1. 10: Sleep
Cognitive Neuroscience
David Eagleman
Jonathan Downar

2. Chapter Outline Sleep and the Brain The Circadian Rhythm
Why Do Brains Sleep?
Dreaming
Sleep Deprivation and Sleep Disorders

3. Sleep and the Brain The Brain Is Active during Sleep
The Neural Networks of Sleep
The Brain during REM Sleep

4. The Brain Is Active during Sleep
We spend about 1/3 of our lives asleep.
Without sleep, we suffer significant cognitive impairment.
A network of brain areas is involved in both sleep and maintaining wakefulness.
Even during sleep, the neurons are very active.

5. The Brain Is Active during Sleep
Sleep follows a regular cycle each night.
Each cycle lasts 90 – 100 minutes.
There are 4 – 5 cycles per night.
Rapid eye movement (REM) alternates with non-REM (NREM) sleep.

6. The Brain Is Active during Sleep
NREM
Makes up about 80% of sleep
Three stages
Heart rate and breathing slow
No dreams
REM
Makes up about 20% of sleep
One stage
Heart rate and breathing speed up
Dreams
Muscles of the body are paralyzed

7. The Brain Is Active during Sleep
FIGURE 10.4 Sleep cycles and typical patterns of brain waves during sleep. (a) The sleeping brain cycles through the different stages during the night, repeating four or five approximately hour-and-a-half cycles. (b) EEG recordings from different sleep stages.

8. The Neural Networks of Sleep
The ventrolateral preoptic nucleus (VLPO) in the hypothalamus is important for promoting sleep.
An arousal network also exists.
Locus coeruleus
Raphe nucleus
Tuberomammillary nucleus
These networks are mutually inhibitory.

9. The Neural Networks of Sleep
FIGURE Arousal network of the brain. The brain structures involved in wakefulness and alertness include the locus coeruleus, raphe nucleus, tuberomammillary nucleus, and reticular activating system. The ventrolateral preoptic nucleus of the hypothalamus acts in opposition to the arousal network, promoting sleep.

10. The Neural Networks of Sleep
FIGURE Flip-flop circuit for sleep. The brain regions responsible for the sleep and awake states are mutually inhibitory, resulting in either sleep or wakefulness, but not both at the same time.

11. The Brain during REM Sleep
Increased neural activity in 30 – 70 Hz range.
Acetylcholinergic neurons in pons trigger paralysis.
PGO waves spread from pons to the lateral geniculate nucleus and occipital lobe.

12. The Brain during REM Sleep
FIGURE Cholinergic neurons involved in both arousal and REM sleep. The neurons projecting from the basal forebrain and the pons use the neurotransmitter acetylcholine.

13. The Circadian Rhythm Entrainment of the Circadian Rhythm by Light Cues
The Circadian Rhythm Is Not Fixed
The Circadian Rhythm and Napping

14. Entrainment of the Circadian Rhythm by Light Cues
Most people need 6.5 – 7 hours of sleep per night.
How much sleep you need is influenced by genetics.
The circadian rhythm lasts about 24 hours and influences the sleep-wake cycle.

15. Entrainment of the Circadian Rhythm by Light Cues
FIGURE Physiological changes tied to the circadian rhythm. The circadian rhythm runs on an approximately 24-hour cycle and controls sleep-wake cycles. It also influences other physiological and cognitive processes, including temperature, alertness, blood pressure, and hormone levels.

16. Entrainment of the Circadian Rhythm by Light Cues
The circadian rhythm is generated internally, but it is reset by external stimuli, known as zeitgebers.
The strongest zeitgeber is light, which influences the suprachiasmatic nucleus via the retinohypothalamic tract.
The pineal gland produces melotonin, which promotes sleep.

17. Entrainment of the Circadian Rhythm by Light Cues
FIGURE The suprachiasmatic nucleus. The suprachiasmatic nucleus is part of the hypothalamus and is located just above the optic chiasm. It is important in maintaining the circadian rhythm.

18. Entrainment of the Circadian Rhythm by Light Cues
FIGURE Anatomy and circadian rhythm of sleep. (a) The location of the pineal gland along the midline of the brain. (b) Blood levels of melatonin change as a function of time.

19. The Circadian Rhythm Is Not Fixed
The circadian rhythm can be shortened to 23.5 hours or lengthened to hours using false light cues.
Some people (owls) tend to be more alert at night while others (larks) tend to be more alert in the morning.

20. The Circadian Rhythm and Napping
In polyphasic sleep, individuals sleep multiple times per day for shorter periods of time.
Polyphasic sleep is common through the animal kingdom.

21. The Circadian Rhythm and Napping

22. Why Do Brains Sleep?
Four Theories of Sleeping: Restoration, Survival, Simulation, Learning
Rehearsal
Forgetting
Insight and the Restructuring of Information

23. Four Theories of Sleeping
Sleep is restorative.
Sleep helps the body recover from the activity of the day.
High level of neural activity during sleep makes this questionable.
Sleep is a survival advantage.
Sleep protects organisms with poor night vision from predators.
We could just evolve night vision.

24. Four Theories of Sleeping
Sleep simulates rare situations.
REM sleep enables us to test out activities before using them in the real world.
Research has not supported this.
Sleep helps with information processing.
Sleep is necessary for learning and memory.
This theory is the best supported.

