Lack of Long-Trial-Improvement of Impaired Prism Adaptation in Multiple System Atrophy

Abstract Background : Prism adaptation (PA) is impaired in cerebellar disorders. We reported that trial number increment normalized its impairment in pure cerebellar spinocerebellar degeneration (pSCD) (long-trial-improvement). It remains to be determined whether this feature applies to multiple system atrophy (MSA). Objectives: To clarify PA profiles in MSA. Methods: We measured performance parameters of PA tasks with 50 or 200 trials in 26 MSA, 26 pSCD patients, and 39 healthy volunteers. Results: With 50 trials, the adaptation ability (final error of PA) was similarly impaired in both disorders. While 200 trials normalized the PA performance in pSCD, 200 trials did not restore it in MSA. The degree of adaptation deficits correlated with clinical ataxia severity in MSA but not in pSCD. Conclusion: No long-trial-improvement should reflect severe cerebellar adaptation circuits involvements, including middle cerebellar peduncle, dentate nucleus, brainstem nuclei and other areas, in MSA compared to mild involvements, only in cerebellar cortex, in pSCD.