Researchers have identified a signal from the brain noise that uniquely characterizes dreaming or REM Sleep, a new study suggests.
During the REM stage, or as a person dreams, the brain is filled with electrical activity that is mostly identical to brain activity when awake. A team from the University of California, Berkeley have reportedly isolated a signal unique to this sleep phase.
The study, titled "An electrophysiological marker of arousal level in humans," is published in the latest edition of the journal eLife.
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Confirming REM Sleep States Via EEG
The researchers used electroencephalogram (EEG) readings from patients and volunteers in a variety of sleep states--awake, asleep, or under an anesthetic. Electrodes placed on either the scalp or into the brain of the volunteers have demonstrated that the spectral slope can distinguish between those who are experiencing wakefulness from anesthesia, deep non-REM sleep, and deep sleep state.
These variations in the spectral slope illustrated an accurate description of the degree of arousal, displaying high temporal precision across a wide range of time scales. In theory, this allows a more precise method of monitoring sleep or anesthesia-induced sleep conditions. It has applications in understanding sleep problems, where patients are hooked to an EEG that monitors brain activity as the patient moves between states.
Furthermore, a concrete marker for REM sleep offers a definite way to tell if someone is actually in a deep sleep. Existing EEG analysis techniques can not distinguish between wakefulness or dream states. Doctors identify deep sleep by recording rapid eye movements (REM) and muscle tone. The body, during deep sleep, is relaxed and in a general paralysis to keep it from moving around - even as you feel like moving in your dreams.
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Moreover, a new method for confirming deep sleep via EEG scans will allow doctors to observe people under anesthesia, such as during surgery, to finally settle whether a narcotic-induced sleep is actually different from a naturally achieved one.
`We really now have a metric that precisely tells you when you are in REM sleep. It is a universal metric of being unconscious," Robert Knight said. Knight is a professor of psychology and neuroscience at UC Berkeley, as well as the senior author of the study.
Relevance of the REM Sleep
Rapid eye movement sleep has remained among the most interesting topics of research in neurobiology, often being referred to as the deepest sleep stage. According to the National Institute of Neurological Disorders and Stroke (NIH), REM sleep usually occurs about 90 minutes after falling asleep.
Most of the research work focused on deep sleep focuses on brain activity, starting with the slow waves associated with deep sleep to the higher frequencies often detected in this sleep phase. Mixed brain frequency signals, usually dismissed as noise, is what makes deep sleep appear similar to a wakeful state under the EEG. These general activity brain waves are also called 1/f, dismissed in most studies.
However, as pointed out in the UC Berkeley study, it is markedly decreased in N3 sleep, REM sleep, and general anesthesia compared to wakefulness. Using the 1/f slope as an indication of arousal states, and inhibition, REM sleep appeared to have the highest level of inhibition.
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