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Biological Rhythms, Sleep, and Dreaming

Biological Rhythms. Different Kinds of Biological Rhythms. Circadian rhythmAbout a day24 hoursUltradian rhythmLess than a day90 minute cycles of lighter and deeper sleepInfradian rhythmGreater than one dayMenstrual cycle. The SleepWaking Cycle: A Circadian Rhythm. Biological clockSiffre (

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Biological Rhythms, Sleep, and Dreaming

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    1. Biological Rhythms, Sleep, and Dreaming There is a wide variety of biological rhythms—periodically recurring features of biological organisms, which are classified by the period of the cycle. In this lecture, we explore biological clocks, and the external and internal cues of different cycles Sleep is the most well-known cycle, and we look at studies of sleep deprivation, the theories explaining the purpose of sleep, and the theories of why we dream

    2. Biological Rhythms

    3. Different Kinds of Biological Rhythms Circadian rhythm About a day 24 hours Ultradian rhythm Less than a day 90 minute cycles of lighter and deeper sleep Infradian rhythm Greater than one day Menstrual cycle

    4. The Sleep–Waking Cycle: A Circadian Rhythm Biological clock Siffre (1975) – spent 2 months in a cave. Wever (1979) – several months in a bunker. 25 hour cycle suggests a biological clock that needs a small amount of external correction – imp for travel, seasonal variations. Neural substrate of the biological clock Suprachiasmatic nucleus (SCN) (sub cluster of hypothalamus). Direct link to optic nerve and pineal gland so ideal for translating external light dark cycle into hormonal fluctuations. Shows periodicity in its firing rate to release of melatonin from pineal gland, a key hormone that regulates sleep. Melatonin correlates with sleep probability, lesions of SCN abolish cycle, and SCN grafts restore it.

    7. Exogenous factors Campbell and Murphy (1998): light on skin was used to shift sleep cycle to new light-dark cycle. Light as the dominant “zeitgeber” or “timer giver” Miles et al. (1977) - case study of blind man. Luce and Segal (1966) – arctic circle dwellers ignore light-dark cycle – i.e. Can be overridden. Internal versus external control Shiftwork – 10 years shortened life expectancy. Jet lag Seasonal variation

    8. The Menstrual Cycle: An Infradian Rhythm (longer than one day)

    9. The Menstrual Cycle: External cues Reinberg (1967) – cave dwelling shortened cycle Russell (1980) – female armpit sweat caused menstrual synchrony. Synchronised cycles through pheromones of other women McClintock (197) – females who work with men have shorter cycles, which may be mediated by male pheromones.

    10. Circannual Rhythms Rhythms that last for about 1 year or more Hibernation – undertaken in stable lab conditions indicating that it is endogenous Migration – same as above. Seasonal Affective Disorder (SAD) Severe depression during the winter months Seasonal variation in the production of melatonin (Barlow & Durand, 1995) More common in northern latitudes where winter days are very short (Terman, 1988) Phototherapy (Barlow & Durand, 1995)

    11. The Consequences of Disrupting Biological Rhythms Jet lag Changing time zones – not travel per se Klein et al. (1972) westbound flights less disruptive to the sleep–waking cycle than eastbound flights. Suggested that with west, the day is lengthened and so we stay awake when we should asleep. This may be easier to cope with than eastern flights, where the night is shortened, so we are woken prematurely from sleep, which may be harder to cope with. Melatonin and aircrew – US airforce have banned its use. Shiftwork Moore-Ede (1993) shiftworker fatigue costs $77 billion Monk and Folkard (1983) – rapid rotation appears better then slow rotation as it allows a fairly constant cycle, which repeated disruptions, rather then a constantly changing cycle. Czeisler et al. (1982) Phase advance appears to be better.

    12. Sleep Description and function.

    13. Stages of Sleep: An Ultradian Rhythm Electroencephalography provides a non-invasive objective measure of brain processes during sleep. Stage 1 Relaxation with synchronous brain waves Stage 2 EEG becomes slower and larger Stage 3 EEG consists of long, slow delta waves Stage 4 Slow-wave sleep (SWS) Stage 5 Rapid eye movement or REM sleep

    17. REM Sleep and Dreaming Aserinsky and Kleitman (1955) First discovered the association between REM sleep and dreaming Dement and Kleitman (1957) Between 70% and 75% of participants woken in REM sleep report dreaming Green (1994) 30% of sleepers in SWS report dreaming REM dreams Are vivid and detailed Non-REM dreams Are vague and less coherent

    18. Theories of Sleep Recovery/restoration – deprivation studies show physical/cognitive deficits. Adaptive/ecological – evolutionary conservation and functional significance.

    19. Studies of Sleep Deprivation Produces impairments in cognitive performance. Increases negative mood Increased effects over time Suggests sleep serves a restorative function.

    20. Theories of Sleep Recovery or restoration theories Physiological restoration Babies spend substantially loner sleeping than adults. This may be related to their growth or to predator avoidance.

    21. Adaptive or evolutionary theories Suggests sleep in not necessary, but serves a survival function. Sleep as a protection against predation, or should they stay vigilant (non-falsifiable)? Meddis (1975) Prey species have less REM. Hibernation theory Webb (1982) – conserves energy. Recovery or adaptation? Sleep is probably necessary for recovery, but can be modified to some extent by evolutionary pressures.

    22. Dreaming A large portion of sleep involves REM/dreaming, and therefore it must serve an important function, but what? REM appears to be linked to cerebral quotient and so may be associated with higher cognitive function.

    23. The Nature of Dreams Remembering your dreams 95% of dreams are forgotten An objective method for the study of dreaming Dement and Kleitman (1957) high correlation between amount of time spent in REM and verbal reports of dreaming (number of words used to describe the dream). Was greater in REM than deep/slow wave sleep. Dreaming and consciousness Empson (1989) lucid dreams

    24. Theories of the Functions of Dreaming Neurobiological theories Activation-synthesis theory Hobson and McCarley (1977) dreamers try to make sense of random brain activation. Paralysis occurs in the spine. Reverse-learning theory Crick and Mitchison (1983) gets rid of useless information stored in the brain We forget 95% of our dreams. Dolphins and spiny anteater do not have REM What about new borns – pruning?

    25. Psychological theories Freud’s wish-fulfilment theory dreamers dream of repressed desires manifest content of dream is latent content disguised Problem-solving theory Webb and Cartwright (1978) problem-solving after sleep—“sleep on it” manifest content is the real content Survival strategy theory Winson (1997) memories of new experiences are placed close together with older memories to form a strategy for survival

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