normal eeg wave patterns.

1. Normal EEG Wave Pattern
Dr.Roopchand.PS
Senior Resident(Academic)
Dept. Of Neurology
TDMC Alappuzha

2. Normal EEG:
• Variety of wave forms.
▫ Frequency
▫ Amplitude
▫ Spatial distribution
▫ Reactivity to different stimuli
• The frequency of clinically relevant EEG
between 0.3 to 70Hz

3. TYPES:
• EEG Waves are named on the basis of their
frequency range.
• Delta – Below 3.5 HZ ( 0.1-3.5Hz)
• Theta – 4 to & 7.5Hz
• Alpha – 8 to 13 Hz
• Beta – Above 13Hz (14-40Hz)

4. • The voltage of the EEG signal determines its
amplitude.
• Normal range is between 10 to 100µV.
• Amplitude is measured from peak to peak.
▫ Called range
• A specific frequency band has a defined
amplitude range.
• More than 50% amplitude difference between
two homologous brain areas in two hemispheres
is abnormal.

5. Alpha Rhythm:
• Frequency of 8-13Hz
▫ During wakefulness
▫ Over posterior regions of the head.
• Amplitude < 50µV.
• Best seen with eyes closed and physical and
mental relaxation.
• Attenuated by attension
▫ Visual or mental effort.

6. • 60% individuals alpha amplitude range between
20 -60µV, 28% below 20 and 6% above 60µV.
• Amplitude higher on the right.
• Morphology : rounded or sinusoidal.
• Spatial distribution: Posterior half of the head.
▫ Occipital, Parietal, posterior temporal.
• Alpha reactivity
▫ Eye opening, sensory stimuli, mental activity.

7. • Three types of alpha
waves.
▫ P- persistent
▫ R- responsive
▫ M- minimal
• Origin of alpha
waves:
thalamus, cortex and
corticothalamic
reverberating circuits.

8. Beta Rhythm:
• Any rhythmical EEG activity above 13HZ.
▫ 18-25Hz(common), 14-16Hz(less common), 35-
40Hz(rare).
• Amplitude 10 - 20µV
• Spatial distribution:
▫ Frontal beta: common, very fast, no relationship to
physiological rhythm.
▫ Central beta: mixed with rolandic mu rhythm, blocked
by tactile stimuli.
▫ Posterior beta: fast alpha equivalent, blocked by eye
opening.
▫ Diffuse beta: fast, no relationship to physiological
rhythm.

9. • The voltage of Beta is the first to reduce in
cortical injury, subdural or epidural collection.
• Very fast activity > 35Hz seen in organic
psychosis.
• Beta depression may occur transiently after focal
seizures.

10. Theta rhythm:
• Frequency between 4 – 8Hz.
• Amplitude below 15mV
• Present in frontocentral area.
• Augmented by emotional stress and mental task.
• Temporal theta with episodic delta rise -
abnormal

11. Mu rhythm:
• Rhythm of alpha frequency.
• In young adults
• Arch like morphology.
• Blocked by motor movement.
• Not affected by eye opening.
• Blocked by mental arithmetic.

12. Lambda rhythm:
• Sharp transients occuring over the occipital
region.
▫ During awake state.
▫ During visual exploration.
• 50µV amplitude, 200-300msec duration.
• Related to occulomotor visual integration and
arousal mechanism.

13. Sleep EEG:
• NREM Sleep:
▫ I Drowsiness
▫ II Light sleep
▫ III Deep sleep
▫ IV Very deep sleep
• REM sleep

14. Stage I NREM Sleep:
• Early drowsiness :slow activity and drop out of
alpha.
• Trains of 2-3Hz and 4-7Hz waves diffusely
prominent.
• Paradoxical Alpha: If patient aroused in this
stage, posterior alpha activity reappears with a
higher amplitude than individuals regular
rhythm.

15. • Deep drowsiness: Vertex waves
▫ Small spiky discharge of positive polarity followed
by a large negative wave.
▫ Maximum at the vertex.
▫ Physiologic.

16. Positive Occipital Sharp Transients
of Sleep (POSTS):
• Physiologic potentials of deep drowsiness.
• In stage II and III NREM
• Spontaneous monophasic triangular waves in
the occipital region.

17. NREM stage II:
• Slow and fast frequencies: back ground
frequency, high intraindividual variation.
• Sleep spindles: rhythmic waves of 12-
14Hz, amplitude gradually increases and then
gradually decreases.
• Frontocentral in location.
• With deep sleep frequency slows down to 6-
10Hz.

18. • Vertex sharp waves:
• K complexes: Seen in Stage II, III IV NREM
sleep.
▫ Frontal and central region
• Initial sharp component followed by a slow
component.
• Sharp component is biphasic.
• Slow component represented by large waves
followed by superimposed spindles representing
fast component.

20. Stage III NREM Sleep:
• Background activity shows delta frequency (0.7-
3Hz).
• Rhythmic 5-9Hz low voltage activity.
• Sleep spindles- less prominent
• K complexes.

