Researchers from the University of California, Los Angles, have found that, even during sleep, the brain behaves as if it is remembering something. In a study published in the journal Nature Neuroscience, researchers measured the activity of neurons from multiple parts of the brain involved in memory formation.

Lead study author Mayank R. Mehta, a professor of neurophysics in UCLA's departments of neurology, neurobiology, physics and astronomy, observed three connected brain regions in mice. Researchers observed the neocortex (the new brain), the hippocampus (the old brain) and the entorhinal cortex (the region that connects the old and new brain).

Prior research has only suggested a connection between the old and new brain during sleep was essential for memory formation, but this study included the contribution of the entorhinal cortex. It was discovered the entorhinal cortex displays persistent activity, even during sleep. Persistent activity is believed to be responsible for working memory when an individual is conscious, such as when people pay close attention to remember things like a phone number.

"The big surprise here is that this kind of persistent activity is happening during sleep, pretty much all the time." Mehta said. "These results are entirely novel and surprising. In fact, this working memory-like persistent activity occurred in the entorhinal cortex even under anesthesia."

Researchers believe this process occurs during sleep as a way to organize memories and remove irrelevant information processed during the day.

This study defies former theories of brain communication during sleep. Researchers now know there is a third factor in the dialogue between the new and old brain. The neocortex is influencing the entorhinal cortex, which in turn behaves as if it is remembering something. That, in turn, drives the hippocampus, while other activity patterns shut it down.

In addition, Alzheimer's disease occurs in the entorhinal cortex and Mehta proposes his findings may have an effect in that particular area of science.