This month, Arctic ground squirrels emerge in Alaska after eight months’ hibernation. It hasn’t been easy: during hibernation, their body temperature can drop as low as -2.9C, a record for mammals, and stay there for two to three weeks before they undergo a bout of shivering to warm up. Scientists are scrutinising this mechanism to see how temperature management can help humans to recover from cardiac arrests and strokes.

“We and others have identified at least one mechanism that the [squirrel] brain uses to control this onset of hibernation,” says Professor Kelly Drew, who studies hibernation biology at the University of Alaska Fairbanks. “That mechanism has potential to guide development of drugs that uses the same mechanism to cool people.”

In energy-saving mode, the squirrels’ metabolism becomes more thrifty. Not only is body weight lost but the animals also lose synapses in their brains, junctions over which signals are sent between neurons. Yet, intriguingly, this loss is reversible. “Synapses sprout when the animals re-warm. Indeed animals learn better after they come out of hibernation,” she says.

What’s more, “tau” proteins in the neurons of their brains are modified by a process called hyperphosphorylation. In humans, this has been found to trigger a tangling of such proteins in the neurons – a hallmark of Alzheimer’s disease. “Remarkably this hyperphosphorylation reverses without forming tangles when the hibernating animals rewarm,” she says. Understanding these processes could provide clues to reversing neurodegeneration in humans.

We are only just waking up to the possibilities …