I knew that trauma and pregnancy change the size of the brain, but it turns out, changing seasons also affect the volume of certain structures of the brain. Several sub-cortical structures grow larger in the winter and smaller in the summer. Other structures, such as the cerebellum, are larger in the summer and smaller in the winter.

Researchers are slowly working toward understanding these seasonal shifts in both humans and animals, but the reasons behind these volume shifts remain a mystery. Discover Magazine published a story about this topic and recent discoveries, which is a short and interesting read. You can find the article here and one of the studies on which the story is based, conducted at the Olin Neuropsychiatry Research Center in Connecticut, here.