opens with a general method section, Chapter 3, which includes a concise description of techniques, methods and measures used in the experimental research, as well as some descriptions for standard practices. Following on, Chapter 4 is a report of two behavioural experiments on perceptual timing (Zeni & Holmes, 2018). The aim of these experiments was to examine whether a regular sequence of sounds can modulate the perceived duration of time intervals embedded in the sequence, as shown by Barnes and Jones (2000). These experiments should have provided the grounding for the following research on motor timing, but the result did not replicate. An argument was made around the impact of methodological choices on the results.
Chapter 5 is a report of two cerebellar transcranial magnetic stimulation (TMS) experiments that were run to examine whether single-pulse TMS delivered over the cerebellum could be used to interfere with auditory-motor synchronization, studied with the finger-tapping task. Notice that a similar use of repetitive TMS had been proven successful. Both intermittent and continuous rhythmic movements were examined, to test the hypothesis of dissociation between these two movement types, as suggested by previous behavioural and clinical evidence. TMS affected fingertapping performance, but the effect observed, which was short-lasting and not hemispheric-specific, most likely resulted from the discomfort and the nonhabituating startle-like reflex elicited by TMS, rather than from a direct interference of the stimulation with cerebellar function.
Chapter 6 is a report of a two-session, simultaneous EMG-fMRI experiment on the function of the cerebellum in auditory-motor synchronization. In this experiment, both intermittent and continuous rhythmic movements, both paced and unpaced by an external auditory stimulus, were examined. Intermittent and continuous rhythmic movements are thought to require different processing, and the cerebellum is suggested to be involved in this dissociation. More specifically, temporally constrained intermittent movements are thought to rely on cerebellar functioning. Representational similarity analysis was used to test whether the difference between intermittent and continuous movements and between paced and unpaced tasks were encoded in the functional activity of the cerebellum. Alternative models built out of behavioural data were tested to decide whether the cerebellum was more likely to encode aspects specific to synchronisation performance, rather than motor execution. Contrary to predictions, continuous movements activated the cerebellum (ipsilateral lobules V, VI and VIII) more than intermittent movements. Moreover, this activation was more likely to reflect differences in the motor component of the task, rather than aspects of synchronisation performance.
The thesis concludes with a general discussion of the experimental work, reported in Chapter 7. This final chapter includes a summary of the research questions addressed, a description of how the conclusions are supported by the results and are integrated in the existing body of knowledge. Limitations and implication for future studies were also discussed.
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