Electroencephalography

Electroencephalography (EEG) is a noninvasive method used to record electrical activity in the brain. EEG measures voltage fluctuations resulting from the synchronous activity of thousands or millions of neurons, providing valuable information about brain function.

EEG_cap

EEG

History

The concept of recording electrical activity in the brain was first introduced by the British physician Richard Caton in 1875. However, the modern EEG was developed by German psychiatrist Hans Berger in 1924, who coined the term "electroencephalogram."

Procedure

During an EEG, electrodes are placed on the scalp, and the electrical activity of the brain is recorded. The placement of the electrodes typically follows the International 10-20 System, which defines the specific locations on the scalp for accurate and consistent recordings. The electrical signals are then amplified and displayed as a series of waveforms, providing insights into brain function and potential abnormalities.

Sleep EEG Stage 1

Indications

EEG is used for various purposes, including:

• Diagnosing epilepsy and identifying seizure types
• Evaluating sleep disorders
• Assessing brain death or coma
• Investigating cognitive or psychiatric conditions
• Monitoring brain function during surgery
• Researching brain function and neurophysiology

Interpretation

EEG waveforms are characterized by their frequency, amplitude, and shape. The basic waveforms include:

• Delta waves: slow waves with a frequency of 0.5-4 Hz, typically seen during deep sleep or in certain brain disorders
• Theta waves: frequency of 4-8 Hz, usually observed during light sleep or in a state of drowsiness
• Alpha waves: frequency of 8-12 Hz, present during relaxed wakefulness, predominantly in the occipital and posterior regions of the brain
• Beta waves: frequency of 12-30 Hz, associated with active thinking, alertness, or anxiety
• Gamma waves: frequency of 30-100 Hz, related to higher cognitive functioning and information processing

Abnormal EEG findings may indicate neurological or psychiatric disorders and can help guide diagnosis and treatment.

Limitations

While EEG provides valuable information about brain function, it has some limitations:

• Limited spatial resolution: EEG is not ideal for pinpointing the exact location of brain activity.
• Sensitivity to artifacts: EEG signals can be affected by factors such as eye movement, muscle activity, and electrical interference.
• Inability to detect deep brain activity: EEG primarily measures activity from the cerebral cortex and may not accurately reflect activity in deeper brain structures.
• Despite these limitations, EEG remains an essential tool in the field of neurology and neuroscience due to its noninvasive nature, cost-effectiveness, and ability to provide real-time information on brain function.

Electroencephalography Resources
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