Hibernation wipes out half of brain synapses—but mice remember everything

The dominant model of memory storage holds that learning physically strengthens and enlarges the connections between neurons. Yet these synapses are remarkably dynamic, shifting significantly over short timescales. A team led by neuroscientist Kazumasa Tanaka at the Okinawa Institute of Science and Technology Graduate University sought to understand how stable, long-lasting memories could survive such fluid neural architecture.

An extreme test of memory persistence#

In a recent Science study, Tanaka's team put this question to a dramatic test: they induced a hibernation-like state in mice that disrupted the structure of more than half their synapses. Strikingly, the animals retained their memories despite this wholesale rewiring of their neural hardware. According to Tanaka, when comparing the synaptic landscape between day one and day four or five under normal conditions, "it's very, very different"—so the dormancy experiment represents an accelerated version of the change that naturally occurs.

Engineering hibernation in the lab#

The hibernation response is governed by neural circuits that are preserved across all mammals, including species like mice that never hibernate in nature. In 2020, researchers led by Takeshi Sakurai at the University of Tsukuba developed a technique to artificially activate these circuits by stimulating Q neurons in the hypothalamus, producing what they termed QIH—Q-neuron-induced hypothermia and hypometabolism.

Using this protocol, scientists can cool a mouse's body to approximately 20° Celsius while sharply reducing heart rate and breathing. This induced state sits partway along the hibernation spectrum: bears maintain near-normal body temperature (36–37° Celsius) during hibernation while dramatically cutting metabolism, whereas some ground squirrels plunge into extreme torpor with body temperatures near freezing. The artificial version falls between these extremes, offering a controlled way to study how the brain copes with dramatic metabolic slowdown.