A study published in Science found that a brief hibernation-like state in mice eliminated more than half of their synapses while the animals retained memories.

Memory is thought to reside in the strength of synaptic connections, which are plastic and change over days.

Neuroscientist Kazumasa Tanaka and colleagues at the Okinawa Institute of Science and Technology induced artificial hibernation by activating Q neurons in the hypothalamus, lowering body temperature to about 20°C for 48 hours.

Electrophysiological recordings showed neuronal activity fell by roughly 70 percent during the state.

Electron microscopy of hippocampal tissue revealed loss of more than 50 percent of synapses, including both random connections and engram synapses.

Despite the extensive synaptic loss, mice performed equally well on contextual fear conditioning and a plus‑maze reward task after awakening.

Place cell firing patterns and a decoder that read population activity reproduced locations with the same accuracy as before the hibernation.

Further analysis using eGRASP showed that engram synapses located in tight clusters were preserved, while solitary engram synapses were eliminated.

A control group subjected to prolonged anesthesia and a drug that blocks synapse growth also lost many synapses and exhibited impaired fear memory, indicating that clustering may protect memory traces.

The authors noted that they cannot selectively manipulate synapse clustering to test causality, describing the work as associative rather than causal.

They also reported that brief hibernation suppressed the development of epilepsy in an epileptic mouse model, suggesting a return to a default network state.

The researchers cautioned that safety and ethical considerations will be needed before applying the approach to humans, and that future work will involve larger mammals such as rats or monkeys.

Long‑term studies are required to determine whether artificial hibernation can reliably preserve brain function in complex organisms.