Mental representation of the body in action in Parkinson’s disease

Abstract Mixed fndings characterize studies in Parkinson’s disease (PD): some studies indicate a relationship between physical impairments and the ability to mentally represent the body, while others suggest spared abilities for this cognitive function. To clarify the matter, in the present study we explored the mental representations of the body in action in the same PD patients, taking also into account lateralization of symptoms and visual imagery skills. 10 PD patients with left- (lPD), 10 with right (rPD) lateralized symptoms (lPD), and 20 matched healthy controls have been recruited for the study. All patients were screened for neuropsychological impairments. To explore a more implicit component we used the hand laterality task (HLT), while the mental motor chronometry (MMC) was used to explore a more explicit one. Two control tasks, with objects instead of body parts, were administered to control for visual imagery skills. In the HLT, we detected the efects of biomechanical constraints efects in both controls and PD patients. In the latter group, importantly, this was true independently from lateralization of symptoms. In the MMC, we found the expected positive correlation between executed and imagined movements for both hands in controls only, while all PD patients, again independently form lateralization, only showed this efect for the left hand. In terms of visual imagery, only rPD patients difered from controls when asked to implicitly rotate letters, and in terms of accuracy only. However, this diference is explained by executive functions measured through the neuropsychological assessment rather than by a “pure” visual imagery impairment. In summary, our fndings suggest that two diferent aspects of the mental representations of the body in action, one more implicit and the other more explicit, can be diferently afected by PD. These impairments are unlikely explained by a basic visual imagery defcit. When present, impairments concern a higher dimension, related to motor functions and awareness, and not driven by sensory impairments, as shown by the independence of efects from physical laterality of symptoms.