Sleep, Dreaming and Circadian Rhythms PDF

13/02/2025  1930s: major changes in human EEG during the course of a night sleep was first observed;...

13/02/2025  1930s: major changes in human EEG during the course of a night sleep was first observed;  1953: Aserinsky and Kleitman discovered that rapid eye movements (REM) occur under the closed eyelids of sleeping subjects during the period of low- voltage, fast EEG activity;  1962: Berger and Oswald discovered that there is also a loss of electromyographic activity in the neck muscles during these same sleep periods.  Electroencephalogram (EEG) – a measure of electrical energy of the brain, commonly recorded through scalp electrodes;  Electrooculogram (EOG) – a measure of eye movement;  Electromyogram (EMG) – a measure of electrical activity of muscles.  The EEG of a subject during a typical night’s sleep is  Stage 1 sleep: is a low amplitude high-frequency commonly divided into four separate classes: stage 1, 2, signal that is similar to, but slower than, that of 3 and 4. active wakefulness;  After the subject shuts his/her eyes and prepares to go  As the subject continues to sleep, there is a progressive to sleep, alpha waves (8 to 12 Hz) begin to punctuate increase in amplitude of the EEG waves and a slowing of the low amplitude, high frequency EEG of active their frequency, which is customarily divided into 3 wakefulness. stages: 2, 3 and 4.  It can be considered as the transition period between wakefulness and sleep. It is characterized by the presence of theta waves. 1  13/02/2025  Stage 2 sleep: is punctuated by two characteristic  Stage 3 sleep: is defined by the occasional presence wave forms: of delta waves, the largest and slowest EEG waves,  K complexes – composed of a single large negative wave with a frequency of 1-2 HZ; (upward deflection) followed by a single large positive  The transition stage between light sleep and very deep wave (downward deflection); and sleep. Deep, slow brain waves known as delta waves  Sleep spindles – 1-2 second waxing and waning bursts of begin to appear. 12 to 14 Hz waves.  Stage 4 sleep: also known as delta sleep because of  Body temperature starts to decrease and the heart the predominance of delta waves. This deep sleep begins to slow down. It lasts for approximately 20 approximately lasts for 30 minutes. minutes.  Stage 5 or the REM sleep: is characterized by rapid  The high correlation between REM sleep and eye movements, loss of core muscle tone, and dream recall provided an opportunity to test some emergent stage 1; common beliefs about dreaming;  Another physiological correlates are cerebral activity  The following are the beliefs that have been (e.g., oxygen consumption, blood flow, and neural firing subjected to empirical tests: in many structures) increases to near-waking levels;  External stimuli can become incorporated into dreams;  There is also a general increase in autonomic nervous  Dreams last only an instant; system activity (e.g., blood pressure, pulse and  Some people do not dream; respiration);  Penile erections are commonly assumed to be indicative  Occasional twitching of the muscles of extremities and some degree of penile and clitoral erection. of dreams of sexual content;  Sleep talking or sleep walking occurs during sleep.  Emergent sleep 1 is often called paradoxical sleep because the EEG and automatic activities that are associated with it are similar to those of wakefulness;  After the first cycle of sleep EEG (Stage 1 to REM Stage), the rest of the night is spent back and forth through the stages.  Each sleep cycle tends to be about 90 minutes long, therefore we go through the sleep cycle 4 or 5 times a night. 2  13/02/2025  Sigmund Freud believed that  Activation-synthesis theory – a theory of dreaming dreams are triggered by developed by researchers J. Allan Hobson and Robert unacceptable repressed wishes; McCarley;  First proposed in 1977, this theory suggests that the  Dreams are the royal road to physiological processes of the brain cause dreams. unconscious.  Circuits in the brain stem are activated during REM sleep. Once these circuits are activated, areas of the limbic system involved in emotions, sensations, and memories, including the amygdala and hippocampus, become active;  The brain synthesizes and interprets this internal activity and attempts create meaning from these signals, which results in dreaming.  While the activation-synthesis model of dreaming  Lucid dreams – refers to dreams in which the dreamer relies on physiological processes to explain dreaming, is aware that he or she is dreaming and can influence it does not imply that dreams are meaningless. the course of the dream.  