Theory of mind in Parkinson's disease: A meta-analysis

Non-motor symptoms of Parkinson's disease (PD) include cognitive deficits and impairment in the recognition of emotions. Recently, a number of studies have investigated theory of mind (ToM) deficits in PD. In this meta-analysis of 18 studies, the ToM performance of 487 non-demented individuals with Parkinson's disease (PD) was compared with 459 healthy controls. Meta-regression analyses were conducted to investigate the relationship between ToM deficits and demographical and clinical features in PD, including medication, stage of the illness and neurocognition. PD was associated with significant ToM impairment (d = 0.83) in both verbal and visual tasks. In individual task analyses, PD patients performed worse than controls in both faux pas recognition (d = 0.55) and reading the mind from the eyes (d = 0.67) tests. Severity of ToM impairment was significantly associated with cognitive impairment. Impairments in social cognitive abilities, including ToM, may be important contributors to the functional impairments observed in PD.