What does C4 refer to in the 10-20 electrode system?

In the context of the 10-20 electrode system, C4 refers specifically to an electrode placed over the right central area of the scalp. The 10-20 system is a standardized method used for positioning electrodes on the scalp for EEG monitoring and neurophysiological studies, and the naming convention uses letters and numbers to denote specific regions.

The letter "C" signifies that the electrode is located on the central line of the scalp, which runs from the front to the back. The number "4" indicates its position relative to midline landmarks; in this case, C4 is situated to the right of the midline, making it over the right central area of the scalp.

Understanding this nomenclature is essential for accurately placing electrodes for recording and interpreting brain activity, as it helps ensure consistent and reliable results across different testing environments and studies.