The frozen squirrel : how animals survive deep hibernation

"One truly remarkable beetle, the red flat bark beetle (Cucujus clavipes puniceus) from Alaska, can supercool its body fluids to -50C. But there is huge variation between individuals – some can tolerate body temperatures as low as -100C. These deep-supercooling beetles have higher levels of antifreeze proteins and cryoprotectants like glycerol, which help them to minimise ice formation even at such extreme temperatures.

Several scientists are trying to work out how the Arctic ground squirrel (Spermophilus parryii) became the only known warm-blooded mammal to be able to tolerate subzero body temperatures. Solving the mystery could hold the key to freezing human organs for transplant without damaging them.

Although the exact mechanism remains a mystery, Barnes’ research suggests the ground squirrels may achieve this by producing masking agents, which neutralise ice-nucleators before ice has a chance to form around them. “The Arctic ground squirrel can survive body temperatures to -3C, but they do not freeze”, he explains. “Instead body fluids within the arctic ground squirrel enter a ‘supercooled’ state”. Without any effective nucleators to get the ice crystals started, water in the squirrel’s blood simply can’t freeze."

I was curious about how the squirrel avoids brain damage. According to this article :
http://www.scientificamerican.com/article/arctic-ground-squirrel-brain/
It doesn't. Although their brains don't go below freezing, and blood is still pumped around their bodies, they still suffer heavy damage. But every few weeks the squirrels warm up and the brains heal themselves, in fact ending up with even more synapses than they had before. I wonder if anyone's done a study on personality changes in squirrels due to hibernation....
http://www.bbc.com/earth/story/20160308-how-one-squirrel-manages-to-survive-being-frozen