Why We Sleep

This is the first of two chapters to consider the deadly consequences of sleep deprivation. In this chapter, Walker explores how inadequate sleep impacts the brain, including links to various neurological and psychiatric conditions.

Walker discusses three key findings from 30 years of research on the impacts of sleep deprivation on concentration. The first is that the brain begins to fail after being awake for 16 hours. To maintain cognitive performance, humans need at least seven hours of sleep each night. Sleep deprived individuals are more likely to experience episodes of microsleep, which are fleeting, uncontrollable episodes of sleep that last under a few seconds. Performance deterioration also builds up over time. The brains of individuals who get just seven hours of sleep for 10 days are just as dysfunctional as those who stay awake for 24 hours. No amount of recovery sleep is sufficient to restore performance back to normal levels after sleep deprivation. Even naps and caffeine, which “momentarily increase basic concentrations under conditions of sleep deprivation” (145), are not enough to salvage the brain’s performance. Finally, humans cannot recognize how sleep-deprivation negatively impacts their mental aptitude and physical vitality.

Inadequate sleep not only impacts concentration but plays havoc with human emotions. Sleep-deprived individuals often act irrational. The reason behind “this primitive pattern of uncontrolled reactivity” (147) is due to the decoupling of the prefrontal cortex, which is associated with decision-making and rationality, from the amygdala, a structure in the brain responsible for triggering strong emotions and the fight-or-flight response. In well-rested individuals, the cortex regulates the strong emotions of the amygdala but cannot do so in sleep-deprived individuals. Extreme swings in positive and negative emotions due to sleep deprivation are dangerous, leading to depression, suicidal thoughts, suicide attempts, violence, risk-taking, and addiction.

To Walker, this research demonstrates that otherwise healthy individuals can experience neurological patterns of brain activity similar to individuals with psychiatric conditions, calling into question the long-held belief that mental disorders cause sleep disruption. The author notes that “improving sleep quantity, quality, and regularity” (151) might have therapeutic potential for many psychiatric illnesses. 

Walker starts with the simple and truthful expression, “Unhealthy sleep, unhealthy heart” (165). Studies link sleep deprivation with both high blood pressure (hypertension), which is a contributing factor to cardiac failure, heart disease, kidney failure, and stroke, and the closing of critical passageways that feed blood to the heart, increasing the risk of a coronary heart attack. The sympathetic nervous system, which is responsible for activating the fight-or-flight stress response, plays a critical role in the degradation of cardiovascular health. During deep NREM sleep, the brain sends a calming signal to this system to prevent it from activating. However, sleep deprivation causes it to remain “stuck in the ‘on’ position for long durations of time” (167), leading to “an escalation of this physiological stress that is synonymous with increased blood pressure, heart attack, heart failure, and stroke” (168).

Another example is the relationship between sleep loss, immune deficiency, and cancer. Sleeping less than seven and a half to eight hours a night weakens the immune system. For example, one study found that a single night of four hours of sleep removed 70% of the natural killer cells in an individual’s immune system, which are responsible for identifying and removing tumors and virally infected cells. Therefore, poor sleep quality increases the risk of cancer development. Moreover, if cancer is established, the body has a harder time fighting it due to the prolonged impacts of sleep loss on the immune system.

The closing example of this chapter is the most troubling because it illustrates that “chronic sleep loss will erode the very essence of biological life itself: your genetic code and the structures that encapsulate it” (187). Genes in the brain depend on consistent and sufficient sleep quality and quantity for their regulation. Insufficient sleep alters the activity of many genes, which leads some to shut down and others to increase, including those linked to factors that cause cardiovascular disease. It also damages the physical structure of DNA, which represents the genetic essence of humans. To Walker, humans are conducting genetic engineering experiments on themselves and their children, which should make all of us uncomfortable.