Sleep and Circardian Rythms.pptx

Sleep
Types of sleep
CIRCARDIAN Rhythms

1. Sleep , Dreaming, and Circadian Rhythms Pavithra Narasimhan

2. Sleep Sleep is a behavior and an altered state of consciousness Sleep is associated with an urge to lie down for several hours in a quiet environment Few movement occur during sleep (eye movements)

3. The nature of consciousness is changed during sleep We experience some dreaming during sleep We may recall very little of the mental activity that occurred during sleep We spend about a third of our lives in sleep A basic issue is to understand the function of sleep

4. Characteristics of sleep Slow-wave sleep progressive decrease in spinal reflexes progressive reduction in heart rate and breathing rate reduced brain temperature and cerebral blood flow increased hormone secretion (e.g. growth hormone) synchronised cortical activity

5. Characteristics of sleep REM sleep spinal reflexes absent rapid eye movements bihind closed eyelids increased body temperature and cerebral blood flow desynchronised cortical activity dreams

6. hypnagogic hallucinations . Common examples of this phenomenon include feeling like you are falling or hearing someone call your name. wakefulness to sleep (hypnagogic) or from sleep to wakefulness (hypnopompic). 

7. NREM Stage 1 Stage 1 is the beginning of the sleep cycle, and is a relatively light stage of sleep. Stage 1 can be considered a transition period between wakefulness and sleep.

8. NREM Stage 2 During stage 2 sleep: People become less aware of their surroundings Body temperature drops Breathing and heart rate become more regular Stage 2 is the second stage of sleep and lasts for approximately 20 minutes. The brain begins to produce bursts of rapid, rhythmic brain wave activity known as sleep spindles .

9. How Much Sleep Do We Need? The vast amount of time spent sleeping suggests that sleep has a significant biological function Most people sleep over 175,000 hours in their lifetime

10. NREM Stage 3 During stage 3 sleep: Muscles relax Blood pressure and breathing rate drop Deepest sleep occurs This stage was previously divided into stages three and four. Deep, slow brain waves known as delta waves begin to emerge during stage 3 sleep. This stage is also sometimes referred to as delta sleep .

11. REM Sleep During REM sleep: The brain becomes more active Body becomes relaxed and immobilized Dreams occur Eyes move rapidly

12. Most dreaming occurs during the fourth stage of sleep, known as rapid eye movement (REM) sleep. REM sleep is characterized by eye movement, increased respiration rate and increased brain activity. people spend approximately 20 percent of their total sleep in this stage.

13. Three Standard Physiological Measures of Sleep Electroencephalogram (EEG) Reveals “brainwaves” Electrooculogram (EOG) Records eye movements seen during rapid eye movement (REM) sleep Electromyogram (EMG) Detects loss of activity in neck muscles during some sleep stages

14. Sleep as an active process Electroencephalographic (EEG) recordings showed abundant neuronal activity in cortex during sleep Therefore not passive neuronal quiescence Pattern of the EEG was very different in sleep than in waking

15. Waves of activity, indicating synchronous firing of cortical neurones Synchronising stimulus coming from sub-cortical areas Reticular formation still seen as important Several different levels of sleep Sleep is a complex combination of different aspects

16. Four Stages of Sleep EEG Alpha waves Bursts of 8- to 12-Hz EEG waves Eyes closed, preparing to sleep EEG voltage increases and frequency decreases as one progresses from stage 1 through 2, 3, and 4

17. Four Stages of Sleep EEG Continued Stage 1 Similar to awake EEG, but slower Low-voltage, high-frequency Stage 2 K complexes – one large negative (upward deflection) wave followed by one large positive wave Sleep spindles – bursts of 12-14 Hz waves Stages 3 and 4 – delta waves, large and slow

18. Brain activity during sleep Awake Low amplitude high frequency EEG Light sleep Increasing amplitude decreasing freq. EEG Deep sleep High amplitude low frequency EEG Rapid eye movement (REM) sleep Low amplitude high frequency EEG

19. FIGURE 14.2 The EEG of alert wakefulness, the EEG that precedes sleep onset, and the four stages of sleep EEG. Each trace is about 10 seconds long.

