Electroencephalography

First demonstrated by the German psychiatrist and neurologist Hans Berger in 1924 (Karbowski, 2002), electroencephalography (EEG) is the measurement of brain electrical activity via recording electrodes placed on the scalp. Rhythmic variations in this electrical activity assume the form of waves that vary with respect to two key parameters: frequency (the speed of the wave cycles) and amplitude (the size of the wave). A number of distinct rhythms, based on these parameters and denoted using Greek letters, have been identified and are systematically related to variations in consciousness. For instance, the delta rhythm consists of very tall, slow waves that are apparent during deep sleep. The alpha rhythm consists of shorter, faster waves that are apparent during states of relaxation. The beta rhythm consists of short, very fast waves that are apparent during periods of effortful cognitive exertion.