sleep brain and behavior

sleep

is a naturally recurring, reversible state characterized by

reduced responsiveness to our environment. Sleep is NOT a single state, however.

Electroencephalography (EEG)

• Records electrical activity using electrodes placed on the scalp.

• Different states of consciousness produce different patterns of brain activity.

• Using EEG, we can identify four different sleep stages

NREM 1

Light sleep

• Transition from wakefulness to sleep

• Easily awakened

NREM 2

Deeper sleep

• Characterized by sleep spindles and k-complexes

NREM 3

Deep/slow-wave sleep

• Dominated by slow delta waves

• Difficult to awaken

REM

Rapid Eye Movement

• Brain activity becomes more “wake” like.

• Vivid dreaming is common.

• Skeletal muscles become paralyzed.

We cycle through the stages of NREM and REM sleep repeatedly throughout

the night.

• One complete sleep cycle lasts approximately 90 minutes.

• NREM 3 (deep, delta wave sleep) is more prominent early in the night.

• REM sleep becomes longer and more prominent later in the night.

Sleep deprivation produces

several cognitive and behavioral impairments.

• Attention and reaction time decline

• Learning and memory suffer

• Mood and emotional regulation are disrupted

Sleep also supports

physiological restoration and regulation

• With prolonged deprivation, these effects become increasingly severe.

• Severe deprivation: Anxiety, panic, delusions, paranoia, hallucinations

Dreaming

Vivid dreaming is especially common during REM sleep.

• Brain activity during REM can be surprisingly wake-like.

• Visual and association areas are highly active.

• Skeletal muscles are largely paralyzed

Sleep deprivation can impair

• Attention and reaction time

• Learning and memory

• Mood and emotional regulation

Fatal Familial Insomnia (FFI)

An extremely rare, inherited prion disease that progressively damages the brain (thalamus).

• Produces a progressive inability to maintain normal sleep

As the disease progresses:

• Severe insomnia and disruption of normal sleep architecture

• Autonomic dysfunction

• Cognitive and neurological deterioration.

FATAL

The longer we are awake, the stronger our

homeostatic

sleep pressure becomes

Adenosine

a neuromodulator, is a critical signal.

• Builds up in the brain during prolonged wakefulness.

• Promotes sleepiness

• Decreases during sleep

Caffeine is an adenosine receptor antagonist

It binds to adenosine receptors without activating them.

• This reduces adenosine’s ability to signal sleep pressure

Caffeine does not eliminate the underlying need for sleep.

• Adenosine/sleep pressure can continue to accumulate while caffeine is active

Circadian Timing

Homeostatic sleep pressure depends largely on how long you’ve been awake

Sleepiness also changes according to an internal circadian rhythm.

A roughly 24-hour biological cycle

• Helps regulate when we feel awake or sleepy.

• This circadian rhythm persists even without obvious external cues

Suprachiasmatic nucleus (SCN)

Located in the hypothalamus

• Functions as the brain’s primary circadian clock.

• Coordinates 24-hour rhythms

• Uses light to synchronize internal clock with the outside world

The role of light in our internal clocks

Light entrains, or sets, the internal clock.

• Recall ganglia cells within the retina is where light is transduced into a neural

signal

melanopsin

Some of these retinal ganglion cells contain a photopigment called

retinohypothalamic tract

These specialized cells send information from the retina to the SCN along the

Melatonin

The pineal gland releases melatonin, primarily during darkness.

• The SCN regulates the daily rhythm of melatonin secretion

• Light SUPPRESSES melatonin production.

• Darkness = Increased melatonin

• Light = Decreased melatonin

• Melatonin helps signal to the body that it is biologically nighttime.

• It does NOT “knock you out”. It regulates sleep timing.

• Often helpful to take when traveling across time zones (jet lag)

Circadian Misalignment

• Your internal circadian clock does NOT immediately adjust to a new light/dark

schedule.

• When your internal clock and environment disagree you have circadian misalignment.

Jet lag:

• Sleepiness at inappropriate times

• Difficulty sleeping at the desired time

• Impaired attention and performance

• Exposure to light is one of the strongest ways to reset the circadian clock.

What keeps you awake?

• Wakefulness is actively maintained by several neurotransmitter systems.

Important arousal signals include:

• Acetylcholine

• Norepinephrine

• Serotonin

• Histamine

• Orexin

Broadly, these neurotransmitters promote cortical activation and wakefulness.

• Sleep = need to reduce activity of these systems!

Switching gears between wakefulness and sleep

• Ventrolateral preoptic area (VLPO) is located in the hypothalamus.

• Becomes more active during sleep.

• Neurons in the VLPO release GABA

• GABA inhibits the brains arousal systems

• Histamine, norepinephrine, etc.

• Promotes sleep.

• VLPO ON —> Arousal systems OFF

Disorders of Sleep: Insomnia and Sleep Apnea

Primary insomnia

+ Difficulty falling asleep after going to bed or after awakening during the night

Secondary insomnia

+ Inability to sleep due to a mental or physical condition

Sleep Apnea

Cessation of breathing while sleeping, disrupting sleep

Nearly all people have occasional episodes, but does not interfere with sleep

Narcolepsy

A relatively rare disorder categorized by sleep attacks, cataplexy,

and sleep paralysis

Often caused by the loss of orexin-producing neurons.

+ Sleep attacks

Primary symptom of narcolepsy

Overwhelming urge to sleep

Generally lasts for 2–5 minute

Cataplexy

Muscle weakness, could lead to temporary paralysis

Precipitated by strong emotional reactions or sudden physical effort

+ Sleep Paralysis

Inability to move just before the onset of sleep or on waking

Possibility of dreaming while lying awake, paralyzed, called hypnagogic hallucinations