Advanced Theory of Mind in patients at early stage of Parkinson's disease

Advanced Theory of Mind (ToM) refers to the sophisticated ability to infer other people's thoughts, intentions, or emotions in social situations. With appropriate advanced ToM, one can behave well in social interactions and can understand the intention of others' behavior. Prefrontal cortex plays a vital role in this ability, as shown in functional brain imaging and lesion studies. Considering the primary neuropathology of Parkinson's disease (PD) involving the frontal lobe system, patients with PD are expected to exhibit deficits in advanced ToM. However, few studies on this issue have been explored, and whether advanced ToM is independent of executive functions remains uncertain. Thirty-nine early non-demented PD patients and 40 normal control subjects were included. Both groups were matched in age, level of education, and verbal intelligence quotient. Each participant received advanced ToM, executive functions, and verbal intelligence quotient tests. We discovered that the performance of the PD patients on the Cartoon ToM task was significantly poorer than that of their normal counterparts. Correlation analysis revealed that performance scores of advanced ToM in PD patients were significantly associated with their executive functions scores; however, this is not the case for normal controls. We conclude that dysfunction of advanced ToM develops in early PD patients, who require more cognitive abilities than their normal counterparts to generate advanced ToM. Our findings might be helpful in developing educational and medical care programs for PD patients in the future.