Researchers found that inducing a hibernation-like state in mice erases over half of their synapses, yet the animals' memories remain intact.
Key facts
- •The hibernation-like state, called QIH, reduced neuronal firing activity in mice by approximately 70 percent.
- •Mice performed normally on memory tasks despite the loss of more than half of their synapses.
- •Engram synapses organized in tight spatial clusters were preserved during hibernation, while isolated ones were eliminated.
- •A third of the surviving clustered engram synapses were attached to multisynaptic boutons, a rare neural structure.
- •The team found that artificial hibernation suppressed the development of epilepsy in a mouse model.
A team led by neuroscientist Kazumasa Tanaka at the Okinawa Institute of Science and Technology induced a hibernation-like state in mice, resulting in the loss of more than half of their synapses. Despite this significant reduction in synaptic connections, the mice retained memories from prior training tasks. The study, published in Science, suggests that memory storage may rely on broader neural architecture rather than individual synapses.
By the numbers
Inducing Artificial Hibernation
The researchers utilized a technique developed in 2020 by Takeshi Sakurai to activate Q neurons in the hypothalamus, triggering a state known as Q-neuron-induced hypothermia and hypometabolism (QIH). During this 48-hour state, the mice experienced a drop in body temperature to approximately 20° Celsius, alongside significant decreases in heart and breathing rates.
Synaptic Preservation and Memory
While hibernation eradicated over 50 percent of synapses, the mice performed as well as non-hibernating controls on contextual fear conditioning and maze navigation tasks. Brain imaging revealed that 82 percent of the vanished synapses reappeared at their original locations after the mice woke up. Specifically, engram synapses—those connecting memory-storing neurons—were preserved when arranged in tight spatial clusters, often associated with rare multisynaptic boutons.
Implications for Brain States
The study suggests that the brain may return to a default network state after hibernation. In unpublished observations, the researchers found that inducing artificial hibernation in mice prone to epilepsy completely suppressed the development of seizures, hinting that the process might reset the brain to a baseline configuration.
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This article was independently rewritten by ManyPress editorial AI from reporting originally published by Ars Technica.
