Groundbreaking research connects specific brain activities to the facial expressions we make when in pain.
This study suggests that understanding these connections could enhance how pain is assessed in clinical environments, making it possible to read pain levels from patients’ faces with greater accuracy.
Brain Activity Linked to Facial Expressions
Stubbing your toe on a table leg or fracturing your wrist often triggers an automatic wince — and maybe a few choice words. This natural reaction isn’t just about coping with pain; facial expressions serve as powerful signals, communicating the unpleasant sensory and emotional experience to others. They let those around us know we’re hurt and might need help.
Despite their importance, the neural mechanisms behind these nonverbal pain signals have been largely overlooked. Marie-Eve Picard, a doctoral student working under Pierre Rainville — a professor at Université de Montréal’s Faculty of Dentistry and researcher at the Montreal University Institute of Geriatrics Research Centre — set out to explore this fascinating connection.
In a new study, Picard and Rainville show that facial expressions triggered by painful stimuli can be predicted from brain activity. Their findings reveal that the neural mechanisms underlying these expressions are largely distinct from those associated with other manifestations of pain, such as subjective verbal reports of perceived intensity.
Neurobiological Model for Predicting Pain Expressions
Picard and her colleagues developed a neurobiological model that predicts facial expressions elicited by painful stimuli. Using machine-learning algorithms trained on magnetic resonance brain imaging data, they created a Facial Expression Pain Signature.
Healthy volunteers underwent painful thermal stimulation and their facial expressions were measured using the Facial Action Coding System, a standardized tool that analyzes facial movements based on the activity of several groups of facial muscles.
Activation of each muscle group causes a specific change in facial expression. For example, pain-related expressions often include furrowed brows, elevated cheeks, squinting, wrinkled nose, and raised upper lip.
Importance of Facial Expressions in Clinical Pain Assessment
In clinical settings, accurately assessing a patient’s pain is important for appropriate pain management.
“The importance of facial expression in pain assessment receives less attention than the role it plays in social interactions,” said Picard. “However, our results suggest that this behavioral indicator of pain can be a valuable complement to verbal reports of perceived intensity.”
The study was informed by an understanding of pain as multidimensional, meaning that considering its various manifestations can improve assessments of its severity.
Future Research and Implications
Picard’s work shows the existence of brain signatures, or patterns of brain activity, that are predictive of pain-related facial responses. While these results advance our understanding of the brain mechanisms behind pain and nonverbal communication, further research will be needed to test their generalizability and determine their applicability to conditions such as chronic pain.
Reference: “A distributed brain response predicting the facial expression of acute nociceptive pain” by Marie-Eve Picard, Miriam Kunz, Jen-I Chen, Michel-Pierre Coll, Étienne Vachon-Presseau, Tor D Wager and Pierre Rainville, 29 August 2024, eLife.
DOI: 10.7554/eLife.87962.2
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2 Comments
Is this person happy or sad? I’m glad researchers are finally getting a handle on painful emotions. Now, maybe US MDs will have evidence to buck DEA proscriptions.
People with chronic pain usually figure out ways to work around it most of the time – the pain is there, but they don’t respond to it the way a healthy 20 year old with no chronic pain would respond to the same pain. So the relationship of pain to facial expressions is much more complex than this simple and limited study could handle – yes, further research will be needed.