A mouse finds its companion unconscious. It sniffs, grooms—and then pries open the companion's mouth with its paws and pulls out the tongue. This is not aggression. This is first aid.
In February 2025, a team of neuroscientists at the University of Southern California (USC) led by Wenjian Sun published a striking finding in *Science*: mice instinctively perform "emergency rescue" behaviors on unconscious companions—from gentle sniffing and grooming to vigorous tongue-pulling to clear the airway. In more than 50% of cases, this "first aid" helped companions regain consciousness faster.
An Accidental Discovery
The most dramatic part of the story: the researchers were not studying altruistic behavior at all. Sun first noticed the behavior incidentally during an unrelated experiment—a mouse repeatedly approaching an anesthetized cage mate, sniffing and licking it, then forcefully pulling its tongue.
"I had never seen this behavior in mice before," Sun said.
A Structured Rescue Sequence
In controlled experiments pairing an anesthetized "patient" with an awake "helper," recorded on high-speed video, the helper's behavior followed a clear escalation:
1. Sniffing — assessing the patient's state, like a medic checking for breathing. 2. Grooming — licking the body, especially the head, like checking vital signs. 3. Forceful intervention — if no response, biting open the mouth and pulling out the tongue—strikingly similar to "opening the airway" in human first aid.
Most convincingly, when researchers placed a harmless plastic ball in the anesthetized mouse's mouth, helpers removed the foreign object in 80% of trials. But if the object was placed elsewhere (e.g., the genital area), helpers ignored it entirely. The mice were targeting the airway—not playing or acting out of curiosity.
Rescuing Familiars Only
Helpers rescued familiar cage mates almost immediately, with greater intensity and duration. Toward unfamiliar mice, they approached and sniffed but showed weakened rescue behavior. Sleeping or active mice received no special treatment. Mice can distinguish "needs help" from "doesn't need help"—and help friends far more readily than strangers.
What Happens in the Brain: A Dual Oxytocin Pathway
The USC team used optogenetics and calcium imaging to show that the medial amygdala, a key region for social behavior, is strongly activated during rescue.
A follow-up study published in *PNAS* in April 2025 by Hui Li's team (Institute of Psychology, Chinese Academy of Sciences) and Zoufeng Chen's team (Shenzhen Medical Academy of Research and Translation) revealed how oxytocin coordinates rescue via two parallel pathways:
- The central amygdala pathway — "feeling distress." When a helper detects distress signals, oxytocin neurons in the hypothalamic paraventricular nucleus release oxytocin into the central amygdala, decoding the emotional meaning: "something bad happened to my companion."
- The dorsal bed nucleus of the stria terminalis pathway — "taking action." Simultaneously, oxytocin released into this region drives the concrete rescue actions—licking, grooming, tongue-pulling.
Helping Others Helps Yourself
Helpers' stress hormone (corticosterone) rose during rescue and dropped once the companion recovered. Helping relieves the helper's own distress. This is not the tragic, self-sacrificing version of altruism—it is a subtle, sustainable reciprocity: see distress, feel anxious, act, recover together.
From an evolutionary standpoint, this makes complete sense. Individuals wired to feel anxious at a companion's distress—and to act on it—survived better in groups. The seed of altruism may not be planted in morality, but in anxiety.
The Evolutionary Lineage of First Aid
Dolphins push sick companions to the surface to breathe; elephants support injured peers with their trunks; chimpanzees lick wounds. But those animals have large, complex brains. Mice do not. If even mice perform first aid, this behavior's evolutionary roots may run far deeper—back to the common ancestor of all mammals.
This implies altruism may not be a product of "higher intelligence" but a basic mammalian configuration—written into our lowest-level biological code, like heartbeat and breathing.
Should We Anthropomorphize?
The researchers caution against over-anthropomorphizing: the mice's rescue behavior may be instinct-driven, not a conscious decision. But the same oxytocin systems, amygdala responses, and corticosterone fluctuations that we call "empathy," "anxiety," and "relief" in humans operate through the same molecules and brain regions in mice. Perhaps the truth is not "mice are like humans," but "humans are also mammals." Our altruism is not a civilizational miracle—it is an instinct inherited from mammalian ancestors over 100 million years ago, merely wrapped in more refined packaging by language, culture, and moral philosophy.
Epilogue
A mouse weighing less than 30 grams pries open its companion's mouth and pulls out its tongue. It knows nothing of CPR, airway obstruction, or the golden four minutes. It only knows: my companion is not moving, this makes me uneasy, I must do something.
That impulse to "do something" may be the starting point of all altruistic behavior—from a mouse's tongue-pull, to dialing emergency services, to international rescue teams heading for disaster zones. The scale differs; the underlying code may be the same.
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References: 1. Sun, W. et al. "Reviving-like prosocial behavior in response to unconscious or dead conspecifics in rodents." *Science* (2025). DOI: 10.1126/science.adq2677 2. Zhang, F.-R. et al. "Distinct oxytocin signaling pathways synergistically mediate rescue-like behavior in mice." *PNAS* (2025). DOI: 10.1073/pnas.2423374122