4.3 - stages of sleep

1. REM vs. Non-REM (NREM) Sleep

REM Sleep (Rapid Eye Movement)

• Characterized by rapid, darting eye movements under closed eyelids.

• EEG resembles wakefulness: low amplitude, mixed-frequency waves (similar to beta activity).

• Most dreaming occurs during REM.

• Voluntary muscles are paralyzed (except for those controlling breathing/circulation)—this is why REM is sometimes called “paradoxical sleep.”

• Plays a critical role in learning, memory consolidation, and emotional processing.

Non-REM (NREM) Sleep

• Three substages: Stage 1, Stage 2, Stage 3.

• EEG shows progressively slower (lower frequency), higher amplitude brain waves as sleep deepens.

• Muscle tone and body temperature drop, and heart/respiratory rates slow with increasing depth.

• Associated more with physical restoration, immune function, and certain types of memory (especially declarative/explicit memory).

2. The Three Stages of Non-REM Sleep

Stage 1 (NREM 1)

• Transition phase between wakefulness and sleep.

• Brain waves shift from beta (wakeful) to alpha, then to theta (4–7 Hz, higher amplitude).

• Breathing, heart rate, and core body temperature decrease.

• Muscle relaxation begins.

• Lightest sleep stage; easy to awake from; often report “not having been asleep.”

Stage 2 (NREM 2)

• Deeper relaxation, continued presence of theta waves.

• Unique features:

  • Sleep spindles (brief ~0.5–2 second bursts of rapid, high-frequency waves) believed to play a role in learning and memory.

  • K-complexes (single, very high amplitude waves), may aid in responding to external stimuli and memory consolidation.

• Harder to awaken than Stage 1.

Stage 3 (NREM 3) — Deep or Slow-Wave Sleep

• Body reaches its deepest state of relaxation.

• Dominated by delta waves (very low frequency, <3 Hz, high amplitude).

• Heart rate, breathing, and brain activity are at their lowest points.

• Hardest to awaken; waking up can cause grogginess/confusion.

• Stage most strongly associated with physical restoration, tissue repair, and immune function.

3. Role of REM and NREM Sleep in Learning and Memory

REM Sleep

• Related to consolidation of:

  • Procedural memory (skills, habits, motor tasks)

  • Emotional memory and stress processing

  • Creative problem-solving (“sleep on it” effect)

• REM rebound: If deprived of REM, individuals make up for it by spending more time in REM in subsequent sleep, supporting its importance for brain and emotional health.

NREM Sleep

• Shares a special role (especially Stage 2 and Stage 3) in:

  • Consolidation of declarative (explicit/factual) memories

  • Integration of learned information and skill reinforcement (via sleep spindles and slow waves)

• Stage 3 (deep sleep/slow wave) is crucial for body restoration and for memory storage.

4. Summary Table: Sleep Stages

5. Additional Notes

• Cycle: Sleep cycles through NREM stages (1 → 2 → 3) then REM; cycle repeats every ~90 minutes.

• Deprivation: Loss of NREM or REM sleep leads to memory, learning, and emotional deficits.

• REM Rebound: Demonstrates the brain's need for this phase after deprivation.