This is the scientific reason you can’t always remember your dreams

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Paradoxical sleep, first coined by french neuroscientist,  Michael Jouvet, refers to the contradictory waves of awareness and inactivity that attends the four stages of sleep.  First, come the alpha waves, relaxing muscle tone throughout the body and mimicking the sensation of falling.  As you begin to dose off, you experience sleep spindles and K complexes beholden to environmental stimuli like the sound of a siren or running water. Eventually, you reach REM sleep, which features the visually distinctive dreams of all the sleep stages. Although the impression remains, the contents are rarely committed to memory. The phantom prey Lucretius observed are perhaps rough translations neurological engineered to feel relevant to the experiencer. To prevent an overload of information, our brains enter a period of active-forgetting during REM sleep, thanks to a stout band of neurons located in the hippocampus.

Honing in on a hormone associated with managing sleep in sufferers of narcolepsy, called orexin/hypocretin, Thomas Kilduff, Ph.D., the director of the Center for Neuroscience at the SRI International research institute in Menlo Park, CA, and his team of researchers revealed some interesting finds in the journal Science over the weekend regarding the role neurons play in preserving memories. From the report:

“The neural mechanisms underlying memory regulation during sleep are not yet fully understood. We found that melanin concentrating hormone-producing neurons (MCH neurons) in the hypothalamus actively contribute to forgetting in rapid eye movement (REM) sleep. ”

To sleep perchance to dream but you don’t remember

Previously conducted research published by Kilduff on mitigating symptoms consequenced by innovatory sleep, inspired the latest trials applied to mouse models. Using electronic recordings of the sleeping rodents the researchers discovered that a group of neurons in the hippocampus produce a molecule known as melanin-concentrating hormone (MCH). MCH has a lot of roles in the body including regulating feeding behavior, mood, energy balance, and most relevantly sleep-wake cycles.

“From previous studies done in other labs, we already knew that MCH cells were active during REM sleep,” explained Kilduff to Medical News Today. “After discovering this new circuit, we thought these cells might help the brain store memories.”

When the scientists made these neurons inactive with the use of a genetic ablation, the rodents retained memory more successfully. This result was only achieved when the MCH producing neurons were shut off during REM sleep. Kilduff wrote, “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. These results suggest that MCH neurons help the brain actively forget new, possibly, unimportant information,”