Electrodes.
The electrical potentials of the brain are quite small and their electrical field may be restricted. Detecting these potentials is difficult especially as the distance between the electrode and the generator increases. Noninvasive electrodes only 'sample' the electrical activity synchronized over a large area of the brain. The international 10/20 system of electrode placement, the T1,T2 electrodes and other more closely placed electrodes record activity generated mainly from the brain convexities. Nasopharyngeal, ethmoidal, and sphenoidal electrodes record activity generated primarily from basal structures. Invasive electrodes including epidural and subdural electrode arrays and depth electrodes permit detection and precise localization of electrical activity generated from deep or relatively small brain regions.
D000200:Action Potentials; D001921:Brain / Q000502:physiology; D004553:Electric Conductivity; D004566:Electrodes / Q000592:standards; D004567:Electrodes, Implanted; D004569:Electroencephalography / Q000379:methods*; D004827:Epilepsy / Q000175:diagnosis; D005071:Evoked Potentials; D006801:Humans; D008433:Mathematics; D008839:Microelectrodes; D012535:Scalp / Q000502:physiology; D012886:Skull / Q000502:physiology