Background & Aims

Facial expressions are evolutionarily adaptive for visually communicating an organism’s state to others in its surroundings. Research shows that facial expressions relating to various emotions (e.g., fear) in humans, non-human primates, and other non-human animals are lateralized, with stronger facial expressions of emotion seen on the left side of the face (Lindell, 2013). This is presumably due to the greater involvement of the right hemisphere in cortical processing of emotion. Whether pain expression is similarly lateralized has never been assessed in any species. We sought to investigate whether facial expression of pain as measured by the Mouse Grimace Scale (MGS) is also lateralized, and whether the pain model used, or the location of the pain in the body, alters the lateralization of grimacing (Mogil, Pang, Dutra, & Chambers, 2020).

Methods

Mice were given intraperitoneal injections of acetic acid, unilateral injection of complete Freund’s adjuvant or zymosan into the left or right hind paw, or unilateral injection of carrageenan into the left or right ankle or received a spared nerve injury to the left or right tibial and peroneal nerves (sparing the left or right sural nerve). Subsequently, we video-recorded facial grimacing for 30 min at time points corresponding to maximal presumed pain in these assays. Videos were sampled every 2 minutes to obtain several left- or right-side-only image types. These were: 1) left and right profile images (i.e., side view), 2) symmetrical front-facing images of only the left and only the right half the face (i.e., hemiface), and 3) facial chimeras produced by mirroring hemiface images about the center y-axis (i.e., composite). These images were then blindly scored using the Mouse Grimace Scale (MGS). We hypothesized that the left side of the face would yield higher MGS score

Results

Grimacing was significantly stronger on the right side of the face than on the left for all image types and all pain assays tested. Additionally, pain faces were lateralized to the right side of the face regardless of the location of the pain. That is, non-lateralized visceral pain, left-side pain and right-side pain still showed significantly stronger expression on the right side of the face.

Conclusions

We are currently investigating the underlying neurobiology of grimace asymmetry by unilaterally chemogenetically inhibiting areas associated with pain expression (e.g., central amygdala), as well as assessing if human pain-induced facial grimacing is similarly lateralized.

References

Lindell, A. K. (2013). Continuities in emotion lateralization in human and non-human primates. Frontiers in human neuroscience, 7, 464.

Mogil, J. S., Pang, D. S., Dutra, G. G. S., & Chambers, C. T. (2020). The development and use of facial grimace scales for pain measurement in animals. Neuroscience & Biobehavioral Reviews, 116, 480-493.

Presenting Author

Alicia S. Zumbusch

Poster Authors

Alicia Zumbusch

MSc

McGill University

Lead Author

E-mail

Elodie Nickner

McGill University

Lead Author

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Susana Sotocinal

MSc

McGill

Lead Author

E-mail

Gabriel Firanescu

McGill University

Lead Author

E-mail

Paula Sanchez

McGill University

Lead Author

E-mail

Lilian Yoffe

McGill University

Lead Author

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Janik Falcarek-Hope

McGill University

Lead Author

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Topics

  • Evidence, Clinical Trials, Systematic Review, Guidelines, and Implementation Science