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1 basics of eeg and fundamentals of its measurement

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Swathy Ravi

The document discusses the basics of EEG and its measurement. It provides a timeline of EEG invention from 1875 to 1924. It describes how EEG signals are generated from neuronal structures and propagated through electrical signals. It explains how EEG is recorded using a modern EEG machine and electrode placement systems. It discusses filters, amplifiers, polarity conventions, montages, artifacts, and clinical applications of EEG for monitoring brain activity.

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BASICS OF EEG AND FUNDAMENTALS OF ITS 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 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
Cerebral generators of EEG potentials Figure: Neuronal structure Figure: Neuron Neuron connection
Electrical signal propagation Figure: Signal transmission Figure: Signal transmission
Figure: Pyramidal cells 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 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
Polarity Convention - Example
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, Unit6.25.24. https://doi.org/10.1002/0471142301.ns0625s52
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1 basics of eeg and fundamentals of its measurement

  • 1. BASICS OF EEG AND FUNDAMENTALS OF ITS 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 cells 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
  • 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, Unit6.25.24. https://doi.org/10.1002/0471142301.ns0625s52

Editor's Notes

  • #5: Summation of EPSP TRIGGERS AN ACTION POTENTIAL
  • #6: Volume Conduction: Bioelectric potentialss flow from the source in the body to the recording electrodes.