Some animals, like mice and birds, are able to bring their body temperature and metabolism way down to conserve energy, going into a sleep-like state called torpor. Now researchers have identified the brain cells that trigger this state, showing they can activate it on demand. The team was even able to do it in rats, which don’t normally do it at all, suggesting that such a “suspended animation” state might eventually be possible in humans. Torpor seems to have evolved as a survival strategy during times of food scarcity, allowing animals to snooze through cold nights or even entire winters without wasting too much energy keeping their body temperature up. That of course allows them to survive until things warm up again, and food becomes more plentiful. Scientists have toyed with the idea of inducing this kind of hibernation state in humans to reduce the resources and room required for long treks into space. Now researchers at Harvard and the University of Tsukuba in Japan may have made progress towards doing just that. The team started off by studying just how mice regulate their body temperature during torpor. They identified that a set of neurons in the hypothalamus are behind this feat of biology, and named them quiescence-inducing neurons (Q neurons). Next, the researchers tested whether these neurons could be controlled. They found that they could be activated on demand using light signals (optogenetics) or chemical molecules (chemogenetics), and in doing so could induce a torpor state in the mice that lasted for over 48 hours. That’s more than twice as long as mice would naturally stay in torpor. The opposite was also true. When the researchers blocked the activity of Q neurons, the mice were unable to enter a torpor state. The team checked that the extended nap didn’t harm the mice. They observed no changes to their behavior, and no tissue or organ damage, after they woke up. But mice already go into torpor naturally – the real test was whether the state could be induced in animals that don’t normally do it. To that end, the researchers stimulated the same neurons in rats. And sure enough, they also entered a hibernation-like state. The team says that this finding suggests that the Q neuron circuits are conserved in a range of mammals, even those that don’t naturally go into hibernation or torpor. This could include humans – although for now, it’s unknown whether we do have them, let alone whether they could be activated in the same way. If it turns out to be possible though, the researchers say that inducing this kind of suspended animation could be useful for long space voyages, preserving organs for transplant, and for minimizing tissue damage after events like heart attacks. The research is due to be published in two papers in the journal Nature.