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BASICS OF EEG AND FUNDAMENTALS OF
IT��S MEASUREMENT

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 �C Sensory stimulus can induce spontaneous
and rhythmic oscillation
1912
? Vladimir Pravdich Neminsky �C Produced first animal
EEG and evoked potential of mammalian dog
1924
? Hans Berger - Recorded the first human EEG
Figure: Hans Berger and his invention

Cerebral generators of EEG potentials
Figure: Neuronal structure Figure: Neuron �C Neuron connection

Electrical signal propagation
Figure: Signal transmission Figure: Signal transmission

Figure: Pyramidal cell��s alignment
Figure: Single pyramidal cell

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

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

Filters
Figure: Low frequency Filter Figure: Low frequency Filter characteristics

Figure: High Frequency Filter Figure: High Frequency Filter Characteristics

Figure : 60 Hz notch filter Figure : 60 Hz notch filter characteristics

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 �C Cancels out the external noise

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

Montage
?Logical and orderly arrangement of channels/electrode pairs on the display
? Bipolar Montage
? Common electrode reference montage
? Average reference montage
? Laplacian montage

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

Figure: Referential montage Figure: Laplacian montage

Figure: Normal EEG in awake state

1 basics of eeg and fundamentals of its measurement

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

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

? 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.

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.

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�C6.25.24. https://doi.org/10.1002/0471142301.ns0625s52

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1 basics of eeg and fundamentals of its measurement

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