 These variations in electrical potential can be recorded with the use of contact electrodes; in most academic situations they are connected to a signal amplifier and an inkjet instrument that reacts to the variations of potential and amplitude of the input data.This instrument, commonly known as electroencephalograph, has been of the utmost importance regarding studies on the functioning of cerebral activity during the awakened state of an individual, the sleeping state, emotional states, and during physiological and psychological disturbances.The recorded data, electroencephalogram, are permanent memories of a distinct period of cerebral activity.