The EEG is a diagnostic method designed for the measuring of brain activity. Variations of voltage are deduced from the brain thus allowing inferences to the neurotransmission of the brain. The measurements are taken off of the surface of the patient’s head by way of electrode pads. The obtained waves are reproduced in a diagram. 
The EEG is needed for example to diagnose epilepsy (seizure disorder), encephalitis (inflammation of the brain), tumours of the brain, but also in case of headaches of all kinds, such as migraine, or unexplained vision disorders, imbalance etc.