Memories can survive even after the brain temporarily loses more than half of its synaptic connections, according to a new mouse study, which challenges the long-held view that long-term memories depend on stable individual synapses. Instead, the findings suggest that memory is preserved by resilient patterns of neural architecture that enable the brain to rebuild its circuitry while retaining stored information. Long-term memory depends on lasting changes in the brain and has been thought to depend on strengthened connections between neurons. However, research has shown that these synaptic changes and the neural patterns associated with memories can be surprisingly unstable over time, raising unanswered questions about how memories persist despite constant remodeling of the brain. This suggests that memory relies not on preserving individual synaptic connections, but on maintaining broader patterns of neural organization.
Here, Yu-Ju Lin and colleagues used a mouse model of artificial hibernation to examine structural mechanisms underlying memory retention. According to the authors, hibernating mammals provide a unique opportunity to study this process, as their brains undergo dramatic reductions in activity and structural changes during dormancy while retaining memories upon waking. Through brain structure imaging and analysis as well as behavioral tests, Lin et al. found that even after hippocampal activity dropped by about 70% and more than half of synapses were eliminated during artificial hibernation, the animals retained memories and recovered their original neural organization after returning to normal conditions. The finding indicates that memory may be preserved not through individual synapses, but through resilient patterns of neural architecture, including specific clusters of connected synapses that remain protected during widespread hibernation-associated brain remodeling. These preserved structural motifs may act as a "core memory trace," allowing the brain to rebuild functional networks after major disruptions while maintaining stored memories.
