Source derivation in clinical routine EEG.

A special multi-electrode derivation of the EEG signal was recently described by Hjorth (1975b). It is more selective than bipolar and common average reference derivations and is called source derivation. The present study aimed at testing the new method in routine EEG work and comparing the results with these obtained with conventional recording technique. EEGs were simultaneously recorded with the two techniques and visual and quantitative comparisons were made in 80 and 30 cases, respectively. Only in one EEG out of 80 was an abnormality detected in source, but not in conventional, derivations. In 25% of the records, however, focal abnormalities were somewhat more pronounced or epileptogenic potentials were sharper in source, than in conventional, derivations. It is concluded that the source derivation technique facilitates EEG interpretation in a significant number of cases.