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New Study Reveals Why You Often Forget Your Dreams

New research suggests your brain is clearing out memories during sleep.

Ever had a vivid dream that felt so real, it was uncanny—and then you forget it the moment you wake up? For years science has been trying to pinpoint how and why our brains retain some knowledge and toss out the rest—including dreams. Many scientists believe that our brain clears itself of useless information to make room for the new. Others maintain that forgetting keeps us mentally flexible, encouraging creativity and imagination. There have even been studies finding that clearing itself of useless memories reduces the risk of Alzheimer's.

However, recently, a group of scientists stumbled deeper into the science of memory, while studying sleep regulation in mice. In their new paper, published on Thursday in the journal Science, Japanese and US researchers claim that during the rapid eye movement (REM) deep sleep stage, the brain actively forgets. Aside from explaining why dreams are often forgotten during REM sleep, it also suggests that neurons found inside the brain might be controlling memory in general.

"Ever wonder why we forget many of our dreams?" was the question posed by Thomas Kilduff, Ph.D., director of the Center for Neuroscience at SRI International, Menlo Park, California, and a senior author of the study. "Our results suggest that the firing of a particular group of neurons during REM sleep controls whether the brain remembers new information after a good night's sleep."

While looking at Orexin, a hormone being studied for obesity and narcolepsy, researchers noticed that melanin concentrating hormones, (MCH) neurons—molecules associated with both sleep and appetite—were activating most frequently (52.8 percent) when mice were in the REM stage of sleep. While the mice were awake, they only 35 percent fired and 12 percent activated at both times.

They also found clues that these MCH cells might be playing a role in memory and learning. "From previous studies done in other labs, we already knew that MCH cells were active during REM sleep," Dr. Kilduff continued. "After discovering this new circuit, we thought these cells might help the brain store memories."

During memory tests researchers turned MCH neurons on and off. They were surprised to find that "turning on" the cells during retention worsened memory, while turning them off actually improved memories. Through more testing they determined that MCH neurons exclusively played this role during REM sleep.

"These results suggest that MCH neurons help the brain actively forget new, possibly, unimportant information," said Dr. Kilduff. "Since dreams are thought to primarily occur during REM sleep, the sleep stage when the MCH cells turn on, activation of these cells may prevent the content of a dream from being stored in the hippocampus—consequently, the dream is quickly forgotten."

While our brain's selective forgetfulness is interesting in and of itself—as is the potential reason we forget many of our dreams—researchers hope that by solidifying the relationship between MCH neurons and forgetting, neuroscience research will be able to forge ahead. Janet He, Ph.D., program director at NINDS, points out that this could be incredibly useful in terms of memory-related diseases, including post-traumatic stress disorder and Alzheimer's.

"This study provides the most direct evidence that REM sleep may play a role in how the brain decides which memories to store," she said.

Some experts aren't overly enthused about these new findings, claiming the study has major flaws, especially when it comes to its potential implications with Alzheimer's."The study makes staggering assumptions such as what constitutes a useless memory for a mouse?" Carolyn Dean, MD, ND, author of The Everything Alzheimer's Book and Founder of RNA Rese tells Eat This, Not That! Health. She also points out that researchers didn't take into account the diet and nutritional status of the mice, important variables that should not be overlooked "as the body's functions work in synergy and not independent of other systems."

"Certainly diet and nutrition as well as environmental factors and toxic heavy metals have been implicated as has pineal calcification in the pathology of Alzheimer's," Dr. Dean maintains, emphasizing magnesium as one of them. Preliminary and conflicting information can point to the absence of root cause. However, "this information may be a random factor in the pathology but not a root cause so it tends to act as a distraction or adds to confusion." To sleep better, be happier and sleep tighter, once and for all read these 40 Surprising Facts You Didn't Know About Your Sleep.

Leah Groth
Leah Groth has decades of experience covering all things health, wellness and fitness related. Read more about Leah
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