Why We Sleep

by Matthew Walker

  Cartwright’s data offered further psychological affirmation of our biological overnight therapy theory, but it took a chance meeting at a conference one inclement Saturday in Seattle before my own basic research and theory would be translated from bench to bedside, helping to resolve the crippling psychiatric condition of post-traumatic stress disorder (PTSD).

  Patients with PTSD, who are so often war veterans, have a difficult time recovering from horrific trauma experiences. They are frequently plagued by daytime flashbacks of these intrusive memories and suffer reoccurring nightmares. I wondered whether the REM-sleep overnight therapy mechanism we had discovered in healthy individuals had broken down in people suffering from PTSD, thereby failing to help them deal with their trauma memories effectively.

  When a veteran soldier suffers a flashback triggered by, say, a car backfiring, they can relive the whole visceral traumatic experience again. It suggested to me that the emotion had not been properly stripped away from the traumatic memory during sleep. If you interview PTSD patients in the clinic, they will often tell you that they just cannot “get over” the experience. In part, they are describing a brain that has not detoxed the emotion from the trauma memory, such that every time the memory is relived (the flashback), so, too, is the emotion, which has not been effectively removed.

  Already, we knew that the sleep, especially the REM sleep, of patients suffering from PTSD was disrupted. There was also evidence suggesting that PTSD patients had higher-than-normal levels of noradrenaline released by their nervous system. Building on our overnight therapy theory of REM-sleep dreaming and the emerging data that supported it, I wrote a follow-up theory, applying the model to PTSD. The theory proposed that a contributing mechanism underlying the PTSD is the excessively high levels of noradrenaline within the brain that blocks the ability of these patients from entering and maintaining normal REM-sleep dreaming. As a consequence, their brain at night cannot strip away the emotion from the trauma memory, since the stress chemical environment is too high.

  Most compelling to me, however, were the repetitive nightmares reported in PTSD patients—a symptom so reliable that it forms part of the list of features required for a diagnosis of the condition. If the brain cannot divorce the emotion from memory across the first night following a trauma experience, the theory suggests that a repeat attempt of emotional memory stripping will occur on the second night, as the strength of the “emotional tag” associated with the memory remains too high. If the process fails a second time, the same attempt will continue to repeat the next night, and the next night, like a broken record. This was precisely what appeared to be happening with the recurring nightmares of the trauma experience in PTSD patients.

  A testable prediction emerged: if I could lower the levels of noradrenaline in the brains of PTSD patients during sleep, thereby reinstating the right chemical conditions for sleep to do its trauma therapy work, then I should be able to restore healthier quality REM sleep. With that restored REM-sleep quality should come an improvement in the clinical symptoms of PTSD, and further, a decrease in the frequency of painful repetitive nightmares. It was a scientific theory in search of clinical evidence. Then came the wonderful stroke of serendipity.

  Soon after my theoretical paper was published, I met Dr. Murray Raskind, a remarkable physician who worked at a US Department of Veterans Affairs hospital in the Seattle area. We were both presenting our own research findings at a conference in Seattle and, at the time, we were each unaware of the other’s emerging new research data. Raskind—a tall man with kindly eyes whose disarmingly relaxed, jocular demeanor belies a clinical acumen that is not to be underestimated—is a prominent research figure in both the PTSD and Alzheimer’s disease fields. At the conference, Raskind presented recent findings that were perplexing to him. In his PTSD clinic, Raskind had been treating his war veteran patients with a generic drug called prazosin to manage their high blood pressure. While the drug was somewhat effective for lowering blood pressure in the body, Raskind found it had a far more powerful yet entirely unexpected benefit within the brain: it alleviated the reoccurring nightmares in his PTSD patients. After only a few weeks of treatment, his patients would return to the clinic and, with puzzled amazement, say things like, “Doc, it’s the strangest thing, my dreams don’t have those flashback nightmares anymore. I feel better, less scared to fall asleep at night.”

  It turns out that the drug prazosin, which Raskind was prescribing simply to lower blood pressure, also has the fortuitous side effect of suppressing noradrenaline in the brain. Raskind had delightfully and inadvertently conducted the experiment I was trying to conceive of myself. He had created precisely the neurochemical condition—a lowering of the abnormally high concentrations of stress-related noradrenaline—within the brain during REM sleep that had been absent for so long in these PTSD patients. Prazosin was gradually lowering the harmful high tide of noradrenaline within the brain, giving these patients healthier REM-sleep quality. With healthy REM sleep came a reduction in the patients’ clinical symptoms and, most critically, a decrease in the frequency of their repetitive nightmares.

  Raskind and I continued our communications and scientific discussions throughout that conference. He subsequently visited my lab at UC Berkeley in the months that followed, and we talked nonstop throughout the day and into the evening over dinner about my neurobiological model of overnight emotional therapy, and how it seemed to perfectly explain his clinical findings with prazosin. These were hairs-on-the-back-of-your-neck-standing-up conversations, perhaps the most exciting I have ever experienced in my career. The basic scientific theory was no longer in search of clinical confirmation. The two had found each other one sky-leaking day in Seattle.

