Objective: The aim of this study was to investigate emotional facial muscle responses in Huntington’s Disease (HD). We examined induced experience-related responses when viewing emotional scenes, as well as facial mimicry responses when viewing emotional facial expressions.

Background: Deficits in emotion processing, such as impaired facial emotion recognition and altered subjective emotional experience, are frequently reported in HD. Facial expressions are an important part of emotion processing that has received little attention, despite the motor symptoms characterizing HD. Facial expressions of emotion reveal spontaneous responses to emotional stimuli, providing a key insight into a person’s emotional experience. Furthermore, facial expressions play a crucial role in social communication. For example, the spontaneous mimicry of other people’s expressions has been suggested to serve social functions.

Methods: We tested a HD participant group (N=23) and a healthy age-matched control group (N=25) and used electromyography (EMG) to measure the activity of five facial muscles in two tasks; a face task and a picture task. Each muscle was predominantly associated with one of four emotions: anger, disgust, fear and happiness. Emotional responses were defined as stronger EMG activity associated with emotional compared to neutral stimuli.

Results: We found significant group differences for disgust and happiness. The HD group lacked emotional responses of the levator labii muscle when viewing disgusting scenes. However, facial mimicry of disgust remained intact. By contrast, the HD group showed intact responses of the zygomaticus major muscle and the orbicularis oculi muscle to happy scenes, but lacked mimicry of happy facial expressions.

Conclusions: The observed effects do not appear to be caused by a motor deficit, as muscle responses were reduced only in one of two tasks for each affected emotion. Reduced disgust responses in the picture task, in spite of intact disgust mimicry in the face task, might reflect a reduced subjective disgust experience in HD. Reduced happiness mimicry, in combination with intact experience-related happiness responses, suggests a specific social-emotional impairment. Happiness mimicry is assumed to serve an affiliative function in social relationships; accordingly, our finding has implications for the understanding of difficulties that HD patients experience in their social lives.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/emotional-facial-emg-responses-are-affected-in-huntingtons-disease/