Chapter 9 Wakefulness and Sleep

1. Chapter 9Wakefulness and Sleep

2. Functions of sleep include: Restoration of the brain and body Energy conservation Memory consolidation/learning Why Sleep?

3. Why Sleep?Restoration of the Brain and Body • Moderate sleep deprivation can result in: • impaired concentration • irritability • hallucinations • tremors • unpleasant mood • decreased immune system function

4. Why Sleep?Restoration of the Brain and Body • Optimal sleep time: 8-10 hrs

5. Why Sleep?Restoration of the Brain and Body • Prolonged sleep deprivation in laboratory animals results in: • Increased metabolic rate, appetite and body temperature • Immune system failure • Decrease in brain activity

6. Why Sleep?Energy Conservation • Evolutionary Theory of Sleep: The function of sleep is to conserve energy by: • decreasing body temperature 1-2 Celsius degrees in mammals • decreasing muscle activity • Sleep is analogous to the hibernation of animals

7. Fig. 9-17, p. 287

8. Why Sleep? Memory and Learning • Sleep enhances: • learning and memory • performance on a newly learned task • Increased brain activity occurs in the area of the brain activated by a newly learned task while one is asleep

9. Activation-synthesis hypothesis: dreams begin with spontaneous activity in pons Pons activates many parts of cortex Cortex synthesizes story from pattern of activation Normal sensory information cannot compete with the self-generated stimulation and hallucinations result. Why Dreams?Activation synthesis hypothesis

10. Why Dreams?The clinico-anatomical hypothesis • Clinico-anatomical hypothesis: Dreams are similar to thinking, just under unusual circumstances. • Dreams begin with arousing stimuli that are generated within the brain. • Stimulation is combined with recent memories and current sensory stimulation. 

11. Rhythms of Waking and Sleep • Endogenous: generated from within • Endogenous circannual rhythms: internal mechanisms that operate on an annual cycle • Examples: • Birds migratory patterns • Animals storing food for winter

12. Rhythms of Waking and Sleep • Endogenous circadian rhythms, internal mechanisms that operate on an approximate 24 hour cycle: • sleep/ wake cycle • frequency of eating and drinking • body temperature • secretion of hormones • volume of urination • sensitivity to drugs

13. The Circadian Rhythm(AKA: The Biological Clock) • Free-running rhythm: rhythm that occurs when no stimuli reset or alter it • Human circadian clock generates a rhythm slightly longer than 24 hours when it has no external cue to set it • Most people can adjust to 23- or 25- hour day but not to a 22- or 28- hour day

14. Sunrise= Light + increasing temperature Sunset= Dark + decreasing temperature Biological cues

15. Purpose of circadian rhythm: to keep our internal workings in phase with the outside world Light is critical for periodically resetting our circadian rhythm. Zeitgeber: term used to describe any stimulus that resets circadian rhythms: exercise, noise, meals, temperature and more The Circadian Rhythm:Resetting the Biological Clock

16. The Circadian Rhythm:Resetting the Biological Clock • Jet lag: disruption of circadian rhythm due to crossing time zones • Characterized by sleepiness during the day, sleeplessness at night, and impaired concentration.

17. Suprachiasmatic Nucleus (SCN): Part of the hypothalamus Main control center of circadian rhythms for sleep and temperature Genetically controlled and independently generates circadian rhythm Rhythms of Waking and Sleep:Biological Mechanisms

18. Light resets the SCN via a small branch of the optic nerve known as the retinohypothalamic path. Travels directly from the retina to the SCN. Rhythms of Waking and Sleep:Biological Mechanisms

19. SCN regulates the pineal gland (endocrine gland located posterior to the thalamus) Pineal gland secretes melatonin, a hormone that increases sleepiness. Rhythms of Waking and Sleep:Biological Mechanisms

20. Electroencephalography (EEG) allowed researchers to discover that there are various stages of sleep Polysomnography measures both EEG and eye-movement records Stages of Sleep And Brain Mechanisms

21. Fig. 9-9, p. 276

22. Over the course of about 90 minutes: a sleeper goes through sleep stages 1, 2, 3, and 4 then returns through the stages 3 and 2 to a stage called REM. Stages of Sleep And Brain Mechanisms

23. Stages of Sleep And Brain Mechanisms • Alpha waves = state of relaxation • Stage 1 sleep is when sleep has just begun. • the EEG is dominated by irregular, jagged, low voltage waves. • brain activity begins to decline.

