Practical considerations in the positioning of EEG electrodes

Although the 10-20 system of the International Federation was originally proposed as a basis for discussion, there has been little published comment on its strengths and weaknesses or suggestions for its improvement. There are inherent ambiguities in the system, which cannot be applied strictly in accordance with the published specification unless the 4 measurements between the right and left preauricular points and the nasion and the inion are all equal. A study of the cranial measurements of 20 normal adults showed that this criterion was fulfilled to within a margin of 10% in less than half. Further, the standard placements of the 10-20 system cover less than 3/4 of the cerebral convexity. A study of fronto-temporal epileptiform phenomena in 100 subjects indicated that in the majority these were of maximum amplitude over the anterior temporal region, some 20 mm below the typical positions of F7 and F8. In the light of these and previous studies, modifications of the 10-20 system are suggested.