A new study suggests that memory may be far more resilient than once believed. Researchers found that mice retained learned memories even after more than half of the synapses in the hippocampus disappeared and neuronal activity dropped sharply.
A surprising test of memory resilience
The team, led by scientists at the Okinawa Institute of Science and Technology, used an artificial hibernation-like state called Q-neuron-induced hypometabolism, or QIH, to slow metabolism and lower body temperature in mice. Before that, the animals were trained in two memory tasks: one linked a chamber odor with mild foot shocks, and the other tested spatial learning in a maze.
After about 48 hours in this suspended state, hippocampal firing fell by roughly 70%, while more than half of the synapses in the region vanished. Even so, the mice later showed the same fear response and performed normally in the spatial task.
What stayed intact
Using advanced imaging methods, the researchers found that memory-related synapses were not lost evenly. Those clustered close together along dendrites were more likely to survive, while isolated ones disappeared more often. After recovery, many of the missing connections returned, and about 82% reappeared in the same locations.
This points to a broader idea: memory may depend not only on the strength of individual synapses, but also on the architecture of connected clusters that help preserve information even during major neural remodeling.
Although the experiment was done in mice and does not directly translate to human sleep or disease, it offers a fresh view of how the brain stores information. Published in Science, the findings may guide future research into protecting memory networks and understanding brain resilience.
In the future, this line of research could help shape new strategies for preserving cognition by focusing on the brain's hidden structural patterns.
