Mirror Perception in Mice: Preference For and Stress Reduction by Mirrors

The amount of time mice spent in a compartment with either a mirror or an opaque screen was measured and mice stayed longer in the compartment with the mirror. This finding suggests that mice prefer mirrors. They also showed a preference for the mirror over unfamiliar live mice but did not show a differential preference for the mirror over a familiar live mouse (cage mate). Restraint stress caused hyperthermia (known as stress-induced hyperthermia) in the mice. When cage mates received the restraint stress together, the hyperthermia was reduced. Placement of mirrors instead of the cage mates also showed stress-reducing effects, while restraint with unfamiliar mice did not reduce the hyperthermia. These results suggest that mirrors have familiar cage mate-like social effects in mice.