Over a century ago, Edgar Allan Poe famously asked, “Is all that we see or seem, but a dream within a dream?” It was a somewhat dreary sentiment as the speaker in his poem watched the most important things in life slip away while standing powerless, but a valid question nonetheless that neuroscience may have an answer to — understanding the definitive difference between the world we perceive when awake versus the world we take in when we dream.
While we’re asleep, we may find ourselves wandering through a vivid and complex world, stuffed with the same sensory details we experience when wakeful. We sleep and have dreams as a way to forget the unnecessary stresses and more trivial information the brain absorbs during the course of the day — yet sleeping brains and wakeful brains look largely the same, with a steady oscillation of alpha waves.
The difference, however, is within the slight bouts of aperiodic activity, which experts like Dr. Janna Lendner, a researcher at UC Berkeley, refer to as the brain’s “white noise.” Lendner and her colleagues have been able to define dreaming, a process that occurs commonly during REM sleep, by the nature of the white noise activity in the brain, something once ignored as background noise. Along with her team of researchers, they have also been able to differentiate REM sleep from comatose patients or patients under anesthesia.
Lendner acquired her data from monitoring hundreds of thousands of volunteers who sign up for overnight sleep studies, where they volunteer to be hooked up to an electroencephalogram (EEG) machine in order to monitor their brain activity as they move from wakefulness to deep and slow wave sleep before falling into REM sleep. However, even an EEG reading can’t say if you’re awake or dreaming. This has traditionally been determined by observing eye movements and muscle tone of the patients as they move in their sleep. When you begin to experience dreams, the body moves into a slight state of paralysis to protect the body from carrying out every motor function you experience in your dreams — it’s why you’ve probably dreamt of walking in a field, but your legs don’t physically leave your bed.
“We really now have a metric that precisely tells you when you are in REM sleep. It is a universal metric of being unconscious,” says Dr. Robert Knight, a UC Berkeley professor of psychology and neuroscience, who is the senior author of a paper describing the study’s research in the journal eLife.
Beyond metaphysical curiosities, there are some significant reasons for why this study is groundbreaking — and how it could alter the fields of neuroscience and medicine.
“These new findings show that, buried in the electrical static of the human brain, there is something utterly unique — a simple signature,” says the study’s co-author Dr. Matthew Walker, UC Berkeley professor of psychology and neuroscience, whose interests include sleep research. “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.”
Being able to determine REM sleep through the reading of an EEG will give doctors an opportunity to monitor patients suffering from various sleep disorders and possibly find patterns in the brain connections for such cases. It’s also a chance to monitor people under anesthesia during surgery, to further examine the difference between narcotic-induced unconsciousness and normal sleep — a still-unsettled controversy that got Lendner, a medical resident in anesthesiology and the study’s first author, interested in constructing the study. Where there is a faster drop-off of high-frequency activity, after a period of low-frequency activity, there is an indication of REM sleep.
“We often tell our patients that, ‘You will go to sleep now,’ and I was curious how much these two states actually overlap,” says Lendner, who is currently in her fourth year of residency 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.”
There are myriad reasons for why we sleep — as it enhances our cognitive abilities — learning and memorization, as well as weighing in on our ability to make logical, informed decisions and choices. Therefore, sleep deprivation is a threat to all of this — affecting us on a cognitive as well as an emotional and physical level. This is why Knight and his lab have spent the past decade studying white noise in EEGs — and have already found a few things it can tell us about the brain.
In research published in The Journal of Neuroscience, along with his postdoctoral assistant, Knight discovered that as our brains mature, a white noise signal becomes much more dominant within the organ, and the researchers discovered correlation between white noise and a decline of working memory due to advanced age. Lendner was initially fascinated by the possibility of what this noise could indicate in the developing brains of infants, but the problem is that infant brains also don’t produce the typical alpha wave troughs we are used to seeing, leading her colleagues to question when these waves begin to develop in the first place and even how they start to form.
“There is this background activity, which is not rhythmic, and we have overlooked that for quite a long time,” says Lendner. “Sometimes, it has been called noise, but it is not noise; it carries a lot of information, also about the underlying arousal level. This measure makes it possible to distinguish REM sleep from wakefulness by looking only at the EEG.”
Periods of restfulness are associated with slow waves in the brain, while high frequency activity is associated with alertness. The sharp drop-off could indicate that the brain is actively shutting down many of its activities, particularly those involving muscle movement, in order to prepare for REM sleep.
This new measure gives a ratio for the allotment of brain activity during different frequencies. It looks over how much activity is taking place during frequencies that range between 1 cycle per second to 50 cycles per second — and then it looks at the slope — how fast does the activity slow down. This drop-off from your brain’s general activity happens more sharply when you drift off into REM sleep than when you’re awake and alert — or if you have been given anesthesia before surgery.
Lendner observed this characteristic metric after reviewing the nighttime brain activity of 20 patients, with data recorded through EEG scalp electrodes in Walker’s UC Berkeley sleep lab. An additional 10 people she used as test subjects had had electrodes placed into their brains to determine what triggered their epileptic episodes, before they underwent brain surgery to reduce the likelihood of seizures.
She then looked at brain activity in 12 patients with epilepsy and another nine patients who were anesthetized with Propofol before undergoing spinal surgery.
For the next part of her research, Lendner is studying the brain recordings from comatose patients, to get a consistent pattern of their daily brain activity. Along with her team, she hopes that by measuring this drop-off in brain waves, they can determine the likelihood of whether a comatose patient can one day wake up. If it’s a reliable indicator, a great deal of public interest and support could follow.
