Putting mice into hibernation causes a major loss of synapses

Scientists have discovered that inducing a hibernation-like state in mice dramatically reduces the number of neural connections in their brains. Surprisingly, despite this significant synaptic pruning, the animals appear to retain previously formed memories, raising fascinating questions about how memory is actually stored and maintained in the brain.

Researchers studying hibernation have found that placing mice into a torpor-like state causes a dramatic reduction in synapses — the connections between brain cells that are widely believed to underpin learning and memory. The scale of synaptic loss was significant enough that scientists expected to see corresponding memory deficits in the animals.

However, the mice appeared to retain memories even after this substantial neural pruning, challenging some long-held assumptions about the relationship between synaptic density and memory storage. The findings suggest that either memories are encoded in ways more resilient than previously understood, or that the brain has mechanisms to rapidly rebuild necessary connections upon waking.

This research could have broader implications for understanding neurological conditions in humans, as well as potential insights into how the brain protects itself during metabolic stress — a topic of growing interest in neuroscience and medicine.

A new study has found that artificially inducing a hibernation-like state in mice leads to a dramatic loss of synaptic connections throughout the brain. Synapses are the junctions through which neurons communicate, and the prevailing view in neuroscience has long held that these connections are the primary physical substrate of memory and learned behavior. The sheer scale of synaptic reduction observed in the hibernating mice was enough to make researchers expect serious cognitive consequences.

What made the findings particularly striking was what did not happen: the mice did not appear to lose memories they had formed before entering their dormant state. Upon emerging from torpor, they could still recall and act on previously learned information, despite having far fewer synaptic connections than when they went under. This disconnect between structural change and cognitive outcome is scientifically surprising and demands explanation.

One possibility is that memories are stored with significant redundancy — encoded across many more synapses than the minimum necessary to retrieve them. Another theory is that the brain may rapidly reconstruct the most important connections after waking, essentially rebuilding a functional memory network from some deeper, more stable blueprint. Researchers are now working to understand which of these mechanisms, or what combination of them, might be responsible.

Why it matters: Understanding how the brain preserves memory through dramatic structural changes could have major implications for treating human neurological conditions. Diseases like Alzheimer's are characterized in part by synaptic loss, and if the brain has natural mechanisms to protect memory even when connections are severely reduced, those processes might eventually be harnessed therapeutically. Similarly, the research touches on questions relevant to anesthesia, coma recovery, and extreme survival medicine.

More broadly, the study nudges neuroscientists to reconsider their models of where and how memories live in the brain. If a brain can lose vast numbers of synapses and still retain coherent memories, the story of memory storage is clearly more complex — and more resilient — than current textbooks suggest.