Electroencephalography, or the recording of action potentials of the brain, is being utilized increasingly as a laboratory aid in studying a variety of cerebral dysfunctions.
Hans Berger1 first reported in 1929 that he had recorded spontaneous electric discharges from the human brain and established that this electric activity originates in the neurons.
Satisfactory amplification of the extremely small potential changes depends upon a very sensitive and delicate instrument capable of responding to minute potential changes. The instrument consists of a preamplifier, an amplifier, and a recording pen. The most satisfactory instruments consist of several channels and are able to record voltage changes simultaneously from several points. The instrument can record frequencies of 1 to 40 per second and will respond to changes in potential from 5 to 300 microvolts. Each record is carefully standardized before and after the recording so that voltage of the waves can be determined, and the recording paper runs at a constant speed so that the frequency of the waves can be counted.
The usual record takes only thirty to sixty minutes to record and is taken without pain or discomfort to the patient. The patient is usually placed in a shielded room to exclude extraneous electrical impulses which might produce artifacts in the record. The record is made with the patient relaxed but not asleep, as free from all sensory stimuli as possible, and within two hours after a meal. The patient should be free from the effect of medication before the record is made.