Chapter 5
The (Relatively) New
Science of Sleep
The modern era of research into sleep and its anomalies was inaugurated in the mid Twentieth Century at the University of Chicago. There in the 1950s, physiologist Nathaniel Kleitman developed a method for investigating what happens in our crania and the rest of our bodies during sleep. Electrodes he attached to subjects’ heads recorded brain waves and eye movements.
Sleep, Professor Kleitman discovered, is divided into approximately ninety-minute cycles. In the first stage, major physiological systems quiet down, as if we are entering hibernation. Respiration and heart rate decrease; body temperature drops; brain waves shift from the rapid, waking rate to high-amplitude, slow waves. After about 90 minutes, bodily systems begin to revive, except for major muscles that relax abruptly, as the eyes start moving quickly behind closed lids. During this active or rapid eye movement (REM) sleep, if one awakens subjects, they usually report dreams. (REM sleep and its relation to dreaming had been noted in 1937 by another University of Chicago physiologist, Edward Jacobson). If you arouse subjects during non-REM periods, they are less likely to report dreams. They may report a thought or a simple dream image. These NREM dreams typically lack the narrative complexity and weird features we associate with more shareworthy dreams.
There are exceptions to every rule. Some people, such as light sleepers, do have more complex dreams during NREM sleep. These individuals are sometimes referred to as nonREM dreamers. People in highly anxious states and individuals deprived of REM sleep are also prone to these more complex NREM dreams. They occur more toward the end of a night’s sleep rather than in the beginning.
Nathaniel Kleitman’s research led to a deluge of studies with human volunteers and animals. Soon his techniques were applied to troubled sleepers. A new medical subspecialty was born. In 1968, Canadian neurologist and neuroscientist Roger Broughton became the Director of possibly the world’s first Sleep Medicine Center. Similar clinics, treating a growing variety of nocturnal problems, opened at other university-affiliated facilities. In 1975, the American Academy of Sleep Medicine was founded. Their International Classification of Sleep Disorders has undergone several revisions. Over seventy-five different sleep disorders have been identified. This number continues to expand.
New technologies, such as positron emission tomography (PET) scans and functional magnetic resonance imaging (fMRI), provide ever more sophisticated ways of observing what goes on in our brains. These machines enabled us to see that there are different patterns of activation and deactivation in the brain during the three states we cycle through every twenty-four hours (waking, NREM and REM sleep). During REM, there is less activity in the prefrontal cortex, the seat of our executive functions (logical thinking, judgment, decision-making, self-reflection). There is increased activity in sensory association areas and sites associated with emotion (limbic and paralimbic regions). In healthy people, the level of heightened activation in these regions is greater than that manifested while awake. The implication is that during REM sleep we are likely to see and hear illogical things that have emotional associations. Unhealthy subjects, such as those suffering from major depression or sleepwalking, may have different patterns of activation and deactivation in these brain areas.
Following his pioneering laboratory research demonstrating that sleepwalking typically begins following an EEG (electroencephalographic) awakening reaction during slow brain wave nonREM sleep, Broughton (Gastaut & Broughton, 1965; Broughton, 1968) proceeded to define not only somnambulism but also nocturnal terrors and confusional awakenings as nonREM disorders of arousal.
Commenting on the Kenneth Parks case, Berit Brogaard (2012), Director of University of Miami’s Brogaard Lab for Multisensory Research, and Kristian Marlow noted that normally sleepers are not consciously aware of sensory input from their surroundings. Furthermore, a gating mechanism blocks input from their cognitive brain to their motor system. The chemical messenger gamma-aminobutyric acid (GABA) inhibits the brain’s motor system. In less contemporary neurophysiological terms, Sigmund Freud, the Viennese neurologist who went on to found psychoanalysis as a subdiscipline of psychology, wrote that it is safe for us to indulge forbidden impulses while dreaming because access to motility has been disabled. In somnambulism, this important gating mechanism is defective, allowing the brain to issue effective commands to our muscles.
In children, neurons that release GABA are still developing. They have not yet fully established a network of connections to keep motor activity under control. Consequently, many youngsters occasionally sleepwalk. As they get older, they usually no longer engage in these nocturnal strolls. For some adults, this gating mechanism remains underdeveloped, or functions less effectively due to sleep deprivation, fever, anxiety, or drugs. As a result, they continue having somnambulistic episodes.