Background: Many studies have shown that about 45-65% of multiple sclerosis (M.S) patients suffer from cognitive impairments. Semantic memory as one of the subcategories of cognition is quite important for effective communication. In the present study, category-semantic memory was studied in order to evaluate the semantic memory organization in normal individuals and MS patients.

Methods: Ninety voluntaries participated in this study. Participants comprise of 45 MS patients and 45 normal individuals. All participants were matched in terms of age, sex and education. Variables such as the reaction time and the number of correct responses for retrieval (recognition) of natural (animal and fruit) and artifact (object) words were measured in both groups by presentation software. Data analyzed by t-paired and One-Way ANOVA tests. Ethical committee of Tehran University of Medical sciences approved the study.

Results: The results of current study showed significant differences in reaction time and correct responses of artifact and natural categories between the MS and normal individuals (p<0.05). Furthermore, there was significant difference between reaction time and number of correct responses to natural and artifact categories in each group (p<0.05).

Conclusions: This study showed that the organization of semantic categorization as natural and artifact categories is still preserved in multiple sclerosis patients. However, the processing of semantic categorization was different in term of reaction time and number of correct responses between MS patients and normal subjects and the processing of semantic-memory is slower than normal individuals.