3. What is EEG ?
• EEG (Electroencephalogram) refers to recording and analysis
of electrical activity of brain recorded by amplifying voltage
differences between electrodes placed on scalp or cerebral
cortex .
• This electrical potential is produced by excitatory or inhibitory
post synaptic electrical discharges from neuronal dendrites at
cortical surfaces.
• Such neurons constitute only 5% of total neurons of the brain.
• Voltage recorded on EEG is only 10% of the voltage recorded
on ECG due to high resistance of skull.
3
5. RECORDINGS FROM ANIMAL BRAIN
• First person to record electrical
activity from animal brain in
1874.
RICHARD CATON , 1874 5
6. RECORDING FROM HUMAN BRAIN
• First recording from human
scalp in 1924.
• Report published in 1929
• Danis William started clinical
use to localize brain trauma
during ww II in oxford.
HANS BERGER 1924 6
7. Hans Berger 1835-1911: Human EEG
Prof of Psychiatry, University of Jena
Germany, Removed from job in one
day notice by the Nazis, committed
suicide
Berger wave
7
13. • Montage refers to the particular combination of electrodes
examining at a particular point of time.
• When a single reference point is used for all electrodes
Referential montage.
• When several referential points are used for recording Bipolar
montage.
• In bipolar montage the electrodes form a chain passed side by side
or front to back.
MONTAGE
13
14. REFERENCE MONTAGE • Connects active
scalp electrodes
and an inactive
electrode placed
away from the
scalp e.g. on ear,
nose or chin
[Reference
electrode]
– Disadvantage
with ear-
some brain
activity
– Chin & nose-
heart activity
• Useful for seeing
amplitude of
waves
14
15. BIPOLAR MONTAGE
• Connects two active
scalp electrodes
• Each channel is
attached to two
different electrodes
• Arrangement of
channels in
montages-
– Anteriorly placed
electrodes on
initial channels-
helps see
progression of
waves
– Alternate left and
right electrodes-
helps compare the
two sides
15
16. • Electrodes- 21
• Sensitivity- 5-10 micro volts/mm ( avg 7)
• Paper speed – 3 cm/ sec ( adjustable)
• Length of recording – 2 min each montage
- 30 min awake record (10 min
sleep)
• Activation – Hyperventilation – 3min + 1min
- Photic st -30 cm 10,15,20,30,40 Hz
,each in trains of 10 sec.
STANDARDS
16
19. Found in normal eye
closed EEG
Highly rhythmic
Frequency 8 to 13 HZ
Prominent in the posterior
cortex
Mainly occipital , temporal
and parietal cortex
NORMAL ALPHA WAVES
19
20. NORMAL BETA WAVE
Frequent in normal
eye open EEG
EEG waves of >13 HZ
Usually of low voltage
Found in frontal and
central region
20
22. NORMAL THETA WAVES
Small amount of
sporadic and isolated
activity found in normal
awake state
Prominent in drowsy
and sleep EEG tracing
EEG activity of 4 to 7
HZ
found in frontal and
temporal region
22
23. NORMAL DELTA ACTIVITY
Not present in normal
awake EEG
Prominent in normal
deeper stage of sleep.
A frequency of < 4 Hz.
23
25. Amplitude
• Measured: peak to peak
• Expressed as range i.e 40-50μv
• Depends on
– Inter electrode distance
– Type of montage
– Type of recording
• surface (10-100 μv)
• Depth 500-1500 μv
25
27. • Hyperventilation - causes cortical hypocapnia-> cerebral
vasoconstriction and hypoxia -> may allow epileptic foci to
become evident
• Photic stimulation - a strobe light flashing at 8-15 Hz is used to
capture the occipital α frequency - α frequency adjusts to
match that of the strobe - may allow epileptic foci to be seen
and may even induce epileptic seizures, as may a flickering
television screen
• Sleep deprivation.
