1 basics of eeg and fundamentals of its measurement

1. BASICS OF EEG AND FUNDAMENTALS OF
IT’S MEASUREMENT

2. Timeline of EEG invention
1875
• Richard Caton - Presence of continuous and
spontaneous electrical activity from the brain surface
of rabbits and monkeys
1890
• Adolf Beck – Sensory stimulus can induce spontaneous
and rhythmic oscillation
1912
• Vladimir Pravdich Neminsky – Produced first animal
EEG and evoked potential of mammalian dog
1924
• Hans Berger - Recorded the first human EEG
Figure: Hans Berger and his invention

3. Cerebral generators of EEG potentials
Figure: Neuronal structure Figure: Neuron – Neuron connection

4. Electrical signal propagation
Figure: Signal transmission Figure: Signal transmission

5. Figure: Pyramidal cell’s alignment
Figure: Single pyramidal cell

6. EEG Recording
Figure: Schematic diagram of a modern EEG Machine from the
subject to the data retrieved
Figure: Illustration of EEG electrodes and signal

7. Figure: 10/20 System of EEG electrode placement
• Nasion
• Inion
• Left and right
auricular points
Figure: EEG Scalp electrodes
EEG Electrode Placement

8. Filters
Figure: Low frequency Filter Figure: Low frequency Filter characteristics

9. Figure: High Frequency Filter Figure: High Frequency Filter Characteristics

10. Figure : 60 Hz notch filter Figure : 60 Hz notch filter characteristics

11. Amplifier
• All EEG amplifiers are differential amplifiers.
• Differential amplifier takes two input
voltages and produces an output that is an
amplified version of the difference between
the two inputs
• Advantage – Cancels out the external noise

12. Rules of Polarity on EEG
 If input 1 is negative with respect to input 2, there is an
upward deflection
 If input 1 is positive with respect to input 2, there is a
downward deflection
 An upward deflection is surface negative, and a
downward deflection is surface positive
 When there is no deflection, the inputs are equipotential
and are either equally active or inactive
Equipotential

13. Polarity Convention - Example

14. Montage
Logical and orderly arrangement of channels/electrode pairs on the display
• Bipolar Montage
• Common electrode reference montage
• Average reference montage
• Laplacian montage

15. Figure : Commonly used bipolar longitudinal
pattern (Double Banana)
Figure : EEG of Bipolar montage

16. Figure: Referential montage Figure: Laplacian montage

17. Figure: Normal EEG in awake state

19. EEG Artifacts
• Artifacts are unwanted noise signals in an EEG record.
• Classification of artefacts is based on the source of generation:
Physiological artifacts and external artifacts.
• Physiologic artifacts:
• Any minor body movements
• EMG
• ECG
• Eye movements etc.
• Non Physiologic artifacts:
• Damage of electrodes
• Cable movements
• Broken wire contacts
• Impedance fluctuation
• 60/50 H artifact etc
Figure: EEG Artifacts

20. Advantages & Applications of EEG
• Excellent temporal resolution
• EEG can determine the relative strengths and positions of electrical activity in different brain regions.
• EEG does not involve exposure to high intensity magnetic field
• Relatively cheap and simple to operate
• Applications of the EEG in humans and animals involve:
 Research
 Clinics

21.  Clinical application- EEG is one of the main diagnostic tests for epilepsy
Normal EEG compared to EEG including a seizure: (A) Normal EEG of 15 seconds; (B) EEG
of the same patient having an epileptic seizure visible on electrodes P8 and T8.

22. Clinical applications
• Monitor alertness, coma and brain death
• Locate areas of damage following head injury, stroke, tumor.
• Monitor cognitive engagement (alpha rhythm)
• Control anesthesia depth
• Investigate epilepsy and locate seizure origin
• Investigate sleep disorder and physiology.
• Etc.

23. References
• Teplan, M. (2002). FUNDAMENTALS OF EEG MEASUREMENT.
• Britton JW, Frey LC, Hopp JLet al., authors; St. Louis EK, Frey LC, editors. Electroencephalography (EEG):
An Introductory Text and Atlas of Normal and Abnormal Findings in Adults, Children, and Infants [Internet].
Chicago: American Epilepsy Society; 2016. Available from:
https://www.ncbi.nlm.nih.gov/books/NBK390354/
• https://doi.org/10.1684/epd.2020.1217
• Light, G. A., Williams, L. E., Minow, F., Sprock, J., Rissling, A., Sharp, R., Swerdlow, N. R., & Braff, D. L.
(2010). Electroencephalography (EEG) and event-related potentials (ERPs) with human participants. Current
protocols in neuroscience, Chapter 6, Unit–6.25.24. https://doi.org/10.1002/0471142301.ns0625s52

24. Thankyou…