Mice may exhibit revival-like behaviors to help unconscious cage mates.
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Li Zhang has anesthetized a lot of mice in his research career.
Several years ago, the University of Southern California neuroscientist began noticing that sometimes, when he placed an anesthetized mouse back in its cage, its cage mate would start acting strangely, sniffing and biting around the unconscious mouse’s face. To Zhang, it almost seemed like the mouse was trying to revive its knocked-out partner with something like first aid.
Such behaviors have been anecdotally observed in other species, like elephants or dolphins who help incapacitated group members. While other mouse researchers have noticed similar behaviors toward unconscious mice, it’s never been closely studied, says Zhang.
Now, he and his colleagues show that unconscious mice elicit a suite of behaviors from cage mates that seem to speed recovery from anesthesia. Oxytocin neurons, which underlie helping behaviors in a range of species, help activate the revival-like behaviors in mice, researchers reported in the journal Science.
“To me, this looks very much like a behavior that’s driven by what I would call the altruistic impulse,” says James Burkett, a neuroscientist at the University of Toledo who wasn’t involved in the study. “We can’t infer just from our observations that these mice have an intention to help. We only know that they’re responding to an animal in need and they perform a behavior that does benefit them.”
Zhang and his colleagues studied this behavior by presenting a mouse with an unconscious cage mate and an active mouse. They found that the subject mouse spent much more time interacting with the unconscious cage mate, exhibiting a consistent set of behaviors that escalated over time.
First, the mouse would just sniff and groom its knocked-out cage mate. But as the mouse remained unresponsive, the subject mouse would start biting its partner’s mouth, and even pulling out its tongue.
“It seems that the mouse can perform, deliberately, this whole set of behaviors,” says Huizhong Whit Tao, a neuroscientist at USC and study co-author. Those behaviors must be instinctual, Whit Tao says, since these mice had never had the occasion to learn, having never encountered an unconscious mouse before. “This is the first time that we’ve reported these kinds of emergency-like responses from animals.”
These emergency-like responses were also directed toward dead mice, for a time, but rarely toward active or even sleeping mice. Mice were also much more likely to spring into action for familiar mice, as opposed to strangers.
“That familiarity bias tells you that the animal’s not responding in a reflexive manner to the stimuli that they’re seeing,” says Burkett. “They’re actually taking into account aspects of the situation and the identity of the animal when they’re forming their response.”
Is the “first aid” truly helping?
All the poking and prodding paid off for the unconscious mice, as it somewhat sped up their recovery from anesthesia. Tongue pulling proved especially powerful, as the researchers found that it expanded the airways of unconscious mice. The team even placed small objects in the unconscious animal’s mouths, which tongue pulling dislodged.
“This was the most surprising part of the study,” says Whit Tao. “Obviously the effects are beneficial.”
Demonstrating that the mice are intending to help is obviously trickier than showing that the unconscious mice are helped, says Peggy Mason, a neuroscientist at the University of Chicago who wasn’t involved in the study.
“If I drop $20, by mistake, on the street and someone else picks it up, that person has been helped, but I have not helped them,” says Mason. “They found a great behavior, I don’t dispute that. I dispute the interpretation of it.”
An alternative interpretation is that mice are simply more curious about an unresponsive mouse plopped into their cage, especially if they know them. To test for this possibility, the researchers repeated their experiment over five days. If curiosity were the driving force, you’d expect the behavior to decrease as time goes on, Whit Tao says, as the novelty wears off.
“However, we saw the opposite,” she says. “There is no reduction in behavior, there’s a little bit of an increase.”
Mason remains unconvinced, suggesting it might take longer to get habituated. Burkett, on the other hand, thinks the researchers have shown this isn’t mere curiosity, especially when taking into account the neurobiological findings of the study.
The researchers found that oxytocin circuits in the brain were crucial in activating the revival-like behaviors. Oxytocin underlies helping behavior in a variety of species, suggesting something similar is at play here, says Burkett. “That was a really well done part of the study showing that this is engaging social behavior networks in the brain,” he says, though he stresses intentionality can’t necessarily be inferred from these results.
Given that the oxytocin circuits that help produce this innate, “first-aid-like” behavior are widespread across the animal kingdom, Zhang and Whit Tao suspect that such behaviors might be widespread too, given their potential benefit.
“That remains to be seen,” says Burkett. Still, the study suggests “that animals are engaging in the emotions and behaviors of others around them in a way that’s much richer than we previously realized.”