Chapter 8 - Wakefulness and Sleep

Rhythm of Wakefulness and Sleep

Rhythm of Wakefulness and Sleep

Our brain has neural mechanisms that can generate rhythms preparing to wake up at certain times and to sleep at other times according to sunlight

Two Types of Endogenous Rhythmic Cycles

1. Endogenous Circannual Rhythm

2. Endogenous Circadian Rhythm

Endogenous Circannual Rhythm

An internal calendar that operates on a yearly cycle to prepare species for annual seasonal changes

Typically seen in migratory birds - light-dark pattern tells them when to fly south for winter and fly north for summer

Endogenous Circadian Rhythm

An internal clock that lasts about a day (24hrs) and regulates the times for wakefulness and for sleepiness in a 24hr cycle

Normally set by sunlight

(TRUE/FALSE) The sunlight indicates you feel less sleepy

True

Your urge to sleep mainly depends on __

The time of day, not how long you have been awake - regulated by circadian rhythm that is strongly set and reset by sunlight

(TRUE/FALSE) The circadian rhythm is changing

False

Fixed Circadian Rhythm (Flying Squirrel Experiment)

A flying squirrel was kept in total darkness for 25 days; even in this unchanging environment, the animal generated a consistent rhythm of wakefulness and sleepiness roughly in a 24-hour cycle

(TRUE/FALSE) Only humans generate endogenous 24hr cycles of wakefulness and sleepiness, no animals

False; Both humans and many animals

Circadian Rhythm (also present in?)

Regulating eating, drinking, urination, secretion of hormone, sensitivity to drugs, body temperature, and other variables

Circadian Rhythm (mood? at what time do most people report is their most and least pleasant mood?)

Circadian Rhythms may affect mood as well; most people report their most pleasant mood at 5-7pm and their least pleasant mood at 5-7am

Circadian Rhythms (how they differ, and change based on age?)

Circadian rhythms differ among individuals and lead to different patterns of wakefulness alertness (morning vs evening people); Circadian rhythms may change with age (children sleep earlier and wake up earlier, adolescents stay up later and waking up later up to about 20 years old then gradually reverse)

Setting

Biological clock (circadian rhythm) is set most strongly according to sunlight; the primary zeitgeber (German for “time giver”) that operates as constant light or constant darkness

The Primary Zeitgeber

Sunlight (german for time giver)

Resetting

Biological clock (circadian rhythm) is often reset by secondary zeitgebers, such as switching to daylight saving time or using an alarm clock

The Secondary Zeitgeber

Any stimulus that can reset circadian rhythms, like a clock, traveling across time zones, tides, exercise, meals, arousal of any kind, noise, temperature of environment; more difficult to reset due to the setting/resetting of the primary zeitgeber overpowering it

Jet Lag (what is it? what does it stem from?)

A temporary sleep disorder that produces a disruption of our biological rhythm due to crossing time zones; stems from a mismatch of the internal circadian clock and external

Phase-Delay

The effect on our circadian rhythm due to traveling west

Phase-Advance

The effect on our circadian rhythm due to traveling east

Shift Work (potential reason for not adjsuting)

Body temperature continues to peak when they are trying to sleep in the day instead of while they are working at night

Three Major Elements of the Neural Mechanisms Behind Circadian Rhythm

1. Retinohypothalamic Path

2. Genes

3. Melatonin

Suprachiasmatic Nucleus (SCN)

A nucleus of the hypothalamus located above the optic chiasm, that regulates the circadian rhythm

Retinohypothalamic Path

A small branch of the optic nerve that extends directly from the retina → transmits information about lightness and darkness to the neurons of the SCN receive to generate impulses setting a circadian rhythm

(TRUE/FALSE) The SCN sets circadian rhythms in a learned manner.

False; the SCN sets circadian rhythms in a genetically controlled, unlearned manner

SCN (damage?)

Results in less consistent body rhythms, as a result, our body is no longer synchronized to environmental patterns of light and dark

Retinohypothalamic Path (seasonal changes?)

