This document provides an overview of normal EEG patterns in adults. It begins with a brief history of EEG and then describes the basic electrical activity generated by the brain and how EEG recordings work. It outlines the normal frequency bands seen in EEG - delta, theta, alpha, beta and gamma. Specific normal EEG patterns like the alpha rhythm, vertex waves, sleep spindles and K-complexes are described. It also discusses benign variants and activation procedures. In summary, the document serves as a reference for the typical EEG patterns seen in healthy, awake and sleeping adults.

1. Normal EEG
 Dr. Sachin Adukia
 Dr. Gopal Krishna Dash

2. Contents
 Introduction
 Descriptors of EEG activity
 Normal EEG (Wakeful adult)
 Normal Sleep EEG
 Benign or normal EEG variants
 Activation procedures

3. Brief History
 Vladimirovich (1912)
 first animal EEG study (dog)
 Cybulski (1914)
 first EEG recordings of induced seizures
 Berger (1924)
 first human EEG recordings
 'invented' the term electroencephalogram (EEG)
 American EEG Society formed in 1947
 Aserinsky & Kleitman (1953)
 first EEG recordings of REM sleep

4. Introduction
 What
 Electrical potential generated by summation of cortical nerve cell
(Pyramidal cell) Exictatory and Inhibitory Postsynaptic Potential
 Not Action potential

5.  Generator
 Thalamic pacemaker cells in nucleus reticularis
 Thalamocortical neurons stimulated excitatory impulses to
cortex.
 Tracing
 EEG is difference in voltage between 2 recording electrodes
plotted over time

7.  EEG recording depends upon differential amplification:
 output - expressed as d/b 2 inputs in an electrode: called a channel.
 Typically, 21 or more channels in a montage
 Common average reference
 Each electrode is compared to avg signal from all other electrodes
 Those susceptible to artifact (Fp1, Fp2, O1, O2) are excluded
 Bipolar montage
 each channel consists of comparison of 2 adjacent electrodes
 Transverse bipolar
 Electrode pairs are arranged in a L-R pattern, starting in the front
moving posteriorly
 AKA “coronal” montage

8. Basic descriptors
 Frequency
 Delta – Below 3.5 HZ ( 0.1-3.5Hz)
 Theta – 4 to & 7.5Hz
 Alpha – 8 to 13 Hz
 Beta –13 to 30 Hz
 Gamma – Greater than 30 Hz
 Amplitude- uV, peak to peak
 Spatial distribution
 Reactivity to different stimuli

9. Alpha
 Origin: thalamus, cortex and corticothalamic reverberating circuits
 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: Visual or mental effort, eye opening, alerting stimuli.
 Amplitude higher on the right.
 Morphology : rounded or sinusoidal.
 Spatial distribution: Posterior : Occipital, Parietal, posterior temporal.

10. Alpha Rhythm

12. Beating

14.  8 Hz - by age 3
 progressively increases until 9-12 Hz is reached by adolescence
 Very stable in an individual, rarely varying >0.5 Hz.
 With drowsiness may decrease by 1-2 Hz
 Difference >1 Hz between the two hemispheres is significant.
 Alpha reactivity
 Eye opening, sensory stimuli, mental activity

15. EYES CLOSED

16. EYES OPEN

17. EYES CLOSED

18. EYES CLOSEDEYES CLOSED EYES OPEN

19. Beta
 Frequency - Over 13 Hz
 Upper beta range ~ gamma range
 2 main types
 precentral type:
 predominantly anterior and central regions
 related to sensorimotor cortex functions, reacts to movement or touch.
 The generalized beta activity:
 induced or enhanced by drugs
 may attain amplitude over 25 microvolts
 Accentuates in
 Drowsiness and stage 1 sleep.
 Excess medication (BDZ & Barbiturate)
 Amplitude
 Assymetry ~ > 35% is abnormal
 Breach rhythm
 Localised increase in beta activity in skull defect areas.

20. Diffuse beta

22. Breach

24. Theta
 term Theta -Gray Walter, 1944, ? related to function of thalamus.
 Frequency between 4 – 8Hz.
 Amplitude below 15mV
 normal rhythm during drowsiness
 4 months  8 years: predominance over fronto-central regions
 In adolescents: can occur over anterior head regions
 In adults: diffusely or over posterior head regions

27. Mu rhythm
 Wicket/comb rhythm
 <5% EEG: young adults
 7-11Hz
 For few seconds in central or centroparietal area
 Intermittent & asymmetrical : persistent asymmetry on same side is
abnormal
 Accentuate: scanning visual images.
 Attenuate
 ~ voluntary/ reflex/passive movement/intention to move /tactile
stimuli
 Physiological significance
 Somatosensory process associated with movement.

