I spy with my little eye: The detection of changes in emotional faces and the influence of facial feedback in Parkinson's disease.

BACKGROUND Parkinson's disease (PD) is a progressive neurodegenerative disorder that affects the motor system but also involves deficits in emotional processing such as facial emotion recognition. In healthy participants, it has been shown that facial mimicry, the automatic imitation of perceived facial expressions, facilitates the interpretation of the emotional states of our counterpart. In PD patients, recent studies revealed reduced facial mimicry and consequently reduced facial feedback, suggesting that this reduction might contribute to the prominent emotion recognition deficits found in PD. METHODS We investigate the influence of facial mimicry on facial emotion recognition. Twenty PD patients and 20 healthy controls (HC) underwent a classical facial mimicry manipulation (holding a pen with the lips, teeth or non-dominant hand) while performing an emotional change detection task with faces. RESULTS As expected, emotion recognition was significantly influenced by facial mimicry manipulation in HC further supporting the hypothesis of facial feedback and the related theory of embodied simulation. Importantly, patients with PD generally and independent from the facial mimicry manipulation were impaired in their ability to detected emotion changes. Our data further show that PD patients facial emotional recognition abilities are completely unaffected by mimicry manipulation, assuming that PD patients cannot profit from an artificial modulation of the already impaired facial feedback. CONCLUSIONS These findings suggest that it is not the hypomimia and the absence of the facial feedback per se, but a disruption of the facial feedback loop, which leads to the prominent emotion recognition deficit in PD patients