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Sleep and Dreaming

Lu Chen, Ph.D. MCB, UC Berkeley

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1 Why Do We Sleep?

It is one of the greatest standing mysteries of life: we spend 1/3 of our life sleeping and still don’t know what for. People who cannot sleep die (fatal familial insomnia).

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What Is Sleep?

1) Reduced motor activity 2) Decreased response to stimulation 3) Stereotypic postures 4) Relatively easy reversibility

Can be monitored by electrical recordings: Electromyography (EMG): muscle activity Electro-oculography (EOG): eye movement Electroencephalography (EEG): Cortical neuron activity

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2 Stages of Sleep

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Stages of Sleep

Non-REM sleep has four stages Stage 1: transition from wakefulness to the onset of sleep.

EEG: Slower frequency emerges, mixed-frequency pattern. EMG: Some activity of skeletal muscle EOG: no rapid eye movement, slow rolling eye movement

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3 Stages of Sleep Non-REM sleep has four stages Stage 2: EEG shows burst of sinusoidal waves (sleep spindles) and high-voltage biphasic waves (K complexes)

Stage 3: EEG shows high-amplitude, slow delta waves Stage 4: slow-wave activity increase and dominates the EEG record. In human, stage 3 & 4 are also called slow-wave sleep.

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Stages of Sleep

REM sleep : the active form of sleep (body temp. and metabolic rate rise) REM sleep EEG patterns are similar to those during wakefulness.

Neurons in the pons, the LGN, and the occipital cortex fire more intensely than during wakefulness (PGO waves).

- Easily aroused by meaningful stimuli; if awakened, appears alert and attentive. - Dreaming - Complete sleep cycle ~90 min - Each cycle ~20 min REM - Slow-wave sleep occurs mostly during first half of night.

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4 Physiological Mechanisms of sleep and waking

Arousal – controlled by brainstem Locus coeruleus in pons release norepinephrine, which is associated with vigilance. Posterior hypothalamus produced serotonin – also involved in arousal, mostly behavioral activation (anti-histaminic drugs promotes sleep). Slow-wave sleep Anterior hypothalamus and basal forebrain region: lesions in rats cause insomnia, leading to coma and death.

REM sleep Serotonergic neurons and noradrenergic neurons become silent. Acetylcholinergic neurons in pons become active. This results in: PGO waves, rapid eye movement, muscular paralysis

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Sleep and brain development

1) Infants sleep much more than adults, mostly REM sleep. The fetus seems to spend 80% of their time in REM sleep. Young birds, even young flies sleep more than adults. 2) REM sleep may be important in providing early stimulation and activity requirements of the growing brain. It has been hypothesized that REM sleep generates specific patterns of intrinsic activity in neuronal populations whose development is dependent upon activity. (sounds familiar? Visual pathway development…) 3) Suppression of neonatal REM sleep in rats alters ventilatory pattern, metabolism, and regional brain concentrations of neurotransmitters and their receptors at maturity, suggesting adverse adult consequences on brain re-wiring due to disruptions in sleep in early life. 4) premature infants in intensive care nurseries are at greatest risk for early disruptions in sleep and sleep-related brain maturation due to constant medical and nursing procedures.

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5 Sleep and memory consolidation

Memory categories Episodic (memory of events of one’s past) Declarative (Knowing “what”) Semantic (memory of general knowledge) memory

Procedural (learning of actions, skills, habits, etc) Non-declarative (Knowing “how”) Implicit learning (conditioning) Memory stages

Encoding/ Consolidation Recall Reconsolidation Acquisition (stabilization/enhancement)

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Sleep and memory consolidation

1) Suggested by Roffwarg, Musio and Dement in 1966 that repetitive firing of neurons during REM sleep in human fetuses was associated with neuron growth and development, and this synaptic reinforcement continued in adult life during REM sleep. 2) By studying patients with retrograde amnesia, it was determined that the "replay" of information in the hippocampus leads to permanent storage of information in the neocortex. 3) Experiments done in rats revealed similar brain activity during learning and during sleep after learning. (Bruce McNaughton)

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6 Sleep and memory consolidation

Same in humans…

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Sleep and memory consolidation

3) Significant increase in post-training REM sleep after intensive foreign language learning, with the degree of successful learning correlating with the percentage increase of REM sleep.

Greater improvement of motor skill after sleep.

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7 Sleep and memory consolidation

4) Impaired learning and memory after sleep deprivation.

Experiments on humans found that REM sleep deprivation leads to poor performance on a variety of recall tests or logical tasks. It has also been found that memory loss occurs when sleep is deprived on the same night or two nights after material has been learned.

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Sleep and memory consolidation

Counter theory

An alternative theory suggests that REM sleep functions to dispose of unwanted memories through a mechanism called reverse learning. Reverse learning operates during REM sleep to prevent the brain from being overloaded with massive amounts of information stored during wakefulness.

Direct test is difficult, remains speculative…

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8 What’s the minimum amount of sleep?

Minimum sleep for normal performance in a detection task after 1 night of reduced sleep is 3 hrs. There is little REM during the first 3 hours of sleep.

Minimum sleep for normal performance in a detection task after several nights of reduced sleep is 5 hrs.

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Sleep disorders Obstructive Sleep Apnea (OSA)

-periodic obstruction of the upper airway during sleep - Affects 3-8 % of human population. - Periods of apnea lasts about 90 sec, can occurs several hundred times per night.

-Some symptoms

•Loud, habitual snoring •Pauses in breathing during sleep •Non-refreshing sleep/inability to wake up •Morning headaches •Daytime fatigue/sleepiness •Irritability/Personality changes •Obesity •Hypertension •Memory and concentration problems

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9 Sleep disorders Narcolepsy

-The disease is principally characterized by a permanent and overwhelming feeling of sleepiness and fatigue. - Affects 1 in every 2000 Americans. - Involve abnormalities of dreaming sleep, such as dream-like hallucinations and finding oneself physically weak or paralyzed for a few seconds

-Some symptoms •Abnormal REM sleep •Excessive sleepiness •Cataplexy (a pathological equivalent of REM sleep atonia unique to narcolepsy, is a striking, sudden episode of muscle weakness triggered by emotions). •Sleep paralysis (a frightening symptom considered to be an abnormal episode of REM sleep atonia, the patient suddenly finds himself unable to move for a few minutes, most often upon falling asleep or waking up). •Hypnagogic hallucinations (patients experience dream-like auditory or visual hallucinations, while dozing or falling asleep). -Recent research found a link between Orexin and narcolepsy. Neurons containing the neuropeptide orexin (hypocretin) are located exclusively in the lateral hypothalamus and send axons to numerous regions throughout the central nervous system, including the major nuclei implicated in sleep regulation.

Orexin (named after Greek orexis for “appetite”) also regulates food intake and autonomic activity.

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Sleep disorders Insomnia

- In its chronic form, this disorder affects approximately nine percent of the population. - Can last for weeks, months, or even years and may be related to the following symptoms: •Worry, anxiety or stress •Psychiatric disorders •Primary sleep disorders •Substance abuse •Medical problems

Parasomnia - Refers to a wide variety of disruptive, sleep-related events or “disorders of arousal.” •Sleep Walking •Sleep terrors (pavor nocturnes) •Nightmares •Partial seizures •Violent behavior during sleep •REM behavior disorder (acting out dreams)

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