ABSTRACT
Recording the net electrical activity of the brain by means of surface electrodes attached to the scalp is termed electroencephalography (EEG). Large numbers of cerebral cortical cells fire in synchrony and consequently their summed activity produces local field potentials (LFPs) big enough that they can be recorded with scalp electrodes. By using an array of electrodes, activity of different brain areas can be examined simultaneously. The recording may be monopolar—each scalp electrode measures the potential with respect to a distant indifferent electrode—or bipolar, in which the potential is measured between a pair of scalp electrodes. The LFPs vary in frequency and the frequency ranges are conventionally grouped: 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 example, sleep, arousal, or learning. 340Sensory, perceptual or cognitive stimuli can generate brief fluctuations in the EEG termed evoked potentials (EPs) or event-related potentials (ERPs). These potentials are used to investigate the context, timing, and brain regions implicated in the process of interest.
