Occasional sleep disturbances are annoying and may impair performance the following day. About 15 percent of people complain of ongoing sleep problems; an additional 20 percent complain of occasional sleep problems. As people age, the incidence of complaints increases.

In the extreme, a rare genetic condition, fatal familial insomnia, causes individuals to stop sleeping altogether. Their insomnia contributes to death after a number of months without sleep. Prions (misfolded proteins) are proposed to cause the condition. A proposed treatment is doxycycline, an antibiotic with antiprion activity (Forloni et al., 2015). In this section we consider more common dysfunctions of NREM sleep and REM sleep (for more about prion disorders, see Chapter 16).

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The two most common sleep disorders occur during NREM sleep are insomnia, prolonged inability to sleep, and narcolepsy, uncontrollably falling asleep at inappropriate times. Insomnia and narcolepsy are related, as anyone who has stayed up late at night can confirm: a night without sleep is often accompanied by a tendency to fall asleep at inconvenient times the next day.

Insomnia

Our understanding of insomnia is complicated by the wide variation among people in how much time they spend asleep. Some short sleepers may think they should sleep more, and some long sleepers may think they should sleep less. Yet the sleeping pattern may be appropriate for each.

People’s sleep is disrupted by lifestyle choices such as those described in Clinical Focus 13-1. Staying up late, for example, may set a person’s circadian rhythm forward, encouraging a cascade of late sleep followed by staying up still later. Indoor and outdoor light pollution contributes to sleep disorders by disrupting circadian rhythms. Some sleep problems are brought on by shift work or by jet lag, as described in Section 13-1. Other common causes of sleep disorders are stress, long work hours, and an irregular lifestyle. Just worrying about insomnia is estimated to play a major role in 15 percent of cases.

Depressed people may sleep too much or too little. Anxiety and depression account for about 35 percent of insomnias. Quantitative differences also exist in depressed patients’ sleep because they enter REM sleep very quickly, as do people who are sleep-deprived.

Insomnia is brought on by sedative-hypnotic drugs, including Seconal, sodium amytal, and many minor tranquilizers. These sleeping pills do help people get to sleep, but the person is likely to feel groggy and tired the next day, which defeats the purpose of taking the drug. Although sleeping pills promote NREM sleep, they deprive the user of REM sleep. In addition, people develop tolerance to these medications, become dependent on them, and display rebound insomnia when they stop taking them. A person then may increase the dose each time the drug fails to produce the desired effect. The syndrome in which patients unsuccessfully attempt to sleep by increasing their drug dosage is called drug dependence insomnia.

Narcolepsy

Like many people, you may suddenly have been overcome by an urge to sleep at an inconvenient time, perhaps while attending a lecture. For some people such experiences with narcolepsy are common and disruptive. J. S., a junior in college, sat in the front row for his course on the brain. Within a few minutes after each class began, he dropped off to sleep. The instructor became concerned and asked J. S. to stay after class to discuss his sleeping behavior.

J. S. reported that sleeping in classes was a chronic problem. Not only did he sleep in class, he fell asleep whenever he tried to study. He even fell asleep at the dinner table and in other inappropriate locations. His sleeping problem had made getting through high school a challenge and was making it difficult for J. S. to pass his college courses.

About 1 percent of people have narcolepsy, which takes surprisingly varied forms. J. S. fell asleep while sitting still, and his sleeping bouts consisted of brief spurts of NREM sleep lasting 5 to 10 minutes. This pattern is similar to napping and to dropping off to sleep in class after a late night but is distinguishable as narcolepsy by its frequency and disruptive effect. J. S. eventually discussed his problem with his physician and received a prescription for Ritalin, an amphetaminelike drug that stimulates dopamine transmission. The treatment proved helpful.

Studies of narcoleptic people in sleep clinics resulted in a surprising discovery concerning one cause of narcolepsy: sleep apnea, an inability to breathe during sleep. Clinical Focus 13-5, Sleep Apnea, describes a person who spent all night every night waking up to breathe. This nighttime behavior left him extremely tired and caused him to nod off in the daytime. Being overweight contributes to sleep apnea as well as to metabolic syndrome. Clearly the relationship between sleep and health is both complex and interconnected.

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Several sleep disorders are associated with the unexpected onset of atonia and dreams, two main features of REM sleep. We describe three: sleep paralysis, cataplexy, and REM sleep behavioral disorder.

Sleep Paralysis

In sleep paralysis both atonia and dreaming can occur when a person is awake, usually just falling asleep or waking up. L. M., a college senior, recounted the following experience.

