An Investigation of Event-Related Brain Potentials Evoked by Feedback During Prism Adaptation
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Prism adaptation (PA) demonstrates how the brain can adapt to a shifted visual field and also serves as a promising rehabilitation approach for treating visuo-spatial neglect (VSN) – a condition marked by deficits in attending and responding to contralesional stimuli. Visuo-motor aiming errors following PA, or aftereffects, suggest that adaption is achieved in part by undergoing a basic transformation of spatial maps and egocentric coordinates. This process, referred to as spatial realignment, thus plays a critical role in eliciting improved VSN symptoms following PA. Despite several theoretical accounts of the mechanisms involved in PA, there are limited means to directly measure neural processes engaged during PA that lead to robust aftereffects. The present set of studies investigated event-related brain potentials (ERPs) evoked by different provisions of feedback during blocks of PA performed by young healthy adults. The main purpose of the studies was to identify ERP components that index neural processes during adaptation that lead to robust aftereffects. Previous research has shown that feedback events at the end of reaching movements during PA can evoke an error-sensitive component of the ERP (the error-related negativity, ERN) as well as a component sensitive to phase – i.e. early, middle, late – of adaptation blocks (the P300). Thus the following studies investigated whether the ERN, P300, or any novel ERP components reflect adaptive processes associated with subsequent aftereffects. The different provisions of feedback used here were predicted to evoke either relatively weak, or relatively strong magnitudes of aftereffects. Thus, ERPs were compared between feedback provisions. Feedback events evoked a number of different ERPs across all conditions, thus providing evidence that the brain recruits different systems to support adaptation depending on the feedback condition. The major results from the studies suggest that a purported neural reinforcement learning system, indexed by the ERN, is sufficient to undergo error compensation across adaptation blocks but not sufficient to yield strong aftereffects. Results also suggest, however, that a parieto-occipital component sensitive to phase, resembling the P300, reflects processing associated with spatial realignment as it is consistently evoked by conditions leading to strong aftereffects but absent otherwise. Although further research is necessary, development of PA paradigms can be improved by using feedback conditions that evoke the aforementioned parieto-occipital component response. The use of feedback-evoked brain potentials may also assist clinicians in determining why, or how a person with neglect responds to PA treatment successfully or poorly.