How can rats smile? - briefly
Rats produce a smile-like expression by pulling their whiskers back and relaxing the muscles around the mouth, creating a subtle upward curve. This behavior signals contentment and is observed in social and comfortable contexts.
How can rats smile? - in detail
Rats possess a set of facial muscles that can produce a slight upward curvature of the mouth, a movement often interpreted by humans as a grin. Electromyographic studies have identified activation of the zygomaticus major and levator labii superioris muscles during positive social interactions, such as grooming or play. This muscular pattern is accompanied by changes in whisker positioning and ear orientation, creating a recognizable expression.
When rats encounter rewarding stimuli—food, social contact, or novel objects—they display the following physiological and behavioral markers:
- Rapid, low‑amplitude whisker forward thrusts
- Slight elevation of the labial margin
- Increased ultrasonic vocalizations in the 50 kHz range
- Reduced cortisol levels measured in blood samples
Neurobiological research links these responses to dopaminergic pathways in the nucleus accumbens and to oxytocin release in the amygdala. Functional imaging in awake rodents shows heightened activity in the facial motor cortex during the expression, confirming a central control mechanism rather than a reflexive twitch.
Experimental protocols for observing the phenomenon typically involve:
- Baseline video recording of the animal in a neutral environment.
- Introduction of a positive stimulus (e.g., a preferred food pellet).
- High‑speed camera capture of facial movements synchronized with audio recordings of ultrasonic calls.
- Surface electromyography to quantify muscle activation.
- Post‑session analysis comparing frequency and amplitude of the mouth curvature against control conditions.
The combined data indicate that rats can produce a facial expression analogous to a smile, driven by specific muscular actions and reinforced by reward circuitry. This expression serves as a communicative signal within rat colonies, facilitating affiliative behavior and reducing aggression.