Over 70 years ago, Polish zoologist August Dehnel observed that shrews have smaller bodies and heads in winter, returning to standard size in summer. Dehnel’s phenomenon, named after its discoverer, is not a simple proportional resizing. Instead, each organ, including the brain, shows a distinct response. This seasonal effect continues to puzzle scientists even today, but new research from the Max Planck Institute of Animal Behavior sheds more light.

The study, led by behavioral ecologist Dina Dechmann, compiled all existing data on this phenomenon to better understand how seasons influence shrew brain reorganization. She found that the brain shrinks by 13 percent in preparation for winter and regrows by 10 percent in spring. Interestingly, like the seasonal human brain changes, not all brain regions respond similarly. “Brain regions behave almost independently of each other, some shrinking and growing, some just shrinking or not changing at all,” Dechmann says. And like the human findings, these effects are intimately tied to climate and seasonal shifts.

Why does this seasonal adaptability exist? Well, the brain is a powerful organ that has high energy demands. Dechmann theorizes that shrews may shrink in fall to save energy for winter’s scarce food supplies — noting that “reducing the energetically costly brain may help.”

Perhaps the mammalian brain changes with the seasons as a survival tactic, sacrificing some brain functionality to do so. And though humans aren’t foraging in the wild anymore, this seasonal adaptation may still be evolutionarily hardwired. Despite these similarities, however, shrews and humans are vastly different and there is still much more to learn.