Visual and olfactory signals of conspecifics induce emotional contagion in mice

Emotional contagion occurs in many animals, including rodents. To
determine the social signals of emotional state-matching between
individuals in mice, we conducted an empirical laboratory experiment using
visual, olfactory, and auditory stimuli. The Japanese wild-derived mouse
strain MSM/Ms (MSM) was tested as observers, since our initial experiments
indicated that MSM mice showed higher sensitivity to others’ pain compared
to the laboratory strain C57BL/6J (B6). MSM observers were shown footage
of an unfamiliar B6 mouse receiving painful foot shocks via a screen. For
olfactory stimuli, one of the following was presented during observation:
(1) urine collected from a shocked B6 mouse, (2) urine collected from an
unshocked B6 mouse, or (3) reverse osmosis water. Consequently, MSM mice
observing the footage with shocked urine demonstrated significantly higher
fear-induced freezing behaviour than in the other two conditions.
Regarding visual and auditory stimuli, observing the pixelated video clip
was significantly associated with reduced freeze responses, whereas
blocking auditory cues did not affect the duration of freezing. These
results provide clear-cut evidence that multiple cues, including olfactory
and visual information, are sufficient social signals for emotional
contagion of pain in mice.