Parkinson's disease (PD) affects millions of people worldwide. It's a progressive disease that affects the brain and impacts a person's ability to control their movements. As a result, many everyday activities become a struggle, including walking, taking care of oneself, and communicating. Facial expressions are affected as well. In fact, a mask-like facial expression is one of the early symptoms of Parkinson's disease. But what is the relation between these changes in facial expressions and the severity of PD? 

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The role of facial expressions in emotion

Facial expressions are essential in communication and social interactions. Not only do we use them to express our feelings, but they also play a role in reading and sharing emotions. That's because we have subtle feedback mechanisms that mimic others' expressions, which helps us to understand each other. As a result, people with impaired facial expressions may be misunderstood or unable to share their experiences with another person. 

How Parkinson's disease affects the face

An important symptom of Parkinson's disease (PD) is impaired motor ability, which affects facial muscles and expressions as well. Research has shown that people with PD have slower and less pronounced facial movements. Also, their facial muscles may react more strongly to negative emotions (like anger or sadness) compared to more positive ones.

Facial expression analysis during a phonation test

How can we better understand the link between these changes in facial expression and the severity of Parkinson's disease? That's what researcher Yang and their team aimed to find out. 

They studied two groups of participants during a phonation test, which involves sounding out different vowels and consonants. Specifically, they included a single-syllable, double-syllable, and multi-syllable test. 

Earlier research from this group showed that these tests are good indicators of stiffness in the face. Using FaceReader for facial expression analysis, they observed muscle group movements and facial expressions for neutral feelings, happiness, sadness, anger, surprise, fear, disgust, valence, and arousal.

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Comparing PD patients with healthy controls

To study the link between disease severity and facial expressions, the research team compared performance on the phonation test between a patient group and a healthy control group.

Their study included 16 patients with Parkinson's disease (average age of 71.38 years) and a matched control group of 16 participants (average age of 66.69 years). For the patient group, the researchers noted disease duration and dosage of anti-PD drugs. Furthermore, they included measures of disease severity from a neurology evaluation, using the Hoehn-Yahr scale (H&Y) and the Unified Parkinson's Disease Rating Scale (UPDRS III).

Parkinson's disease, face changes, and severity of disease

Consistent with earlier research, the team found that patients with PD showed decreased expressions for neutral feelings, happiness, surprise, valence, and arousal. The patient group also showed increased facial expressions of sadness, anger, fear, and disgust. These results applied to all variations of the phonation test.

Furthermore, the researchers found significant correlations between disease severity and facial expressions. In other words, when severity increased, all changes in facial expressions were more pronounced. According to the team, these results suggest that patients with PD may show dull expressions in the middle and late stages of the disease.

Parkinson research

When we know more about how specific symptoms progress with disease severity, we'll know better how to help people who are dealing with Parkinson's disease. And that's why Parkinson research is so important. As there is no cure for PD, we need to keep developing and refining the best type of treatment.

Reference

Yang, L.; Chen, X.; Guo, Q.; Zhang, J.; Luo, M.; Chen, Y.; Zou, X.; Xu, F. (2022). Changes in facial expressions in patients with Parkinson’s disease. Computer Speech & Language, 72(3), https://doi.org/10.1016/j.csl.2021.101286.