• Sleep EEG
ACTIVATION
27
28. • Depth electrodes
• Ambulatory (24-hour) EEG
• Q-EEG/BEAM/Brain Mapping/rEEG
Multichannel recording of eyes-closed, resting EEG - visually
edited & a sample of artifact-free data, analyzed, using the
Fast Fourier Transform (FFT) to quantify the power at each
frequency of the EEG averaged across the entire sample,
known as the power spectrum.
QEEG findings are then compared to a normative database
This database consists of brain map recordings of several
hundred healthy individuals
Comparisons are displayed as Z scores, which represent
standard deviations from the norm.
EEG TECHNIQUES
28
29. • Absolute power
This refers to the amount of activity within a specific frequency
band of brain waves
• Relative power
This refers to the relative amount of activity within a specific
frequency band compared to all the other frequency bands
• Coherence
Measure of synchronization between activity in two channels
• Symmetry
Ratio of power in each band between a symmetrical pair of
electrodes 29
30. LORETA (Low Resolution Electromagnetic Tomography) -
Complex mathematical calculations to construct a visual image
of the 3D electrical activity of deep parts of the brain from
surface electrical measures
30
31. EEG techniques (continued..)
• Video EEG/Video telemetry- Simultaneous recording of brain
activity on an EEG and behavior on tape or digital video
• ERP - An event-related potential (ERP) is any stereotyped
electrophysiological response to an internal or external
stimulus.
• Polysomnography – Simultaneous recording of EEG, muscle
tone, oculogram, respiration.
31
41. • In deep drowsiness, stage I (may persist during
stage II & III)
• 50-80% in normal adults
• Location – occipital
• Monophasic, triangular
• 1Hz (4-6 Hz rare)
POSITIVE OCCIPITAL SHARP TRANSIENT OF SLEEP
(POSTS)
41
44. • 12-14Hz, slowed with ↑sleep
• Waxing & waning
• Location: fronto cental
• Origin: Deep frontal & thalamus
SLEEP SPINDLES
44
45. • Positive followed by large negative
wave
• May precede or follow smaller waves
of opposite polarity
• Maximum at vertex may extend to
frontal & parietal region
• Bilaterally synchronous
• Appear by 5month, prominent in
youth
• Not suppressed by focal lesion
VERTEX SHARP WAVES
45
53. AWAY FROM NORMALITY
WAVE EEG
AMPLITUDE SPIKES / SHARP WAVES
RHYTHM SLOW / FAST / PERIODIC DISCHARGES
COMMON IS THE PERMUTATION AND COMBINATION OF THE TWO
53
55. SPIKES
It is a transient discharge , clearly distinguished from the
background activity , having pointed peak and duration of 20
to 70 m sec. in conventional paper speed.
The main component is generally negative and amplitude is
variable.
The after coming slow wave is surface negative and depict
long hyper polarization.
Positive waves are common in in depth recording.
Spikes increased after seizure , but not increased prior to
seizure (Gotman 1984)
55
57. ROLANDIC SPIKES
Misnomer as the total
duration is more than 70 m
sec
Appears as isolated spikes
in centrotemoral region.
In BCECTS
The entire complex
consists of 80 to 120 ms
57
58. SHARP WAVES
• Sharp waves are defined as transient discharges clearly
distinguished from background activity having pointed peak
and at conventional paper speed it has a duration of 70 – 200
m sec.
• The main component is usually negative with ascending
component is sharp but descending component is slow.
58
67. ABRUPT LOSS OF VOLTAGE DUE TO DESYNCHRONYSATION
THERE IS 20 – 40 HZ FAST ACTIVITY
1 - 3 SEC
APPROXIMATELY 10 HZ SPIKE WAVE WITH HIGH AMPLITUDE
APROXIMALTELY 10 SEC
FREQUENCY SLOWS DOWN AND COME TO DELTA RANGE
ONCE 4 HZ REACHED THEN SLOW WAVES INTERUPT THE RECURRING
RHYTHM
IT FOLLOWS THE POST ICTAL FLATNESS
GRADUALLY DETA , ALPHA THE BETA RANGE WAVES RETURNS
GENERALIZED TONIC CLONIC SEIZURE
67
69. ABSENCE SEIZURE
Characteristics are 3 HZ spike
wave complex
Appears and goes of abruptly on
normal background activity
Maximum at frontal and midline
region
Starts at 4 HZ then slows down to
3.5 HZ then up to 2.5 Z
Hyperventilation precipitate such
attacks
Paroxysm of more than 5 sec
leads to clinical seizure69
70. SIMPLE PARTIAL SEIZURE
• Consciousness is fully preserved.
