The canthomeatal line is also referred to as the orbitomeatal line and is defined as running from the lowermost point of the eye’s bony orbit to the preauricular point. In the image below the canthomeatal line is indicated by the red dashed line:
In 10-20 EEG placement, electrodes (typically 19-21 electrodes) all are placed above the cantomeatal line.
In contrast, high density EEG (128 – 256 electrodes) covers area on the scalp well below the canthomeatal line as shown in the image below:
A recent study from the University of Geneva shows this to be important for capturing activity originating from lower brain regions.