20. Four Stages of Sleep EEG Continued Progress to stage 4 sleep and then back to stages 3, 2, and (emergent) stage 1 Emergent stage 1 differs from initial stage 1 REMs Loss of body core muscle tone Progress through sleep stages in 90-minute cycles Durations of emergent stage 1 periods lengthen as night progresses

21. FIGURE 14.3 The course of EEG stages during a typical night’s sleep and the relation of emergent stage 1 EEG to REMs and lack of tone in core muscles.

22. Four Stages of Sleep EEG Emergent stage 1 sleep = REM sleep All other stages = Non-REM (NREM) sleep Stages 3 + 4 = slow-wave sleep (SWS) During REM sleep: REMs, loss of core muscle tone, low-amplitude/high-frequency EEG, increased cerebral and autonomic activity, muscles may twitch, penile erection

23. Disorders of sleep Insomnia - reduction or absence of sleep - transient or persistent Hypersomnia (narcolepsy) - excessive drowsiness and falling asleep Sleep-wake schedule disturbance - transient or persistent Partial arousal - e.g. sleep-walking, nightmares Often associated with anxiety, psychological disturbance or drug taking Little known about causes Limited capacity for pharmacological treatment of sleep disorders

24. REM Sleep and Dreaming

25. REM Sleep and Dreaming 80% of awakenings from REM yield reports of story-like dreams External stimuli may be incorporated into dreams Dreams run on real time Everyone dreams Sleepwalking and talking are less likely to occur while dreaming

26. Presence of beta activity (desynchronized EEG pattern) n Enhanced respiration and blood pressure Rapid eye movements (REM) Pontine-Geniculate-Occipital (PGO) waves Loss of muscle tone (paralysis) Vivid, emotional dreams Signs of sexual arousal

27. Interpretation of Dreams Freud’s explanation: dreams are triggered by unacceptable repressed wishes Manifest dreams – what we experience Latent dreams – the underlying meaning No evidence for this Activation-Synthesis Modern alternative to Freud’s explanation of dreams Dreams due to cortex’s attempt to make sense of random brain activity (Hobson, 1989)

28. Why Do We Sleep, and Why Do We Sleep When We Do? Recuperation theories Sleep is needed to restore homeostasis Wakefulness causes a deviation from homeostasis Adaptation theories Sleep is the result of an internal timing mechanism Sleep evolved to protect us from the dangers of the night

29. Comparative Analysis of Sleep All mammals and birds sleep – must have an important function Not a special higher-order human function Not necessarily needed in large quantities No clear relationship between species’ sleep time and activity level

30. Effects of Sleep Deprivation It is difficult, if not impossible, to separate the effects of stressors used to prevent sleep from the effects of lost sleep

31. Effects of Sleep Deprivation Continued Recuperation theories predict: Long periods of wakefulness will result in disturbances Disturbances will get worse as deprivation continues After deprivation, much of the missed sleep will be regained

32. Two Classic Sleep-Deprivation Case Studies Sleep-deprived students By the third night, subject found desire for sleep overpowering Randy Gardner Stayed awake for 11 days Only slept 14 hours the first night after the study

33. Experimental Studies of Sleep Deprivation in Humans Little effect of sleep deprivation: Logical deduction, critical thinking Physical strength and motor performance Larger effect of sleep deprivation: executive function (prefrontal cortex) Assimilating changing information Updating plans and strategies Innovative, lateral, insightful thinking Reference memory

34. Experimental Studies of Sleep Deprivation in Humans Continued 3-4 hours of deprivation in one night Increased sleepiness Disturbances displayed on written tests of mood Poor performance on tests of vigilance 2-3 days of continuous deprivation Experience microsleeps, naps of 2-3 seconds

35. Sleep-Deprivation Studies with Laboratory Animals Carousel apparatus used to deprive rats of sleep When the experimental rat’s EEG indicates sleep, the chamber floor moves – if the rat does not awaken, it falls into water Yoked controls – subjected to the same floor rotations Experimental rats typically die after several days Postmortem studies reveal the extreme stress experienced by the experimental rats

36. FIGURE 14.5 The carousel apparatus used to deprive an experimental rat of sleep while a yoked control rat is exposed to the same number and pattern of disk rotations. The disk on which both rats rest rotates every time the experimental rat has a sleep EEG. If the sleeping rat does not awaken immediately, it is deposited in the water. (Based on Rechtschaffen et al., 1983.)

