Where are the reference electrodes M1 and M2 placed on the head?

Where are the reference electrodes M1 and M2 placed on the head?

• A. On the earlobes
• B. On either side of the Cz electrode placement
• C. Both "on the earlobes" and "in the preauricular area behind the ear"
• D. In the preauricular behind the ear

Answer: (D)

Reference electrodes M1 and M2 are placed on the mastoid processes behind each ear. This mastoid location provides a relatively quiet, electrically stable reference point, letting the scalp electrode signals reflect true brain activity rather than common reference noise. In practice, M1 sits behind the left ear and M2 behind the right ear. Placing references on the earlobes or at central sites like Cz would introduce more brain signal or muscle noise into the reference, which is not desirable. So the correct placement is behind the ears in the mastoid region.

Reference electrodes M1 and M2 are placed on the mastoid processes behind each ear. This mastoid location provides a relatively quiet, electrically stable reference point, letting the scalp electrode signals reflect true brain activity rather than common reference noise. In practice, M1 sits behind the left ear and M2 behind the right ear. Placing references on the earlobes or at central sites like Cz would introduce more brain signal or muscle noise into the reference, which is not desirable. So the correct placement is behind the ears in the mastoid region.