Unaltered emotional experience in Parkinson's disease: Pupillometry and behavioral evidence

Recognizing emotions in others is a pivotal part of socioemotional functioning and plays a central role in social interactions. It has been shown that individuals suffering from Parkinson's disease (PD) are less accurate at identifying basic emotions such as fear, sadness, and happiness; however, previous studies have predominantly assessed emotion processing using unimodal stimuli (e.g., pictures) that do not reflect the complexity of real-world processing demands. Dynamic, naturalistic stimuli (e.g., movies) have been shown to elicit stronger subjective emotional experiences than unimodal stimuli and can facilitate emotion recognition.

In this experiment, pupil measurements of PD patients and matched healthy controls (HC) were recorded while they watched short film clips. Participants' task was to identify the emotion elicited by each clip and rate the intensity of their emotional response. We explored (a) how PD affects subjective emotional experience in response to dynamic, ecologically valid film stimuli, and (b) whether there are PD-related changes in pupillary response, which may contribute to the differences in emotion processing reported in the literature.

Behavioral results showed that identification of the felt emotion as well as perceived intensity varies by emotion, but no significant group effect was found. Pupil measurements revealed differences in dilation depending on the emotion evoked by the film clips (happy, tender, sadness, fear, and neutral) for both groups.

Our results suggest that differences in emotional response may be negligible when PD patients and healthy controls are presented with dynamic, ecologically valid emotional stimuli. Given the limited data available on pupil response in PD, this study provides new evidence to suggest that the PD-related deficits in emotion processing reported in the literature may not translate to real-world differences in physiological or subjective emotion processing in early-stage PD patients.