consciousness / sleep study guide (copy)

Theories of Consciousness

• Consciousness is hard to measure and define.

• Many theories try to explain consciousness, but none fully capture all its aspects.

Integrated Information Theory of Consciousness

• Consciousness can be described as having different levels.

• IIT proposes that consciousness arises from integrating information in the brain.

• The more interconnected and complex brain activity is, the “higher“ the level of consciousness.

• Are awake, dreaming, deep sleep, and drug-induced states different levels of one thing?

• IIT suggests these states have different degrees of consciousness:

  • Awake: high integration → vivid experience.

  • Dreaming (REM): some integration → vivid, but disconnected from reality.

  • Deep sleep (non-REM): low integration → minimal or no conscious experience.

  • Drug-induced: altered integration → psychedelics increase connectivity, or anesthesia decreases connectivity.

• It’s hard to measure integration directly.

• Doesn’t fully explain why some brain networks produce consciousness while others don’t.

Global Workspace Theory of Consciousness

• Changes in consciousness involve alertness and wakefulness.

• GWT compares consciousness to a “theater stage“ where only certain information is “in the spotlight“ at any time.

• Examples:

  • Awake: Information is shared efficiently. → clear consciousness.

  • Sleep/dreaming: limited workspace access → fragmented or altered consciousness.

  • Drugs: disrupts workspace communication → loss or distortion of consciousness.

• Doesn’t fully explain subjective experience.

• Focuses more on access to information than on the nature of consciousness itself.

Key Differences Between the Two Theories

• Integrated information (IIT): consciousness = complexity of brain connections.

• Global workspace (GWT): consciousness = information sharing in the brain.

Default Mode Network

• The brain is active even when it’s not actively doing anything.

• When daydreaming or letting your mind wander, your brain isn’t “off,“ it’s running the DMN.

• The DMN is the brain’s baseline rate when not engaged externally.

• Unlike task-focused networks (e.g., solving math problems), the DMN is most active during restful introspection.

• Functions:

  • Mind-wandering and creativity.

  • Reflecting on yourself and others.

  • Consolidating memories, such as replaying the day’s events during rest.

Default Mode Network Brain Regions

• Prefrontal cortex: self-referential thoughts (“what do I think about this?“) and future planning (“what should I do tomorrow?“).

• Posterior cingulate cortex: memory integration (linking past experiences to the present) and emotional processing (reflecting on personal feelings).

• Angular gyrus: language (understanding metaphors) and mental time travel (imagining past/future scenarios).

Bremer’s Work

• Sleep is a behavior, not the absence of behavior.

  • Before Bremer, some scientists thought this, similar to a computer turning off.

• Bremer’s research showed that the brainstem actively generates sleep.

• By studying cat brains, lesions between the spinal cord and brainstem displayed a normal sleep-wake cycle.

  • While lesions disconnecting the forebrain from the brainstem put the cat into a permanent sleep-like state (no wakefulness).

Sleep Function #1: Memory Consolidation

• While sleeping, the brain organizes and solidifies new information, transferring it from short-term to long-term storage.

• When songbirds sleep, their brains reactivate the same neural patterns from when they practiced songs while awake.

• Sleep isn’t passive, it’s offline practice.

• Real-world examples:

  • Cramming vs Sleep: Pulling an all-nighter? Without sleep, the brain cannot consolidate the material effectively.

  • Skill Mastery: Athletes and musicians improve faster with quality sleep because of “neural rehearsal.“

  • Disorders: Poor REM sleep is linked to memory deficits such as Alzheimer’s Disease.

• Hippocampal activity spikes during REM.

  • The hippocampus “replays” the day’s events for storage.

  • More learning = more REM sleep.

  • For example, medical students in exam periods show longer REM phases.

  Wake: Learn song → Hippocampus encodes

  ↓

  Sleep: Neural replay → Strengthen connections

  ↓

  Next day: Better performance

  Sleep Function #2: Energy Conservation

• Humans sleep to conserve energy; sleep reduces energy use by lowering metabolism when activity is inefficient.

• Species that sleep more have higher metabolic rates:

  • Elephants → slow metabolism → very short sleep duration.

  • Bats → high metabolism → very long sleep duration.

• As we age, metabolism goes down, so does the amount of sleep.

  • Children → high metabolism → more deep sleep.

  • Elderly → slow metabolism → less deep sleep, more fragmented sleep.

Other Proposed Functions

• Brain development in children and teens.

• Sleep may be a safe place to discharge emotions and relieve stress.

• Possibly needed for physical health.

  • Deep sleep is when human growth hormone is released in children and teens.

Stages of Sleep

• Slow Wave Sleep Stage 1:

  • Stage 1: transitional phase.

  • Alpha wavjes: when eyes are closed and relaxed.

  • Theta waves: when you start to drift off.

  • Beta waves.

  • Jerks and twitches, easily awakened, muscle tone relaxes.

