The EEG was discovered in the 1920’s and applied in humans by Hans Berger, a psychiatrist. The field was touted as likely to give the psychiatric professionals an insight into the brain’s function, though failed in producing this.
The electrical patterns were found to have neurological correlates in the 1930’s for some disorders, such as epilepsy and tumors in work by Frederick Gibbs, MD, and Charles Yeager, MD as well as others. The 1940’s and 50’s found the instrumentation advancing, with commercially available equipment fostering establishment of laboratories throughout the nation.
The frequency patterns seen in the EEG have been divided into bands, with somewhat arbitrary division into the standard bands of delta, theta, alpha and beta. The frequency bands, however, are to this day still not set as a standard, with the resultant confusion if the names and not the detailed frequency parameters are used.
The delta band starts as low as the bandpass filter will allow, with the upper limit set at 3.5 or 4. Theta starts at 4 and goes to 7 (or less properly to 8). Alpha starts at 7-8 and goes to 12-13, with beta being the desynchronized faster activity above alpha, occasionally divided into beta subtypes. Gamma, or “40 Hz”, is an area of current interest, and is being associated with neural network “binding”.
In the 1960’s and the 1970’s the digitizing of the EEG was undertaken, with the subsequent computer analysis of this data. The original aspiration of Berger and the psychiatric community only then began to see the correlation of the EEG with psychiatric conditions, as well as the brain’s detailed response to medication intended to treat these disorders.
Though medication effects in the EEG were previously reported, their presence was merely an artifact in the interpretation of the EEG, not able to be systematically studied.