Feeling sluggish? You're not alone.
Many people feel sadder in the winter, according to a new study published Monday in the Proceedings of the National Academy of Sciences journal.
The study suggests a change in seasons can also make you dumber.
Researchers scanned the brains of healthy volunteers at different times of the year and found the areas involved in sustained attention appeared least active in winter and most active in summer.
Also, the activity of areas required for more complex thinking peaked in fall and dropped in the spring.
The journal article about the research is called "Seasonality in human cognitive brain responses."
Study: Seasons affect how the brain works