21. Stage IV NREM Sleep:
• Prominent Delta activity.
• Sleep spindles and K complexes are rare.
• Arousal at this stage associated with sleep
disorders.
▫ Somnambulism
▫ Nocturnal terror
▫ Enuresis

22. REM sleep:
• Seldom recorded in routine EEG.
• Low voltage polyrhythmic activity.
• Ocular potentials.
• Alpha bursts.
• Arousal from sleep:
▫ Quick process
▫ Single and sharp K complexes followed by
immediate change to awake pattern.

23. EEG in Newborn:
• Electrical activity of brain is discontinuous with
long periods of quiescence – trace discontinua.
▫ < 34 wks GA
• Trace alterenant – semi periodic voltage
attenuation.
• Hemisphere synchrony is less in preterms.
• Beta – Delta complexes : Hall mark of
prematurity(24-38wks).
• Temporal theta bursts: mid temporally B/L

24. • Frontal sharp waves: 35-44wks, found in
transitional stage of sleep, B/L synchronous.

25. GA 24 to 27wks 28 to 31wks 32 to 35 wks 36 to 41 wks
Trace + + +NREM -
discontinua
Trace alternant - - - +NREM
Continuous - - + +awake &REM
Symmetry - - +occipital +
Sleep awake - - + +
diff
Post. Basic - - - -
rhythm
Awake slow High voltage Very slow Occipital Slow delta
activity bursts
Fast activity Small B of 16Hz Frequent ripple 16-20Hz sparse
Sleep slow/fast slow Slow+little fast Irreg.slow in oc Delta, theta
Sharp waves bursts intermittent + Minor sharp
bursts
Spindles, K - - - -
comp, vertex
sharp, frontal

26. Infants (2mo to 12mo):
• 2-3.5Hz, 50-100µV irregular delta activity.
• Stable 5hz occipital rhythm by 5 mo.
• 6-7Hz by 12 mo
• Photic driving response @ 3-4mo (theta range).
• EEG changes of drowsiness by 5mo.
• Hypnogogic hypersynchrony: prominent thea
activity(4-6Hz) over centroparietal region seen
during drowsiness.

27. • NREM: 0.7-3Hz,100-150µV occipital waves.
• Sleep spindles appear at 2mo.
• Sharp spindle configuration.
• Absence of spindles at 3 to 8 mo – abnormal
• Vertex waves and K complex – 5th mo.
• REM: 5% at birth, 40% at 3-5mo, 30% at 6mo.
• Sharp occipital activity of 2-4Hz

28. 12-36 moths:
• Posterior occipital rhythm: 6-7 Hz at 2nd yr, 7-
8Hz at 3rd yr.
• Eye opening associated with biphasic occipital
rhythm.
• 18-25Hz fast activity s/o mild CP.
• Generalized slow voltage(4-6HZ) activity during
drowsiness- hypnogogic theta activity.
• NREM: high voltage 1-3Hz and medium voltage
4-6Hz activity mainly in the occipital region.

29. • Vertex waves are seen, K complexes abundantly
present.
• POSTS are poorly developed.
• Arousal: high voltage 4-6Hz superimposed with
slower frequency.
• Prolonged frontal sharps waves between 2-12 yrs
–abnormal.

30. 3-5 years:
• Posterior basic rhythm reaches to alpha range.
• Slow fused transients: Posterior slow activity
may be preceded by sharp contoured potentials.
• Rolandic Mu waves starts appearing.
• Hypnogogic theta activity is not seen.
• Posterior slowing of theta to delta range appears
in drowsiness.
• 6 and 14Hz spikes may appear and disappear
during deep drowsiness.
• Well defined spindles and K complexes, POSTS
poorly developed.

31. 6-12 years:
• Posterior alpha rhythm reaches 10H by 10 years.
• Rolandic rhythm rises and peaks by 13-15yrs.
• Anterior rhythmical theta (6-7Hz) appears by 6-
12yrs and peaks by 13-15yrs.
• Hyperventilation: 1.5-4Hz slowing.
• Drowsiness characterized by gradual alpha drop
out.
• Vertex waves, spindles, K complexes are
seen, POSTS start to appear.

32. 13-20 years:
• Only subtle difference between children and
adolescent
• Amplitude of alpha is slightly less than children.
• Fast activity is seen in the fronto-central area.
• Rolandic mu waves sometimes seen.
• Mature occipital lamda waves.
• Anterior 6-7Hz theta activity falls after 15 years.
• Response to hyperventilation is less prominent
than children.
• IPS reveals photic driving response in medium
and fast range of flicker(6-20Hz)

33. • Voltage of K complex and sleep spindles are
higher.
• POSTS are abundant in stage II NREM sleep.

34. OLD age:
• Normal healthy pattern seen till 60-70 years.
• Alpha slowing: MC finding in old age.(9Hz).
▫ Poor alpha blocking
▫ Related to decline in mental function.
• Increased fast activity: suggest well preserved
mental faculty.
• Diffuse slowing: 1.5-2Hz, anterior
bradyarrythmia.
▫ Normal or may be associated with vascular
ds, headache, dementia, ataxia.

35. • Diffuse slowing may be seen in hypotension.
• Focal alteration:
▫ Minimal temporal slow waves : dizziness, head
ache.
▫ Burst of rhythmical temporal theta: CVA
▫ Temporal slow & sharp waves: Vertibrobasilar
insufficiency.
• Wicket spikes seen during sleep(6Hz spikes with
negative component)