Theory of Mind and Executive Functions are Dissociated in Multiple Sclerosis

Objectives: To investigate the relationship of executive functions (EF) and theory of mind (ToM) in multiple sclerosis (MS), clarifing whether ToM impairment in MS is related to EF dysfunction or whether they represent dissociable processes which can be independently impaired in MS. Methods: We enrolled 60 consecutive MS patients and 60 healthy controls (HC) matched on age, gender, and education level. All participants underwent ToM testing using the Eyes Test and the Videos Test and neuropsychological testing tapping different EF subdomains. A correlation analysis and a hierarchical cluster analysis were used to determine the similarity between explained variance between EF measures and ToM tests. Results: MS patients had lower scores on both tasks of ToM compared to HC, i.e., Eyes Test (21.1 +/- 5.0 vs. 29.5 +/- 3.8, p < .001; Cohen's d: 1.9) and Videos Test (19.6 +/- 2.4 vs. 22.9 +/- 1.8, p < .001; Cohen's d: 1.6). They also performed significantly worse on different measures of EF. ToM performance was not significantly correlated with EF tests. The hierarchical cluster analysis showed that ToM measures in MS were clustered separately from the EF measures, revealing three executive clusters (Attention/working memory cluster; Inhibitory control/shifting ability cluster; Verbal Initiative/Abstract reasoning cluster) and one ToM cluster. Conclusion: This study suggests a dissociation of EF and ToM in MS, meaning that the MS-related neurobehavioral symptoms may be associated with a significant impairment in ToM independent of the level of EF performance. Ultimately, this discrimination of ToM deficits in MS may help to identify the appropriate cognitive and behavioral interventions.