Chapter 9 Wakefulness and Sleep Why Sleep Functions

Chapter 9 Wakefulness and Sleep

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

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

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

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

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

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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

Why Dreams? Activation synthesis hypothesis • 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? 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.

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

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

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

Biological cues • Sunrise= Light + increasing temperature • Sunset= Dark + decreasing temperature

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

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

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

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Stages of Sleep And Brain Mechanisms • 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 • 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.

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.

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.

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

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).

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

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.

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

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

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

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

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

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

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).

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.