Brain noise contains unique signature of dream sleep.
When we dream, our brains are filled with noisy electrical activity that looks nearly identical to that of the awake brain.
But University of California, Berkeley, researchers have pulled a signal out of the noise that uniquely defines dreaming, or REM sleep, potentially making it easier to monitor people with sleep disorders, as well as unconscious coma patients or those under anesthesia.
Each year, hundreds of thousands of people undergo overnight studies to diagnose problems with their sleep, most of them hooked up to an electroencephalogram (EEG) to monitor brain activity as they progress from wakefulness to deep, slow-wave sleep and on into REM sleep. But EEGs alone can not tell whether a patient is awake or dreaming: Doctors can only distinguish REM sleep by recording rapid eye movement — hence, the name — and muscle tone, since our bodies relax in a general paralysis to prevent us from acting out our dreams.
“We really now have a metric that precisely tells you when you are in REM sleep. It is a universal metric of being unconscious,” said Robert Knight, UC Berkeley professor of psychology and neuroscience and senior author of a paper describing the research that was published July 28 in the online journal eLife.
“These new findings show that, buried in the electrical static of the human brain, there is something utterly unique — a simple signature,” said co-author and sleep researcher Matthew Walker, UC Berkeley professor of psychology and neuroscience. “And if we measure that simple electrical signature, for the first time, we can precisely determine exactly what state of consciousness someone is experiencing — dreaming, wide awake, anesthetized or in deep sleep.”
The ability to distinguish REM sleep by means of an EEG will allow doctors to monitor people under anesthesia during surgery to explore how narcotic-induced unconsciousness differs from normal sleep — a still-unsettled question. That’s the main reason first author Janna Lendner, a medical resident in anesthesiology, initiated the study.
“We often tell our patients that, ‘You will go to sleep now,’ and I was curious how much these two states actually overlap,” said Lendner, a UC Berkeley postdoctoral fellow in her fourth year of residency in anesthesiology at the University Medical Center in Tübingen, Germany. “Anesthesia can have some side effects. If we learn a little bit about how they overlap — maybe anesthesia hijacks some sleep pathways — we might be able to improve anesthesia in the long run.”