The preservation of implicit learning in multiple sclerosis

Abstract

Multiple sclerosis (MS) is a debilitating disease of the central nervous system (CNS), affecting Caucasians more than any other ethnic group. Previous research has indicated that implicit learning, measured by performance on motor skill learning and perceptual priming tasks, is preserved for MS participants, whereas explicit learning is impaired. However, a study conducted by Rao et. AI. (1993), which measured the performance of MS participants on a serial reaction time task (SRT), seemed to produce some ambiguous results. According to this study the MS participants performed as well as controls, but the graphed data indicates otherwise, ie. that they demonstrated less learning than the controls. The present research was conducted to clarify this apparent discrepancy. Eighteen participants diagnosed with multiple sclerosis (MS) were compared with 20 controls on two tasks of implicit learning. Implicit learning was measured by performance on a verbal version of the serial reaction time task (SRT) and an artificial grammar task (AGT). Additionally, the Rey Auditory Verbal Learning Test (RAVLT) was conducted as an explicit learning measure. On both implicit learning tasks, the MS participants performed as well as controls, but were impaired on the explicit learning task, thus providing further support that implicit learning is preserved in MS, but the converse is true for explicit learning. Additionally, MS participants and Alzheimer Disease (AD) patient groups have exhibited similar performance on the SRT, which differs from the performance of those with the subcortical dementias, ie. Huntington's Disease (HD) and Parkinson's Disease (PD), who exhibit impaired implicit learning. This suggests that although MS has been termed a subcortical disease, that the classification of a white matter dementia may be more appropriate.