Electro-oculogram

A record of the electrical changes in the skin around the eye as it moves. The eyeball carries a small voltage between front and back, so its movements can be picked up by electrodes.

In 1953 Eugene Aserinsky and Nathaniel Kleitman recorded eye movements with electrodes above and below and on either side of one eye. To tell eye movements apart from brain waves and muscle activity they compared the trace with one from the forehead, watched sleepers directly under dim light, and filmed two of them without waking them^[1].

These recordings revealed the periods during sleep when both eyes move together in rapid jerks, the periods later called REM sleep^[1].