EEG-132 Pract. (1).ppt

ELECTROENCEPHALOGRAPHY
(EEG)
Dr. Shaikh Mujeeb Ahmed
M.B.B.S. MD. (PHYSIOLOGY)

EEG
 The electroencephalogram (EEG) is a
recording of the electrical activity of
the brain from the scalp.
 The first recordings were made by
Hans Berger in 1929

Electroencephalogram
 EEG is the record of electrical activity
of brain( superficial layer i.e. the
dendrites of pyramidal cells) by
placing the electrodes on the scalp.

Generation of large EEG signals by
synchronous activity

Objectives of EEG practical
 Familiarize with the principles of
techniques involved
 Count frequencies and measure the
amplitudes of the record obtained.
 Categories the records into
appropriate rhythms – α, β, θ,and δ.
Cont…

Objectives of EEG practical
 Identify and describe changes
produced by provocation tests.
e.g. eye opening & closing, intermittent
photic stimulation (IPS) clapping
sound, induce thinking &
hyperventilation.
 Appreciate clinical uses of EEG

EEG Waves
 Alpha wave -- 8 – 13 Hz.
 Beta wave -- >13 Hz. (14 – 30 Hz.)
 Theta wave -- 4 – 7.5 Hz.
 Delta waves – 1 – 3.5 Hz.
 D T A B

Different types of brain waves in
normal EEG

EEG Recording From Normal Adult Male

Alpha wave
 rhythmic, 8-13 Hz
 mostly on occipital lobe
 20-200 μ V
 normal,
 relaxed awake rhythm with eyes
closed

Beta wave
 irregular, 14-30 Hz
 mostly on temporal and frontal lobe
 mental activity
 excitement

Theta wave
 rhythmic, 4-7 Hz
 Drowsy, sleep

Delta wave
 slow, < 3.5 Hz
 in adults
 normal sleep rhythm

Different types of brain waves in
normal EEG
Rhythm Frequency
(Hz)
Amplitude
(uV)
Recording
& Location
Alpha(α) 8 – 13 50 – 100 Adults, rest, eyes closed.
Occipital region
Beta(β) 14 - 30 20 Adult, mental activity
Frontal region
Theta(θ) 5 – 7 Above 50 Children, drowsy adult,
emotional distress
Occipital
Delta(δ) 2 – 4 Above 50 Children in sleep
D T A B

Requirements
 EEG machine (8/16 channels).
 Silver cup electrodes/metallic bridge
electrodes.
 Electrode jelly.
 Rubber cap.
 Quiet dark comfortable room.
 Skin pencil & measuring tape.

EEG Electrodes
Sliver Electrodes Electrodes Cap

Procedure of EEG recording
 A standard EEG makes use of 21
electrodes linked in various ways
(Montage).
 Ask the subject to lie down in bed.
 Apply electrode according to 10/20%
system.
 Check the impedance of the
electrodes.

10 /20 % system of EEG electrode
placement

 Ask the subject to close his/her eyes.
 Select a montage.
 Press run switches on to run the
paper.

 Press the calibration knob to check
voltages & time constant.
 Always observe subject for any
abnormal muscle activity.
 Ask the subject to open eyes for 10
sec.and ask him/her to close eyes.
(do this procedure for several times
in each montage)

EEG Electrodes
 Each electrode site is labeled with a letter
and a number.
 The letter refers to the area of brain
underlying the electrode
e.g. F - Frontal lobe and T - Temporal lobe.
 Even numbers denote the right side of the
head and
 Odd numbers the left side of the head.

Two types of recording
 Bipolar – both the electrodes are at
active site
 Bipolar montage are parasagital montage.
 Unipolar – one electrode is active and
the other is indifferent kept at ear
lobe.
 Always watch for any abnormal muscle
activity.
 Ask the subject to open eyes for 10 sec.
then ask them to close the eyes.

Montage
 Different sets of electrode
arrangement on the scalp by 10 – 20
system is known as montage.
 21 electrodes are attached to give 8
or 16 channels recording.

