Abstract
People with Parkinson’s disease (PD) often experience a decrease in their facial expressivity, but little is known about how the coordinated movements across regions of the face are impaired in PD. The face has neurologically independent regions that coordinate to articulate distinct social meanings that others perceive as gestalt expressions, and so understanding how different regions of the face are affected is important. Using the Facial Action Coding System, this study comprehensively measured spontaneous facial expression across 600 frames for a multiple case study of people with PD who were rated as having varying degrees of facial expression deficits, and created correlation matrices for frequency and intensity of produced muscle activations across different areas of the face. Data visualization techniques were used to create temporal and correlational mappings of muscle action in the face at different degrees of facial expressivity. Results showed that as severity of facial expression deficit increased, there was a decrease in number, duration, intensity, and coactivation of facial muscle action. This understanding of how regions of the parkinsonian face move independently and in conjunction with other regions will provide a new focus for future research aiming to model how facial expression in PD relates to disease progression, stigma, and quality of life.
Highlights
Expression of emotion is important in maintaining social relationships that prevent loneliness and foster social support across the lifespan
We found that as severity of facial expression deficit increased, mappings showed a detectable decrease in the number, duration, intensity, and coactivation of muscle movement across the face
Since blinks are always coded at an intensity of one, the only summary statistics reported for that action unit are the percent of frames active and the number of times the person blinked
Summary
Expression of emotion is important in maintaining social relationships that prevent loneliness and foster social support across the lifespan. People, including clinicians, typically form impressions of the face as gestalt emotional expressions, without explicitly recognizing the underlying relationships between the different regions of the face This is reflected in the current clinical measure of facial masking (Item 3.2 of the Movement Disorder Society’s Unified Parkinson’s Disease Rating Scale; MDS-UPDRS) which uses general impressions to classify people with PD as having none, slight, minimal, moderate, or severe facial masking (Goetz et al, 2008). These gestalt impressions are useful heuristics in making impressions of the face Since different regions of the face are motorically and neurally independent, in order to assess how facial masking influences coordinated movement across the face, facial muscle activation needs to be measured with specificity to each individual movement (Rinn, 1984)
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