As you snooze, you’ll repeatedly cycle through four stages of sleep, each of which is linked with specific brain waves and neuron activity.
The first three stages are non-REM sleep, and the final stage is REM sleep, which first occurs roughly 90 to 120 minutes after you first fall asleep, says Nishi Bhopal, MD, a board-certified integrative psychiatrist and sleep specialist.
The first REM period might be just 10 minutes long, but as the night goes on, REM sleep gets progressively longer. By the end of your sleep cycle, your REM stage might be as long as an hour, says Bhopal.
During REM sleep, your brain wave activity, heart rate, and blood pressure are similar to when you’re awake. Your breathing will quicken, and your eyes will move rapidly (hence the name), per the NIH.
This sleep stage is particularly important for emotional regulation, says Bhopal. “When people aren't getting enough sleep, and if their REM sleep is disrupted, it can lead to emotional dysregulation during the day,” she notes.
“When you learn something new, your brain cells make this synaptic connection—that's where the new thing you learned is stored,” Milstein explains. “So at night during REM sleep, your brain finds those new connections, and the electricity that's running over and throughout your brain is making those connections stronger. So REM sleep…basically solidifies the memories that you learned that day.”
Most vivid dreams with complex storylines also occur during REM sleep, adds Bhopal. As you dream, your brain is strengthening the connections you learned that day and deprioritizing the connections that are no longer important, adds Milstein.
When you don’t get enough REM sleep, you may have more trouble with your memory and recall, says Bhopal; animal studies suggest that depriving REM sleep may impair memory formation during complex tasks, according to research published in Physiological Reviews2.