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Anchorage, Alaska, January 27, 2026 – Imagine a mammal that can intentionally shut down most of its brain activity for nearly three-quarters of the year, than wake up in the spring with its memories and cognitive abilities fully restored. It sounds like science fiction, but the Arctic ground squirrel (Urocitellus parryii) does exactly that every winter.
How a Squirrel freezes Its Brain and Lives to Tell the Tale
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These remarkable creatures survive sub-zero temperatures by entering a state of hibernation unlike any othre, offering clues to protecting human brains from injury.
- Arctic ground squirrels can lower their body temperature below freezing during hibernation.
- Their heart rate slows to less than ten beats per minute, and breathing becomes incredibly shallow.
- Scientists are studying these squirrels to find ways to protect human brains from damage caused by stroke, trauma, and even long-duration space travel.
- The squirrel’s ability to enter “torpor” involves drastically reducing brain activity while preserving neural structure.
The Arctic ground squirrel inhabits some of the coldest regions on Earth, where winter can last up to eight months. Rather of fighting the cold, these squirrels embrace it by entering an extreme state of hibernation. During this time, their body temperature plummets below the freezing point of water, their heart rate slows dramatically, and most brain functions come to a near standstill.
What Happens to the Brain During Prolonged Hibernation?
Q: How does an Arctic ground squirrel survive brain temperatures below freezing?
A: The squirrel reduces brain activity, blood flow, and temperature to levels that would be fatal to humans, but it does so in a controlled way that protects its neurons and allows them to revive in the spring.
In humans, even a slight decrease in brain temperature or oxygen supply can cause irreversible damage or cell death. Research shows that human brain cells are highly vulnerable to a lack of oxygen, or ischemia, frequently enough associated with strokes and traumatic injuries. A study published in the journal Stroke, “The Arctic Ground Squirrel Brain Is Resistant to Injury From Cardiac Arrest During euthermia“, highlights this sensitivity, contrasting it with the Arctic ground squirrel’s resilience.
The Arctic ground squirrel achieves this remarkable feat by reducing brain activity, blood flow, and temperature to such low levels that neuronal firing almost ceases, yet the neurons remain alive. This is made possible by controlled physiological processes that shut down synaptic communication and slow metabolism, a state known as “torpor.”
How the Squirrel’s Brain Survives What Would Kill Ours
The key to this deep torpor is a drastic reduction in cellular activities essential for life.A study in the American Journal of Physiology, “Effects of ambient temperature on metabolic rate, respiratory quotient, and torpor in an arctic hibernator“, found that protein synthesis, a vital cellular process, is reduced to almost undetectable levels during hibernation in