She had just gone to sleep when her roommate came into their room. L. M. woke up and intended to ask her roommate if she wanted to go skating the next morning but found herself unable to speak. She tried to turn her head to follow her roommate’s movements across the room but found that she was paralyzed. She had the terrifying feeling that some creature was hiding in the bathroom waiting for her roommate. She tried to cry out but produced only harsh gurgling noises. In response to these peculiar noises the roommate knocked her out of her paralysis by hitting her with a pillow.

Sleep paralysis is common. In informal class surveys almost a third of students report having had such an experience, as do some war veterans during group therapy sessions. The atonia is typically accompanied by dread or fear. It seems likely that in sleep paralysis a person has entered REM sleep partially. He or she is dreaming, atonia has occurred, but the sleeper remains “awake.” When sleep paralysis occurs as a person wakes up, the paralysis and dreaming characteristic of a REM episode continue.

Cataplexy

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The atonia of REM sleep can also occur while a person is awake and active, a condition called cataplexy. The person loses muscle tone and gradually or even quickly falls to the floor, atonic. The collapse can be so sudden that injury is a real risk. Cataplexy can be triggered by excitement or laughing. While in an atonic condition, the person sees imaginary creatures or hears imaginary voices. People who fall into a state of cataplexy with these hypnogogic hallucinations give every appearance of having fallen into REM sleep while remaining “awake.”

Cataplexy can have a genetic basis. In 1970 William Dement was given a litter of Doberman pinscher dogs and later a litter of Labrador retrievers. These dogs displayed cataplexy. The disease is transmitted as a recessive trait: to develop it, a dog must inherit the gene from both its mother and its father. The descendants of those dogs continue to provide animal models for investigating the neural basis of the disease as well as its treatment.

Jerome Siegel (2004) investigated the cause of narcolepsy in dogs. He found that neurons in the subcoerulear nucleus become inactive and neurons in the magnocellular nucleus of the medulla become active during attacks of cataplexy, just as they do during REM sleep. On the basis of anatomical examinations of the brains of narcoleptic dogs, Siegel suggested that the death of neurons in the amygdala and adjacent forebrain areas is a one-time event that occurs just before the onset of the disease early in life.

A remarkable discovery that came from this line of investigation is that a subset of these affected neurons produces a peptide called orexin (also called hypocretin) that serves as a signaling molecule to maintain wakefulness. Orexin cells, which are located in the hypothalamus, send projections to many other brain regions, as do the nonspecific activating systems using acetylcholine and serotonin. This suggests that orexin plays a role in maintaining activity during waking.

To test the idea that orexin loss is related to cataplexy, investigators have bred knockout mice that lack orexin. When these mice become active, such as at feeding time, they collapse into cataplexy, supporting the idea that an orexin system contributes to healthy waking behavior. Research with mice also suggests that lifestyle may contribute to orexin cell loss. Mice fed a high-fat diet display a reduction in orexin cells and symptoms of cataplexy (Nobunaga et al., 2014). Another proposed cause of narcolepsy in humans is an autoimmune reaction: the immune system attacks and kills orexin cells.

REM Sleep Behavioral Disorder

In Section 13-4 we described REM sleep behavioral disorder (REM without atonia), a symptom displayed by some people who take antidepressant drugs. They wake up seemingly acting out dream activity. In Section 13-5 we described Jouvet’s experiment: he reported that cats with lesions to the subcoerulear region of the brainstem entered REM sleep without accompanying atonia and so apparently acted out their dreams.

A similar condition reported in people may have either a genetic basis or a neurological cause associated with aging. People who display REM sleep behavioral disorder behave as though they are acting out their dreams (Mahowald & Schenck, 2015). Following is the account of a 67-year-old patient (Schenck et al., 1986):

I had a dream where someone was shooting at me with a rifle and it was in a field that had ridges in it, so I decided to crawl behind a ridge—and I then had a gun too—and I look over the ridge so when he showed up I would shoot back at him and when I came to [i.e., awakened] I was kneeling alongside the bed with my arms extended like I was holding the rifle up and ready to shoot.

In the dream the patient saw vivid images but heard nothing and felt afraid. Although many patients have described such experiences, most are elderly and suffer from brain injury or other brain-related disorders. REM sleep behavioral disorder can be treated with benzodiazepines, antianxiety drugs that block REM sleep.

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Sleep Disorders

Before you continue, check your understanding.

Question 1

Question 2

Question 3

Question 4

Question 5

Answers appear in the Self Test section of the book.