2. Hans Berger (1873-1941)
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
4. Electroencephalogram
EEG is the recording of the electrical
activity of brain( superficial layer i.e.
the dendrites of pyramidal cells) by
placing the electrodes on the scalp.
5. Mechanism of EEG
Continuous graph of changing voltage fields
at scalp surface resulting from ongoing
synaptic activity in underlying cortex
Inputs from subcortical structures
Thalamus
Brainstem reticular formation
•EEG signals generated by
cortex
•Currents in extracellular
space generated by
summation of EPSPs and
IPSPs
10. Alpha wave
rhythmic, 8-13 Hz
mostly on occipital lobe
20-200 μ V (Amp)
normal,
Relaxed(wendring) awake rhythm
with eyes closed
low-amplitude, slow,
synchronous waves
11. Beta wave
irregular, 14-30 Hz
mostly on temporal and frontal lobe
mental activity(in problems)
excitement
•Beta:high-amplitude waves seen in
deep sleep and when reticular
activating system is damped
12. Theta wave
Theta :more irregular than alpha waves
Common in newborn some sleep in
adult.
Fra. 4-7 Hz
Drowsy, sleep
Adult indicates severe emotional stress.
temporal and occipital lobes.
13. Delta wave
: high-amplitude waves
Common during sleep and awake infant.
slow, < 3.5 Hz
In awake adult indicate brain damage.
normal sleep rhythm
14.
15. 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
16. Objectives of EEG practical
Familiar with the principles of
techniques which used.
Count frequencies and measure the
amplitudes of the recording EEG.
Records the appropriate rhythms – α,
β, θ,and δ.
Cont…
17. Objectives of EEG practical
Identify and describe changes during
tests.
e.g. eye opening & closing, intermittent
photic stimulation (IPS) clapping
sound, induce thinking &
hyperventilation.
Appreciate clinical uses of EEG
18. 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.
23. 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.
25. Procedure of EEG recording
Ask the subject to close his/her eyes.
Select a montage.
Press run switches on to run the
paper.
26. Procedure of EEG recording
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)
27. 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.
28. 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.
29.
30.
31. 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.
32.
33. 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)
34. 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
40. 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.
41. 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
42. EEG patterns in Sleep
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:
43. 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
44. 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
45. Changes in brain waves during
different stages of sleep &
wakefulness
46. Changes in brain waves during
different stages of sleep &
wakefulness
53. 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.
54. 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
59. 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.
60. 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.
61. 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.
62. 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
63. 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)
