A New Tool for Quantifying Mouse Facial Expressions.

Area of Science:

• Animal behavior and welfare science
• Neuroscience and affective computing
• Rodent models in biomedical research

Background:

• Facial expressions in animal models are crucial for assessing emotional experiences.
• Previous research linked facial features to positive and negative valence, particularly pain.
• Interpreting these expressions in rodents remains a significant challenge.

Purpose of the Study:

• To identify and validate easily visualizable facial parameters in mice for assessing affective states.
• To correlate specific facial expressions with positive and negative stimuli in freely moving mice.
• To establish a reliable facial expression assay for improving rodent research.

Main Methods:

• Identification of seven key facial parameters (eye, ear, mouth, snout, orientation) in mouse profiles.
• Monitoring facial parameter changes over time in response to gustatory and somatosensory stimuli.
• Analyzing facial expressions in freely moving mice during positive and aversive stimulation.

Main Results:

• Facial parameters effectively captured stimulus-specific response profiles and spontaneous movements.
• Eye opening varied with stimulus valence: increased with palatable tastants/touch, decreased with bitter/painful stimuli.
• Mouse ear posture significantly contributed to conveying emotional information, reflecting habituation and stimulus valence.

Conclusions:

• The developed facial expression assay accurately depicts rodent welfare and affective state in a time-sensitive manner.
• This study is the first to detail rodent facial expressions across various positive valence situations, including affective touch.
• The assay holds potential for mechanistic insights into emotional expression and enhancing the translational value of rodent studies on pain and other states.