A Sleep to Remember
There’s a piece of your brain, right next to your hippocampus, called the entorhinal cortex. While the hippocampus is responsible for consolidating the information in your memory, the entorhinal cortex mediates it. So, for instance, if someone tells you a phone number and you decide for some inexplicable reason that you’ll just remember it, that there’s no way you’re writing it down, your entorhinal cortex is working. It’s what allows you to form and access memories while you’re awake. When, later, you remember that phone number, your entorhinal cortex is in a state of “persistent activity.”
Before this new study, scientists generally thought that long-term memory was formed, via REM sleep, when your hippocampus talked to your neocortex (the big, squiggly top layer of your brain, which is active in conscious thought, among many, many other things).
No one had really looked at the entorhinal cortex’s role in memory formation before. So the team, noticing this, devised a brain monitoring technique that allowed them to look at single neurons from different pieces of the brain, and measure their activity. They did this in mice because humans are sort of touchy about letting people into their brains, but the findings apply.
What they found is that during sleep, the entorhinal cortex is working really hard. It’s in a constant state of persistent activity, just like when you’re awake. What’s more, it even does this in anesthesia-induced sleep. These results are completely “novel and surprising,” according to the study’s author.
In other words: when you’re asleep, your brain behaves as if you’re remembering something. Your dreams are just a series of phone numbers you decided not to write down. Thank god your entorhinal cortex was there to mediate the information.