Electroencephalogram

Terms EEG- Elecrtoencephalogram Electroencephalograph ECoG- Electrocorticogram

Electroencephalography

Basic / Normal EEG Waves

In awake, relaxed individual with eyes closed -- alpha rhythm Waves of regular pattern 8 – 12 HZ frequency µv amplitude Most prominent in parieto-occipital area

Alpha and Beta Rhythm

Other EEG Waves Beta Rhythm In aroused, Attentive-- Low Amplitude 18 – 30 Hz frequency Gamma Oscillations 30-80Hz Aroused & focused attention Theta Rhythm 4-7 Hz ( in children ) Delta Rhythm High voltage, slow freq.. Less than 4 Hz

Physiological variations in EEG waves Age Alpha block States: --Sleep patterns

Age In infants: fast waves ( beta like ) are prominent except in occipital region rhythm is slow (0.5-2Hz) which increases during childhood with adult alpha rhythm by adolescence.

Alpha block In a resting relaxed individual alpha rhythm gets replaced by high frequency low voltage on exposure to sensory stimulation, attention, mental concentration etc referred to as ‘ Arousal / Alerting response / Desynchronization of EEG Alpha also affected by low blood glucose, low body temp., low glucocorticoids & high pCO2

Fig: Alpha block

Sleep Patterns / Types Rapid Eye Movement Sleep ( REM ) Non REM / Slow wave Sleep

Four Sleep Stages of Non REM (Slow wave sleep) 1st Stage: EEG begins to show a low voltage mixed frequency pattern with theta rhythm 2nd Stage: Marked by appearance of sleep spindles & some high voltage biphasic waves (K complexes) 3rd Stage: high amplitude delta waves ( Hz) 4th Stage: Maximum slowing with large EEG waves.

Slow Wave Sleep ( Cont. ) Characteristic Feature of deep sleep: Rhythmic slow waves / Marked synchronization of EEG Waves

REM Sleep / Paradoxical Sleep During sleep slow waves are periodically replaced by rapid low voltage EEG waves ( resembles awake EEG )---accompanied by: Rapid eye movements Elevated threshold for arousal by sensory stimuli & RES stimulation Ponto-geniculo-occipital (PGO) Spikes- Reduction in Skl muscle tone Dreams----

Distribution of sleep Stages In a typical night sleep passes through stages 1 to 4 : A brief duration of stage 1 & 2 is followed by stage 3 & 4 (deep sleep). After about 70 to 100min in stages 3 & 4 a REM period follows. After about 90 mins the cycle repeats

Learning Outcomes Describe the normal EEG waves in the awake relaxed and alert state Explain EEG rhythms (alpha, beta, gamma and theta) and state their significance. Describe the EEG waves during sleep. Describe the patterns of sleep [slow wave sleep and REM sleep] Describe the characteristics of REM sleep.

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