Sleep as an Altered State of Consciousness
The risks and benefits of losing consciousness while asleep
By definition, to be asleep is to be unconscious. From a biological perspective, sleeping would seem like a dangerous thing to do, considering the associated vulnerability to predators or competitors; therefore, from an evolutionary standpoint, it must have some significant survival value.
Perhaps there is a Darwinian payoff that derives from the need for a sleeping animal to find a safe retreat and thereby keep out of harm’s way for a significant portion of the day. Another biological benefit of sleep may derive from energy conservation, although surprisingly, calorie consumption is only slightly less than when lying quietly awake. Because sleep is actively promoted by the brain and is such a powerful biological imperative, the reason for its occurrence must lie with some brain process that is best carried out in an unconscious state. Memory consolidation could be one such function.
The restorative quality of sleep is highly dependent on sleep continuity; that is, the duration of continuous unconsciousness between awakenings or arousals. The total time asleep is of secondary importance. A person with sleep apnea may accumulate the same number of minutes of sleep as another person, but nevertheless feel pathologically sleepy during the day because of the repeated arousals (interruptions to sleep) caused by airway obstructions.
Not quite awake, not quite asleep
The dichotomous terms conscious and unconscious imply that consciousness is an either/or state – the brain is either on or off. But the transition from wake to sleep is rarely like turning out the lights. More often there is a gradual reduction in consciousness with fuzzy, halfway states in between. When intentionally awakened from the lightest stage of sleep (Stage I as determined by EEG monitoring), about half the time, people will report that they were, in fact, awake. In other words, it is difficult to perceive the difference.
While falling asleep takes some time (10 to 20 minutes is perfectly normal), the reverse transition, from sleep to wake (as when the alarm rings), should be almost instantaneous. However, if awakened prematurely, or after a long nap, sleepiness persists, generating a groggy, sluggish feeling that is technically known as sleep inertia. It normally goes away with time or a strong cup of coffee.
For people who have more than the usual amount of difficulty with sleep inertia, the term sleep drunkenness is used. These folks can be perfectly nice when fully conscious, but if you try to wake them up before they are ready, they can be quite uncivilized – swearing and even swinging at you.
Sleepwalking (somnambulism) and sleep talking occur commonly in children and in some vulnerable adults. These behaviors can be thought of as extreme forms of sleep inertia in which a person only partially arouses from the deepest levels of sleep – awake enough to mumble some words or maybe even get out the bed and wander around. Amnesia for the episode is the rule.
Even when fully asleep, there are elements of consciousness that are preserved. For example, sleepers normally keep track of their body’s position in space as evidenced by the observation that only confused or brain-injured adults fall out of bed. If it were otherwise, no one would sleep in the top bunk.
Although we usually measure the depth of sleep by how intense a stimulus is required to trigger an awakening, the meaning of the stimulus is also important. For instance, a person is more likely to awaken to the sound of his or her own name than to another name of equal loudness. Moreover, sleeping mothers have an uncanny ability to hear their babies starting to cry during the night (fathers seem to have a higher threshold). Furthermore, some studies have found that mothers are more likely to awaken to the sound of their own baby crying compared to the cry of another baby of equivalent loudness.
During sleep, there is often a sense of time passed, even if one does not specifically awaken or look at the clock. Some people are so good at judging the passage of time while asleep that they never set an alarm, even if they have an airplane to catch.
During rapid eye movement (REM) sleep, the dreaming brain is (in a way) conscious; however, not with regard to the external environment, but rather to an internal theater of images generated from deep within the brainstem. Solipsistic philosophers have difficulty disproving the proposition that our normal waking state is just another kind of dream. (Maybe you can prove you are not just dreaming as you read Open Spaces.)
In other stages of sleep, there can also be a certain amount of mental activity. Although most people in non-REM sleep report being unequivocally unconscious, some say (when tapped on the shoulder) they have been awake and ruminating. In the extreme, this discontinuity between subjective and objective assessments of sleep constitutes a diagnosable sleep disorder called sleep misperception or subjective (as opposed to objective) insomnia. I believe that such people truly feel awake even when our polygraphs indicate they are asleep.
Sleeping pills can counteract the tendency for sleep misperception by inducing amnesia for brief awakenings that are a normal occurrence during sleep. In many clinical trials, sleeping pills seem to have a larger effect on the subjective sense of sleep than on the objective indicators. It is not uncommon for actively treated patients to get only about 15 minutes more sleep than patients given a placebo, but their subjective estimates of sleep time may be increased by an hour or more.
Most people feel that descending into a deeply unconscious state is a desirable aspect of sleep. Bobbing near the surface of wakefulness is an annoying experience, although this could be in some respects an attitudinal problem. In an experiment conducted by Thomas Wehr at the National Institute of Mental Health, subjects were kept in total darkness for 14 hours a day for a month, thereby consigning them to many hours of quiet, relaxed wakefulness. Once they got used to it, many of these people welcomed it as an “altered state of consciousness, not unlike meditation.”
Sleep, General Anesthesia, Coma and Persistent Vegetative State
Being “put to sleep” with a general anesthetic is, in a sense, a metaphor. In some ways, the anesthetized state resembles sleep but just what is going on in the anesthetized brain remains a mystery. Brain waves are present, but there is no response to pain-inducing stimuli and there is no memory of the experience. Curiously, general anesthesia blocks the sense of a passage of time so that even if you have been in surgery for hours, when you “come to,” it seems like almost no time has passed.
Coma is a consequence of acute brain injury. Comatose patients are continuously unconscious and do not have a sleep wake cycle. It can be prolonged but is usually a transitional state. It may be followed by a full recovery or may proceed to a chronic neurological impairment death.
Occasionally a patient with pervasive brain injury recovers a minimal but stable level of function called persistent vegetative state (PVS). Notably, in PVS, the sleep-wake cycle returns even though consciousness, in any conceivable sense, is gone. PVS has been characterized as being awake without being aware. There is neither sentient perception nor response. The occasional vocalizations (not speech) and semi-coordinated, reflexive movements make PVS heart-rending for families. It can appear that the patient is somehow (hope against hope) capable of truly waking up. The deeper brain centers that control breathing, heartbeat, as well as the sleep wake cycle, are functional, but the cerebral cortex, the primary organ of consciousness, is damaged beyond repair. Poor Terri Schiavo’s cerebral cortex was dramatically shrunken and her brain waves were perfectly flat.
Sleeping deeply, thinking deeply
Consciousness is a favorite topic for philosophers. I wonder how we would conceive of consciousness if we never slept and therefore did not regularly experience its absence. René Descartes said, “I think therefore I am.” Apparently this famous equation would have as easily been translated, “I am conscious therefore I am.” In his formulation, Descartes separated mind from body (a division that philosophers have argued about ever since). The formulation also clearly asserted that consciousness is inexorably connected to our definition of being alive. Because, in some sense, we all agree with Descartes, people with beating hearts but no brain function can be considered to be dead. I like to think there is a corollary, extended in the other direction. To be enlightened is to be awakened. The more conscious we are, the more fully alive.
Robert Sack, M.D. is professor emeritus in the Department of Psychiatry at the Oregon Health and Science University. He is a specialist in sleep disorders.
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