Memories Survive Massive Synapse Loss in Artificial Mice Hibernation

Scientists induced a hibernation-like state (QIH) in mice, slashing hippocampal activity by about 70% and erasing more than half of the synapses, yet the mice still recalled trained tasks. After arousal, most lost synapses reappeared, with engram synapses in tight clusters often preserved and returning to the same dendritic spots, suggesting memories can endure without specific synapses. A long-term anesthesia control impaired memory and destroyed clustered engram synapses, highlighting that the pattern of synapse loss matters. The work implies the brain may reset toward a default network state after hibernation and raises questions about how memories are stored at the circuit level.