• Slow Wave Sleep Stage 2:

  • Stage 2: true sleep begins.

  • Theta waves.

  • K complexes in stage 2 (high-voltage spikes).

  • Response to environmental stimuli, such as filtering noise.

• Slow Wave Sleep Stages 3-4:

  • Stages 3-4: deep sleep.

  • Mostly delta waves.

  • Hard to awaken, growth hormone release, body repair occurs.

• REM Sleep:

  • Beta waves: similar to wakefulness.

  • Theta waves: hippocampal activity.

  • Muscle atonia (paralysis), dreaming, and memory consolidation.

The Progression Of Sleep Stages At Night

• The first 4 hours of sleep are slow-wave sleep-dominated for physical restoration.

• The second 4 hours of sleep are REM-dominated for memory and emotional processing.

• Each REM episode occurs every 90-120 minutes.

Locus Coeruleus (Pons)

• Lower-level structure.

• Linked to norepinephrine network.

• Activity linked to wakefulness.

  • Acts as the brain’s alarm system.

Raphe Nuclei (Pons)

• Lower-level structure.

• Serotonergic network—linked to serotonin.

• Activity seems to be linked to slow-wave sleep.

  • For example, SSRIs increase deep sleep.

Gigantocellular Tegmental Field (Pons)

• Acetylcholine-based.

• Activity linked to REM sleep.

• Originates PGO waves (Ponto-Geniculo Occipital) that occur with eye movements.

Preoptic Area Of The Hypothalamus

• Higher level structure.

• Receives serotonin (increases deep sleep) from the raphe nuclei.

• Releases GABA to inhibit wakefulness structures.

• Initiates sleep.

Posterior Hypothalamus

• Higher level structure.

• The area inhibited by the preoptic area that initiates sleep.

• Stimulates cortical arousal; keeps you awake.

Suprachiasmatic Nucleus (SCN)—Circadian Rhythms

• The SCN is the likely center of circadian rhythms, the body’s 24-hour biological clock.

• Retinohypothalamic tract sends information to the SCN.

  • This allows for light to play a role.

  • Light exposure resets the SCN, aligning sleep/wake cycles with day and night.

  • This explains why bright light at night delays sleep, such as phone screens.

• SCN transplants transfer rhythms.

  • Normal hamsters with 24-hour rhythms were given SCNs of hamsters bred with 20-hour cycles.

  • The recipient hamsters adopted the 20-hour cycle of the donor hamsters!

Suprachiasmatic Nucleus (SCN)—Internal Clock

• The SCN is active during the day in diurnal and nocturnal animals.

• It seems to tell animals whether it is day or night, but does not directly drive wake-sleep behaviors.

• Linked to the pineal gland.

  • Secretes melatonin → promotes sleepiness.

• Genetic links to SCN:

  • Light triggers the fluctuation of some proteins.

  • Increasing and decreasing various proteins lead to sleep/wake cycles.

Homeostatic Debt

• Sleep pressure builds while you’re awake until you need sleep.

  • Sleep pressure decreases while asleep.

• Glycogen produces ATP, which is an energy source as well as a reserve.

• As the brain uses energy, ATP breaks down into adenosine.

• Increased adenosine levels lead to slow-wave sleep.

• Adenosine inhibits wakefulness structures.

• Glycogen levels build up during slow-wave sleep.

Insomnia

• A persistent disorder characterized by difficulty falling asleep, trouble staying asleep, and non-restorative sleep.

• Usually treated with GABA agonists (Benzodiazepines) or melatonin agonists.

Sleep Apnea

• A disorder characterized by repeated interruptions in breathing during sleep.

• Obstructive Apnea: physical obstruction of the airway during sleep.

  • Overweight, alcohol/sedative use, anatomical issues.

• Central Apnea: brain fails to send signals to breathe, causing pauses in respiratory effort.

Narcolepsy

• Excessive daytime sleepiness, cataplexy, paralysis, and hallucinations.

  • Cataplexy: sudden, brief loss of voluntary muscle tone, ranging from mild drooping to full-body collapsing.

• Enters REM sleep at inappropriate times.

  • Both throughout the day and nighttime cycles.

Causes Of Narcolepsy

• Low hypocretin levels are possibly due to autoimmune issues.

  • Hypocretin promotes wakefulness.

• Genetic link is possible.

• Brain injuries to REM and wakefulness areas.

Circadian Rhythm Disorders

• When the SCN’s timing doesn’t match societal/work schedules (night shifts) or natural light-dark cycles (jet lag).

Advanced Sleep-Wake Phase Disorder

• When the SCN runs shorter than 24 hours → body clock is ahead of the environment.

• When one falls asleep topo early and wakes up too early.

Delayed Sleep-Wake Phase Disorder

• When the SCN runs longer than 24 hours → body clock is behind environment.

• Falls asleep and wakes up too late.