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Why Do We Forget Our Dreams? Study Sheds Light

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When we sleep, our brains go through four stages. The initial three are non-rapid eye movement (non-REM) stages.

The first stage includes the transition from wakefulness to sleep, when the body slows down from its daytime rhythm and “twitches” its way into sleep.

The second stage, also of non-REM sleep, involves light sleep. The third stage of sleep is deeper, and it provides the profound kind of rest that one needs to feel refreshed in the morning.

Finally, the time when our brains do most of their dreaming is called the REM sleep stage. But why do we forget our dreams most of the time? And when does erasing the memory of our dreams occur?

New research in mice suggests that the REM sleep stage also contains a period of “active forgetting.” This most likely occurs to avoid information overload, according to the new study, and the neurons responsible for this forgetting are also the neurons that help control appetite.

The new findings appear in the journal Science. Thomas Kilduff, Ph.D., the director of the Center for Neuroscience at the SRI International research institute in Menlo Park, CA, led the research in collaboration with Akihiro Yamanaka, Ph.D., from Nagoya University, in Japan.

Neurons that are key for sleep, appetite

Previous studies that Kilduff and Yamanaka had conducted together with their teams focused on a hormone involved in regulating sleep in narcolepsy — a condition that may cause a person to involuntarily fall asleep at inopportune times during the day.

The hormone bears the name orexin/hypocretin, and a loss of neurons that produce it in the hippocampus may be what triggers narcolepsy, Kilduff and Yamanaka have shown.For their new study, the researchers set out to examine a group of neighboring neurons in the hippocampus. These produce melanin-concentrating hormone (MCH), a molecule that helps regulate both sleep and appetite.

The scientists already knew from previous research that these MCH-producing neurons would be active during REM sleep. But electrical recordings of sleep activity in mice and experiments involving neuronal tracing have revealed that these neurons also send inhibitory messages to the hippocampus.

Given that the hippocampus is key for learning and memory, the scientists wondered whether these neurons had “a say” in preserving memories.

MedicalNewsToday, excerpt posted on SouthFloridaReporter.com, Sept. 24, 2019

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