Researchers from the University of California at Los Angeles (UCLA) are reporting this week in the journal Nature Neuroscience that when we're sleeping—or even while under general anesthesia—there remains a part of our brains which appears to act like it's in the process of remembering something.
This is contrary to long-held ideas about sleep, memory and the human brain.
UCLA professor of neurophysics and research leader Mayank R. Mehta and colleagues from both Germany and New England took simultaneous measurements of neural activity in a number of areas of the brain long associated with memory in order to determine which among them was active and which activated other areas.
They looked at three key brain regions: the neocortex, the hippocampus and the entorhinal cortex.
Exploring the role of the entorhinal cortex
According to Dr. Mehta, past research has suggested communication between the neocortex (or 'new' brain) and the hippocampus (the 'old' brain) during sleep contributed to memory retention, but the entorhinal cortex, which acts like an intermediate area connecting the other two parts, had never been explored for its role in this communication.
So the team did just that, and found that the entorhinal cortex displayed a "persistent activity," mediating memory while we're awake and continuing to function while we're asleep.
"The big surprise here is that this kind of persistent activity is happening during sleep, pretty much all the time," said Mehta. "These results are entirely novel and surprising. In fact, this working memory-like persistent activity occurred in the entorhinal cortex even under anesthesia.
"When you go to sleep," he continued, "you can make the room dark and quiet and although there is no sensory input, the brain is still very active. We wanted to know why this was happening and what different parts of the brain were saying to each other."
Sleep is important to memory retention
In addition to discovering new function in the entorhinal cortex, the study confirms the theory that sleep is important to memory retention and that sleep deprivation can have a negative impact not only on one's health but also on one's memory.