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Induced Hibernation in Mice Causes Significant Synapse Loss While Preserving Memory
Key points
- Mice induced into hibernation lost over 50% of their synapses.
- Despite synapse loss, the mice retained their memories.
- This challenges the hypothesis that memories rely on stable synaptic connections.
- Hibernation was induced by activating Q neurons in the hypothalamus.
Synaptic Plasticity and Memory Storage
The prevailing theory for memory storage posits that learning strengthens and enlarges connections between neurons, known as synapses. However, these connections are highly plastic and change significantly over short periods. Kazumasa Tanaka, a neuroscientist at the Okinawa Institute of Science and Technology Graduate University, noted that synaptic arrangements can differ greatly within days.
Induced Hibernation and Synapse Loss
To investigate how memories persist despite this synaptic plasticity, Tanaka's team induced a hibernation-like state in mice. This process, detailed in a recent Science study, led to the erasure of more than half of the mice's synapses. Despite this substantial loss of synaptic connections, the mice appeared to retain their memories.
Technique for Artificial Hibernation
The technique for inducing this state, termed Q-neuron-induced hypothermia and hypometabolism (QIH), was developed in June 2020 by a team led by Takeshi Sakurai. It involves artificially activating Q neurons located in a specific region of the hypothalamus. This activation causes the mice's body temperature to drop to around 20° Celsius, with significant decreases in heart and breathing rates.
Implications for Memory Research
The results suggest that memory storage may not solely depend on the physical stability or size of synaptic connections. The ability of mice to retain memories despite losing a majority of their synapses during induced hibernation opens new avenues for understanding the fundamental mechanisms of long-term memory formation and retrieval, potentially pointing to alternative or more complex storage mechanisms.
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Reporting from
Researchers induced a hibernation-like state in mice, which resulted in the loss of over half their synapses, yet the mice retained their memories. This finding challenges the leading hypothesis that memories are stored through strengthened and physically larger neuronal connections, suggesting memory persistence despite significant synaptic plasticity.