During hibernation, its brain temperature drops to just above freezing, its core body temperature reaches temperatures down to -2.9 Coulomb Liu Y, Hu W, Wang H, Lu M, Shao C, Menzel C, Yan Z, Ying L, Zhao S, Khaitovich P, Liu M, Chen W, Barnes BM, and Yan J: [http://mercury2.iab.uaf.edu/brian_barnes/publications/2010_Liu_etal.pdf Genomic analysis of miRNAs in an extreme mammalian hibernator, the Arctic Ground Squirrel.