10 Sleep Cognitive Neuroscience David Eagleman Jonathan Downar

10: Sleep Cognitive Neuroscience David Eagleman Jonathan Downar © 2018 1

Chapter Outline • • • Sleep and the Brain The Circadian Rhythm Why Do Brains Sleep? Dreaming Sleep Deprivation and Sleep Disorders © 2018 2 2

Sleep and the Brain • The Brain Is Active during Sleep • The Neural Networks of Sleep • The Brain during REM Sleep © 2018 3 3

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. © 2018 4 4

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. © 2018 5 5

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 © 2018 6 6

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 hourand-a-half cycles. (b) EEG recordings from different sleep stages. 7 © 2018 7

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. © 2018 8 8

The Neural Networks of Sleep Figure 10. 5 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. 9 © 2018 9

The Neural Networks of Sleep Figure 10. 6. 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. 10 © 2018 10

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. © 2018 11 11

The Brain during REM Sleep Figure 10. 7 Cholinergic neurons involved in both arousal and REM sleep. The neurons projecting from the basal forebrain and the pons use the neurotransmitter acetylcholine. 12 © 2018 12

The Circadian Rhythm • Entrainment of the Circadian Rhythm by Light Cues • The Circadian Rhythm Is Not Fixed • The Circadian Rhythm and Napping © 2018 13 13

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. © 2018 14 14

Entrainment of the Circadian Rhythm by Light Cues Figure 10. 8 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. 15 © 2018 15

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. © 2018 16 16

Entrainment of the Circadian Rhythm by Light Cues Figure 10. 9. The suprachiasmatic nucleus is part of the hypothalamus and is located just above the optic chiasm. It is important in maintaining the circadian rhythm. 17 © 2018 17

Entrainment of the Circadian Rhythm by Light Cues Figure 10. 10 Anatomy and circadian rhythm of sleep. (a) The location of the pineal gland along the midline of the brain. (b) Blood levels of melatonin c hange as a function of time. 18 © 2018 18

The Circadian Rhythm Is Not Fixed • The circadian rhythm can be shortened to 23. 5 hours or lengthened to 24. 65 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. © 2018 19 19

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. © 2018 20 20

The Circadian Rhythm and Napping Figure 10. 12 Polyphasic sleep. Some people sleep more than once in a 24 -hour period, claiming that this is more natural and enables them to sleep less time overall than they would if they slept just once. Some famous individuals thought to have used this polyphasic sleep schedule include (a) Buckminster Fuller, (b) Leonardo da Vinci, and (c) Thomas Jefferson. (d) Different patterns of polyphasic sleep are shown. 21 © 2018 21

Why Do Brains Sleep? • Four Theories of Sleeping: Restoration, Survival, Simulation, Learning • Rehearsal • Forgetting • Insight and the Restructuring of Information © 2018 22 22

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. © 2018 23 23

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. © 2018 24 24

Four Theories of Sleeping Figure 10. 13. Different animals sleep for different amounts of time. All animals require sleep, but how much they need varies across species. 25 © 2018 25

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. © 2018 26 26

Rehearsal Figure 10. 14 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). 27 © 2018 27

Rehearsal Figure 10. 15. 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. 28 © 2018 28

Rehearsal • Learning repetitive tasks relies on REM sleep to improve performance. • Slow wave sleep is important for rehearsal and learning. © 2018 29 29

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. © 2018 30 30

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. © 2018 31 31

Insight and the Restructuring of Information Figure 10. 17 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). 32 © 2018 32

Dreaming • Dream Content • Can Dreams Shed Light on Consciousness? • Dreams of the Future and How to Study Them © 2018 33 33

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. © 2018 34 34

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. © 2018 35 35

Dream Content Figure 10. 18 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. 36 © 2018 36

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. © 2018 37 37

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. © 2018 38 38

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. © 2018 39 39

Dreams of the Future and How to Study Them Figure 10. 21. Effects of antidepressant medications on sleep. Different classes of antidepressant medication affect sleep in different ways. 40 © 2018 40

Sleep Deprivation and Sleep Disorders • • Sleep Deprivation Insomnia Hypersomnia Parasomnias © 2018 41 41

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. © 2018 42 42

Sleep Deprivation Figure 10. 22. Effects of sleep deprivation on cognitive function and the body. Sleep deprivation affects many cognitive processes, as well as many other body processes. 43 © 2018 43

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. © 2018 44 44

Insomnia Figure 10. 24. Symptoms of insomnia. The frequency of different symptoms of insomnia reported by patients. 45 © 2018 45

Insomnia Figure 10. 25. Effect of benzodiazepine on GABA-A receptor. Benzodiazepines are agonists to the GABAA receptor, allowing more chloride ions to enter the cell, resulting in hyperpolarization. 46 © 2018 46

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. © 2018 47 47

Hypersomnia Figure 10. 26. Narcolepsy. This dog is experiencing cataplexy, a symptom of narcolepsy in which all the muscles weaken suddenly, resulting in collapse. 48 © 2018 48

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. © 2018 49 49

Parasomnias Figure 10. 27. NREM parasomnias in children. Some of the characteristics of night terrors and sleep walking in children. 50 © 2018 50