Behind the Lens: Sensorimotor and Cognitive After-effects of Prism Adaptation

Over a century of research into prism adaptation (PA) has provided many insights into general sensorimotor functions including plasticity and the role of prediction. More recently, the therapeutic value of PA for conditions relating to right hemisphere dysfunction such as hemispatial neglect, and to body schema related conditions such as complex region pain syndrome, have generated a wealth of new knowledge – and more questions (Chapter 1). This thesis examines a cross-section of PA effects: sensorimotor adaptation in healthy participants and cognitive after-effects in a neurological population as well as a group of participants with a virtual lesion. Chapter 2 reports that PA does not induce an after-effect shift in a visual straightahead judgment task, while it does induce after-effects in other tasks which are attributable to a change in state estimates of eye position in the orbit. The results suggest that PA prompts complex changes within ocular proprioception and indicate that the assumption of linear additivity of PA sensorimotor after-effects is a concept requiring re-examination. An increase in priming following both right-shifting and left-shifting PA in patients with a left hemisphere lesion provides a first demonstration of the rehabilitative potential of PA for left hemisphere dysfunctions. Intriguingly, this result also widens the possible candidate mechanisms through which PA facilitates cognitive after-effects (Chapter 3). Finally, this thesis explores the potential influence of the cerebellum in the cognitive after-effects of PA (Chapter 4). It reports, for the first time, that neurodisruption of the right cerebellar hemisphere increases and left cerebellar stimulation decreases word association priming. The results indicate that the two cerebellar hemispheres conjointly schedule the facilitation and inhibition of associative priming. Taken together, the novel findings reported here suggest that previous theoretical stand-points need to be revised and provide a new framework for understanding the relationship between sensorimotor adaptation, cerebellar function and hemispheric interactions in human cognition