 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.There is other psychophysical data, related to human behaviors, which can be tracked along with variations in brain activity; this data is generally defined as biofeedback.