• EEG shows
» Spikes over the involved cortex
» Wide spread desynchronisaton , more or less
theta and delta activity.
» Uninvolved regions shows normal EEG pattern
70
72. COMPLEX PARTIAL SEIZURE
•EEG is variable
•Nasopharyngeal and
sphenoiddal electrode is
helpful in recording
•Temporal spikes are
common.
•The EEG may show 4Hz flat
topped waves and 6 Hz flat-
topped waves
72
73. JAPANESE ENCEPHALITIS
It include the diminution of
electrical activity
Slow waves are important
the changes are not
characteristic
It depicts the severity of
the illness
Improvement occurs with
the corresponding
improvement of the EEG
73
74. HEPATIC ENCEPHALOPATHY
Stage consciousness EEG
I Alert Normal
II Drowsy Slow alpha , poorly developed K-
complex and sleep spindle
III Stupor Theta activity , absence of sleep
pattern
IV Coma Tri-phasic wave
V Deep coma Delta wave
VI Deep coma Flat EEG
74
75. EEG of a case of hepatic encephalopathy after vaproate toxicity , fig1 shows diffuse
slowing of activity , fig 2 shows improvement after treatment ( curtsy – international
journal of neurology Feb’ 09)
EEG OF HEPATIC ENCEPHALOPATHY
Fig 1 Fig 2
75
76. DELIRIUM TREMENS
Beta predominance with
spares normal alpha during
acute florid stage
Persistent delta with little
beta and alpha
During recovery the first to
predominant beta with
spares alpha
Those who exhibits
persistent theta suggests
residual brain damage.Beta prominence in the EEG
76
77. PERIODIC DISCHARGE
• Periodic discharges are of high amplitude and it may me spike
or sharp waves and the duration may exceeds 150 m sec and
recurring at periodic interval.
• It may be the most important EEG finding for ongoing CNS
disease or some CNS infections.
• Morphology me be specific for the disease-
• Burst suppression
• Repetitive sharp waves
• Periodic triphasic
• Focal periodic
• Generalized periodic slow waves
77
78. SSPE
Occurs in a minor percentage of cases of measles
virus infection.
1. Periodic discharge dominates the picture.
2. Duration of 0.5 – 3 sec
3. Average of 500 mic volt
4. Every 4 – 16 sec interval
5. Giant slow waves
6. Discharges are mixed
7. Prominent in the vertex
8. There may be accompanying myoclonus
78
80. CREUZFELDT – JAKOB DISEASE
• It is a prion disease.
• The EEG characteristics are as follows:
– In the first stage there is non specific change in the EEG
– In the 2nd stage patient developed
1. Periodic tri-phasic / bi-phasic complexes
2. Duration of 100-300 m.sec
3. Reparation every 0.5 to 2 sec
4. It is most prominent in anterior region
5. Later stages slow waves become prominent
80
82. HERPES SIMPLEX ENCEPHALITIS
• The EEG finding of HSE is highly suggestive (but not
pathogomonic).
• EEG shows-
• Early stage there is focal or lateralized polymorphic
delta activity on same side.
• Slow wave later involve frontotemporal region.
• Sharp slow wave recurring at every 1-5 sec interval.
• The complex comprises of upto1000ms.
• Usually appears with in 2 to 15 days but may appear
after 30 days.
82
84. CEREBRAL ANOXIA
On flat back ground
generalized synchronous
repetitive simple or
compound sharp waves.
Associated with
myoclonus.
Occurs with a burst and
suppression burst pattern.
