Consciousness
High-Yield Summary
- Consciousness = level of awareness of the world and self. Accepted states: alert, dreaming, sleep, altered (hypnosis, meditation, drugs, sickness, dementia, delirium, coma). Alertness depends on prefrontal cortex circuits communicating with the brainstem's reticular formation.
- EEG wave progression: beta (alert/concentrating) → alpha (awake, relaxed, eyes closed) → theta (Stages 1-2, with sleep spindles + K-complexes in Stage 2) → delta (Stages 3-4, slow wave sleep, hardest to wake from).
- Slow wave sleep (NREM 3-4): cognitive recovery, growth hormone release, declarative memory consolidation. REM ('paradoxical sleep'): active brain + paralyzed muscles, most dreaming, procedural memory consolidation.
- Circadian rhythms are light-controlled: decreasing light → retina-hypothalamus-pineal pathway → melatonin release → sleepiness. Increasing light → hypothalamus releases CRF → pituitary releases ACTH → adrenal cortex releases cortisol → alertness.
- Dream theories: activation-synthesis (Hobson & McCarley — random neural activation the cortex stitches into a narrative), problem-solving, cognitive process, neurocognitive models.
- Dyssomnias (insomnia, narcolepsy, sleep apnea) disrupt falling/staying asleep. Parasomnias (night terrors, sleepwalking) are abnormal NREM behaviors. Narcolepsy cluster: cataplexy, sleep paralysis, hypnagogic/hypnopompic hallucinations.
- Sleep apnea: obstructive (physical airway blockage) vs. central (brain fails to signal breathing). Sleep deprivation causes REM rebound on recovery.
Key Terms
- Reticular formation
- Brainstem structure that communicates with the prefrontal cortex to maintain alertness; injury can cause coma.
- Sleep spindles / K-complexes
- EEG features characteristic of Stage 2 NREM sleep.
- Circadian rhythm
- Internally generated ~24-hour cycle of waking and sleeping, substantially controlled by light.
- Melatonin
- Serotonin-derived hormone from the pineal gland that promotes sleepiness as light decreases.
- Cataplexy
- Sudden loss of muscle control and intrusion of REM sleep during waking hours, usually emotion-triggered; seen in narcolepsy.
- REM rebound
- Earlier onset and greater duration of REM sleep after a period of sleep deprivation.
REM vs. Slow Wave Sleep
| REM ("paradoxical" sleep) | Slow Wave Sleep (NREM Stages 3-4) |
|---|---|
| Active, wakefulness-like brain; body paralyzed | Deepest sleep, hardest to wake from |
| Most dreaming occurs here | Low-frequency, high-voltage delta waves |
| Consolidates procedural memory | Consolidates declarative memory; growth hormone release |
Obstructive vs. Central Sleep Apnea
| Obstructive | Central |
|---|---|
| Physical blockage in pharynx or trachea prevents airflow | Brain fails to send signals needed to make the diaphragm breathe |
The Circadian Hormone Chain
- 1Decreasing light → retina signals the hypothalamus → hypothalamus controls the pineal gland → pineal gland releases melatonin → promotes sleepiness.
- 2Increasing light → hypothalamus releases corticotropin-releasing factor (CRF) → anterior pituitary releases adrenocorticotropic hormone (ACTH) → adrenal cortex releases cortisol → promotes alertness.
Common MCAT Trap
- REM = active brain/paralyzed body/procedural memory/most dreaming. Slow wave sleep = deepest NREM/hardest to wake/declarative memory/growth hormone — don't swap the memory types.
- Cataplexy, sleep paralysis, and hypnagogic/hypnopompic hallucinations are features that can accompany narcolepsy, not unrelated stand-alone disorders.
- Obstructive sleep apnea = physical blockage; central sleep apnea = failed brain signal — a mechanism-based distinction, not a severity one.
- Dementia/delirium and coma are altered states of consciousness alongside hypnosis/meditation/drugs — don't treat 'altered state' as meaning only drug-induced.
Quick Recall
Which EEG wave pattern corresponds to slow wave sleep, and what is it linked to?
A patient has a rapid-onset, fluctuating confusion tied to an infection. What sleep/consciousness-adjacent term describes this, and is it reversible?
What theory holds that dreams result from random neural activation that the cortex tries to stitch into a coherent narrative?
Which hormone chain promotes morning alertness, and what triggers it?
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