Whether you stub your little toe on the corner of a table or break your wrist, you’re likely to wince in pain (and quite possibly swear).
This is only natural, with facial expression playing a central role in communicating this unpleasant sensory and emotional experience. For example, it allows us to let people around us know that we are in pain and that we might need help.
The neural processes associated with this non-verbal manifestation remain little studied, although they are considered an important vector of the experience of pain. It is for this reason that Marie-Eve Picard, doctoral student in the laboratory of Pierre Rainville, professor at the Faculty of Dentistry of the University of Montreal and researcher at the Research Center of the University Institute of geriatrics of Montreal.
In a new study, these scientists have shown that it is possible to predict facial expression caused by painful stimulation from brain activity. Specifically, their results reveal that the neural mechanisms linked to the facial expression of pain are partially distinct from those associated with other pain manifestations, such as subjective verbal reports of perceived intensity.
Facial muscles analyzed
Marie-Eve Picard
Credit: Courtesy
Marie-Eve Picard and her colleagues have designed a neurobiological model that can predict facial expression caused by painful stimulation. This brain signature was developed using machine learning algorithms powered by magnetic resonance brain imaging data.
To achieve this, a painful thermal stimulus was applied to healthy volunteers and facial expression was measured using the Facial Action Coding System. This standardized tool dissects facial movements based on the possible movements of several groups of facial muscles.
Activation of each group results in a distinctive change in facial expression. In the case of the physical expression of pain, we see, for example, a lowering of the eyebrows, a raising of the cheeks, a wrinkling of the eyes and nose and a raising of the upper lip.
For a more precise assessment
This study highlights the existence of a cerebral representation predictive of facial responses related to pain. “The importance of facial expression in pain assessment is often downplayed compared to the role that facial expression plays in social interactions. However, according to our results, this behavioral measure in the experience of pain would be complementary to verbal reports of perceived intensity,” explains Marie-Eve Picard.
In a clinical context, continues the doctoral student, it is important to accurately assess patients’ pain in order to then manage it adequately. This research is therefore based on the conviction that pain is multidimensional and that it is beneficial to take into account its different manifestations to better determine its severity.
If these results deepen knowledge on the brain mechanisms of pain and non-verbal communication, future research must be carried out to test their generalizability, such as their application to chronic pain contexts for example.
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