24. Stages of Sleep And Brain Mechanisms • Stage 2 sleep is characterized by the presence of: • Sleep spindles - 12- to 14-Hz waves during a burst that lasts at least half a second. • K-complexes - a sharp high-amplitude negative wave followed by a smaller, slower positive wave.

25. Stages of Sleep And Brain Mechanisms • Stage 3 and stage 4 together constitute slow wave sleep (SWS) and is characterized by: • EEG recording of slow, large amplitude wave. • Slowing of heart rate, breathing rate, and brain activity. • Highly synchronized neuronal activity.

26. Stages of Sleep And Brain Mechanisms • Rapid eye movement sleep (REM): periods characterized by rapid eye movements during sleep • Also known as “paradoxical sleep” because it is like deep sleep in some ways, but light sleep in other ways. • EEG waves resemble awake state • Postural muscles of the body are more relaxed than other stages

27. Stages of Sleep And Brain Mechanisms • REM is strongly associated with dreaming, but people also report dreaming in other stages of sleep. • Stages other than REM are referred to as non-REM sleep (NREM).

28. Stages of Sleep And Brain Mechanisms • Sleep stages change as the night progresses: • Deep sleep (stages 3 & 4) gets shorter as the night progresses • REM sleep gets longer as the night progresses

29. Why Sleep? Why REM? Why Dreams? • REM deprivation results in: • Increased attempts of the brain/ body for REM sleep throughout the night • Increased time spent in REM when no longer REM deprived. • Subjects deprived of REM for 4 to 7 nights increased REM by 50% when no longer REM deprived.

30. Why Sleep? Why REM? Why Dreams? • Possible functions of REM sleep: • Brain may discard useless connections • Learned motor skills may be consolidated • Oxygen may be delivered to the corneas

31. Sleep Disorders • Insomnia: inability to fall asleep or stay asleep • Causes: noise, stress, pain medication, epilepsy, Parkinson’s disease, depression, anxiety, other psychiatric conditions • Treatment: relaxation techniques, sleeping pills

32. Sleep Disorders • Sleep apnea: periodic inability to breathe while sleeping • Causes: obesity, growth in windpipe, weak lungs, deterioration of brain mechanisms that control breathing • Can result in cognitive impairment if there is a loss of neurons due to insufficient oxygen levels • Treatments include: Weight loss, surgery, forced air

33. Sleep Disorders • Narcolepsy: frequent periods of sleepiness • 4 main symptoms: • Gradual or sudden attack of sleepiness • Cataplexy - muscle weakness triggered by strong emotions • Sleep paralysis- inability to move while asleep or waking up • Hypnagogic hallucinations- dreamlike experiences the person has difficulty distinguishing from reality

34. Sleep Disorders • Narcolepsy: frequent periods of sleepiness • Cause: Lack of hypothalamic cells that produce neurotransmitter orexin • Treatments: Napping schedules and stimulant drugs

35. Sleep Disorders • Periodic limb movement disorder: repeated involuntary movement of the legs and arms while sleeping • Legs kick once every 20 to 30 seconds for periods of minutes to hours. • Usually occurs during NREM sleep. • Treatment: tranquilizers

36. Sleep Disorders • REM behavior disorder is associated with vigorous movement during REM sleep. • Usually associated with acting out dreams. • Occurs mostly in the elderly and in older men with brain diseases such as Parkinson’s. • Presumed cause: damage to pons (inhibits spinal neurons that control large muscle movements).

37. Sleep Disorders • Night terrors: experiences of intense anxiety from which a person awakens screaming in terror. • Usually occurs in NREM sleep. • Sleep talking: occurs during both REM and NREM sleep. • Sleepwalking: runs in families, mostly occurs in young children, and occurs mostly in stage 3 or 4 sleep.