47 pages • 1 hour read
Matthew WalkerWhy We Sleep
Nonfiction | Book | Adult | Published in 2017A modern alternative to SparkNotes and CliffsNotes, SuperSummary offers high-quality Study Guides with detailed chapter summaries and analysis of major themes, characters, and more.
Part 3, Chapters 9-11Chapter Summaries & Analyses
Part 3: “How and Why We Dream”
Chapter 9 Summary: “Routinely Psychotic: REM-Sleep Dreaming”
Chapter 9 focuses on REM sleep and the dreams that occur during this sleep stage. The arrival of magnetic resonance imaging (MRI) scanners in the early-21st century revolutionized our understanding of “how it is that we dream (e.g., logical/illogical, visual/non-visual, emotional/non-emotional)” (194), “what it is that we dream about (e.g., experiences from our recent waking lives/de novo experiences)” (194), and “why it is that we dream” or the purpose(s) of REM-sleep dreaming (194). Prior to MRI, scientists only used electrodes placed on the scalp, which measure the electrical activity of the brain. In contrast, MRI scanners provide a structural map of the brain, enabling scientists to examine the different brain areas.
During REM sleep, the visual, motor, emotional, and autobiographical memory regions of the brain “light up” (195), indicating an increase in brain activity compared to deep NREM sleep. Regions of the prefrontal cortex, which controls rational thought, also deactivate during REM sleep. Different activity levels in the four brain regions allow scientists to determine the form of someone’s dream. For example, if there was greater motor activity and minimal visual and emotional activity, then the dream contained lots of movement with few emotions and visual scenes and objects. Recent findings from a Japanese research team also suggest that scientists might predict what someone dreams about.
An age-old question humanity has about sleep is: Where do dreams come from? The ancient Egyptians and the ancient Greeks believed dreams were sent by the gods, although the Greek philosopher Aristotle dismissed this idea and instead believed recent waking events served as the source material for dreams. Sigmund Freud, an Austrian neurologist and father of psychoanalysis (i.e., a type of therapy that aims to bring repressed emotions and memories to consciousness to help the client heal), was the first scholar to situate dreams within the brain, although the rest of his theories around decoding dreams are unscientific. Brain scanning methods have helped begin to uncover the source of dreams. The hippocampus plays a role in providing source material for dreams. However, dreams are not simply “a wholesale replay of our waking lives,” and in fact waking life events only comprise a small portion of dreams. Rather, emotions and concerns that individuals experience while awake are more likely to resurface in dreams.
Chapter 10 Summary: “Dreaming as Overnight Therapy”
The title of this chapter summarizes one of two key emotional benefits of REM-sleep dreaming: It serves as “a form of overnight therapy” (207). Walker’s own scientific studies illustrate that rather than dreaming being a byproduct of REM sleep with no function itself, dreams are critical to remembering painful events without the “visceral reaction that was presented and imprinted at the time of the episode” (209). REM-sleep dreaming is the only time that concentrations of noradrenaline, a stress-related brain chemical similar to the body chemical adrenaline, are shut-off. As a result, the brain processes emotion-specific memories in a safe, stress-free environment. For individuals to overcome depression and anxiety from emotional trauma, they must dream about the painful experience itself. Failure to do so results in individuals not overcoming the past event.
The second emotional benefit of REM-sleep dreaming is that it nightly recalibrates the region of the brain “whose job it is to read and decode the value and meaning of emotional signals, especially faces” (215). REM sleep-deprived individuals lose their ability to read facial expressions, and slip “into a default of fear bias” (216). These individuals view the social world around them as much more threatening than reality. The inability to read the emotions of others could lead doctors, nurses, law enforcement, military personnel, parents, and others to make inappropriate decisions that have life-altering consequences on their fellow humans.
Chapter 11 Summary: “Dream Creativity and Dream Control”
The final chapter of Part 3 examines the creative benefit of REM-sleep dreaming, which has led to “revolutionary leaps forward in human progress” (219). To determine how REM sleep produces creativity, Walker and a colleague performed a study, where they woke up subjects from NREM and REM sleep throughout the night and had them perform a cognitive test (i.e., an anagram task with scrambled words) for 90 seconds. Because the subjects were in this transitional sleep phase, meaning the brain had not yet fully awakened, the sleep scientists believed they could “capture some of the functional properties of the sleep stage from which the participant was woken” (223). The participants ability to solve the anagrams was much higher when woken from REM-sleep over NREM-sleep. Furthermore, the solution to the problem was more effortless “when the brain was being bathed in the afterglow of dream sleep” (224) compared to other sleep and awake stages. This experiment, along with others, revealed that REM sleep allows the brain to build creative and novel connections between distantly related sets of information that are not obvious during the waking day.
Part 3, Chapters 9-11 Analysis
Part 3 scientifically explains “the fantastical world of dreams” (11). The invention of brain-imaging machines drove recent scientific advances in REM-sleep dreaming. To illustrate the difference between data from brain scanners and traditional electroencephalogram (EEG) recordings, Walker uses a sports stadium analogy. He notes that “dangling a microphone over the stadium can measure the summed activity of the entire crowd” (194) but does not allow you to understand differences in reactions between different segments of the crowd. EEG recordings provide similar nonspecificity when measuring brain wave activity. In contrast, MRI scanners “carve up the stadium (the brain)” (195) into discrete segments, which scientists then map. These maps allow researchers to examine changes in brain activity between NREM sleep and REM sleep dreaming.
The main argument in Part 3 is that dreams have therapeutic, emotional processing, problem-solving, and creative functions. For a vivid visual of the link between dreaming and overcoming trauma, Walker refers to research he and others conducted on individuals with post-traumatic stress disorder (PTSD). Individuals living with this mental health condition cannot strip away the emotion from the trauma memory. PTSD patients have higher than normal concentrations of noradrenaline, which prevents the brain from divorcing the emotion from the memory. As such, PTSD patients have repetitive nightmares about the traumatic event. By suppressing concentrations of stress-related noradrenaline in the brain, PTSD patients have healthier REM sleep quality. In turn, this reduces the frequency of the PTSD patient’s repetitive nightmares.
Another example of the creative function of dreaming is how humanity solved the “baffling puzzle of how all constituents of the known universe fit together” (221). Russian chemist Dmitri Mendeleev believed there was a logical way to organize the known chemical elements. He created a set of playing cards, with each card representing one of the chemical elements. Mendeleev “maniacally” (220) tried to determine the order of these elements using his card deck. After allegedly three days of no sleep, Mendeleev slept and dreamt of a table where all of the elements fell into logical order. Upon waking, he wrote down the table of periodic elements.
The closing focus of Part 3 is on lucid dreaming, where an individual is conscious during a dream. Studies within the last few years demonstrate that lucid dreaming is not a sham. However, it remains unclear whether this dreaming state provides adaptative benefits. Some argue that “if gaining voluntary dream control were so useful, surely Mother Nature would have imbued the masses with such a skill” (234). Walker disagrees with this notion because it assumes that evolutionary pressures no longer shape sleep. In fact, he posits that lucid dreaming might be the next phase in humanity’s evolution, one in which we deliberately harness the creative problem-solving benefits of REM sleep dreaming.
