Memories Ripple Through The Different Areas Of Brain During Sleep: Study

The connection between the left side of the brain and the right is crucial for the formation of memories. A study by a team of scientists has shown that sleep boosts communication between the regions.

Scientists from the National Institute of Health (NIH) in a project partially funded by the Brain Research through Advancing Innovative Neurotechnologies (BRAIN) Initiative, used the "NeuroGrid" technology to study the workings of the brain.

Nick Langhals, program director at NIH’s National Institute of Neurological Disorders and Stroke, in a report said, "using new technologies advanced by the BRAIN Initiative, these researchers made a fundamental discovery about how the brain creates and stores new memories."

The hippocampus region of the brain is known to be the area responsible for making new memories and storing them while we sleep.

New York University professor György Buzsáki, senior author of the study said, "high-frequency bursts of neural firing called ripples in the hippocampus during sleep and suggested they play a role in memory storage. The current study confirmed the presence of ripples in the hippocampus during sleep and found them in certain parts of association neocortex, an area on the brain’s surface involved in processing complex sensory information."

The team developed the NeuroGrid system to study the brain in never-seen-before depths. Placing recording electrodes deeper into the brain, the researchers were able to study activity in several parts of rats’ brains during non-rapid eye movement (NREM) sleep.

The NeuroGrid links together tiny electrodes like the weave of a fabric. This sheet is then placed across the area of the brain so it can be studied. The electrodes monitor the activity of a different set of neurons continuously to provide cutting-edge information about that area of the brain.

"This particular device allows us to look at multiple areas of the brain at the same time," said Jennifer Gelinas, the study’s co-first author and assistant professor at Columbia University.

The team saw that the neocortex was involved during sleep, along with the hippocampus, during the study of the rats. This was unique and unexpected which prompted them to believe that the brain goes through a "dialogue" to process and store memories. This effect was seen as a ripple of activity that goes through different parts of the brain to store complex permanent memories during sleep.

They examined the rats’ brain activity during NREM sleep. They used rats specially trained to locate rewards in a maze and compared it to rats that explored the maze in a random fashion. "In the latter group of animals, the ripples in the hippocampus and cortex were no more synchronized before exploring the maze than afterwards. In the trained rats, the learning task increased the cross-talk between those areas, and a second training session boosted it even more, further suggesting that such communication is important for the creation and storage of memories," the report said.

"Identifying the specific neural patterns that go along with memory formation provides a way to better understand memory and potentially even address disorders of memory," Gelinas said.

The study was funded by the National Institute of Neurological Disorders and Stroke and the National Institute of Mental Health and was published in the journal Science.