37. REM-Sleep Deprivation Two consistent effects Proceed more rapidly into REM as REM deprivation increases REM rebound – more time spent in REM when deprivation is over REM rebound suggests that REM sleep serves a special function

38. Purpose of REM Processing of explicit memories? Inconsistent findings Antidepressant REM-blocking drugs do not interfere with memory Default theory: it is difficult to remain in NREM sleep Nycamp and others (1998) awoke sleepers in REM for 15 minutes. Result: no sleepiness or REM rebound the next day REM-blocking drugs cause periods of wakefulness

39. Sleep Deprivation Increases Sleep Efficiency After sleep deprivation, most of lost stage 4 is regained and SWS is increased Short sleepers get as much SWS as long sleepers Naps without SWS do not decrease the night’s sleep Gradual reductions in sleep time lead to decreases in stages 1 and 2 Little sleepiness produced with repeated REM awakenings, unlike SWS

40. Circadian Sleep Cycles Circadian rhythms – “about a day” Virtually all physiological, biochemical, and behavioral processes show some circadian rhythmicity Zeitgebers – environmental cues that entrain circadian cycles

41. Free-Running Circadian Sleep-Wake Cycles Remove zeitgebers – still see circadian sleep-wake cycles? Free-running periods vary, but are usually constant within a subject Most are longer than 24 hours - ~ 25 What happens on days when you don’t need to get up?

42. Jet Lag and Shift Work Jet lag – zeitgebers are accelerated or decelerated Shift work – zeitgebers unchanged, but sleep-wake cycle must be altered Both produce a variety of deficits Can the effects be prevented or minimized?

43. Reducing Jet Lag Gradually shift sleep-wake cycle prior to travel Administer post-flight treatments to promote the needed shift Phase advance following east-bound travel with intense light early in the morning Hamster studies suggest a good early morning workout may also help

44. Biorhythms Many functions show natural biological rhythms Circadian rhythms (daily cycle) Body temperature, heart rate, respiration, sleep Circannual rhythms (yearly cycle) Hibernation, mating behaviour, migration Linked to: Light/dark cycle Season (day length probably critical)

45. Circadian rhythms Bodily functions linked to day length Light/dark cycle important determinant. How does light/dark information affect body systems? Optic tract lesion Circadian rhythm maintained, even in constant light Periodicity changed Suprachiasmatic nucleus lesion Circadian rhythm abolished No periodicity Therefore suprachiasmatic nucleus important for circadian rhythm

46. Suprachiasmatic nucleus (SCN) Located in hypothalamus, just above optic chiasm Cells in SCN show oscillations of activity Related to circadian rhythm Believed to form the ‘biological clock’ Many functions (e.g. sleep wake cycle) are maintained in constant light or constant dark Periodicity may not be 24 hours In normal light/dark cycle SCN rhythm is ‘phase locked’ to light dark

47. A Circadian Clock in the Suprachiasmatic Nucleus (SCN) Lesions do not reduce sleep time, but they abolish its circadian periodicity Exhibits electrical, metabolic, and biochemical activity that can be entrained by the light-dark cycle Transplant SCN, transplant sleep-wake cycle

48. Neural Mechanisms of Entrainment Cutting the optic nerves before the optic chiasm eliminated the ability of the light-dark cycle to entrain circadian rhythms However, cutting after the chiasm did not have this effect Later the retinohypothalamic tracts were identified Leave the optic chiasm and project to the adjacent suprachiasmatic nuclei Mechanisms of entrainment of SCN cells to light-dark cycle Rare retinal ganglion cells with no rods or cones

49. Genetics of Circadian Rhythms Several mammalian circadian genes have been identified Some of these have also been identified in other species of other evolutionary ages Expression of these genes follows a circadian pattern Most of the gene expression appears to be entrained by activity of the SCN

