Harvard Health Publishing: Robert Stickgold, professor of psychiatry at Harvard Medical School, speaks about how the brain does its nighttime job of finding connections.

When you get into bed, the brain does a triage and “rifles through the events of the day and sees what’s left unfinished,” he says. It’s picking out what has some “affective buzz,” the emotions that happened during or shortly after something took place. The brain uses these memory “tags” as indicators that the event was important and that there’s more to figure out. Essentially, the brain is saying, “I think I can help you.”

Two elements make this happen. The prefrontal cortex gets shut down. This part of the brain handles executive decision-making (which includes rational thinking and impulse control), but now there’s no critical edge or categories to put ideas in. The brain can freely associate and, as Stickgold says, “process in the background.”

And when you get into the REM stage of sleep, the neuromodulators norepinephrine and serotonin are turned off. Norepinephrine enhances focus on immediate, concrete problems. “It’s the reason you don’t want to hear about someone’s ‘brilliant idea’ when you’re approaching a deadline,” he says.

There’s little known about what happens when serotonin is shut off, but Stickgold suggests it biases the brain into identifying looser connections as valuable. With both neurochemicals at bay, fragments of ideas can come together. “You have enhanced discovery of weak associations, ones you’d never notice,” Stickgold says.

Get the full story at harvard.health.edu.