Facial feedback effect explains the autonomic impairment in PD for emotional recognition

Parkinson’s Disease (PD) is a degenerative neurological disorder of the central nervous system with a strong impact on both social and emotional level. Parkinson patients typically present with emotional processing impairment in emotional experience and emotion recognition. However, it is not yet known whether these patients have lost the capability to feel the emotions intrinsically, to modulate to emotional experience associating subjective response with physiological modulations, or to decipher emotions in others. The present research aims at investigating the contribution of central, peripheral and facial feedback measures in PD patients when they processed emotional cues using a multilevel approach, comparting selfreport (appraisal), autonomic (Skin Conductance Response, SCR) and motor electromyographic (EMG zygomaticus and corrugators facial muscles) measures. The integration of these measures allowed firstly a direct comparison between the explicit appraisal of emotions (with specific reference to the two parameters of valence and arousal) and the autonomic responsiveness to emotions. Secondly the role of EMG (zygomaticus and corrugators muscle) in determining the central and peripheral modulation was explored. Indeed the facial feedback model supposed that the autonomic facial response by facial muscles may affect both the emotional appraisal and the physiological modulation. 20 patients have been selected and 34 healthy volunteers (HC), matched for age and education. PD patients observed and evaluated affective pictures that were chosen from International Affective Picture System (IAPS). These pictures concerned four types of stimuli: 10 pleasant – low and high arousal; 10 unpleasant – low and high arousal, 5 neutral. PD patients seemed to not adequately answer to the emotional categories which were considered salient in standard conditions (HC). Indeed, there was an autonomic impairment for a category- specific emotion (negative and high arousal). Particularly, patients have revealed an inadequate sensibility (reduced SCR) only for negative emotional condition. In parallel EMG behavior was disrupted (reduced corrugators activity) in response to negative high arousal emotional cues. However, PD patients were able to correctly categorize the emotional cues based on their valence/arousal, probably due to a “gap” between this central process and the autonomic system activity. Then, the regression analysis pointed out the predictive role of the corrugators activity to explain the impaired autonomic response: a reduced corrugators mimic was linked to a reduced peripheral responsiveness toward the negative and high arousal emotional stimuli.