Objective: We aimed to evaluate if Parkinson’s disease (PD) patients show decreased micro expressions in spontaneous laughing according to Action Units (AU) activation.

Background: Hypomimia, or reduced facial expression of emotions, is one of the distinct clinical characteristics in PD. It negatively affects their quality of life since hypomimia can lead misunderstanding of patients’ emotions, making them feel socially rejected. It has been reported that voluntary smiling or movement of the lip are impaired in PD patients, however, there is scarce data quantifying the facial expression in triggered smiling or laughing.

Method: 53 PD patients and 19 age-gender matched healthy controls (HC) underwent cross-sectional study. We recorded subjects’ face while they were watching 80-second-long amusing video. The intensity of 17 AU according to the Facial Action Coding System (FACS) was automatically obtained by BioObserver software. The intensity of happiness emotion was also detected. AUs and happiness intensity were calculated every 5 seconds, and the intensity during the funniest part of the video was compared between PD and HC groups. Subjects also underwent a comprehensive neuropsychological evaluation.

Results: There was a significant difference in happiness emotion between PD group and HC group. The activity of the following AUs was significantly reduced in the PD group compared to the HC group: AU10 (Upper lip raiser), AU12 (Lip Corner Puller), AU14 (Dimpler), AU23(Lip tighten), p<0.05.

Conclusion: Hypomimia in PD patients is shown by laughing triggered emotion. This is characterized mainly by reduced activity of the lower face muscles.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/hypomimia-in-triggered-smiling-in-patients-with-parkinsons-disease/