Electroencephalography (EEG)

Recording the net electrical activity of the brain through means of surface electrodes attached to the scalp is termed electroencephalography EEG. Huge numbers of cerebral cortical cells fire in consequently and synchrony their summed activity produces LFPs (local field potentials) big enough in which they can be recorded with scalp electrodes. Through using an array of electrodes, activity of different brain fields can be examined concurrently. The recording may be monopolar each scalp electrode measures the potential with respect to a distant indifferent electrode or bipolar, in that the potential is measured among a pair of scalp electrodes. The LFPs vary in frequency and the frequency ranges are conventionally grouped that are: alpha (8–13 Hz), beta (13–30 Hz), delta (1–4 Hz), theta (4–7 Hz). Activity in these frequency bands correlates with behavioral state, for instance, arousal, sleep or learning.

Sensory, perceptual or cognitive stimuli can generate short fluctuations in the EEG termed evoked potentials (EPs) or event-related potentials (ERPs). These potentials are used to investigate the circumstance, timing and brain regions implicated in the procedure of interest.