Study finds why deep sleep is helpful for memory

• Adequate sleep is an important factor in a person’s overall health.
• Poor sleep is a risk factor for cognitive problems such as memory loss.
• Researchers at the Charité – Universitätsmedizin Berlin have clarified what happens during deep sleep – also known as slow-wave sleep – to support the formation of memories in the brain.
• The study adds to evidence that sleep plays a crucial role in memory consolidation and could help scientists develop preventive strategies against dementia.

“Sleep deprivation in humans leads to all sorts of problems and can cause serious damage,” said Franz Xaver Mittermaier, a research fellow at the Institute of Neurophysiology at the Charité – Universitätsmedizin Berlin in Germany Medical News Today.

“It’s fair to argue that the brain is the organ that needs the most sleep. Sleep separates the brain from the outside world. The flow of sensory information stops. This allows past experiences to be repeated without “outside interference,” which is necessary to consolidate memories of those experiences — that is, move them into long-term memory,” he said.

Mittermaier is the lead author of a new study recently published in the journal Nature communication This provides an explanation for how deep sleep – also known as slow-wave sleep – supports the formation of memories in the brain.

For this study, Mittermaier and his team used intact tissue samples Neocortex – part of it cerebral cortex of the brain – taken from 45 study participants.

“The neocortex is the outermost part of the brain. Whenever we see an image of the brain, the surface we are looking at is the neocortex – the walnut-shaped surface. It is a structure that contains 16 billion neurons (electrically active brain cells). The neocortex is greatly enlarged in humans and plays a central role in the cognitive abilities that make us human: language, imagination, memory, emotions, etc.”
— Franz Xaver Mittermaier

“In 2017, we began developing a platform on which we collect brain samples from neurosurgical procedures that would otherwise be thrown away,” said Mittermaier. “We have managed to improve our methods to keep these tissue samples alive in physiological solutions for more than 24 hours. This allows us to study human brain cells and connections between them (Synapses) using high-quality, high-resolution recording methods.”

“Once we had the opportunity to do these recordings, it was very obvious to look at the mechanisms of memory. Prof. Geiger and Henrik Alle – a co-author of the current study – had published A Science Journal article from 2006 in which they identified some interesting synaptic mechanisms. These mechanisms were our starting point and the project developed from there,” he explained.

At the end of the study, the researchers found that the slow electrical waves generated in the brain during deep sleep help strengthen the synaptic connections between neurons in the neocortex, making it more “receptive” to forming memories.

“During deep sleep, when the sensory stream from the outside world stops, the neocortex shows a very interesting activity consisting of UP and DOWN states that alternate about once per second,” Mittermaier explained. “UP and DOWN states arise from synchronous changes in the electrical voltage of many thousands of neurons in the neocortex.”

“With our experiments, we were able to show that these UP and DOWN state sequences actually tune the synapses (i.e. the connections) between the brain cells and make them particularly strong when the neocortex switches from a DOWN state to an UP state.” “he continued.

“During this time window, the neocortex is placed in a state of heightened receptivity to information. When the hippocampus – the region of the brain that stores short-term memories – plays a memory in this time window, there is greater activation of neocortical brain cells, which in turn leads to transfer to long-term storage. “, he said MNT.

“We are only beginning to scratch the surface of the mechanisms that actually occur when the brain sleeps. Additionally, much of the research to date has been conducted on laboratory animals rather than human tissue samples (as in our study). We still have a lot of work to do to truly understand the sleeping human brain. Our study is just the beginning. Understanding the sleeping brain will help us combat disorders such as memory impairment in older people.”
— Franz Xaver Mittermaier

MNT spoke with Verna Porter, MD, a board-certified neurologist and director of the Division of Dementia, Alzheimer’s Disease and Neurocognitive Disorders at the Pacific Neuroscience Institute at Providence Saint John’s Health Center in Santa Monica, California, who commented that this study is both exciting and… thought-provoking It illuminates the critical role of slow-wave activity (SWA) during deep sleep in synaptic plasticity and memory consolidation.

“What is particularly interesting is SWA’s ability to strengthen synapses and stabilize memories at a precise cellular level,” explained Porter.

“For me as a neurologist, this highlights the critical importance of healthy sleep patterns in maintaining cognitive function. Given that patients with dementia often experience deep sleep disorders, these results highlight the need to better understand and address sleep deficits as part of dementia care and prevention.”
—Verna Porter, MD

“Next steps should focus on determining how SWA-controlled synaptic mechanisms are altered in neurodegenerative diseases such as Alzheimer’s and other forms of dementia. Longitudinal studies are needed to assess whether improving deep sleep can slow cognitive decline or improve memory retention in at-risk populations,” she continued.

MNT also spoke with Manisha Parulekar, MD, FACP, AGSF, CMD, director of the Division of Geriatrics at Hackensack University Medical Center and co-director of the Center for Memory Loss and Brain Health at Hackensack University Medical Center in New Jersey, about this study.

“Deep sleep, particularly slow-wave sleep, plays a critical role in memory consolidation – the process of stabilizing and strengthening newly acquired memories. This study highlights possible effects of sleep on memory and outlines a possible mechanism for improving memory consolidation.”
— Manisha Parulekar, MD, FACP, AGSF, CMD

“Dementia continues to be an important public health challenge. Studies suggest that the pathophysiology begins much earlier, 10 to 20 years before cognitive symptoms. The results could help identify possible prevention strategies and explore treatment approaches to support memory formation,” said Parulekar.

“A next step could be further studies examining the effects of cognitive behavioral therapy for insomnia (CBT-I), mindfulness-based stress reduction, sleep hygiene education, light therapy, and other noninvasive approaches on memory consolidation and their potential cognitive benefits. ” she added.