If C4 must be relocated 4mm anteriorly due to a central scalp lesion, what should happen to C3?

The correct response involves adjusting the position of C3 in relation to the alteration made to C4. When C4 is moved 4 mm anteriorly due to a central scalp lesion, maintaining the relative positions of the electrodes is important for the consistency and accuracy of the EEG recording.

C4 and C3 are placed symmetrically on the scalp, and the International 10-20 system dictates specific distances between electrodes based on anatomical landmarks. By relocating C4 anteriorly, it is essential to also relocate C3 to maintain the symmetrical relationship between these electrode sites. Thus, moving C3 4 mm anteriorly ensures that the electrodes continue to reflect the same relative spatial configuration as intended in the standard placement guidelines, preserving the integrity of the recordings.

Making no changes to C3 would disrupt the balance between the electrodes, while relocating it posteriorly or changing the electrode placement entirely would place further inconsistencies in the electrode positioning, potentially leading to inaccurate EEG readings. Keeping the correct relative positioning of the electrodes is crucial for interpreting brain wave activity accurately.