Are non-literal language comprehension deficits related to a theory of mind deficit in Parkinson's disease?

Abstract

Theory of mind (TOM), i.e. the capacity to attribute mental states to oneself and others, would be impaired in Parkinson's disease (PD). Nonliteral language (NLL) comprehension would also be impaired in this disease. The goal of this study was to verify the presence of an association between the TOM and NLL comprehension deficits. We assessed 15 individuals in the early stages of PD and 17 healthy controls (HC), comparable on gender, age and education. Each subject completed a TOM evaluation task and a NLL task (i.e. metaphor comprehension). They also completed executive functioning (mental flexibility, inhibition and working memory) evaluation tasks. Our results showed that patients with PD had significant difficulties in the TOM and NLL comprehension tasks compared to HC participants. A significant relationship was found between TOM and NLL comprehension results. Moreover, NLL scores were associated with a task evaluating mental flexibility. Thus, PD might cause both TOM and NLL comprehension deficit even in the early stages of the disease. Our results showed that there would be a close relationship between TOM and NLL in people with PD.