ABSTRACT
One major source of information about neurophysiological activity in the normal human derives from electrical reactions recorded from the surface of the skull. The first tracings of electrical activity from over the human skull were published by Hans Berger, although he had difficulty in finding acceptance for his conclusions among the scientific community. Brain waves have been classified primarily by their frequency range, possibly because the amplitude values are so much more variable among people. The brain, not being equipotential throughout, produces potential differences that may be sensed by EEG electrodes. As with electromyograms, the main source of resistance when using surface electrodes is the skin—in this case, the skin on the scalp. Efforts to develop lawful relationships involving the ever-changing patterns of electrical gradients generated by the brain have resulted in a wide variety of methods of analysis.
