Stages of Sleep & Brain Mechanisms

Sleep

actively induced, highly organized brain state

4 Qualities of Sleep

1. Reduced motor activity

2. Lowered response to sensory stimulation

3. Adoption of stereotypical postures (such as lying down with the eyes closed)

4. Easy reversibility

Coma

unconsciousness due to head trauma, disease, or stroke in which an individual cannot be awakened or brought to consciousness

"Vegetative State" (Unresponsive Wakefulness Syndrome or Persistent Visceral State)

alternation between sleep and moderate arousal without awareness of surroundings (no clear signs of purposeful activity)

cognitive motor dissociation (CMD)

despite no purposeful activity, the individual may maintain some level of consciousness (cognitive tasks detected on fMRI & EEG)

Minimally Conscious State

Brief periods of purposeful activity and some speech comprehension (no production)

• some can improve over time, never completely (no independence)

Brain Death

no sign of brain activity in either the cerebrum or cerebellum and no response to stimuli (for 24 hours)

Conditions for Brain Death

1. persistent coma

2. absence of brainstem reflexes

3. lack of ability to breathe independently

electroencephalograph (EEG)

• recording device attached to head measures patterns of electrical activity

• measures alpha, beta, theta, and delta waves

Awake States (EEG)

1. alpha waves: relaxed mental state

2. beta waves: alert mental state

Asleep States (EEG)

enter into several different states including theta & delta waves which are much slower

polysomnograph

combines the EEG, heart beat, breathing rate, oxygen (O2) level, & eye movement detector (electrooculograph EOG)

Non-REM Sleep

• Stages N1 to N3

• may be dreaming, less intense

• about 75-80% of total sleep time in adults

Stage N1

mixed frequencies (theta waves)

Stage N2

Sleep spindles and K-complex waves

Stage N3

Slow waves (delta) > 20% ("deep sleep")

Stage R (REM ("Rapid Eye Movement") Sleep)

• Brain waves (similar to awake state or Stage N1)

• Rapid eye movements

• Almost complete loss of muscle control ("atonia")

• penile erection & vaginal moistening

• Easy to awaken

• more intense, vivid dreams

Sleep Cycle

• Stage N1 to Stage N3, back to Stage N1

• Stage R substitutes for Stage N1 sleep during cycle

• 90-110 minutes to move through an entire cycle

• Each night = 3 to 5 complete cycles

• Toward the end of sleeping, individual often does not reach Stage N3

Sleep and the Inhibition of Brain Activity

• Sleep requires a lowering of sensory input to the cortex

• an overall decrease of activity in the thalamus where the neurons become hyperpolarized in sleep

Role of Gaba

inhibit signaling between neurons in localized areas of the cerebral cortex

Role of Pons & medulla

during REM, send signals to the spinal neurons controlling large muscles (legs, arms) to inhibit their movement

sleep paralysis

Occasionally, the signals from the pons/medulla doesn't shut off when people awaken (aware but cannot move muscles)

Sleepwalking (somnambulism) ==>

much of the brain is asleep, but the motor and a few other areas are not

Brain Function in REM Sleep

• Activity in pons triggers REM sleep which is associated with a distinctive pattern: PGO waves

• Activity decreases in prefrontal, primary visual, & motor cortex, but increases in temporal & parietal cortex

Neurotransmitters & REM

• Acetylcholine (ACh) moves sleeper into REM → Carbachol (which stimulates ACh synapses) quickly moves sleeper into REM

• Serotonin & norepinephrine interrupt or shorten REM

parasomnias

“category of sleep disorders that involve abnormal movements, behaviors, emotions, perceptions, and dreams → occur while falling asleep, sleeping, between sleep stages, or during arousal from sleep"

Insomnia

not sleeping enough due to…

1. difficulty falling asleep (onset insomnia)

2. frequent awakening during sleep (maintenance insomnia)

3. waking up too early (termination insomnia)

Sleep Apnea

intermittent stopping of breathing during sleep due to obstruction of the airway or central nervous system problems (treated by CPAP device)

Narcolepsy

frequent, unexpected periods of sleep or sleepiness during the day

Symptoms of Narcolepsy

1. Gradual/sudden onset of sleepiness

2. Cataplexy: muscle weakness while remaining awake (Often triggered by strong emotions, occasionally)

3. Sleep paralysis: inability to move when falling asleep or waking up

4. Hypnagogic hallucinations: dreamlike experiences at the beginning of sleep

   (treated with Ritalin or Cylert)

orexin (= hypocretin)

axons using this neurotransmitter in the hypothalamus connect to areas that increase arousal & wakefulness (ppl w/ narcolepsy do not have these cells in the hypothalamus)

Periodic Limb Movement Disorder

during NREM sleep individual moves legs and sometimes arms every 20-30 seconds for minutes or hours (treated with tranquilizers)

REM Behavior Disorder

during REM sleep individual moves vigorously or violently (kick, punch, etc.); dreams of violent nature (older men)

Night Terrors

an experience intense anxiety involving crying and screaming, but often not actually awakening (under 12 yrs age, during NREM sleep)

Sleepwalking

• children 2-12 years old

• harmless; occasional accidents

• unknown causes, possibly genetics

• no danger to wake the person up, no treatment