1. Capturing Brain Activity: The electrical signals generated by the brain are extremely small (microvolts). To capture them effectively, electrodes must be placed as close as possible to the cerebral cortex. The Scalp provides the ideal surface for this measurement.
2. The 10-20 System: In clinical EEG, electrodes are placed on the scalp according to a standardized layout called the "International 10-20 System." This system uses specific anatomical landmarks—the nasion (bridge of the nose) and the inion (bump at the back of the head)—to ensure that electrode placement is consistent and reproducible across different patients and labs.
3. Why the Scalp?: While some specialized electrodes might touch the forehead or be clipped to the ears (often used as "reference" or "ground" points), the primary data-gathering electrodes that measure the activity of the different brain lobes (frontal, temporal, parietal, and occipital) are spread across the entire
Scalp.