Theory of mind and joint action in Parkinson's disease.

It has been suggested that the Theory of Mind (ToM) may rely on more basic processes of social cognition, such as action control (e.g., joint action), even if little is known about this relationship. The relationship between ToM and joint action can be studied in patients with Parkinson's disease (PD), because they are characterized not only by a deficit in ToM (and in its cognitive and affective subcomponents) but also by a deficit in the inhibition of competing responses. Sixty PD patients and 60 matched healthy controls (HCs) performed a go/no-go Flanker task in both joint and individual conditions. Cognitive (Advanced Test or AT) and affective (Emotion Attribution Task or EAT) ToM also were measured. Thirty-five PD patients and matched HCs also performed the standard Flanker task, as a control measure. In patients, only individuals with high AT scores exhibited a joint Flanker effect, whereas in HCs the joint effect was found irrespectively of AT score. Patients with low EAT scores showed a greater interference effect than patients with high scores, whereas the opposite pattern was found for HCs. In regression analysis AT and EAT scores predicted the Flanker effect in the joint condition only. In the standard task, both groups showed a Flanker effect. The role of different fronto-striatal circuits, especially in PD patients, could explain the different involvement of cognitive and affective ToM in joint tasks. The Flanker effect is discussed considering the referential coding account and the attention-focus account as possible candidates to explain joint action effects.