  Mutually informed by each other’s work, and based on the strength of Raskind’s studies and now several large-scale independent clinical trials, prazosin has become the officially approved drug by the VA for the treatment of repetitive trauma nightmares, and has since received approval by the US Food and Drug Administration for the same benefit.

  Many questions remain to be addressed, including more independent replication of the findings in other types of trauma, such as sexual abuse or violence. It is also not a perfect medication due to side effects at higher doses, and not every individual responds to the treatment with the same success. But it is a start. We now have a scientifically informed explanation of one function of REM sleep and the dreaming process inherent in it, and from that knowledge we have taken the first steps toward treating the distressing and disabling clinical condition of PTSD. It may also unlock new treatment avenues regarding sleep and other mental illness, including depression.

  DREAMING TO DECODE WAKING EXPERIENCES

  Just when I thought REM sleep had revealed all it could offer to our mental health, a second emotional brain advantage gifted by REM sleep came to light—one that is arguably more survival-relevant.

  Accurately reading expressions and emotions of faces is a prerequisite of being a functional human being, and indeed, a functional higher primate of most kinds. Facial expressions represent one of the most important signals in our environment. They communicate the emotional state and intent of an individual and, if we interpret them correctly, influence our behavior in return. There are regions of your brain whose job it is to read and decode the value and meaning of emotional signals, especially faces. And it is that very same essential set of brain regions, or network, that REM sleep recalibrates at night.

  In this different and additional role, we can think of REM sleep like a master piano tuner, one that readjusts the brain’s emotional instrumentation at night to pitch-perfect precision, so that when you wake up the next morning, you can discern overt and subtly covert micro-expressions with exactitude. Deprive an individual of their REM-sleep dreaming state, and the emotional tuning curve of the brain loses its razor-sharp precision. Like viewing an image through frosted glass, or looking at an out-of-focus picture, a dream-starved brain cannot accurately decode f
acial expressions, which become distorted. You begin to mistake friends for foes.

  We made this discovery by doing the following. Participants came into my laboratory and had a full night of sleep. The following morning, we showed them many pictures of a specific individual’s face. However, no two pictures were the same. Instead, the facial expression of that one individual varied across the images in a gradient, shifting from friendly (with a slight smile, calming eye aperture, and approachable look) to increasingly stern and threatening (pursed lips, a furrowed brow, and a menacing look in the eyes). Each image of this individual was subtly different from those on either side of it on the emotional gradient, and across tens of pictures, the full range of intent was expressed, from very prosocial (friendly) to strongly antisocial (unfriendly).

  Participants viewed the faces in a random fashion while we scanned their brains in an MRI machine, and they rated how approachable or threatening the images were. The MRI scans allowed us to measure how their brains were interpreting and accurately parsing the threatening facial expressions from the friendly ones after having had a full night of sleep. All the participants repeated the same experiment, but this time we deprived them of sleep, including the critical stage of REM. Half of the participants went through the sleep deprivation session first, followed by the sleep session second, and vice versa. In each session, a different individual was featured in the pictures, so there was no memory or repetition effects.

  Having had a full night of sleep, which contained REM sleep, participants demonstrated a beautifully precise tuning curve of emotional face recognition, rather like a stretched out V shape. When navigating the cornucopia of facial expressions we showed them inside the MRI scanner, their brains had no problem deftly separating one emotion from another across the delicately changing gradient, and the accuracy of their own ratings proved this to be similarly true. It was effortless to disambiguate friendly and approachable signals from those intimating even minor threat as the emotional tide changed toward the foreboding.

  Confirming the importance of the dream state, the better the quality of REM sleep from one individual to the next across that rested night, the more precise the tuning within the emotional decoding networks of the brain the next day. Through this platinum-grade nocturnal service, better REM-sleep quality at night provided superior comprehension of the social world the next day.

  But when those same participants were deprived of sleep, including the essential influence of REM sleep, they could no longer distinguish one emotion from another with accuracy. The tuning V of the brain had been changed, rudely pulled all the way up from the base and flattened into a horizontal line, as if the brain was in a state of generalized hypersensitivity without the ability to map gradations of emotional signals from the outside world. Gone was the precise ability to read giveaway clues in another’s face. The brain’s emotional navigation system had lost its true magnetic north of directionality and sensitivity: a compass that otherwise guides us toward numerous evolutionary advantages.

  With the absence of such emotional acuity, normally gifted by the re-tuning skills of REM sleep at night, the sleep-deprived participants slipped into a default of fear bias, believing even gentle- or somewhat friendly looking faces were menacing. The outside world had become a more threatening and aversive place when the brain lacked REM sleep—untruthfully so. Reality and perceived reality were no longer the same in the “eyes” of the sleepless brain. By removing REM sleep, we had, quite literally, removed participants’ levelheaded ability to read the social world around them.