28. Pre discharge

29. discharge

30. discharge

31. Post discharge

32. Posterior slow waves of youth
 During awake state
 Notched broad (slow) waves
 Notching d/t merging of normal alpha waves in wakefulness
 Can be confused with epileptiform discharges

35. Like Alpha, post slow waves attenuate with eye opening

36. Reappear with eye closure

37. Normal sleep EEG (adults)
 Elements of normal sleep activity
 Slow waves
 Positive occipital sharp transients
 Vertex sharp transients
 Sleep spindles
 K complexes
 Sleep stages
 Drowsiness
 II Light sleep
 III Deep sleep
 IV Very deep sleep
 Sleep cycle

38. Stage 1
 In adults, most sensitive sign of drowsiness is the
disappearance of eye blinks and slow eye movements
 Slowing, dropout or attenuation of the background
 Occurrence of theta activity over posterior regions

39. Just before sleep

42. Deep Drowsiness
 Vertex waves
 Maximum at the vertex.
 Young adults- sharp or spiky appearance , high voltages
 Older adults - more blunted appearance
 may be asymmetrical
 Physiologic , not to mistake for epileptiform activity
 Sometimes trains or short repetitive series, clusters, or bursts of in
quick succession

46. Vertex waves may be asymmetrical

48. Stage 2
 Positive Occipital Sharp Transients of Sleep (POSTS)
 Sharp-contoured, monophasic, surface-positive transients
 single or in trains of 4-5 Hz over occipital regions
 Similar appearance to lambda waves of awake record
 Usually bilaterally synchronous, may be asymmetric
 Predominantly during drowsiness and light sleep

53. Sleep spindles
 frequency of 13-14 Hz
 symmetric and synchronous
 at intervals of 5-15 seconds
 Spindle trains ranging from 0.5-1.5 sec duration
 prolonged trains or continuous spindle ? Medication: BZP

57. K- complex
 Broad diphasic or polyphasic waveform (>500 msec)
 Seen in Stage II, III, IV NREM sleep.
 Frontal and central region
 Initial sharp component f/b slow component.
 Sharp component is biphasic.
 Slow component represented by large waves followed by
superimposed spindles representing fast component.
 can occur in response to afferent stimulation and may be linked to
an arousal response

59. Stage 3
 Background activity shows delta frequency (0.7-3Hz).
 Rhythmic 5-9Hz low voltage activity.
 Sleep spindles- less prominent
 K complexes

60. Stage 4
 rarely obtained in routine office EEG
 Prominent Delta activity.
 Sleep spindles and K complexes are rare

64. Sleep Cycle
 Each cycle contains all stages NREM & REM: 4-7 cycles /sleep
 1st cycle shortest: later 80-120 min. :
 REM sleep ~ appears 70-90 min after onset of sleep.
 Young adults:
 stage 1 5-10%
 stage 2 30-50%
 stage 3&4 20-40%

65. Benign discharges:-
Transients and rhythms

66. BSSS- Benign spordic sleep spikes

70. Wicket Spikes

71. Pre discharge

72. discharge

73. Post discharge

74. 14 and 6 spike waves

75. Pre discharge

76. discharge

77. Post discharge

78. RMTD-
Rhythmic mid-temporal theta discharges

79. Pre discharge

80. discharge

81. Post discharge

82. SREDA
Subclinical Rhythmic Electrographic Discharge Of Adults

83. Pre discharge

84. discharge

85. discharge

86. discharge

87. Post discharge

88. Hypersynchronous hypnogogia

89. Pre discharge

90. discharge

91. Post discharge

92. discharge

93. Hyperventilation
 Often produces little change in the EEG in adult
 If there is a change, usually consists of generalized slowing.
 either gradual or abrupt onset in theta or delta range
 may continue as series of rhythmic slow waves or consist of
repeated bursts of slow waves at irregular intervals

94. Pre discharge

95. discharge

96. Post discharge

97. discharge

98. Photic stimulation
 Driving response- posterior , time locked to stimulus
 Photo-myoclonic resonse
 electrical activity of frontal scalp muscles- Frontalis and Orb Oculi
 Repeated contractions of these musc. produces time locked response
 Anterior
 Same freq as the flash

104. References
 Abou-Khalil B, Misulis KE. Atlas of EEG & seizure
semiology: Text with DVD. Butterworth-Heinemann;
2005 Oct 12.
 Laoprasert P. Atlas of pediatric EEG. McGraw Hill
Professional; 2010 Dec 31.

105. Thank You