Q 1.32. Electroencephalography (EEG)

Q 1.32. Electroencephalography (EEG)

1. What is EEG?

    • Electroencephalography (EEG) is a non-invasive diagnostic test that evaluates brain wave activity.
    • It involves placing multiple small, metal electrodes along the scalp to detect electrical changes in the brain.
    • These electrodes pick up signals produced by the brain, which are then recorded by a machine.


2. Purpose and Applications:

    • Diagnosing Epilepsy: EEG helps diagnose epilepsy by detecting abnormal electrical patterns associated with seizures.
    • Other Brain Disorders: It can also identify abnormalities related to other brain disorders.
    • Monitoring Consciousness: EEG is useful for evaluating altered consciousness episodes with uncertain causes.


3. Normal EEG Patterns:

    • The awake EEG typically shows:
      • Alpha waves (8-12 Hz, 50 μV) over the occipital and parietal lobes.
      • Beta waves (>12 Hz, 10-20 μV) frontally.
      • Theta waves (4-7 Hz, 20-100 μV).
    • Abnormalities include:
      • Asymmetries between hemispheres (suggesting structural disorders).
      • Excessive slowing (1-4 Hz, 50-350 μV delta waves) seen in depressed consciousness, encephalopathy, and dementia.
      • Abnormal wave patterns, which may be nonspecific or diagnostic (e.g., epileptiform sharp waves).


4. Activation Techniques:

    • If routine EEG is normal but a seizure disorder is suspected:
      • Hyperventilationphotic stimulationsleep, and sleep deprivation can help elicit evidence of seizures.
      • Nasopharyngeal leads may detect temporal lobe seizure foci.
      • Video EEG combines video monitoring with EEG to assess seizure types.


5. Continuous Monitoring:

    • Ambulatory EEG (over 24 hours or longer) can determine if memory lapses or episodic motor behavior result from seizure activity.
    • Video EEG is used before surgery to identify epileptogenic foci.


Remember, EEG is a valuable tool in neurology for understanding brain function and diagnosing various conditions.




1 msdmanuals.com

2 med.uth.edu

3 nhs.uk

4 health.harvard.edu

Verified by Dr. Petya Stefanova