Impairments in social cognition in early medicated and unmedicated Parkinson disease

Background: Theory of mind (ToM) refers to the ability to infer others' mental states, including intentions and feelings, and is considered to be a critical part of social cognition. Earlier studies in individuals with Parkinson disease (PD) have shown ToM deficits in the more advanced stages of the disease. There is currently no evidence of social cognition deficits in patients in the early stages of PD. Methods: In this study, we compared patients with early PD (n=36) and a control group of healthy subjects (n=36). Patients were assessed with 2 ToM tasks designed to differentially detect subtle deficits in the affective and cognitive aspects of ToM. Patients were also assessed with a complete neuropsychologic battery which included classic executive tests aimed at investigating the relationship between ToM and executive functions. Performance of medicated (n=16) and unmedicated (n=20) patients was also compared. Results: Our results are the first to indicate that ToM is affected in the early stages of PD. As has already been reported in more advanced stages of PD, such deficits seem to be related to the cognitive aspects of this domain. In our study, these deficits were not related with performance on executive functioning, depression, or medication usage. Conclusions: These results provide evidence for ToM impairments early in the course of PD. Recognition of ToM impairments in early PD is important, as these deficits may impact patients' social interactions and quality of life.