EEG and Sleep Stages Overview

Overview

The lecture explains EEG waveforms through the stages of sleep, describing their characteristics, significance, and order.

EEG During Waking and Relaxed States

• Awake with eyes open and active mental concentration shows beta waves (14–30 Hz, low amplitude).
• Beta waves reflect busy, organized brain activity.
• Closing eyes leads to alpha waves (9–13 Hz), indicating relaxed wakefulness with decreased visual processing.

Stages of Non-REM Sleep

• Stage 1: Light sleep, reduced consciousness, EEG shows theta waves (4–8 Hz); also present in deep meditation.
• Stage 1 accounts for about 5% of total sleep time in adults.
• Stage 2: Similar to stage 1 but features sleep spindles (bursts of rhythmic activity) and K complexes (brief large spikes).
• Sleep talking and teeth grinding can occur in stage 2, which makes up about 45% of sleep time.
• Stage 3: Deepest sleep, characterized by delta waves (<4 Hz, high amplitude); about 25% of total sleep time.
• Stage 3 is when sleepwalking, night terrors, and bedwetting may happen.

REM (Rapid Eye Movement) Sleep

• REM sleep is about 25% of total sleep time and completes a sleep cycle.
• EEG during REM shows sawtooth-like, low-voltage, high-frequency waves resembling beta waves.
• There is loss of motor tone except for extraocular muscles; rapid eye movements occur.
• REM is associated with vivid dreaming and is believed important for memory consolidation.

Key Points & Mnemonics

• High-frequency EEG waves correspond to more intense brain activity.
• The mnemonic "at night bats drink blood" helps remember the order: Alpha, Night (theta), Beta, Delta, Beta (REM).

Key Terms & Definitions

• EEG (Electroencephalogram) — A recording of the brain's electrical activity.
• Beta Waves — High frequency (14–30 Hz), low amplitude, indicate active mental work.
• Alpha Waves — Medium frequency (9–13 Hz), follow eye closure and relaxation.
• Theta Waves — Slow (4–8 Hz), appear in stage 1 sleep or deep meditation.
• Sleep Spindles — Short bursts of rapid rhythmic brain activity seen in stage 2 sleep.
• K Complexes — Large, brief spikes in brain activity, also in stage 2 sleep.
• Delta Waves — Lowest frequency (<4 Hz), high amplitude, characterize deep sleep (stage 3).
• REM Sleep — Stage with rapid eye movement, vivid dreams, and EEG similar to wakefulness.

Action Items / Next Steps

• Practice drawing and labeling the six EEG waveforms in the correct order using the mnemonic.
• Memorize the sleep stage percentages and their main EEG characteristics.