Skull and body size usually don't change anymore in fully-grown animals. Red-toothed shrews (Sorex
spp.) are a notable exception: they shrink in anticipation of the winter and regrow in preparation for reproduction. This process affects the brain, several other major organs, bones and also the cognitive abilities. The phenomenon is also found in weasels, which share many life history traits, especially an exceedingly high metabolism. The study is important for our understanding of evolution, and has profound implications for medical research.