  Now think of occupations that require individuals to be sleep-deprived, such as law enforcement and military personnel, doctors, nurses, and those in the emergency services—not to mention the ultimate caretaking job: new parents. Every one of these roles demands the accurate ability to read the emotions of others in order to make critical, even life-dependent, decisions, such as detecting a true threat that requires the use of weapons, assessing emotional discomfort or anguish that can change a diagnosis, the extent of palliative pain medication prescribed, or deciding when to express compassion or dispense an assertive parenting lesson. Without REM sleep and its ability to reset the brain’s emotional compass, those same individuals will be inaccurate in their social and emotional comprehension of the world around them, leading to inappropriate decisions and actions that may have grave consequences.

  Looking across the life span, we have discovered that this REM-sleep recalibration service comes into its own just prior to the transition into adolescence. Before that, when children are still under close watch from their parents, and many salient assessments and decisions are made by Mom and/or Dad, REM sleep provides less of a re-tuning benefit to a child’s brain. But come the early teenage years and the inflection point of parental independence wherein an adolescent must navigate the socioemotional world for himself, now we see the young brain feasting on this emotional recalibration benefit of REM sleep. That is not to suggest that REM sleep is unnecessary for children or infants—it very much is, as it supports other functions we have discussed (brain development) and will next discuss (creativity). Rather, it is that this particular function of REM sleep, which takes hold at a particular developmental milestone, allows the burgeoning pre-adult brain to steer itself through the turbulent waters of a complex emotional world with autonomy.

  We shall return to this topic in the penultimate chapter when we discuss the damage that early school start times are having on our teenagers. Most significant is the issue of sunrise school bus schedules that selectively deprive our teenagers of that early-morning slumber, just at the moment in their sleep cycle when their developing brains are about to drink in most of their much-needed REM sleep. We are bankrupting their dreams, in so many different ways.

  Chapter 11

  Dream Creativity and Dream Control

  Aside from being a stoic sentinel that guards your sanity and emotional well-being, REM sleep and the act of dreaming have another distinct benefit: intelligent information processing that inspires creativity and promotes problem solving. So much so, that some individuals try controlling this normally non-volitional process and direct their own dream experiences while dreaming.

  DREAMING: THE CREATIVE INCUBATOR

  Deep NREM sleep strengthens individual memories, as we now know. But it is REM sleep that offers the masterful and complementary benefit of fusing and blending those elemental ingredients together, in abstract and highly novel ways. During the dreaming sleep state, your brain will cogitate vast swaths of acquired knowledge,fn1 and then extract overarching rules and commonalities—“the gist.” We awake with a revised “Mind Wide Web” that is capable of divining solutions to previously impenetrable problems. In this way, REM-sleep dreaming is informational alchemy.

  From this dreaming process, which I would describe as ideasthesia, have come some of the most revolutionary leaps forward in human progress. There is perhaps no better illustration highlighting the smarts of REM-sleep dreaming than the elegant solution to everything we know of, and how it fits together. I am not trying to be obtuse. Rather, I am describing the dream of Dmitri Mendeleev on February 17, 1869, which led to the periodic table of elements: the sublime ordering of all known constituent building blocks of nature.

  Mendeleev, a Russian chemist of renowned ingenuity, had an obsession. He felt there might be an organizational logic to the known elements in the universe, euphemistically described by some as the search for God’s abacus. As proof of his obsession, Mendeleev made his own set of playing cards, with each card representing one of the universal elements and its unique chemical and physical properties. He would sit in his office, at home, or on long train rides, and maniacally deal the shuffled deck down onto a table, one card at a time, trying to deduce the rule of all rules that would explain how this ecumenical jigsaw puzzle fit together. For years he pondered the riddle of nature. For years he failed.

  After allegedly having not slept for three days and three nig
hts, he’d reached a crescendo of frustration with the challenge. While the extent of sleep deprivation seems unlikely, a clear truth was Mendeleev’s continued failure to crack the code. Succumbing to exhaustion, and with the elements still swirling in his mind and refusing organized logic, Mendeleev lay down to sleep. As he slept, he dreamed, and his dreaming brain accomplished what his waking brain was incapable of. The dream took hold of the swirling ingredients in his mind and, in a moment of creative brilliance, snapped them together in a divine grid, with each row (period) and each column (group) having a logical progression of atomic and orbiting electron characteristics, respectively. In Mendeleev’s own words:fn2

  I saw in a dream a table where all the elements fell into place as required. Awakening, I immediately wrote it down on a piece of paper. Only in one place did a correction later seem necessary.

  While some contest how complete the dream solution was, no one challenged the evidence that Mendeleev was provided a dream-inspired formulation of the periodic table. It was his dreaming brain, not his waking brain, that was able to perceive an organized arrangement of all known chemical elements. Leave it to REM-sleep dreaming to solve the baffling puzzle of how all constituents of the known universe fit together—an inspired revelation of cosmic magnitude.

  My own field of neuroscience has been the beneficiary of similar dream-fueled revelations. The most impactful is that of neuroscientist Otto Loewi. Loewi dreamed of a clever experiment on two frogs’ hearts that would ultimately reveal how nerve cells communicate with each other using chemicals (neurotransmitters) released across tiny gaps that separate them (synapses), rather than direct electrical signaling that could only happen if they were physically touching each other. So profound was this dream-implanted discovery that it won Loewi a Nobel Prize.