Grimace Scale Scoring
Automated pain assessment via facial action units, replacing hours of manual video scoring with real-time, objective pain quantification.
What It Measures
Key Metrics
Composite Pain Score
Weighted composite of all facial action units scored 0 (not present), 1 (moderate), or 2 (obvious).
Individual Action Units
Each facial action unit scored independently: orbital tightening, nose bulge, cheek bulge, ear position, whisker change.
Temporal Pain Profile
Pain score tracked across time to capture onset, peak, and resolution of analgesic response.
Inter-rater Agreement
Automated vs. human expert agreement measured via Intraclass Correlation Coefficient.
Validated Grimace Scales
Validated Scales
| Species | Scale Name | Action Units | Status | Reference |
|---|---|---|---|---|
| Mouse | Mouse Grimace Scale (MGS) | Orbital tightening, nose bulge, cheek bulge, ear position, whisker change | Development | Langford et al., 2010. Nat Methods 7(6):447-449. |
| Rat | Rat Grimace Scale (RGS) | Orbital tightening, nose/cheek flattening, ear changes, whisker changes | Development | Sotocinal et al., 2011. Mol Pain 7:55. |
| Cat | Feline Grimace Scale (FGS) | Ear position, orbital tightening, muzzle tension, whisker change, head position | Research | Evangelista et al., 2019. Sci Rep 9:19128. |
| Horse | Horse Grimace Scale (HGS) | Stiffly backward ears, orbital tightening, tension above eye, prominent strained chewing muscles, mouth strained, strained nostrils, flattening of profile | Research | Dalla Costa et al., 2014. PLoS One 9(3):e92281. |
| Sheep | Sheep Pain Facial Expression Scale (SPFES) | Orbital tightening, cheek tightening, lip/jaw profile, ear position, nostril/philtrum shape | Research | McLennan et al., 2016. Appl Anim Behav Sci 181:132-140. |
From Video to Pain Score
Processing Pipeline
Face Detection
Locate the animal face in each video frame using a species-specific detection model.
Landmark Extraction
Identify key facial landmarks: eyes, ears, nose, whiskers, mouth corners.
Action Unit Scoring
Score each facial action unit (0, 1, or 2) using a trained classification network.
Composite Pain Score
Compute the weighted mean across all action units for a single pain score per frame.
Temporal Aggregation
Aggregate frame-level scores into session-level statistics: mean, peak, area under curve.
Published Benchmarks
Published Benchmarks
Research Applications
Research Applications
Analgesic Drug Testing
Quantify pain relief efficacy in pre-clinical drug trials. Automated scoring enables higher throughput and reduced observer bias.
Surgical Pain Monitoring
Continuous post-operative pain assessment to optimize recovery protocols and humane endpoints.
Chronic Pain Models
Track pain progression and resolution in neuropathic, inflammatory, and cancer pain models over weeks.
Welfare Auditing
Cage-side monitoring for institutional animal care committees (IACUC) and regulatory compliance.
Equipment Requirements
Equipment Requirements
Camera
- Standard cage-side USB or IP camera (720p minimum, 1080p recommended)
- Frame rate: 15 fps minimum for temporal scoring
- IR illumination for dark-phase recording
Compute
- GPU: NVIDIA RTX 3060 or better for real-time inference
- CPU-only mode available for batch processing (slower)
- 8 GB RAM minimum, 16 GB recommended
Integration
- Compatible with ConductVision Behavior video pipeline
- RTSP/USB camera input or pre-recorded video files (MP4, AVI)
- Export: CSV, JSON, or direct ConductVision database
References
Citations
- Langford DJ, et al. Coding of facial expressions of pain in the laboratory mouse. Nat Methods. 2010;7(6):447-449.
- Sotocinal SG, et al. The Rat Grimace Scale: a partially automated method for quantifying pain in the laboratory rat via facial expressions. Mol Pain. 2011;7:55.
- Evangelista MC, et al. Facial expressions of pain in cats: the development and validation of a Feline Grimace Scale. Sci Rep. 2019;9:19128.
- Dalla Costa E, et al. Development of the Horse Grimace Scale (HGS) as a pain assessment tool in horses undergoing routine castration. PLoS One. 2014;9(3):e92281.
- McLennan KM, et al. Development of a facial expression scale using footrot and mastitis as models of pain in sheep. Appl Anim Behav Sci. 2016;181:132-140.
Partner with us on welfare assessment research
We collaborate with labs and institutions to develop and validate automated welfare scoring tools.
