Sleeping brain acts as if remembering something

Researchers who measured during sleep the activity of a brain region involved in learning, memory and Alzheimer’s discovered that it behaves as if it is remembering something, even under anaesthesia.

The finding counters existing theories about memory consolidation during sleep. Researchers simultaneously measured the activity of single neurons (brain cells) from multiple parts of the brain involved in memory formation,

The technique allowed them to determine which brain region was activating other areas of the brain and how that activation was spreading, said study senior author Mayank R. Mehta, professor of neurophysics at the University of California Los Angeles, the journal Nature Neuroscience reports.

Mehta and his team looked at three connected brain regions in mice — the new brain or the neocortex, the old brain or the hippocampus, and the entorhinal cortex, an intermediate brain that connects the new and the old brains, according to a California statement.

While previous studies have suggested that the dialogue between the old and the new brain during sleep was critical for memory formation, researchers had not investigated the contribution of the entorhinal cortex to this conversation, which turned out to be a game changer, Mehta said.

His team found that the entorhinal cortex showed what is called persistent activity, which is thought to mediate working memory during waking life, for example when people pay close attention to remembering things temporarily, such as recalling a phone number or following directions.

“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 anaesthesia,” concluded Mehta.

The findings are important, Mehta said, because humans spend one-third of their lives sleeping and a lack of sleep results in adverse effects on health, including learning and memory problems.