René Descartes conceived his idea of a mind through a lucid dream. He dreamed that he was interpreting the dream as it occurred. Later, when awake, he reasoned that if he could think and analyze a dream while asleep, his mind must function during both waking and sleeping. He proposed therefore that the mind must be independent of the body that undergoes sleeping and waking transitions. Contemporary fMRI studies suggest that lucid dreaming is especially common in people who display high levels of prefrontal cortex activity in Brodmann’s areas 9 and 10 (Filevich et al., 2015).

As described in preceding sections, what we colloquially refer to as waking comprises at least three states. First, alert consciousness without accompanying movement is associated with cholinergic system activity. Second, consciousness with movement is associated with serotonergic system activity. Third, the peptide orexin also plays a role in maintaining waking activity.

Similarly, sleep consists of NREM and REM phases. NREM sleep consists of the four stages indicated by the EEG (see Figure 13-12A). REM sleep periods consist of at least two stages, one in which small twitching movements occur and one in which such motion twitching is absent.

REM neurobehavioral events can occur relatively independently. Sleepers may awake to find themselves in a condition of sleep paralysis, during which they experience the hallucinations and fear common in dreams. People who are awake may fall into a state of cataplexy: they are conscious of being awake during the atonia and visual and emotional features of dreams.

Sleep researcher J. Allan Hobson reported his peculiar symptoms after a brainstem stroke (Hobson, 2002). For the first 10 days after the lesion, he had complete insomnia, neither REM nor NREM sleep. Whenever he closed his eyes, however, he did have visual hallucinations that had a dreamlike quality. This experience suggested that eye closure is sufficient to produce the visual components of REM sleep but with neither loss of consciousness nor atonia. Hobson eventually recovered typical sleeping patterns, and the hallucinations stopped.

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Beyond teaching us that the neural basis of consciousness is extremely complex, the study of sleep states and dreaming may help to explain some psychiatric and drug-induced conditions. For example visual and auditory hallucinations are among the symptoms of schizophrenia. Are these hallucinations dream events that occur unexpectedly during waking? Many people who take hallucinogenic drugs such as LSD report visual hallucinations. Does the drug initiate the visual features of dreams? People who have panic attacks suffer from very real fright that has no obvious cause. Are they experiencing the fear attacks that commonly occur during sleep paralysis and cataplexy?

What the study of sleep tells us about consciousness is that a remarkable number of variations of conscious states exist. Some are associated with waking and some with sleeping, and the two can mix together to produce a variety of odd conditions. When it comes to consciousness, there is far more to sleeping and waking than just sleeping and waking.