SlideShare verwendet Cookies, um die Funktionalität und Leistungsfähigkeit der Webseite zu verbessern und Ihnen relevante Werbung bereitzustellen. Wenn Sie diese Webseite weiter besuchen, erklären Sie sich mit der Verwendung von Cookies auf dieser Seite einverstanden. Lesen Sie bitte unsere Nutzervereinbarung und die Datenschutzrichtlinie.
SlideShare verwendet Cookies, um die Funktionalität und Leistungsfähigkeit der Webseite zu verbessern und Ihnen relevante Werbung bereitzustellen. Wenn Sie diese Webseite weiter besuchen, erklären Sie sich mit der Verwendung von Cookies auf dieser Seite einverstanden. Lesen Sie bitte unsere unsere Datenschutzrichtlinie und die Nutzervereinbarung.
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
• This electrical potential is produced by excitatory or inhibitory
post synaptic electrical discharges from neuronal dendrites at
• 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.
RECORDINGS FROM ANIMAL BRAIN
• First person to record electrical
activity from animal brain in
RICHARD CATON , 1874 5
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
Hans Berger 1835-1911: Human EEG
Prof of Psychiatry, University of Jena
Germany, Removed from job in one
day notice by the Nazis, committed
• 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
• When several referential points are used for recording Bipolar
• In bipolar montage the electrodes form a chain passed side by side
or front to back.
REFERENCE MONTAGE • Connects active
and an inactive
away from the
scalp e.g. on ear,
nose or chin
– Chin & nose-
• Useful for seeing
• Connects two active
• Each channel is
attached to two
• Arrangement of
– Anteriorly placed
– Alternate left and
helps compare the
• 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
• Activation – Hyperventilation – 3min + 1min
- Photic st -30 cm 10,15,20,30,40 Hz
,each in trains of 10 sec.
NORMAL THETA WAVES
Small amount of
sporadic and isolated
activity found in normal
Prominent in drowsy
and sleep EEG tracing
EEG activity of 4 to 7
found in frontal and
NORMAL DELTA ACTIVITY
Not present in normal
Prominent in normal
deeper stage of sleep.
A frequency of < 4 Hz.
• 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
Referral (Ipsilateral ear) Bipolar
EFFECT OF MONTAGE ON AMPLITUDE
• Hyperventilation - causes cortical hypocapnia-> cerebral
vasoconstriction and hypoxia -> may allow epileptic foci to
• 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
• Sleep deprivation.
• Sleep EEG
• 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.
• 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
Measure of synchronization between activity in two channels
Ratio of power in each band between a symmetrical pair of
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
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
• Polysomnography – Simultaneous recording of EEG, muscle
tone, oculogram, respiration.
• Low cost
ADVANTAGES OF EEG
What are normal EEG changes
according to age ?
• At birth up to 6 months – 4 Hz (Delta)
• 6-12 months – 6 Hz (Theta)
• 1-3 yrs – 8 Hz (Alfa coming in)
• 3-11 yrs – 12 Hz (Maturation of Alfa)
• 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
Drowsiness/ drop out alpha & POSTS
Sleep Awake 43
• 12-14Hz, slowed with ↑sleep
• Waxing & waning
• Location: fronto cental
• Origin: Deep frontal & thalamus
• Positive followed by large negative
• 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
• Not suppressed by focal lesion
VERTEX SHARP WAVES
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
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)
MORPHOLOGY OF SPIKES
Morphologically spikes are of mainly three types:
Misnomer as the total
duration is more than 70 m
Appears as isolated spikes
in centrotemoral region.
The entire complex
consists of 80 to 120 ms
• 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
• The main component is usually negative with ascending
component is sharp but descending component is slow.
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
IT FOLLOWS THE POST ICTAL FLATNESS
GRADUALLY DETA , ALPHA THE BETA RANGE WAVES RETURNS
GENERALIZED TONIC CLONIC SEIZURE
Characteristics are 3 HZ spike
Appears and goes of abruptly on
normal background activity
Maximum at frontal and midline
Starts at 4 HZ then slows down to
3.5 HZ then up to 2.5 Z
Hyperventilation precipitate such
Paroxysm of more than 5 sec
leads to clinical seizure69
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
COMPLEX PARTIAL SEIZURE
•EEG is variable
sphenoiddal electrode is
helpful in recording
•Temporal spikes are
•The EEG may show 4Hz flat
topped waves and 6 Hz flat-
It include the diminution of
Slow waves are important
the changes are not
It depicts the severity of
Improvement occurs with
improvement of the EEG
Stage consciousness EEG
I Alert Normal
II Drowsy Slow alpha , poorly developed K-
complex and sleep spindle
III Stupor Theta activity , absence of sleep
IV Coma Tri-phasic wave
V Deep coma Delta wave
VI Deep coma Flat EEG
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
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
Those who exhibits
persistent theta suggests
residual brain damage.Beta prominence in the EEG
• 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
Occurs in a minor percentage of cases of measles
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
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
HERPES SIMPLEX ENCEPHALITIS
• The EEG finding of HSE is highly suggestive (but not
• 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.
On flat back ground
repetitive simple or
compound sharp waves.
Occurs with a burst and
suppression burst pattern.
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
– Less than 4 HZ delta activity
– Continuous or sporadic
– Destructive lesions abscess, hematoma are
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
– Epileptiform activity
– Focal in onset
– Localized hemispheric lesion
– Often accompanied by slowing of activity
• The EEG change in the degenerative disease is non
• 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
• 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
EEG OF A CASE OF ALZHEIMERS DISEASE
EEG of Alzheimer's disease showing irregular theta activity. 90
• S-EEG findings in schizophrenia is non specific
Widespread slow activity
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
• Most of the studies suggests-
• Increased beta / alpha power
• Asymmetric increase in alpha / beta activity in left
• Less alpha power and higher EEG findings are seen in
subclinical and depressed patients relatives.
• Recently Q-EEG used as the predictor for
ANTISOCIAL AND BORDERLINE PERSOANLITY DISORDER
• Antisocial personality disorder:
• Frequently associated with organic brain pathology.
• Abnormal behavior is frequently but non specific EEG
• 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.
ATTENTION DEFICIT HYPERACTIVITY DISORDER
• 1/3rd had EEG abnormality.
• Pediatric Neurology reports Epiletiform discharges in ADHD
• Q-EEG showed increased activity in Frontal region.
• But confounding factors denote that learning disability also
shows similar result.
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
– Associated with anxiety and somatization.
– Some studies demonstrate behavioral discontrol and
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.
Take Home Message
EEG is simple, noninvasive and inexpensive
It can be used for screening as well as
predicting outcome of many neurological and