Analysis
 Electrical activity from the brain
consist of primarily of rhythms.
 They are named according to their
frequencies (Hz) and amplitude in
micro volt (μv).
 Different rhythms at different ages
and different conditions (level of
consciousness)
 Usually one dominant frequency
(background rhythm)

Factor influencing EEG
 Age
 Infancy – theta, delta wave
 Child – alpha formation.
 Adult – all four waves.
 Level of consciousness (sleep)
 Hypocapnia(hyperventilation) slow &
high amplitude waves.
 Hypoglycemia
 Hypothermia
 Low glucocorticoids
Slow waves

Desynchronization or Alpha block
 Cause:
 Eyes opening (after closure)
 Thinking by the subject (mathematical calculation)
 Sound (clapping)

Eye opening
 Alpha rhythm changes to beta on eye
opening (desynchronization / α- block)

Thinking
 Beta waves are observed

Provocation test
 Intermittent photic stimulation
 Increase rate & decrease amplitude
 Hyperventilation
 Decrease rate & increase in
amplitude

Use of EEG
 Epilepsy
 Generalized (grandmal) seizures.
 Absence (petitmal) seizures.
 Localize brain tumors.
 Sleep disorders (Polysomnography)
 Narcolepsy
 Sleep apnea syndrome
 Insomnia and parasomnia
 Helpful in knowing the cortical activity,
toxicity, hypoxia and encephalopathy &
 Determination of brain death.
 Flat EEG(absence of electrical activity) on two
records run 24 hrs apart.

Sleep studies
 The EEG is frequently used in the
investigation of sleep disorders especially
sleep apnoea.
 Polysomnography : EEG activity together
with
 heart rate,
 airflow,
 respiration,
 oxygen saturation and
 limb movement

Sleep patterns of EEG
 There are two different kinds of sleep:
 Rapid eye movement sleep (REM-Sleep)
 Non-REM sleep (NREM sleep)/ slow wave
sleep
 NREM sleep is again divided into 4
stages (I to IV). The EEG pattern in
sleep is given in the following table:

Stages of sleep EEG pattern Somatic or
Behavioral changes
Alert Alpha activity on
eye closed
Desynchronization
on eye opening
Respond to verbal
commands
I (Drowsiness) Alpha dropout &
appearance of
vertex waves &
theta.
Reduced HR & RR
II (Light sleep) Sleep spindles,
vertex sharp
waves & K-
complexes
Reduced HR & RR
III ( Deep Sleep) Much slow
background K-
complexes
Reduced HR & RR

IV (very deep
sleep)
Synchronous delta
waves, some K-
complexes
Reduced HR & RR
REM sleep
(paradoxical
sleep)
Desynchronization
with faster
frequencies
HR, BP & RR irregular
Marked hypotonia
Rapid eye movement
50 – 60 /min.
Dreaming threshold
of arousal

Changes in brain waves during
different stages of sleep &
wakefulness

EEG in different types of epilepsy

Video monitoring
 Simultaneous video monitoring of the
patient during the EEG recording is
becoming more popular. It allows the
physician to closely correlate EEG
waveforms with the patients activity
and may help produce a more
accurate diagnosis.

EEG Artifacts
 Biological artifacts
 Eye artifacts (including eyeball, ocular
muscles and eyelid)
 ECG artifacts
 EMG artifacts
 Glossokinetic artifacts (minor tongue
movements)
 External artifacts
 Movement by the patient
 settling of the electrodes
 Poor grounding of the EEG electrodes
 the presence of an IV drip

What is EEG and what is montage?
 The electroencephalogram (EEG) is a
recording of the electrical activity of
the brain from the scalp.
 Arrangements of electrodes by
10/20% system is known as
montage.

What is the advantage of
provocation test while recording
EEG?
 Provocation test e.g.
hyperventilation, intermittent photic
stimulation are done to trigger the
epileptic focus.

Compare & contrast Alpha & Beta
waves of EEG
 Alpha
 In awake resting
with eyes closed
 Frequency 8 – 13 Hz.
 Voltage – 50uV.
 Beta
 In awake thinking
subjects.
 Frequency - >13Hz.
(14 – 30 Hz.)
 Voltage – 20uV.

What stage of sleep is indicated by
slow waves of EEG(4 – 7Hz.) ?
 4 – 7 Hz. (Theta) waves are seen
during stage 2 & 3 (light and deep )
sleep

In the following tracing of EEG what changes
do you observe after point “A”.
What may be it’s possible cause?
 Rhythm has changed from α toβ(at point “A”) ,it
is called alpha block or desynchronization.
 Causes:
 Eyes opening
 Thinking e.g. mathematical calculations.
 Sound (clapping)

What changes are seen in EEG of an epileptic
child suffering from absence seizure
(petit mal)?
 In petit mal spike and wave (dome
shaped) 3 cps. Pattern is seen.

EEG-132 Pract. (1).ppt

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EEG-132 Pract. (1).ppt