When sunlight is changed because of seasonal changes, it is received by the retinohypothalamic path to regulate SCN activity; circadian rhythms are then reset

Melanopsin

A light-sensitive protein found in the retinohypothalamic path; a photopigment with an opsin

Retinohypothalamic Path (comes from?)

A special population of melanopsin-containing ganglion cells located in the retina near the nasal part that responds directly to SLOW changes in overall duration of light WITHOUT requiring input from rods and cones

How are blind people’s circadian rhythm still set by local patterns of sunlight?

Even with damages rods and cones, melanopsin-containing ganglion cells entrain waking and sleeping cycles to the local pattern of sunlight

Two Genes Involved in Regulating Circadian Rhythms

1. Period

2. Timeless

Period

Produces proteins PER

Timeless

Produces proteins TIM

How does PER and TIM play a role in wakefulness and sleepiness?

Low concentrations of both PER and TIM produces wakefulness (seen in the mornings)

Higher concentrations results in sleepiness (increases throughout the day; high concentration inhibits, halting production)

The Pineal Gland

An endocrine gland located posterior to the thalamus that secretes melatonin and has it activity levels controlled by the SCN (according to lightness and darkness)

Melatonin

A hormone secreted by the pineal gland beginning 2-3 hours before bedtime and increases sleepiness

Melatonin (doses taken?)

Can be used as a sleep aid (good for adjusting to jet lag) by resetting the biological clock, (phase-advancing)

Sleep

A physiological state/process where the brain actively decreases its activity and reduces responses to environmental stimuli; differs from other states (e.g., coma, vegetative state, brain death)

Coma

An extended period of unconsciousness caused by head trauma, stroke, or other diseases characterized by 1) no sleep cycle (most significant); 2) low brain activity that remains fairly steady; 3) little (or no) responses to any strengths of stimuli, including pain

Vegetative State

Characterized by open eyes and the appearance of wakefulness, usually long-lasting (months to years); may even alternate between periods of sleep and moderate arousal (sleep cycle); however, there is NO awareness of surrounding.

NO purposeful activity; some autonomic arousal and response

Minimally Conscious State

The stage higher than a vegetative state marked by occasional brief periods of purposeful action and limited speech comprehension

Brain Death

No sign of brain activity and no response to any stimulus

How are stages of sleep recorded?

EEG and eye movement; comparing brain activity at different times during sleep

Polysomnograph

A chart recorder used for analyzing sleep stages that is a combination of recording EEG and eye-movement

𝜶-waves

Brain waves that have a frequency of about 8-12 per second (Hz) with moderate wave amplitudes; typical of a relaxed state of consciousness

Stage 1 Sleep

When sleep has just begun

NREM (non-REM sleep)

Stage 2 Sleep

Characterized by the presence of 1) sleep spindles and 2) K-complex

NREM (non-REM sleep)

Sleep Spindles

Rhythmic brain waves or burst of neural activity at about 12-14 Hz that last at least 0.5 seconds (short-lasting high frequency)

K-complex

A sharp high-amplitude negative brain wave followed by a smaller, slower positive wave

Slow Wave Sleep

The deepest stage of sleep (stages 3 and 4) characterized by 1) slow, large amplitude waves, 2) slowing of heart rate, breathing rate, and brain activity, and 3) highly synchronized neuronal activity

NREM (non-REM sleep)

Rapid Eye Movement (REM) Sleep

A type of sleep characterized by 1) high brain activity, 2) completely relaxed muscles

Combines deep sleep (point 1) and light sleep (point 2) and features that are difficult to classify as deep or light

What is the difference between REM and paradoxical sleep?

Synonymous but REM is often used for humans and Paradoxical sleep is used for non-humans (because many species lack eye movement)

Why is REM sleep considered light and deep sleep? what ways?

During REM sleep, there is irregular, low-amplitude, fast waves that indicate increased neuronal activity (light sleep); However, the postural muscles of the body are more relaxed (deep sleep)

The sleep cycle consists of what?

Four stages of slow wave sleep followed by REM sleep

What is the sequence of stages in the sleep cycle?

