Memories of a sleeping brain

Researchers have discovered that a region of the brain – involved in learning, memory and Alzheimer’s disease – behaves as if it’s remembering something even during sleep.

The team from UCLA simultaneously measured the activity of single neurons from multiple neural regions involved in memory formation, allowing them to determine which part of the brain was activating other areas and how that activation was spreading. The study appears in Nature Neuroscience.

Mayank R. Mehta, a professor of neurophysics at UCLA said: “The big surprise here is that this kind of persistent activity is happening during sleep, pretty much all of the time. The results are entirely novel and surprisingly.”

The team looked at three connected brain areas in mice: the neocortex (new brain), the hippocampus (old brain) and the entorhinal cortex (intermediate connecting old and new brains). Previous studies indicated that connections between the old and the new brain were critical for memory formation, but the contribution of the entorhinal cortex had not been investigated. These findings indicate that the entorhinal cortex is a key player in memory formation.

"This is a whole new way of thinking about memory consolidation theory," Mehta said. "We found there is a new player involved in this process and it's having an enormous impact. And what that third player is doing is being driven by the neocortex, not the hippocampus. This suggests that whatever is happening during sleep is not happening the way we thought it was. There are more players involved, so the dialogue is far more complex, and the direction of the communication is the opposite of what was thought."

The team theorises that this process occurs during sleep as a way to unclutter memories and remove irrelevant information that was processed in the day. It is worth noting that Alzheimer’s disease begins in the entorhinal cortex and patients tend to have sleeping problems, so the team’s finding may also have implications in AD therapy.