(14) Biological rhythms, sleep and dreaming

Circadian rhythm

A pattern of behavioral, biochemical, or physiological fluctuation that has a 24-hour period. Almost all physiological measures - hormone levels, body temperature, drug sensitivity - change in a regular repeating fashion over the course of the day. The most obvious of these rhythms in human behavior is the bout of sleep (which is synchronized to many external events, including light and dark).

Chronotype

Natural preferences of the body for wakefulness and sleep. An individuals natural preferences is influenced by genetics and driven by circadian rhythms. These preferences affects sleep as well as performance during the day.

Diurnal

Active during the light period of the daily cycle.

Nocturnal

 Active during the dark periods of the daily cycle.

Free-running

Referring to a rhythm of behavior shown by an animal deprived of external cues about time of day. In the absence of external clues, this cycle is not exactly 24 hours long.

Period

The interval of time between two similar points of successive cycles, such as sunset to sunset.

Phase shift

A shift in the activity of a biological rhythm, typically provided by a synchronizing environmental stimulus.

Entrainment

The process of synchronizing a biological rhythm to an environmental stimulus.

Zeitgeber

 Literally “time giver” (in German). The stimulus (usually the lightdark cycle) that entrains circadian rhythms.

Suprachiasmatic nucleus (SCN)

A small region of the hypothalamus above the optic chiasm that is the location of a circadian oscillator. Serves as the biological clock.

Pineal gland

A secretory gland in the brain midline; the source of melatonin release.

Retinohypothalamic pathway

The projection of retinal ganglion cells to the suprachiasmatic nuclei (SCN). This pathway carries information about light to the hypothalamus to entrain behavior.

Melanopsin

A photopigment found in some retinal ganglion cells that project to the suprachiasmatic nucleus (SCN) via the retinohypothalamic pathway. This photopigment is most sensitive to light frequencies in the blue range, which explains why blue light has the largest effect on human circadian systems.

Dimer

A complex of two proteins that have bound together.

Infradian

Referring to a rhythmic biological event whose period is longer than that of a circadian rhythm—that is, longer than a day. Example of this is the 28-day human menstrual cycle.

Circannual

Occurring on a roughly annual basis. Annual rhythms of a period not quite equal to 365 days.

Ultradian

Referring to a rhythmic biological event whose period is shorter than that of a circadian rhythm (a day/24 hours). Usually these periods last from several minutes to several hours long. These rhythms are seen in such behaviors as bouts of activity, feeding and hormone release.

Electroencephalography (EEG)

The recording and study of gross electrical activity of the brain recorded from large electrodes placed on the scalp.

Electro-oculography (EOG)

The electrical recording of eye movements.

Electromyography (EMG)

The electrical recording of muscle activity.

Rapid-eye-movement (REM) sleep

Also called paradoxical sleep. A stage of sleep characterized by small-amplitude, fast-EEG waves, no postural tension, and rapid eye movements. REM rhymes with “gem.” The active-looking EEG coupled with deeply relaxed muscles is typical in this kind of sleep. Breathing and pulse rates become irregular. It is during this sleep, that we experience vivid dreams.

Non-REM (NREM) sleep

Stage of sleep without rapid eye movements. In humans this is divided into stages 1, 2, and 3 sleep.

Beta activity

Also known as desynchronized EEG. EEG activity seen in wakefulness, comprising a mix of many different high frequencies with low amplitude.

Desynchronized EEG

Also called beta activity. A pattern of EEG activity seen in wakefulness, comprising a mix of many different high frequencies with low amplitude.

Alpha rhythm

A brain potential of 8–12 Hz that occurs during relaxed wakefulness.

Vertex spike

A sharp-wave EEG pattern that is seen during stage 1 slow-wave sleep.

Stage 1 sleep

 Also called NREM 1. The initial stage of NREM sleep, which is characterized by small-amplitude EEG waves of irregular frequency, slow heart rate, and reduced muscle tension. Under the closed eyelids the eyes may roll about slowly. Usually lasts several minutes and gives away to stage 2 sleep. Vertex spikes are seen in this sleep stage. If wakened during this stage of sleep, many people will deny that they were asleep, even though they had failed to respond to signals.

