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Sleep and Waking Biological Rhythms: The Physiological Processes of Sleep

Sleep and Waking Biological Rhythms: The Physiological Processes of Sleep

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Sleep and Waking Biological Rhythms: The Physiological Processes of Sleep

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  1. Sleep and Waking Biological Rhythms: The Physiological Processes of Sleep Dr Sue Turnbull Clinical Neuropsychologist

  2. Outline • EEG Recording and brain rhythms • Stages of Sleep • Regulation of Wakefulness and Sleep • Physiological & Neurochemical Mechanisms of Sleep • Functions of Sleep • Sleep Disorders

  3. EEG Recordings • Electrodes attached to skull • Pick up the graded potentials of the sum of thousands of neurons • Bulk of signal from pyramidal neurons in the cortex

  4. Brain Rhythms (1) • Thalamus and brainstem • Act as pacemaker cells • Cortex • Interneurons discharge rhythmically driving rhythm of surrounding pyramidal cells • Pyramidal Cells • Can have intrinsic rhythms with adjacent neurons synchronising pattern • Heart Rate and respiration • Affects rhythms as provide fuel influencing the activity levels of cells

  5. Brain Rhythms (2) • Beta rhythms: low amplitude, high frequency • Alpha rhythms: amplitudes gradually increasing and decreasing, approx 11 cycles per second • Theta rhythms: higher amplitude, 4-7 cycles per second • Delta rhythms: highest amplitude, 1-3 cycles per second

  6. Wakefulness • Alert state • EEG is active and desynchronised • Beta waves • Relaxed states • Alpha waves predominate - rhythmic

  7. nREM sleep • Blood flow progressively diminishes throughout the entire brain • Stage I (light sleep) 5-10% of total sleep • Stage II (slow waves with occasional bursts of rapid waves/sleep spindles, eye movements stop) 40-50% of total sleep • Stage III & IV (slow wave/delta sleep) 20 % of total sleep majority in first third of night

  8. REM Sleep • 20-30% of total sleep, mostly in first third of night • Increased heart and respiratory rate • Increased blood flow in thalamus and primary visual, motor, and sensory cortices • Beta waves • Muscle atonia • Saccadic eye movements • Dreaming

  9. EEG recordings of sleep Stage III-IV sleep REM sleep

  10. Sleep Cycles

  11. Age-Related Changes Lugaresi, E. (1999)

  12. Motor Features of Sleep • Hypnic jerks (sleep startles) • Stage I & II sleep. A sudden motor jerk of all or part of body. Also visual, auditory, somesthetic sleep starts • Gestures • Grimacing, scratching, sighing. Throughout nREM sleep especially stage I & II • Periodic leg movements • Rapid flexion of foot at ankle. Absent in the young, very common in the elderly. Can be present throughout nREM sleep • Postural shifts • Slow changes in posture at beginning and end of REM • Small muscle twitches • Throughout but especially in REM sleep

  13. Regulation of Wakefulness and Sleep Two major regulatory systems that interact and influence each other • Circadian Rhythms • Homeostatic Systems

  14. Circadian Rhythms • Body clock roughly set to 25 hours • Controlled by the suprachiasmatic nucleus in the hypothalamus, set by stimuli from the retina • Influenced by light exposure and other environmental time cues (‘zeitgebers’) • Body temperature fluctuations • Hormones • Growth hormone • Prolactin • Adrenaline • Cortisol • Melatonin

  15. Circadian Rhythms

  16. Homeostatic Influence • Amount of sleep that the individual needs • ‘Sleep debt’ accrues if sleep is deprived with a need for recovery sleep • Sleepiness increases in proportion to prior time awake • Alertness increases in proportion to prior sleep time

  17. Brain Areas Involved in Sleep thalamus hypothalamus cortex brainstem

  18. Sleep Mechanisms • Reticular Activating System • Moruzzi & Magoun (1949) • Brainstem and hypothalamic neuronal groups • GABA and acetylcholine • Oscillations between thalamus and cortex • Sleep spindles • Delta oscillations • Slow cortical oscillations

  19. REM Sleep Mechanisms • Generated by neurons in the pons • Mesencephalic and pontine cholinergic neurons (REM-on neurons) • Serotoneric neurons (REM-off cells) • Ponto-geniculo-occipital (PGO) waves • Motoneurons inhibited by glycine (muscle atonia) • Interaction between forebrain (frontal cortex and amygdala) and pons Siegel (2000)

  20. Functions of Sleep Deprivation • Drowsiness & fatigue • Decreased mental concentration, vigilance, attention, reaction times • Decrease in core body temperature • Decrease in immune system function • Depressed mood, apathy, irritability • Muscle fatigue • Psychotic reactions: delusions or hallucinations

  21. Functions of Sleep • Restorative Functions (nREM sleep) • Replenishment of glycogen stores (Benington & Heller, 1995) • Cognitive functions (REM sleep) • Learning: consolidation of memory traces acquired during waking • Negative learning/forgetting: removal of overloaded/ redundant cortical networks (Roffwarg et al., 1966) • Maintaining body homeostasis • (McGinty & Beahm, 1984) Lugaresi (1999)

  22. Sleep Disorders • nREM sleep parasomnias • REM sleep disorder • Narcolepsies • Insomnias

  23. nREM Sleep Parasomnias • Normal nREM Sleep Phenomena • Sleep Paralysis • Occurs in transition between wakefulness and sleep • Hypnagogic Hallucinations • Hallucinations during sleep paralysis • Abnormal nREM Sleep Phenomena • Sleep Walking • Sleep Terror • Screaming & motor activity, no memory of event

  24. REM Sleep Behaviour Disorder • First described by Schenck et al. (1986) • Loss of muscle atonia during REM sleep • ‘Oneirism’ – dream-enacting behaviour • Most common in elderly • Strong relationship with neurodegenrative conditions Olson et al. (2000)

  25. Narcolepsies • Sleep attacks • Brief periods of sleep usually lasting about 15 minutes • Period of nREM sleep • Cataplexy • ‘strike down’ • Sudden loss of muscle tone • Period of REM sleep

  26. Insomnias • Difficulty initiating and/or maintaining sleep or non-restorative sleep • Faulty Conditioning • Poor Chronological Timing • Physiological Hyper-arousal • Cognitive Hyper-arousal • Dysfunctional Thinking • Sleep Apnoea • Obstructive sleep apnoea • Central sleep apnoea

  27. Learning Objectives • Be able to describe the characteristics of the different stages of sleep. • Understanding of the processes and mechanisms regulating sleep-wake cycles. • Knowledge of the brain areas involved sleep stages • Knowledge of some of the theories of the functions of sleep • Awareness of disorders of sleep

  28. References • Kolb & Wishaw (2003) Fundamentals of Human Neuropsychology, pp150-153, 718-179. • Lugaresi (1999) Sleep, in Beaumont et al (eds) Blackwell Dictionary of Neuropsychology • http://www.neuropat.dote.hu/coma.htm (has links to sleep references including Siegel, J.M. (2000) Brainstem mechanisms generating REM sleep. In: Principals and Practice of Sleep Medicine, Second Edition. Edited by M. K. Kryger, T. Roth, W. C. Dement. New York: Saunders • http://sleepmed.bsd.uchicago.edu/sleepphysiology.html • http://www.elib.scot.nhs.uk/portal/elib/pages/index.aspx search for ‘sleep’ in ebooks. Useful papers on EEGs in stages of sleep and information on sleep disorders. Especially: • Russo (2004) Normal sleep, sleep physiology and sleep deprivation: General Principles • Olson et al., (2000) REM sleep behaviour disorder, Brain, 123, 331-339