The retrospectroscope: electrocorticography

Recording the electrical activity of the exposed brain, known as an electrocorticogram (ECoG), has had a long history. Multichannel recordings from the exposed brain cortex of conscious human patients as a diagnostic procedure to localize epileptic foci began in the early 1940s. Two centers, one at McGill University and the other at Harvard University launched this new field. Relatively unrecognized at that time were the severe requirements for recording microvolt signals in the electrically hostile environment of the operating room. Not only did the electrodes have to be electrically stable initially, but they had to be stable and noise-free after steam sterilization. In 1945, one of the authors (LAG) joined the staff of the Montreal Neurological institute and the Department of Electrical Engineering, both of McGill University, and became deeply involved with the development of ECoG equipment for permanent installation in Wilder Penfield´s operating room. The design goal was that the ECoG and electrodes would function on command. Because it required less than one half hour to steam sterilize the electrodes, a surgical procedure could be scheduled at any time, providing the ECoG and electrodes would perform on command