Rapid eye movement, or REM, sleep is a very fascinating period when a lot of our fantasies are made. Now, in a study of mice, a group of Western and U.S. researchers show that it may also be an occasion when the brain knowingly forgets. Their results suggest that nerves found deep in the brain that were previously acknowledged for making an appetite may control forgetting throughout sleep. The study was financed by the National Institute of Neurological Disorders and Stroke (NINDS), part of the National Institutes of Health.
“Have you ever wondered why we forget a lot of our fantasies?” Thomas Kilduff, Ph.D., head of the SRI International Neuroscience Center in Menlo Park, California, and lead author of the study published in Science. “Our results suggest that the firing of a particular set of nerves during the control of REM sleep, whether the brain remembers or not, is reminiscent of new advice after a good night’s sleep.”
REM is only one of the stages of sleep in which the body performs nocturnal cycles. The stinging eyes appear for the first time about 90 minutes after falling asleep and characterizes it, increases heart rate and promotes brain waves of paralyzed limbs and dream.
For more than a century, scientists have researched the use of sleep . While many have shown that sleeping helps the brain store new memories, others, including Francis Crick, the co-discoverer of their DNA double helix, have increased the risk that sleep — in particular REM sleep — could be an occasion when the brain actively gets or exerts excess information.
Recent studies in mice have shown that throughout sleep – including REM sleep – the brain prunes the neuronal connections created between the nerves.
Sleeping In Oblivion
Until this study, no one knew that it could happen. “Understanding the role of sleep in oblivion can help researchers better understand a wide range of memory-related diseases, such as post-traumatic stress disorder and Alzheimer’s disease,” said Janet He, Ph.D, Program manager at NINDS. “This study provides the most direct evidence that paradoxical sleep could play a role in how the brain decides what memories to keep.”
Dr. Kilduff’s lab and his associate, Akihiro Yamanaka, Ph.D., at Nagoya University in Japan, have also spent years examining the portion of a hormone called hypocretin / orexin in sleep control and narcolepsy. Narcolepsy is a disease that causes individuals to feel the experience of sleeping in temptation.
Their labs and others have helped demonstrate that narcolepsy may be linked to the growing loss of neurons in the hypothalamus, a peanut-sized area in the brain.
As part of this research, Dr. Kilduff worked with Dr. Yamanaka’s lab and Akira Terao, a medical doctor at Hokkaido University in Sapporo, Japan, to examine nearby melanin-concentrating hormone (MCH) cells. A molecule known to have been engaged in the control of hunger and sleep. In agreement with earlier research, the scientists discovered that almost all hypothalamic (52.8%) MCH cells had been shot when the mice had not slept during REM sleep, while about 35 per cent had the mice been more alert and about 12 per cent.
In addition, they found hints indicating that these cells could play a part in memory and learning. Tracing studies and electrical recordings disclosed that a number of MCH cells sent inhibitory messages through the spinning axons to the hippocampus, the center of brain memory.
“From past studies done in different labs, we already knew that MCH cells were more busy during REM sleep. After detecting this brand new circuit, then we thought these cells can assist the brain store memories,” said Dr. Kilduff.
The researchers used a variety of genetic tools to show on / off MCH neurons in mice throughout memory tests, to test this notion. Specifically, they analyzed the role that MCH cells played in retention, the period after learning something brand new but before the newest consciousness is stored, or merged, in to long term memory. The scientists used memory tests including the one that assessed the capacity of mice to distinguish between new and familiar objects.
To their surprise, they found that “turning on” MCH cells slowed down memory retention while turning off enhanced memory. For example, cell activation reduced enough time for mice to sniff around things compared to familiar ones, but turning the cells off had exactly the opposite effect.
Further studies proposed that MCH neurons and this role played throughout REM sleep. When the MCH neurons were switched off during REM sleep mice, they conducted better cognitive trials. On the other hand, turning the nerves as the mice were alert or in sleeping circumstances had no effect on the memory.
Our Conscious Brain
“These findings suggest that maternal and infant health neurons help the brain to consciously forget new, potentially unimportant events,” said Dr. Kilduff. ” In the future, the researchers plan to explore whether this brand fresh circuit is important in memory and sleep disorders.
This work was funded by grants from: NIH (NS098813); both the CREST app of the Japan Science and Technology Agency (JPM JCR 1656); and also the KAKENHI application of the Japanese Society for the Promotion of Science (26293046, 26640041, 16H01271, 17H05563, 18H02523, 18KK0223, 18H05124, 15K07140, 18H02477, 18J21663 to S.I.).
This news release describes a basic research finding. Standard research increases our knowledge of math and individual behavior, which is crucial to improving new and improved ways to prevent, diagnose, and treat illness. Science is an unpredictable and more incremental process — each research progress builds on past discoveries, usually in ways that are unexpected. Most clinical advances would not be possible without the wisdom of research that is fundamental.