Researchers from Columbia University reported at the 2016 Annual Meeting of the American Academy of Neurology that people who experience daytime sleepiness or prolonged sleep duration have decreases in their brain volume in some areas.

In a study involving 501 volunteers ages 65 and older who completed questionnaires on their sleep patterns, subjects underwent MRI scans to determine their brain volumes.

The researchers found that a smaller brain region known as the entorhinal cortex was associated with longer sleep duration.

They also reported that reduced amounts of gray matter located in the outer rim of the brain were associated with greater daytime sleepiness.

The entorhinal cortex is a brain region that gets damaged by Alzheimer’s disease, and the cortex and gray matter contain brain cell bodies that control thinking and memory.

One explanation for the results is that daytime sleepiness and longer sleep duration can indicate the presence of sleep apnea, which is known to increase the risk of cognitive problems associated with smaller brain volumes.