Dr. Matt Walker

in some ways it is a memory of an emotional event, but it is no longer as powerfully emotional itself as it was at the time of the experience.

And I started to wonder, is that time or is that time asleep?

So we did a study and we had people experience these emotional memories, sort of essentially make emotional memories, and they were doing it inside of a scanner.

And then we gave them a night of sleep or even a nap.

And then we brought them back or we just had them learn those emotional memories in the morning and then bring them back after an identical amount of time to try to soften those emotional memories, but without sleep.

we put them back in the scanner and we were able to look to see when you come back later in that second session is your emotional and you recollect those experiences and you relive them is the emotional reactivity at that second session any different to the first session and is that different if that time elapse has contained a full night of sleep versus you've just been awake

And what we found is that in those people who remained awake across the day, having had those emotional memories essentially implanted, implanted sounds a little bit sort of big brother, I don't mean it that way, but they'd learned them.

the amygdala was just still as responsive as they were recalling and reliving and re-experiencing those emotional memories.

But in those people who had the same amount of time to process the memories, but had had a full night of sleep, we saw this incredible emotional amygdala depotentiation.

And what that taught me was that the sleeping brain was able to

almost detox the emotional memory.

Think about it like an informational orange, that the emotional memory has this bitter emotional rind around it, and then you've got the informational orange in the middle.

And what sleep was doing was stripping the bitter emotional rind off the informational orange, so that then when you came back the next day, again, it is now a memory of an emotional event,

but it's no longer triggering that strong visceral reaction.

In other words, and we describe this theory as something called overnight forgetting, which is that when it comes to an emotional memory, you both sleep to forget and sleep to remember respectively, which is that you sleep to remember the information, the memory of the experience,

but it is no longer emotional itself.

And from there, we built a biological model of exactly how this works.

Because when we looked at the sleep group who'd had that full eight-hour opportunity, we asked the question, because we'd measured their sleep, what is it about that sleep that seems to provide this form of, it's almost overnight therapy?

How is it doing that?

What stage of sleep is doing that?