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

3. 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

4. Origin of EEG waves

5. 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.

6. Generation of large EEG signals by synchronous activity

7. 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…

8. 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

9. D T A B 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

10. Different types of brain waves in normal EEG

11. EEG Recording From Normal Adult Male

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

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

14. Theta wave
rhythmic, 4-7 Hz
Drowsy, sleep

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

17. 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) 20
Adult, mental activity
Frontal region
Theta(θ)
5 – 7
Above 50
Children, drowsy adult, emotional distress
Occipital
Delta(δ)
2 – 4
Children in sleep
D T A B

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

19. Computerized EEG Machine

20. Electrode Positioning system

21. EEG Electrodes
Electrodes Cap
Sliver Electrodes

22. 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.

23. 10 /20 % system of EEG electrode placement

24. Procedure of EEG recording
Ask the subject to close his/her eyes.
Select a montage.
Press run switches on to run the paper.

25. 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)

26. 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.

27. 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.

30. 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. 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)

33. 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

34. NORMAL EEG CHANGES

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

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

37. Thinking
Beta waves are observed

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

39. Use of EEG Epilepsy Localize brain tumors.
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.

40. 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

41. 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:

42. 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
III ( Deep Sleep)
Much slow background K-complexes

43. 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

44. Changes in brain waves during different stages of sleep & wakefulness

45. Changes in brain waves during different stages of sleep & wakefulness

47. K - complex
Sleep Spindle

48. EEG & Epilepsy

49. EEG in different types of epilepsy

50. Grandmal seizure

51. Petitmal seizure

52. 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.

53. EEG Artifacts Biological artifacts External 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

55. ECG Artifacts

57. LET’S ANSWER

58. 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.

59. 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.

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

61. 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

62. 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)

63. In petit mal spike and wave (dome shaped) 3 cps. Pattern is seen.
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.