If I go to sleep religiously every night at 10 p.m., are there things that I perhaps do in the preceding hours of the preceding day, like ingest caffeine or alcohol, that can make that first stage of sleep less effective even if I'm going to sleep at the same time?

Alcohol definitely will do that because alcohol is a REM sleep suppressant and it even suppresses some of that stage two transition to REM with those sleep spindles. And those sleep spindles, we didn't talk about their function yet, but they're really important for moving memories to our cortex. It's a unique time when our hippocampus, sort of like the REM of our brains, writes it to a hard disk, which is the cortex.

It's a unique time when they're connected. So if you don't want to miss that, you don't want to miss REM sleep, which is also a part of a consolidation process and schema-changing process. And alcohol, before we go to sleep, will do that. Until we've metabolized alcohol and put it out of our bodies, it will affect our sleep badly.

So probably fair to say no ingestion of alcohol within the four to six hours preceding sleep, given the half-life. Given the half-life. Or it all would be better, but I know some people refuse to go that way. Maybe a little bit is okay. I don't know what the dose response is, but there are studies out there you can look at.

Great. So we're still in the first stage of sleep, and I apologize for slowing us down, but it sounds like it's an incredibly important first phase of sleep. What about the second and third 90-minute blocks of sleep? Is there anything that makes those unique? What is their signature, besides the fact that they come second and third in the night?

There's more and more REM sleep the later, the night we get. There's also a change in hormones, the growth hormone and melatonin levels are starting to decline, but other hormones are picking up. So it is a really different stage that you also don't want to shortchange yourself on. And I think that's the stage many studies are showing that those are the times in sleep when the most creativity can happen.

That's when our dreams can incorporate and put together old and new things together into a new way, and our schema are built during that time. So yeah, we can change our minds best during those phases of sleep.