When people fall asleep, they enter stage 1, followed by stage 2, 3, and 4 → then cycle back from stage 4, to 3 and 2 → and then enters REM sleep (1, 2, 3, 4, 3, 2, REM) → then the sequence repeats around every 90 minutes

At what part does stage 3 and 4 dominant and at what time do they grow shorter? REM?

Early in the night, stages 3 and 4 predominate and toward the morning they grow shorter or don’t even occur. REM grows longer

What part in the sleep cycle is strongly associated with dreaming?

REM sleep; but people report dreaming in other stages of sleep as well

What happens to the sleep cycle in older adults?

Slow-wave sleep is less and more awakenings during the night; depends on health and other factors

Which brain area promotes arousal and attention contributing to wakefulness?

The Reticular Formation (RF)

The Reticular Formation (RF)

A network-like circuitry that extends from the medulla up to the forebrain and has complex mechanisms that promote arousal and attention contributing to wakefulness

Some neurons of the RF have axons that do what?

Some ascend (well suited to regulate arousal) into higher brain and some descend into the spinal cord

What do lesions through RF do and what does that lead to?

Decrease cortical arousal, leading to lower alertness level and prolonged sleep

Where is the Pontomesencephalon located and what does it contribute to?

In the reticular formation located in an area of the pons and midbrain that contributes to cortical arousal

What is the mechanism behind the Pontomesencephalon and what does elevated activity cause?

It receives input from many sensory systems and generates spontaneous activity; elevated activity may awaken a sleeping individual and increase an alert level in someone already awake

Where does axons of Pontomesencephalon extend to?

To the hypothalamus, thalamus, and basal forebrain

What neurotransmitters release from the Pontomesencephalon?

Excitatory transmitters: ACh, glutamate or dopamine

Locus Coeruleus

A small structure in the pons whose axons emit impulses by releasing norepinephrine to arouse various areas of the cortex

(Has norepinephrinergic neurons)

Hypothalamus (type of neurons for arousal)

Contains Histaminergic Neurons that release the neurotransmitter histamine to produce arousal and alertness

(anti-histamine drugs produce sleepiness and drowiness)

Orexin

A neuropeptide released in some nuclei of the hypothalamus that produces the ability to stay awake up to 17 hours or even toward the end of the day

(when the brain orexin levels drop, people can’t stay awake and fall asleep)

The Basal Forebrain

A region near the base of the brain that has pathways projecting from the lateral hypothalamus that plays a key role in regulating wakefulness

What is the role of the pathways to the basal forebrain?

To regulate neurons in the basal forebrain, which in turn provide axons that extend throughout the thalamus and cerebral cortex contributing to wakefulness as some are stimulated by ACh

How does adenosine affect the basal forebrain during prolonged wakefulness? How does caffeine play a role?

Adenosine accumulates inhibiting the basal forebrain cells and increasing sleepiness; caffeine increases wakefulness by inhibiting adenosine from binding to its receptors

How does SCN set and reset the circadian cycle?

By regulating GABA concentration of the basal forebrain; GABA decreases in light and increases in dark

What is sleep associated with actively doing?

Inhibiting the brain activity by GABA release

What happens to the brain during sleep?

Neurons in the thalamus become hyperpolarized, decreasing their response to external stimuli, leading to decreased information sent to the cortex → This is done by the release of GABA in the forebrain (inhibits synaptic spread of information among neurons)

What contributes to sleepwalking, lucid dreaming and other sleep disorders?

Uneven activity levels due to a stronger or weaker GABA-mediated inhibition in one brain area than another

How are sleep waves for REM initiated?

By the pons detecting PGO waves of neural activity (then geniculate, then occipital cortex) and then sending messages to the spinal cord, which inhibits motor neurons, preventing motor movement

PGO wave activity triggered by amygdala where dopamine is released

Pons-geniculate-occipital waves (PGO)

A distinctive pattern of high-amplitude electrical potentials

Insomnia

A sleep disorder characterized by inadequate sleep, caused by factors like noise, stress, pain medication, and could be the result of epilepsy, parkinson’s, depression, anxiety.

Also relying of sleeping pills and shifts in the circadian rhythm can cause this

How do people ordinarily fall asleep and awaken?

Body temperature decline causes people to fall asleep and awaken while it’s rising

Phase-delayed causes what trouble?

