The EEG records electrical activity in the brain from the scalp using electrodes placed according to the 10-20 system. There are different types of brain waves seen on EEG including alpha, beta, theta, and delta waves which vary in frequency and amplitude. Factors like age, consciousness, medications, and stimuli can influence the brain waves observed on EEG. Hans Berger first recorded human EEG waves in 1929, establishing EEG as a tool for examining brain function.

1. ELECTROENCEPHALOGRAM
(EEG)
AKASH KUMAR BHOI
Assistant Professor
SMIT

2. 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

3. Origin of EEG waves

4. Two types of recording
• Bipolar – both the electrodes are at active site
• Unipolar – one electrode is active and the
other is indifferent kept at ear lobe.

5. 10 /20 % system of EEG electrode placement

6. 10-20 System of
Electrode Placement
• F = Frontal
• P = Parietal
• T = Temporal
• O = Occipital
• C = Central
A = Auxiliary
• Odd # = Left
• Even # = Right

7. 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 (deficiency of glucose
in the bloodstream)
• Hypothermia
• Low glucocorticoids
Slow waves

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

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

10. Thinking
• Beta waves are observed

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

13. 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) 13 - 30 20 Adult, mental activity
Frontal region
Theta(θ) 4 – 8 Above 50 Children, drowsy adult,
emotional distress
Occipital
Delta(δ) 0.5 – 4 Above 50 Children in sleep

16. Computerized EEG Machine

21. THANK YOU