Theory of mind: A clue for the interpretation of functional movement disorders

Functional movement disorders (FMD) refer to a heterogeneous group of manifestations incongruent with known neurological diseases. Functional neuroimaging studies in FMD indicate the overlap between cerebral regions in which abnormal activation occurs and those considered crucial for theory of mind (ToM), the ability to attribute mental states. The aim of this study was to explore whether FMD might be related to ToM disorders to the extent that they reduce the ability to make inferences about the mental states underlying motor behaviour during social interaction.

Eighteen subjects with FMD and 28 matched healthy controls (HC) were given a ToM battery. The severity of FMD was rated by the Simplified-FMD Rating Scale (S-FMDRS). Dissociative symptoms were evaluated by the Dissociative Experiences Scale (DES-II).

FMD scored worse than the HC in most ToM tasks: second-order False Beliefs (p = .005), Faux-Pas Recognition Test (p < .001) and Reading the Mind in the Eyes Test (p = .020); control questions elicited normal scores. The DES-II indicated dissociative-borderline psychopathology and negatively correlated with accuracy on the second-order False Belief (Spearman's rho = -.444; p = .032); the positive correlation between DES-II and severity of motor symptoms (S-FMDRS) approached significance (Spearman's rho test = .392; p = .054). ToM disorders were not correlated with S-FMDRS, due to the typical variability in FMD over time with regard to the severity of symptoms and the district of body involved.

Our results are consistent with the hypothesis that FMD are related to ToM deficits, and future studies are needed to define the specific nature of this relationship.