25. Four Theories of Sleeping
FIGURE Different animals sleep for different amounts of time. All animals require sleep, but how much they need varies across species.

26. Rehearsal
Performance on visual discrimination tasks improves following REM sleep.
A nap is as effective as a full night’s sleep for improving performance.
Reactivation of memories during sleep may aid long-term encoding.
The information replayed during sleep may influence what we later remember.

27. Rehearsal
FIGURE Taking a nap improves learning. Researchers found that taking a 60- to 90-minute nap significantly decreased the time needed to find a target among distractors. From Mednick, Nakayama & Stickgold (2003).

28. Rehearsal
FIGURE Patterns of cellular activity during REM sleep resemble patterns in the same cells when learning the task. Rats were trained to explore a circular maze to search for a food reward. While they were doing that, researchers recorded the pattern of activity of 10 place cells within the hippocampus (RUN). Later, the rats were allowed to sleep and the recordings continued (REM). The recordings closely resembled those made while the rats were awake, suggesting the rats were rehearsing what they learned while awake. From Louie and Wilson (2001).

29. Rehearsal
Learning repetitive tasks relies on REM sleep to improve performance.
Slow wave sleep is important for rehearsal and learning.

30. Forgetting One theory of dreaming is that it helps us to forget.
REM sleep erases the inappropriate associations between neurons before they get strengthen by synaptic plasticity.

31. Insight and the Restructuring of Information
Anecdotally, many people report gaining insight while sleeping.
Some experimental evidence supports the idea that sleep can boost insight.

32. Insight and the Restructuring of Information
FIGURE Effects of sleep and wakefulness on the probability of having an insight. Bars show the percentage of subjects gaining insight into a hidden rule of a game. Subjects either slept at night (right bar) or remained awake (during the day or night, left two bars) between the initial training and retesting. From Wagner et al. (2004).

33. Dreaming Dream Content Can Dreams Shed Light on Consciousness?
Dreams of the Future and How to Study Them

34. Dream Content
The amount of time spent in REM sleep decreases over the lifetime, from 50% in babies to 15% in the elderly.
Dreams do occur during NREM sleep, but they are unremarkable and not often remembered.
Most vivid, memorable dreams occur in REM sleep.

35. Dream Content
Dreams rely on a network of brain areas, including the limbic, paralimbic, and association areas.
REM dreams are characterized by hallucinations and strange beliefs.

36. Dream Content
FIGURE The brain network involved in dreaming. Dreaming depends on the normal functioning of a relatively specific neural network located primarily in the parietal association cortex and the limbic and paralimbic systems.

37. Dream Content Activation-synthesis model of dreaming
Dream content is the result of the brain trying to make sense of the random PGO waves.
This model was altered to suggest that the content is influenced by memories, fears, and hopes.
Dream content is similar across cultures.

38. Can Dreams Shed Light on Consciousness?
During REM, as opposed to NREM, sleep, the visual areas, limbic regions, and temporal lobe show more activity.
This may account for the different characteristics of REM dreams as opposed to NREM dreams.

39. Dreams of the Future and How to Study Them
Dream content changes in various diseases and with various medications.
Drugs that affect the dopamine system makes dreams more vivid.
Systematic studies of dreams under these conditions may inform our understanding of the dream network.

40. Dreams of the Future and How to Study Them
FIGURE Effects of antidepressant medications on sleep. Different classes of antidepressant medication affect sleep in different ways.

41. Sleep Deprivation and Sleep Disorders
Insomnia
Hypersomnia
Parasomnias

42. Sleep Deprivation
Short-term sleep deprivation include irritability and difficulty maintaining attention.
Longer-term sleep deprivation results in microsleeps.
Chronic sleep deprivation may affect health, stress levels, and heart disease.

43. Sleep Deprivation
FIGURE Effects of sleep deprivation on cognitive function and the body. Sleep deprivation affects many cognitive processes, as well as many other body processes.

44. Insomnia This is the most common sleep problem.
It involves not getting enough sleep to feel rested.
Hypnotics can be prescribed as sleep aids.
Benzodiazepines and Z-drugs
These drugs affect the GABA receptor to increase inhibition in the nervous system.

45. Insomnia
FIGURE Symptoms of insomnia. The frequency of different symptoms of insomnia reported by patients. From Ancoli-Israel and Roth (1999).

46. Insomnia
FIGURE Effect of benzodiazepine on GABA-A receptor. Benzodiazepines are agonists to the GABA-A receptor, allowing more chloride ions to enter the cell, resulting in hyperpolarization.

47. Hypersomnia Individuals have excessive sleepiness.
Individuals are so tired they feel compelled to nap frequently.
This is one of the main symptoms of narcolepsy.
This can be treated with orexin (hypocretin), which promotes wakefulness.

48. Hypersomnia
FIGURE Narcolepsy. This dog is experiencing cataplexy, a symptom of narcolepsy in which all the muscles weaken suddenly, resulting in collapse.

49. Parasomnias
The brain displays some signs of sleep and wakefulness simultaneously.
These are divided into REM disorders and NREM disorders.
Sleep walking, sleep eating, and night terrors are examples of NREM disorders.
NREM disorders are much more common in children.

50. Parasomnias
FIGURE NREM parasomnias in children. Some of the characteristics of night terrors and sleepwalking in children.