What is the distance from fz to pz as a percentage of the distance between nasion and inion?

The distance from the frontal electrode site at Fz to the parietal electrode site at Pz is indeed approximately 40% of the overall distance between the nasion (the bridge of the nose) and the inion (the bony prominence at the back of the skull). This measurement is taken based on the standardized 10-20 electrode placement system used in EEG, which is designed to provide reliable and consistent electrode positioning across different individuals.

In this system, the nasion to inion distance serves as a reference for calculating the placement of electrodes on the scalp. The 10-20 system specifies that different electrode placements correspond to set percentages of the nasion-inion length, with Fz and Pz being positioned along the midline of the scalp. The specific 40% measurement reflects the established anatomical proportions that guide electrode placement, ensuring that it is both functional and reproducible across different EEG recordings.

Understanding these anatomical landmarks and their proportions is essential for anyone involved in EEG practice, as accurate electrode placement can significantly affect the quality and interpretability of EEG data.