Trouble falling asleep at the usual time, as if the hypothalamus thinks its not late enough due to high body temperature

Phase-advanced causes what trouble?

Falling asleep easily but awakening early

Three Categories of Insomnia (explain)

1. Onset Insomnia - trouble falling asleep (phase-delayed)

2. Maintenance Insomnia - Waking up frequently during the night

3. Termination Insomnia - Waking up too early and not being able to go back to sleep (phase-advanced)

Sleep Apnea

A sleep disorder characterized by the inability to breathe for a prolonged period of time while sleeping resulting in inadequate sleep; caused by obesity, genetics, hormones, old age

Most commonly seen in middle-aged obese men

What are some of the serious consequences of sleep apnea?

Depression, heart problems, and impaired cognition (result from a loss of neurons due to chronically insufficient O2 levels)

Narcolepsy (sleep attack)

A disorder characterized by frequent unexpected attacks of sleepiness during the daytime (can be gradual or sudden)

What are some additional attacks associated with Narcolepsy?

1. Cataplexy - attack of muscle weakness while awake

2. Sleep Paralysis - inability to move while sleeping or waking up

3. Hypnagogic Hallucination - dream-like experiences occurring at the onset of sleep

How are each of the symptoms of narcolepsy interpreted?

REM sleep intruding into wakefulness leading to REM occurring during the daytime

What is a possible explanation and treatment for Narcolepsy?

A deficiency in orexin and is treated with stimulant drugs to enhance dopamine and norepinephrine activity

Periodic Limb Movement Disorder

Repeated involuntary movements of the legs and arms that cause insomnia; mostly occurs during NREM sleep; treated with tranquilizers

REM Behavior Disorder

Associated with vigorous movement of muscle during REM sleep; acting out dreams; occurs in elderly and old men with brain diseases; damage to the pons where PGO becomes abnormal

Night Terrors

Experiences of intense anxiety from which a person awakens screaming in terror (NREM)

Sleepwalking

Walking during NREM sleep; runs in families; mostly in young children; not associated with dreaming; not dangerous to wake a sleepwalker

Why do we need sleep?

1. Survival: during inefficient times, activity becomes wasteful and dangerous due to the GABA-mediated inhibitory process decreased our brain alertness)

2. Energy conservation: A decrease in body temperature and muscle activity (analogous to hibernation in animals

3. Consolidation: sleep plays an important role in enhancing learning and strengthening memory

Replays

Research suggests that the brain replays its daily experiences during sleep, which reinforces the learning through repetition (reinforcing synaptic connections and weakening others)

What is REM sleep hypothesized to be important for? (two hypotheses)

1. Memory storage; it is a way of consolidating some types of memories, particularly, motor learning is impaired if REM is deprived

2. Provide sufficient oxygen to the corneas (by shaking eyeballs back and forth)

Less NREM sleep results in what impairment? Less REM sleep results in what impairment?

Less NREM sleeps results in verbal learning impairment; less REM sleep results in consolidation of learned motor skills impairment

Dream Hypotheses

1. Activation-synthesis hypothesis

2. Neurocognitive hypothesis

What is the activation-synthesis hypothesis

A dream hypothesis that states that dreams begin with spontaneous activity in the pons during REM sleep, producing PGO waves. These waves activate parts of the cortex, which then synthesizes a story based on the random activation patterns.

What is the neurocognitive hypothesis?

A dream hypothesis that suggests that dreams are similar to thinking but occur under unusual conditions, like during REM sleep when the brain gets little sensory input and the motor cortex is suppressed. Dreams are generated from spontaneous brain activity, often influenced by recent memories. Unlike the activation-synthesis hypothesis, it emphasizes that brain activity during dreaming does not rely heavily on PGO waves or the pons, and the limbic and parietal areas are free to create images without sensory or motor interference, leading to irrational, fragmented dream scenes.

What brain regions are involved in dreaming and how?

1. Inferior part of the parietal cortex - an area important for visual-spatial perception

2. Areas outside of V1 - visual imagery of dreams

3. Hypothalamus and amygdala - emotion contents of dreams