50. Evidence of Other Clocks Some circadian rhythms intact after SCN lesion SCN lesions do not eliminate the ability of all environmental stimuli (such as food or water availability) to entrain circadian rhythms Like SCN cells, cells in other parts of the body exhibit free-running circadian rhythms in tissue cultures

51. Four Areas of the Brain Involved in Sleep Two areas of the hypothalamus: posterior hypothalamus and the anterior hypothalamus were related to excessive sleep or inability to sleep, respectively Findings were in patients that had encephalitis lethargica

52. Four Areas of the Brain Involved in Sleep Two areas of the brainstem: Cerveau isolé (“isolated forebrain”) preparation – produced by severing cat brainstem between the superior and inferior colliculi, resulting in continuous SWS Encéphale isolé (“isolated brain”) preparation – produced by transsection caudal to the colliculi, resulting in normal sleep cycle Therefore, wakefulness depends on the function of the reticular formation , or “reticular activating system”

53. FIGURE 14.11 Four pieces of evidence that the reticular formation is involved in sleep.

54. Reticular REM-Sleep Nuclei Similarities between REM and wakefulness suggest that the same brain area might be involved in both REM sleep is controlled by nuclei in the caudal reticular formation, each controlling a different aspect of REM

55. Drugs That Affect Sleep Drugs that increase sleep (hypnotic drugs): benzodiazepines – Valium, Librium Most commonly prescribed hypnotic drugs Effective in the short term Complications Tolerance Cessation leads to insomnia Addiction Use leads to next day drowsiness Increase of stage 2 sleep while decrease of stage 4 and REM

56. Drugs That Affect Sleep Drugs that decrease sleep ( antihypnotic drugs ): stimulants and tricyclic antidepressants Both increase activity of catecholamines Act preferentially on REM – may totally suppress REM with little effect on total sleep time Side effects Loss of appetite Addiction

57. Melatonin Synthesized from serotonin in the pineal gland Melatonin levels follow circadian rhythms controlled by the SCN Pineal gland triggers seasonal reproductive changes in fish, birds, reptiles, and amphibians – human function is unclear Melatonin is not a sleep aid, but may be used to shift circadian rhythms

58. Sleep Disorders Insomnia – disorders of sleep initiation and maintenance Hypersomnia – disorders of excessive sleep or sleepiness REM-sleep dysfunctions

59. Sleep Disorders: Insomnia Sleep apnea – stop breathing during the night leads to repeated awakenings. Two types: Obstructive – obstruction of respiratory passages by muscle spasms or atonia Central – CNS fails to initiate breaths Most commonly seen in males, the overweight, and the elderly

60. Sleep Disorders: Insomnia Continued Periodic limb movement disorder – twitching of the body, usually the legs, during sleep. Most sufferers are not aware of why they don’t feel rested Restless legs – uneasiness in legs that prevents sleep Both are often treated with benzodiaze-pines

61. Hypersomnia – Narcolepsy Severe daytime sleepiness and repeated brief daytime sleeping - “sleep attacks” Cataplexy – loss of muscle tone while awake Sleep paralysis – paralyzed while falling asleep or upon waking Hypnagogic hallucinations – dreaming while awake

62. Hypersomnia – Narcolepsy Continued Appears to be an abnormality in the mechanisms that triggers REM Narcoleptics enter directly into REM Dreaming and loss of muscle tone while awake – suggest REM intruding into wakefulness May be due to genetic orexin deficiency and environmental factors

63. REM-Sleep-Related Disorders Narcolepsy REM without atonia – able to act out dreams – possibly caused by damage to the nucleus magnocellularis or its output Case history: man with assumed damage to caudal reticular formation had no REM sleep and no ill effects

64. Effects of Long-Term Sleep Reduction Differences between short and long sleepers? No consistent differences Long-term reduction of nightly sleep? When reduced to 6h/night subjects often reported daytime sleepiness Otherwise no ill effects Overall sleep was more efficient Effects of napping? Some evidence that polyphasic sleep is more efficient

65. Effects of Shorter Sleep Times on Health Some evidence suggests that 5-7 hours/night of sleep is correlated with greater longevity