According to Hobson, "Dreaming may be our most creative conscious state, one in which the chaotic, spontaneous recombination of cognitive elements produces novel configurations of information: new ideas. While many or even most of these ideas may be nonsensical, if even a few of its fanciful products are truly useful, our dream time will not have been wasted" (1999). 3  13/02/2025  Circadian rhythm – refers to  Recuperation Theory diurnal or daily cycles of body  believes that being awake disrupts the homeostasis of function. Example of this is the the body in some way and sleep is needed to restore it. sleep-wake cycle.  Circadian Theory  argues that sleep has evolved to keep animals inactive  Zeitgebers – also known as time during those times of the day when they do not need to givers. These are environmental be engaging in activities necessary for their survival. cues that can control the timing of circadian rhythms. Example of this is the light-dark daily cycle. Two different disruptions of circadian rhythmicity: Recuperation theory:  Jet lag – occurs when the zeitgebers are  Long period of wakefulness will produce accelerated during eastern flights physiologcial and behavioral disturbances; (phase advances) or decelerated during western flights (phase delays).  These disturbances will grow steadily worse as sleep deprivation continues ; and  Shift work – occurs when the  After a long period of deprivation has zeitgebers stay the same but workers ended, much of the missed sleep will be are forced to adjust their natural sleep- wake cycles in order to meet the regained. demands of changing work schedules. Circadian theory:  Suprachiasmatic Nucleus (SCN) – part of the hypothalamus which serves as the control center of the  There will be no debilitating effects of sleep circadian rhythms for sleep and body temperature. deprivation other than those that can be attributed to an increase in tendency to fall asleep;  The increase in the desire to sleep will be greatest during the phases of the circadian cycle when the subjects normally sleep; and  There will be little or no compensation for the loss sleep once the period of deprivation has ended. 4  13/02/2025  Hypnotic drugs – drugs which increase drowsiness,  The SCN regulates waking and sleeping by controlling decrease the time it takes to fall asleep, reduce the activity levels in other brain areas, including the pineal number of awakenings during a night’s sleep and gland which releases the hormone melatonin. increase total sleep time.  Melatonin secretion starts to increase 2 or 3 hours  Example of hypnotic drugs are benzodiazepines which before bed time. It also feeds back to reset the is a class of anxiolytic drugs (e.g. Valium and Librium). biological clock through its effects on the receptors of the SCN.  Many sleep disorders fall into one of the two major  Antihypnotic drugs – sleep-reducing drugs that can take the form of stimulants (e.g. cocaine, categories: dyssomnia and parasomnia. amphetamine, caffeine) and tricyclic antidepressants.  Dyssomnia – characterized by disturbances in the  These drugs can totally suppress the REM sleep and amount, quality and timing of sleep (e.g. they are often addictive has a lot of side effects. insomnia, hypersomnia, narcolepsy)  Parasomnia – characterized by unnatural and abnormal behaviors, emotions and perception which occur during sleep (e.g. somnambulism, nightmares, sleep terrors)  Insomnia – difficulty initiating  Sleep apnea – sleep is repeatedly disturbed by and maintaining sleep. momentary interruptions in breathing.  Hypersomnolence – excessive  Restless legs syndrome – tension or sleepiness and inability to feel uneasiness in the legs that keeps a person refreshment from sleep. from falling asleep.  Narcolepsy – characterized by  Sleep state misperception – a condition repeated, brief and irresistible wherein people mistakenly perceive daytime sleep attacks. their sleep as wakefulness. 5  13/02/2025  Periodic limb movement disorder – characterized  Somnambulism – sleep walking by repeated involuntary movement of the legs and arms especially when starting to fall asleep.  REM behavior disorder – violent and vigorous body movements during REM sleep.  Bruxism – characterized by teeth-grinding during sleep.  Night terrors – experiences of intense anxiety from which a  Sexomnia - a condition in which a person will person awakens screaming in engage in sexual acts while still asleep and will not terror. remember it afterward. 6