Stage 2 sleep

Also called NREM 2. A stage of NREM sleep that is defined by bursts of EEG waves called sleep spindles, which occur in periodic bursts, and K complexes. If wakened during this stage of sleep, many people will deny that they were asleep, even though they had failed to respond to signals.

Sleep spindle

A characteristic 12–14 Hz wave in the EEG of a person in stage 2 sleep.

K complex

A sharp negative EEG potential that is seen in stage 2 sleep.

Stage 3 sleep

Also called NREM 3. A stage of NREM sleep that is defined by the presence of large-amplitude, very slow waves (delta waves).

Delta wave

The slowest type of EEG wave, about 1 Hz, characteristic of stage 3 sleep.

Slow-wave sleep (SWS)

Also called NREM 3 and, in humans, stage 3 sleep. A stage of NREM sleep characterized by large-amplitude delta waves. During this stage, neighboring cortical neurons tend to have synchronized activity, as if they were all "chanting" together rather than fulfilling different functions as they do in waking.

Nightmare

A long, frightening dream that awakens the sleeper from sleep.

Night terror

A sudden arousal from NREM sleep that is marked by intense fear and autonomic activation. After a night terror the sleeper doesn't recall a vivid dream, but may remember a sense of a crushing feeling on the chest, as though being suffocated. Night terrors, common in children during the early part of an evening's sleep, seem to have a genetic component.

Sleep deprivation

The partial or total prevention of sleep. The most reproducible effects of sleep deprivation are deficits in attention and working memory. Prolonged, total sleep deprivation in mammals compromises the immune systems and leads to death.

Sleep recovery

The process of sleeping more than is normal, after a period of sleep deprivation, as though in compensation.

Fatal familial insomnia

An inherited disorder in which humans sleep normally at the beginning of their life but stop sleeping in midlife and die 7–24 months later.

Sleep cycle

A period of slow-wave sleep (NREM sleep) followed by a period of REM sleep. In humans, a sleep cycle lasts 90-110 minutes.

The four functions most often ascribed to sleep

Energy conservation, niche adaptation, body restoration and memory consolidation.

Ecological niche

 The unique assortment of environmental opportunities and challenges to which each organism is adapted.

General anesthetic

A drug that renders and individual unconscious.

Isolated brain

Sometimes referred to by the French term encéphale isolé. An experimental preparation in which an animal's brainstem has been separated from the spinal cord by a cut below the medulla.

Isolated forebrain

Sometimes referred to by the French term cerveau isolé. An experimental preparation in which an animal's nervous system ahs been cut in the upper midbrain, dividing the forebrain from the brainstem.

Basal forebrain

A ventral region in the forebrain that has been implicated in consciousness and sleep. Electrical stimulation of this area can induce SWS activity, while lesions here suppress sleep.

Tuberomammillary nucleus

A region of the basal hypothalamus, near the pituitary stalk, that plays a role in generating SWS.

Reticular formation

An extensive region of the brainstem (running from the medulla through the thalamus) that is involved in arousal (waking).

Subcoeruleus

Also called sublaterodorsal nucleus. A brain region just ventral to the locus coeruleus that is associated with REM sleep. One job of this nucleus is to profoundly inhibit motor neurons to keep them from firing.

Narcolepsy

A disorder that involves frequent, intense episodes of sleep, which last from 5 to 30 minutes and can occur anytime during the usual waking hours. These sleep attacks occur several times a day - usually about every 90 minutes.

Cataplexy

• Sudden loss of muscle tone, leading to collapse of the body without loss of consciousness. Can be triggered by sudden, intense emotional stimuli, including both laughter an anger. Usually manifests itself between the ages of 15 and 25 and continues throughout life.

  • Treatments:

    • The traditional treatment for narcolepsy was the use of amphetamine in the day-time (concerns about potential abuse of this drug).

    • Another drug, modafinil (Provigil), is sometimes effective for preventing narcoleptic attacks (one study found the drug no more effective than caffeine in this regard).

