Electroencephalography

Electroencephalography (EEG) is the measurement of electrical activity produced by the brain as recorded from electrodes placed on the scalp.
Just as the activity in a computer can be perceived on multiple different levels, from the activity of individual transistors to the function of applications, so can the electrical activity of the brain be described on relatively small to relatively large scales. At one end are action potentials in a single axon or currents within a single dendrite, and at the other end is the activity measured by the scalp EEG.
The data measured by the scalp EEG are used for clinical and research purposes. A technique similar to the EEG is intracranial EEG (icEEG), also referred to as subdural EEG (sdEEG) and electrocorticography (ECoG). These terms refer to the recording of activity from the surface of the brain (rather than the scalp). Because of the filtering characteristics of the skull and scalp, icEEG activity has a much higher spatial resolution than surface EEG.