I Spy Physiology is taking a short break for the holidays. We’ll be back in 2020 with more physiology news, facts and features. While we’re gone, check out these winter-themed posts:

• Is (Winter) Happiness in the Eye of the Beholder?
• Bring on Winter! (But Stay Safe and Healthy)

And don’t forget to catch up on 2019’s most-read posts. Happy holidays!

 —Erica Roth