Researchers induced a hibernation-like state in mice and found that it eliminated more than half of their synapses, yet the animals retained learned memories. The result challenges the simple idea that memories are stored solely in the strength or physical size of individual synaptic connections, and may help explain how long-term memories survive despite continual neural change.

The artificial state, called Q-neuron-induced hypothermia and hypometabolism, lowered mice’s body temperature to about 20°C for 48 hours and reduced brain activity by roughly 70%. Mice still performed normally in contextual fear-conditioning and maze-navigation tests after waking, although both tasks depend on the hippocampus; damaging that region after training erased the memories. Imaging showed that synapses later recovered, but the study suggests memory information may be distributed or preserved in ways not captured by individual connections alone.