Electroencephalography (EEG)

This year marks 100 years of electroencephalography (EEG) in human medicine.

What is Electroencephalography (EEG)? 

• EEG stands for electroencephalography.
• It measures electrical activity in the brain by tracking the movement of electrically charged particles (ions).
  • It measures voltage changes (in microvolts) and the frequency of variations (in hertz).

• Applications

• • Diagnosing epilepsy
  • Monitoring anaesthesia effects
  • Studying sleep patterns
  • Assessing neurological activity during a coma
  • Confirming brain death

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How Does an EEG Test Work?

• Process: During an EEG test, electrodes are placed on the scalp.
• Electrodes placed on the scalp detect voltage changes caused by neuronal activity. 
  • Path of Electrical Activity: Neuronal electrical activity travels through skin, fluid, and bone layers, undergoing reflection, refraction, and scattering.
  • Distance Factor: Electrical activity originates in one location but is detected by electrodes at a distance.
    • These changes are recorded and displayed as an electroencephalogram.
• Electrode Placement: The International 10-20 System is used for standardized electrode placement on the head.
  • Electrodes are placed based on distances. The space between two neighboring electrodes is either 10% or 20% of the total distance between two specific points on the head.

History of EEG Development

• 1875: British physician Richard Caton detected electrical activity in monkey and rabbit brains.
• 1890: Polish scientist Adolf Beck observed fluctuating brain activity in dogs and rabbits.
• 1912: Vladimir Pravdich-Neminsky recorded the first mammalian EEG in a dog’s brain.
• 1924: Hans Berger recorded the first human EEG, named it, and demonstrated its clinical use.

Advantages of Electroencephalography (EEG)

• Non-invasive and painless procedure: EEG uses electrodes placed on the scalp to record electrical activity in the brain.
  • There is no need to break open the skull and it is a painless procedure.
• Wide range of applications: EEG is used in diagnosing various conditions including epilepsy, sleep disorders, head injury, and brain tumors. 
  • It is also used to assess brain death and the effects of anesthesia.
• Relatively simple and cost-effective: EEG equipment is relatively inexpensive and doesn’t require a lot of space. The test is portable and doesn’t use radiation.
• Measures rapid electrical activity: EEG is effective in tracking electrical activity in the brain happening in milliseconds.
• Better than other diagnostic tools for specific purposes: EEG is the best available test to diagnose epilepsy.
• Portable: EEG can be performed in various settings, not just in hospitals.

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Disadvantages of Electroencephalography (EEG)

• Low spatial resolution: EEG measures electrical activity on the scalp surface which makes it difficult to pinpoint the exact location of the activity within the brain.
  • It  is biased towards electrical signals generated closer to the surface of the cortex.
• Difficulty in interpreting data: EEG readings can be affected by volume conduction, which is the movement of electrical activity through the head.
  • Other physiological activities, such as blinking or muscle movement, can also create noise in the data.
• Limited ability to detect deep brain activity: EEG is more sensitive to electrical signals generated by the brain’s surface than those generated by deeper structures.
• Problem of thick hair and Time consuming: Thick hair can interfere with the EEG signal. 
  • The test requires applying gel and precisely placing electrodes on the scalp, which can be time-consuming.

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