    • Antidepressants are often prescribed to suppress episodes of cataplexy (placebo?)

Hypocretins

Also called orexins. Neuropeptides produced in the hypothalamus that are involved in switching between sleep states, in narcolepsy, and in the control of appetite.

Sleep paralysis

A state during the transition to or from sleep, in which the ability to move or talk is temporarily lost (the episodes never last more than a few minutes). In this state people may experience sensory hallucinations. One hypothesis is that sleep paralysis results when the subcoeruleus in the pons continues to impose paralysis for a short while after the person awakens form a REM episode.

Sleep enuresis

Bed-wetting. Are associated with stage 3 sleep/SWS.

Somnambulism

Sleepwalking. Episodes last a few seconds to minutes, and the person usually does not remember the experience. Because such episodes occur during stage 3 SWS, they are more common in the first half of the night (when those stages predominate).

REM behavior disorder (RBD)

A sleep disorder in which a person physically acts out a dream. Is characterized by organized behavior - such as fighting and imaginary foe, eating a meal, acting like a wild animal - in a person who appears to be asleep. Sometimes the person remembers a dream that fits well with this outward behavior. This disorder usually begins after the age of 50 and is more common in men than in women. The onset of RBD is often followed by the early symptoms of Parkinson's disease and dementia, suggesting that the disorder is the beginning of a widespread neurodegeneration. RBD is usually controlled by antianxiety drugs (benzodiazepines) at bedtime.

Paradoxical insomnia

Also called sleep state misperception. Commonly, a person’s perception that he has not been asleep when EEG readings and nonresponsiveness indicate that he has. On the other hand, EEG readings of people who claim they are not sleeping show fewer slow waves, and more of the alpha and beta activity typical of wakefulness, than other sleepers, so perhaps they really are more conscious than other sleepers during NREM, or perhaps some parts of their brain are sleeping without them being aware of it. Typically it occurs at the start of a sleep episode.

Sleep-onset insomnia

Difficulty in falling asleep.

Sleep-maintenance insomnia

Difficulty in staying asleep. Can be caused by drugs, as well as neurological and psychiatric factors. In this type of insomnia, sleep is punctuated by frequent nighttime arousals. This form of insomnia is especially evident in disorders of the respiratory system.

Sleep apnea

A sleep disorder in which respiration slows or stops periodically, waking the person. Excessive daytime sleepiness results from the frequent nocturnal awakening. Respiration becomes unreliable during sleep - breathing may cease for a minute or so, or it may slow alarmingly; blood levels of oxygen drop markedly. Arises either form the progressive relaxation of muscles of the chest, diaphragm, and throat cavity (obstructive apnea) or from changes in the pacemaker respiratory neurons of the brainstem (central apnea). In the former instance, relaxation of the throat obstructs the airway - a kind of self-choking. For some people, breathing through a special machine (CPAP-machine) maintains air pressure in their airways and prevents their collapse. Obstructive apnea is common in very obese people, but it also occurs, often undiagnosed in nonobese people. Sleep apnea is frequently accompanied by loud, interrupted snoring. Untreated sleep apnea may lead to any of several cardiovascular disorders, including hypertension and diabetes.

Sudden infant death syndrome (SIDS)

Also called crib death. The sudden, unexpected death of an apparently healthy human infant who simply stops breathing, usually during sleep. Investigators have speculated that SIDS arises from sleep apnea as a result of immaturity of systems that normally pace respirations. Autopsies of SIDS victims reveal abnormalities in brainstem serotonin systems.

Adenosine

An endogenous neuromodulator that generally reduces neural activity. Caffeine interferes with adenosine binding.

Sleep hygiene

Habits, such as avoiding caffeine shortly before bedtime, that promote healthy sleep. Best advise for insomniacs is to use an alarm clock to wake up faithfully at the same time each day, and then simply go to bed once they feel sleepy. Other sleep hygiene habits include establishing a bedtime routine in a quiet, dark environment to condition sleep onset, and avoiding daytime naps, caffeine at night, and looking at computer screens (their bluish lights stimulates melanopsin in retinal ganglion neurons) just before bedtime.