Inside the Intuitive System: Sleep, Thinking, and Behavior

Francisco Goya, “The Sleep of Reason Produces Monsters.” Los Caprichos, print #43.

“You’ll feel better after a good night’s sleep.” “I’m sleepwalking through life today.” “Let me sleep on it and get back to you.” “I‘m sorry, I must have slept through that part.” These and other sayings highlight the positive and negative roles of sleep in our everyday lives. On one hand sleep is a behavior — you can observe someone doing it, count the amount of time that it lasts, and ask people to rate the quality of their sleep. On the other hand, it’s a biological process with its own heart and breathing patterns, in which you can even quantify the amplitude of brainwaves at different stages. Sleep also provides our most common experience with an altered state of consciousness, in dreams that are generally experienced as outside of conscious control yet often vivid and compelling. Because the conscious, Narrative mind is shut down, many people experience sleep as “non-productive” or even distressing, and fight against it — the picture above suggests that painter Francisco Goya might have been among them. Yet the Intuitive mind is highly active during sleep and may be accessible in a way that it isn’t when the Narrative mind is awake to filter and edit its responses. The post below reviews studies of behavior, biology, and subjective experience to provide three different windows into the ubiquitous yet still mysterious phenomenon of sleep.

To begin with the biological aspect, one simple understanding of the phenomenon is that regular sleep allows body systems to rest and recover from use. Total sleep deprivation is fatal after about 2 weeks based on animal models, generally due to cardiovascular events like heart failure or stroke. After 36 hours without sleep, people begin to show problems with heart functioning including arrhythmia or high blood pressure. Physiological mechanisms that link sleep deprivation to heart problems may include increased activation of the sympathetic nervous system (the "fight or flight" reaction), endothelial dysfunction in the arteries, chronic inflammation, oxidative stress on the heart, and increased release of hormones that constrict the arteries and increase heart rate. Additionally, long-term sleep deprivation increases insulin sensitivity and decreases glucose tolerance, factors that predispose people to diabetes. 

At the level of behavior, sleep deprivation increases hunger and may make people crave certain types of foods (e.g., carbohydrates and sugar); combined with the metabolic effects described above, these changes in eating behavior help to explain the well-documented link between sleep deprivation and obesity. Although regular exercise is often suggested as one way for people to sleep better, lack of sleep actually makes exercise less tolerable -- sleep-deprived individuals perceive more exertion with the same level of heart and lung activity. Sleep deprivation naturally leads to feelings of fatigue, but can also increase people's perceptions of pain and result in poorer everyday mood. In fact, there is a sleep/pain/mood/fatigue symptom cluster in which these experiences commonly co-occur, which has been documented across multiple chronic disease states including cancer and HIV. This package of symptoms is also associated increased release of hormones that cause inflammation of body tissues, which can also over the long term contribute to cognitive problems, heart problems, and diabetes. Among older adults with mild cognitive impairment, improved sleep is associated with better concentration as well as better mood. 

Finally, sleep has important effects on people's conscious experiences. Sleep deprivation leads to altered awareness, and this occurs even if a person spends time physically resting but awake. Just 24 hours without sleep results in decreased memory, coordination, and concentration, with effects comparable to having a blood alcohol content of 0.10%. By 72 hours people begin to hallucinate or show other major cognitive problems. People who go without sleeping for a day or more may begin to sleep involuntarily, typically in the form of “microsleeps” where the conscious brain goes offline for a few seconds or longer. These episodes are physiologically identical to sleep at the level of the brain, but the person experiencing them may not be even aware that they occur. If they happen while performing a complex task like driving, they can be dangerous or fatal. Part of sleep’s function is apparently to permit dreaming, as people who are allowed to sleep but deprived of dreams (e.g., by waking them when their brainwaves show the REM state in which dreams most often occur) tend to drop into a REM state earlier in the sleep cycle over time. Although dream deprivation was once thought to be just as harmful as sleep deprivation itself, and may be associated with increased aggressiveness and sexuality, it now appears that dreams can also occur in other sleep stages to compensate at least somewhat for REM sleep loss.

These findings suggest that sleep cuts across both the Narrative and Intuitive systems proposed by Two Minds Theory. Some of the effects of sleep on the mind are clearly Intuitive, operating outside of awareness and creating potential impairments in behavior and experience that are beyond a person's conscious control. Goya's “Sleep of Reason Produces Monsters” reflects a deep ambivalence that many people feel toward sleep states -- although they are restorative they are also not conscious or controlled. This can be frightening to those of us who identify very strongly with our Narrative systems. But sleep also can provide a readily available window to wisdom that's not available to the conscious mind. This insight is the foundation for some Buddhist dream meditation practices, and long-term meditation can lead to a state of "relaxed alertness" that seems to include components of both waking and sleep. Based on the research presented above, it is a lack of sleep that seems most likely to produce "monsters" in terms of its negative effects on our lives. This is true even for the Narrative system that normally seems to be the antithesis of sleep in its functions of attention and awareness: Without good sleep, we have fewer cognitive resources available in waking life, experience more symptoms, and behave in less healthy ways without even realizing it. 

One of the most remarkable things that my colleagues and I discovered in a 2019 study of fatigue in people living with HIV was that people with HIV often had very poor sleep, yet they were often unaware of this fact. It took daily monitoring using a FitBit sensor to reveal the number of times their sleep was interrupted on an average night. Our participants themselves were very aware that they felt tired, that they didn't exercise as much as they wanted to, and even that they couldn't think as clearly as they wanted to. But they were initially likely to attribute those experiences to having HIV or to the medications they were taking to treat it. In fact, the research reviewed above suggests that many of their experiences could have been related to poor sleep. 

It’s important to note the “shape shifter” (or chicken-and-egg) problem associated with many of the findings reviewed here. Worse sleep could cause inflammation and poor mood, for instance, or it could be the result of those problems. Yet there are many simple nonpharmacological approaches to improve sleep, and better sleep might be one of the simplest ways to improve both our health and our ability to function effectively in everyday life. Addressing sleep problems may therefore be one of the first steps to try in any effort to improve one’s symptoms or overall health.