How many electrodes are usually used in a standard EEG?

In a standard EEG (electroencephalogram) setup, the most common configuration typically involves using 21 electrodes. This arrangement allows for comprehensive coverage of the scalp, enabling the measurement of brain activity from multiple regions. The 21-electrode montage is effective in capturing the electrical signals produced by neuronal activity across the cerebral cortex, providing valuable information for diagnosing various neurological conditions.

Utilizing this number of electrodes strikes a balance between obtaining sufficient spatial resolution to analyze brain activity while maintaining practical considerations like patient comfort and setup time. While other configurations with different numbers of electrodes exist, they may either provide too limited information (like a fewer number) or could be more complex without necessarily yielding proportionately better insights, as seen in setups using higher counts like 30 or more.