Perceptual and semantic priming in patients with multiple sclerosis: is implicit memory preserved?

Introduction: Neuropsychological studies on people with neuropsychological symptoms (e.g. memory deficits) indicate dissociation consisting of some deficits in explicit (declarative) memory and absence of difficulties in remembering and recalling on the priming procedure. In the few studies so far of nondeclarative memory in the MS group it was shown that priming makes possible recollection of information which cannot be remembered intentionally. It is suggested that there is dependence between the implicit recalling and the clinical factors of MS. The aim of our research was to analyse the effect of priming in MS compared to a control group, defining a relation between effects of reminding and kind of priming, course of MS and duration of disability. Material and methods: In the research work 27 people with clinically probable MS (multiple sclerosis) and 30 people from a control group took part. The level of processing stimulus on the phase of presentation (perceptual versus semantic) and kind of priming (perceptual versus semantic) were manipulated. In that way there were created 4 kinds of experimental tasks. Results: The people suffering from MS, compared with the control group, showed significant difficulties in priming tasks which perform perceptual processing in the learning phase and in the recalling phase, and a comparable level of results in semantic priming. Clinical factors (course of illness and disease duration) did not differentiate the results of the MS group, but patients with PPMS (primary progressive MS) exhibited a deficit in perceptual priming. Conclusions: The results indicate a dissociation in implicit memory: normal semantic priming and pathological perceptual priming. Mechanisms of difficulties in perceptual priming depending on course of MS and methodological aspects of the priming procedure are discussed.