Scientists have known for quite some time that sleep plays an important part in choosing which memories get stored, and which get thrown out. But a new study at UCLA suggests that the way the brain talks to itself is actually the opposite of how we thought.
The dominant theory suggests that the hippocampus, which writes new memories, talks to the neocortex, where our most sophisticated and abstract thought takes place.
Dr Mayank Mehta of UCLA, along with colleagues from the German Heidelberg University, the Max Planck Institute, and Brown University, investigated how memories were formed while mice were sleeping. They were interested in the behavior of entorhinal cortex, a region of the brain that plays a part in learning and memory.
This region connects the neocortex with the hippocampus, and the team discovered that it plays a very important part in the conversation. For just about the entire time the mice were sleeping, even under anesthesia, it was active, and acting like it was remembering something.
The activation would last for more than a minute at a time. Most activation in the brain lasts for thousandths of a second.
Just as importantly, the communications were going the wrong way. It was the neocortex that was talking to the entorhinal cortex, which spent most of the night “remembering” these conversations, then talking to the hippocampus.
It was apparently the “thinking” brain that was telling the hippocampus which memories to hang on to, and which to toss out.
This study tells us that the conversation the brain has with itself at night is even more complex than we thought.