Brain cells 'reset' during sleep to prepare for tomorrow's memories

A good night's sleep is crucial for helping people make new memories, a new study says.

Neurons that capture new memories during the day reset while you sleep, researchers reported Thursday in the journal Science .

"This mechanism could allow the brain to reuse the same resources, the same neurons, for new learning the next day," said researcher Azahara Oliva , an assistant professor of neurobiology and behavior at Cornell University, in Ithaca, N.Y.

The process revolves around the hippocampus, a brain region vital to humans' ability to create memories.

Learning something or engaging in a new experience activate neurons in the hippocampus, storing those events as memories.

The same neurons later repeat the same pattern of activity while you sleep, transferring the day's memories in a larger brain region called the cortex.

But what keeps the neurons of the hippocampus from filling up, thus preventing new learning, the researchers wondered.

Electrodes implanted into the hippocampi of mice provided a potential explanation.

It turns out that those neurons that captured the day's memories undergo a reset after feeding the latest memories into the cortex, researchers found.

Two regions of the hippocampus that capture memories, CA1 and CA3, appear to reset during sleep under the direction of a third region called CA2, researchers said.

"We realized there are other hippocampal states that happen during sleep where everything is silenced," Oliva said in a university news release. "The CA1 and CA3 regions that had been very active were suddenly quiet. It's a reset of memory, and this state is generated by the middle region, CA2."

It turns out the brain has parallel circuits regulated by two types of neurons, researchers said. One network of circuits regulates memory, and the other allows for resetting of memory.

This new understanding could help researchers come up with tools to boost memory, by tinkering with the mechanisms of memory consolidation.

The findings also could lay the foundation for new ways to treat problems caused by unwanted memories, like post-traumatic stress disorder (PTSD), or to fix memory disorders like Alzheimer's disease

But overall, the findings help explain why sleep is so crucial for the brain health of all animals, researchers said.

"We show that memory is a dynamic process," Oliva said.

More information

Harvard University has more about how memory works .

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