84
85. FOCAL BRAIN LESIONS
• The types of EEG abnormality in focal brain lesions are:
– Abnormal background rhythm
– Focal absence of neuronal activity tumor area
– Burst suppression pattern abutting area
– Continuous slow wave most distal zone
– Arrhythmic focal hemispheric or generalized delta
activity
– Less than 4 HZ delta activity
– Continuous or sporadic
– Destructive lesions abscess, hematoma are
associated
85
86. FOCAL BRAIN LESION
– Intermittent rhythmic slow activity:
– It may be of theta or delta range
– Independently or mixed
– Infra-tentorial, supra-tentorial or peri-ventricular
tumor.
– Epileptiform activity
– Focal in onset
– Localized hemispheric lesion
– Often accompanied by slowing of activity
86
88. DEGENERATIVE DISEASE
• The EEG change in the degenerative disease is non
specific.
• There was no consistent difference between cortical
or sub-cortical dementia.
• But sub-cortical dementia shows more normal EEG
• Multi-infract condition may show some lateralizing
sign.
88
89. DEGENERATIVE DISEASE
• Alzheimer's disease:
• Initially there was irregular theta activity
• Later become prominent back ground activity
• Lastly delta activity become prominent
• Fronto-temporal dementia :
• EEG remains persistently normal
• Quantitative analysis showed some abnormality
• Huntingtons disease:
• > 10 µv beta activity is characteristic
89
90. EEG OF A CASE OF ALZHEIMERS DISEASE
EEG of Alzheimer's disease showing irregular theta activity. 90
92. SCHIZOPHRENIA
• S-EEG findings in schizophrenia is non specific
Widespread slow activity
Diffuse Dysrhythmia
Spikes or spike-wave complex
• Q- EEG abnormality -extensively examined:
Extensive slow wave rhythm preponderance
Delta activity anterior brain region
Theta activity posterior brain region
Beta activity with small increase in amplitude
92
93. MOOD DISORDER
• Most of the studies suggests-
• Increased beta / alpha power
• Asymmetric increase in alpha / beta activity in left
frontal region
• Less alpha power and higher EEG findings are seen in
subclinical and depressed patients relatives.
• Recently Q-EEG used as the predictor for
antidepressant response.
93
94. ANTISOCIAL AND BORDERLINE PERSOANLITY DISORDER
• Antisocial personality disorder:
• Frequently associated with organic brain pathology.
• Abnormal behavior is frequently but non specific EEG
changes.
• Borderline personality disorder:
• A number of patients subsequently diagnosed as
complex partial seizure.
• 40 – 80 % have back ground slowing of activity.
• ¼ th of cases have 6 to 14 / sec spike activity might be
the correlate of episodic impulsive activity.
94
95. ATTENTION DEFICIT HYPERACTIVITY DISORDER
• 1/3rd had EEG abnormality.
• Pediatric Neurology reports Epiletiform discharges in ADHD
patients.
• Q-EEG showed increased activity in Frontal region.
• But confounding factors denote that learning disability also
shows similar result.
95
96. CONTROVERSIAL WAVE FORMS
RELEVANT TO PSYCHIATRY
• Fourteen and six per second positive spike:
– Age related change in wave form ,
– some psychiatric phenomena are though to be associated,
– etiology presumed to be closed Bain injury or infection.
• Rhythmic mid temporal discharges:
– 1/3rd to ½ patient showed rhythmic mid temporal
discharges
– Associated with anxiety and somatization.
– Some studies demonstrate behavioral discontrol and
autonomic phenomena.
96
97. CONTROVERSIAL WAVE FORMS
RELEVANT TO PSYCHIATRY
• Benign Epiletiform transients of sleep:
• Low-voltage sharp negative or biphasic waves
• some time alternate between right to left hemisphere.
• Associated with vegetative symptoms.
• Six per second spike and wave:
• Also called phantom wave
• Low amplitude waves difficult to recognize
• Associated with impulsivity and vegetative symptoms.
97
98. Take Home Message
EEG is simple, noninvasive and inexpensive
investigation.
It can be used for screening as well as
predicting outcome of many neurological and
psychiatric disorders.
98
