Ch.8 Sleep and wakefulness

Endogenous rhythm:

Self-sustained, internal biological cycles (e.g., circadian ~24h, ultradian) that persist without external cues. They profoundly influence behaviour by regulating sleep-wake cycles, hormone secretion, alertness, mood, and motor activity, with the master pacemaker located in the suprachiasmatic nucleus (SCN)

Endogenous rhythm influence on behavior:

This affects leep-wake cycles, walking speed, speech, and mood fluctuations as it relates to the circadian rhythm and motor control/efficiency.

Cues that set and reset biological clock

Zeitgebers, such as light (specifically sunlight), meal timing, physical exercise, and consistent social routines. These factors influence melatonin production and sleep-wake

Zeitgeber:

stimulus that resets rhythm.

Zeitgeber examples:

sunlight, exercise, meals, temperature.

Weak zeitgebers

Potentially causes mood and performance issues. (e.g., artificial light)

Suprachiasmatic nucleus (SCN):

The main control center of the circadian rhythms of sleep and temperature. generates circadian rhythms automatically.

Superchiasmatic nucleus location:

The optic chiasm and part of the hypothalamus. Also at the base of the brain

Damage to the suprachiasmatic nucleus:

Less consistent body rhythms that are no longer synchronized to environmental patterns of light and dark

Light resets the SCN:

Via a small branch of the optic nerve called the retinohypothalamic path. Travels directly from the retina to the SCN. The retinohypothalamic path comes from a special population of ganglion cells that have their own photopigment.

Melanopsin:

The retinohypothalamic path comes from a special population of ganglion cells that have their own photopigment

Two types of genes are responsible for generating the circadian rhythm:

Period (PER) and Timeless (TIM)

Period:

produce proteins called PER. Mutations can cause abnormal, irregular circadian rhythms or reduced alertness after sleep deprivation.

Timeless:

produce proteins called TIM

PER and TIM proteins:

Increase the activity of certain kinds of neurons in the suprachiasmatic nucleus that regulate sleep and waking.

Stage 1 sleep:

when sleep has just begun. The EEG is dominated by irregular, jagged, and low-voltage waves and brain activity begins to decline.

Stage 2 sleep:

characterized by the presence of sleep spindles and K-complex

Sleep spindles:

Oscillations during NREM stage 2 sleep are critical for consolidating, strengthening, and reorganizing recent memories into long-term storage. They work alongside slow oscillations to facilitate synaptic plasticity and neural "replay" of information. Fast, central-parietal spindles are particularly linked to memory enhancement

Slow-wave sleep (SWS):

EEG recording of slow, large amplitude wave, slowing of heart rate, breathing rate, and brain activity, and highly synchronized neuronal activity.This occurs early in the night and decreases as night progresses

Stages of sleep in order:

stage 1, 2, then slow-wave sleep, then the cycle repeats and then hits REM. (2, s, 2, rem, 2, s, 2, rem)

REM Sleep

predominant later at night, and the length increases as the night progresses. This is strongly associated with dreaming, but people also report dreaming in other stages of sleep.

Brain activity in REM sleep:

It contains a distinctive pattern of high-amplitude electrical potentials known as PGO waves. The stimulus to start this sleep comes from dopamine release in the amygdala

PGO Waves:

Waves of neural activity are detected first in the pons, then in the lateral geniculate of the hypothalamus, and then the occipital cortex.

What does it mean that sleep is controlled locally, and why does it matter?

sleep is not a uniform, all-or-nothing process that shuts down the entire brain at once. Instead, specific regions or circuits of the brain can fall into a sleep-like state (characterized by slow-wave activity and, at times, neuronal silence) while other areas remain awake

Possible functions of sleep:

Resting muscles, decreasing metabolism, performing cellular maintenance in neurons, reorganizing synapses, and strengthening memories

Original function of sleep:

Most likely to conserve energy through decrease in body temperature of about 1–2 Celsius degrees in mammals and decrease in muscle activity

Sleep patterns across species:

Prey animals, such as horses, cows, sheep, sleep less hours and are easily aroused. While predators sleep for longer hours during the day, such as cats and bats. Humans, monkeys, and foxes sleep a moderate amount, around 8–9 hours.

Purpose of REM sleep:

One-fifth is spent in REM. Their species vary in the amount of sleep time spent in REM. The percentage of REM sleep is positively correlated with the total amount of sleep in most animals. Among humans, those who get the most sleep have the highest percentage of REM.

The neurocognitive hypothesis:

posits that dreaming is a cognitive achievement stemming from a specific brain network (the default network) rather than just random brainstem activation. It argues that dreams are continuous with waking thought, representing realistic, imaginative simulations of waking life rather than having adaptive, evolutionary functions

The activation-synthesis hypothesis:

Suggests that dreams begin with spontaneous activity in the pons, which activates many parts of the cortex. The cortex synthesizes a story from the pattern of activation. Normal sensory information is sometimes integrated, but usually is not. When dreaming, you really can’t move; this is also a common dream.

Jet lag:

Refers to the disruption of the circadian rhythms due to crossing time zones. Stems from a mismatch of the internal circadian clock and external time

Symptom of jet-lag:

Sleepiness during the day, sleeplessness at night, and impaired concentration

Traveling west

"phase delays" our circadian rhythms.

Traveling east

“phase-advances” our circadian rhythms.

Short-wavelength light:

boosts wakefulness, alertness, and suppresses melatonin, making it ideal for daytime but disruptive to sleep

long-wavelength light:

light promotes sleep and allows for melatonin production, making it suitable for night-time environments

Night work:

This does not reliably change the circadian rhythm. Even after long periods of working at night, people can still feel groggy, sleep poorly during the day, and body temperature peaks while sleeping instead of while working.

Melatonin

: Aids in promoting sleep; starts rising 2-3 hours before bedtime. This can help reset the circadian clock via SCN receptors. 

Pineal gland:

releases melatonin

Sleep:

is a state that the brain actively produces. Characterized by a moderate decrease in brain activity and decreased response to stimuli

Coma:

extended period of unconsciousness characterized by low brain activity that remains fairly steady. People show little response to stimuli.

Unresponsive wakefulness syndrome:

Person alternates between periods of sleep and moderate arousal but no awareness of surroundings. Some autonomic arousal to painful stimulus. No purposeful activity/response to speech

Minimally conscious state:

one 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

Alpha waves:

present when one begins a state of relaxation.

Reticular formation:

Sends continuous activating signals to the cerebral cortex to maintain alertness, transitioning the brain between sleep and waking states; A part of the midbrain that extends from the medulla to the forebrain and is responsible for arousal.

The Pontomesencephalon:

Axons extend to the hypothalamus, thalamus, and basal forebrain, which release acetylcholine, glutamate, GABA, or dopamine. Produce excitatory and inhibitory effects to widespread areas of the cortex. Stimulation of this awakens sleeping individuals and increases alertness in those already awake.

The Locus Coeruleus:

a small structure in the pons whose axons release norepinephrine to arouse various areas of the cortex and increase wakefulness. Usually dormant while asleep

The hypothalamus

contains neurons that release “histamine” to produce widespread excitatory effects throughout the brain. Hence why antihistamines produce sleepiness.

Orexin:

Released at the lateral and posterior nuclei of the hypothalamus. A peptide neurotransmitter, which aids in staying awake by stimulating neurons responsible for wakefulness and arousal.

Basal forebrain:

An area anterior and dorsal to hypothalamus. a critical node in the ascending arousal system, containing intermingled cholinergic, GABAergic, and glutamatergic neurons that promote wakefulness, cortical activation, and rapid arousal.