Stroop performance in multiple sclerosis: information processing, selective attention, or executive functioning?

Cognitive impairments in information processing speed, attention and executive functioning are widely reported in patients with multiple sclerosis (MS). Several studies have identified impaired performance on the Stroop test in people with MS, yet uncertainty remains over the cause of this phenomenon. In this study, 25 patients with MS were assessed with a neuropsychological test battery including a computerized Stroop test and a computerized test of information processing speed, the Graded Conditional Discrimination Tasks (GCDT). The patient group was compared with an individually age, sex and estimated premorbid IQ-matched healthy control group. The patients' reaction times (RTs) were significantly longer than those of the controls on all Stroop test trials and there was a significantly enhanced absolute (RT(incongruent)-RT(neutral)) and relative (100 x [RT(incongruent)-RT(neutral)]/RT(neutral)) Stroop interference effect for the MS group. The linear function relating RT to stimulus complexity in the GCDT was significantly steeper in the patient group, indicating slowed information processing. The results are discussed with reference to the difference engine model, a theory of diversity in speeded cognition. It is concluded that, in the assessment of people with MS, great caution must be used in the interpretation of performance on neuropsychological tests which rely on RT as the primary measure.

A 5-year follow-up study of an atypical case of myotonic dystrophy.

This study presents 5-year follow-up data on NG, a woman with adult onset myotonic dystrophy and progressive cognitive decline who was first described by Wilson et al. The extent of the cognitive impairment is atypical of symptom-onset in adulthood and of paternal inheritance, both of which apply to this case. Together, the present and earlier studies report the results of regular neuropsychological assessments over a 16-year period. Severe impairment in executive functioning, episodic and semantic memory were apparent early in the history, while visuospatial skills and working memory were only mildly impaired after 16 years of follow-up. There was also a progressive dyslexia, initially characterized by the regularization errors typical of surface dyslexia, but subsequently dominated by visual/phonological reading errors. This pattern of impairment is not typical of myotonic dystrophy but resembles semantic dementia. Whilst the deficits may be attributable wholly to myotonic dystrophy pathology, the co-existence of a form of semantic dementia is also possible. It is noted that the aggregation of tau protein is a neuropathological feature common to both diseases.