Electroencephalograph (EEG) is an instrument used to record the electrical activities occurring in the brain.
The electrical activities are recorded in graphical form, and this graphical representation of the electrical activities is called as electroencephalogram. EEG measures the graded potentials on the cell and is used in the diagnosis of epilepsy, sleep diseases and many other.
Evoked response potential (ERP) allows to measure the electrical activity of many brain regions simultaneously. It is helpful in determining the different kinds of stimuli produced by different brain regions and the order in which the areas come into play.
Both the EEG and ERP are non-invasive, but ERP is less expensive than the other techniques.