- The document discusses different normal EEG patterns seen in awake and sleep states. - It describes the typical frequency bands of EEG waves such as delta, theta, alpha, and beta waves. - Specific normal EEG patterns like alpha rhythm, beta rhythm, mu rhythm, lambda rhythm, vertex sharp waves, POSTS, sleep spindles, K complexes are explained along with their characteristics and figures. - The different stages of sleep like drowsiness, light sleep, deep sleep and REM sleep are outlined along with expected EEG findings in each stage.

1. Normal EEG
Dr. Md. Saiduzzaman Munna
Medical Officer
Department of Neurology
Mymensingh Medical College Hospital
Mymensingh, Bangladesh.

2. Awake EEG
Classification of EEG waves:
- Delta wave: below 4 Hz.
- Theta wave: 4-8 Hz
- Alpha wave: 8-13 Hz
- Beta wave: Above 13 Hz.
 EEG signal of cerebral cortex has to cross leptomeninges, CSF, dura
mater, skull bone and scalp before it is recorded by surface electrodes.

4. Alpha Rhythm
 Frequency 8-13 Hz during wakefulness over the posterior
region of head, usually with higher voltage over occipital areas.
 Amplitude usually below 50 µv.
 Best seen with closed eyes, under physical and mental
relaxation.
 Blocked or attenuated by attention, especially visual or mental
effort.
 Well developed by 3 years of age.

5. Fig: Alpha wave responsiveness to eye opening

6. Alpha Rhythm……….
 Reactivity of alpha rhythm can be tested by-
- Eye opening
- Afferent stimuli- pin prick, noise, touch.
- Mental activities.
 Drowsiness results drop out of alpha activity, replaced by slow waves.

7. Beta Rhythm
 EEG activity above 13Hz. (Upper limit is considered 70 Hz)
 Four types:
1) Frontal beta- common and very fast.
2) Central beta- often mixed with mu rhythm.
- blocked by tactile stimulation and motor activity.
3) Posterior beta- fast alpha equivalent.
- blocked by eye opening.
4) Diffuse beta- no linkage with any physiological rhythm.

8. Beta Rhythm……..
Abnormalities:
 Benzodiazepines and Barbiturate enhance amplitude and frequency
of beta activity.
 May be asymmetrical in 35% of normal individual.
 Voltage reduces in cortical injury, subdural or epidural collection.
 Very fast activity (>35 Hz) seen in organic psychosis.

10. Miscellaneous waves
Mu Rhythm:
 8-10 Hz alpha frequency cerebral rhythm.
 Arch-like morphology.
 See in young adults (Female>Male).
 Characterized by-
- blocked by motor movement.
- lack of effect on eye opening.
- suppressed by somatosensory stimulation and mental
arithmetic activity.

11. Fig: Mu rhythm obliterated by hand movement.

12. Differences between Alpha and Mu rhythm
Features Alpha Rhythm Mu rhythm
Distribution Occipital Central
Blocked by Eye opening Contralateral hand
movement
Effect of mental
arithmetic
Blocked Blocked

13. Lambda Rhythm
 Positive waves occurring over occipital region in awake state.
 Amplitude <50 µV, Duration 200-300ms, biphasic/triphasic, saw-tooth
shaped.
 Usually found in young adults.
 Found in brightly illuminated laboratories.

14. Fig: Lambda waves in both occipital region.

15. Sleep EEG
Stages of Sleep (According to AASM):
1) Stage W- Drowsiness
2) Stage N1- Light Sleep.
3) Stage N2- deep Sleep.
4) Stage N3- Very deep sleep.
5) Stage R- REM sleep.

16. Drowsiness
Early Drowsiness:
- Increased slow activity.
- Dropout of alpha activity.
Deep drowsiness:
- Vertex sharp wave (altered cerebral responsivity)

17. Vertex Sharp Waves
Auditory evoked potentials--------- Converge from cortical projection
areas to regions underlying vertex electrodes (Posterior supplementary
motor cortex along interhemispheric fissure).
Appearance: Small spiky positive discharge------- followed by large
negative wave------ may be followed by another positive discharge.
 Must be differentiated from epileptogenic vertex spikes (more spiky
and pointed).

18. Fig: Vertex Sharp Waves.

19. POSTS
 Positive Occipital Sharp Transients of Sleep.
 Physiological potential of deep drowsiness, may persist up to deep
drowsiness.
 Commonly found in adolescence to middle age.
 Spontaneous, monophasic, triangular waves in occipital region.
 Occurs intermittently, either simultaneously or independently on both sides.
 Usually 1 Hz frequency, moderate amplitude.
 Individuals with prominent lambda waves are more likely to demonstrate
POSTS.

21. Light Sleep
Includes:
- Slow and fast frequencies.
- Sleep spindles.
- Vertex sharp waves.
- K complex.

22. Sleep spindles
A group of rhythmic waves of 12-14
Hz frequency characterized by
gradually increasing and then
decreasing amplitude.
 Fronto-central location.
Common in childhood adolescence.
 Voltage declines with increasing
age.

23. Fig: Sleep Spindles involving both centro-parietal region.

24. K Complex
Usually seen in frontal and
central region in light and deep
sleep stages.
 Initial sharp component
followed by slow component.
 often followed by bursts
of sleep spindles.

25. Fig: K Complex.

26. Fig: Vertex sharp wave, Sleep spindle and K complex.

27. Deep Sleep
 Background activity slows down to delta frequency.
 Sleep spindle and K complex may be present.
 Rhythmic activity of 5-9 Hz low voltage often present.

28. Fig: Delta activity in deep sleep.

29. REM Sleep
 REM sleep is seldom recorded in routine EEG laboratory.
 Almost similar to drowsiness stage.
 Characterized by- low voltage polyrhythmic activity, periods of alpha
wave, short burst of 2-6 Hz saw tooth wave.
 Must include-
- Two channels for electro-oculogram.
- One channel for EMG recording polysomnograph.

30. Fig: REM sleep.

31. Fig: EEG of 32 weeks conceptional age.

32. Fig: EEG of a 4 week old full-term normal neonate.

33. Fig: EEG of 1 year old child showing 6 Hz basic rhythm.

34. Fig: EEG of 9 year old child showing well developed alpha activity.