The EEG test, electroencephalography, is a 20- to 45-minute procedure that provides information about brain function with the use of electrodes. Marked with a grease pencil, measurements of circumference calculate where electrodes will be placed on the scalp. Equidistant electrodes ensure an exact recording of the entire brain. The scalp is cleaned with a slightly abrasive paste to improve recording quality. Oil and hair products on the scalp could hinder recording quality. A conductive cream on the electrodes allows electrical activity to pass from scalp to the computer showing a visual guide to activity in individual areas. The technologist follows an accurate procedure when placing electrodes, using previous measures and marks to avoid omitting a spot. After all 24 electrodes are applied, the EEG machine records the brain's activity by reading electric current that travels from the scalp to the machine. No electricity flows from the machine to the brain. Information regarding various health conditions besides seizures is needed to interpret the EEG accurately. The technologist notes activities such as sleep, swallowing or blinking. In this peaceful environment, sleep may provide additional information. After approximately 10 minutes, tests are performed: opening and closing the eyes and deep, fast breathing (hyperventilation) for five minutes. Near the end of the test, an intermittent strobe flashes into closed eyes. These various procedures may affect brain wave activity, providing helpful information to the neurologist.