FOLLOWING the initial exploratory period of electroencephalography, it became obvious that EEG, as a clinical diagnostic technique, could not differentiate between lesions on the basis of their pathological type. Nevertheless, it was apparent that the majority of focal processes were associated with high-voltage, slow-wave, or spiking activity and that, contrary to this, some foci were associated with low voltages. Most epileptic foci and tumors, for example, are of the high-voltage type. Because such lesions are also commonly associated with mirror foci and generalized slow-wave activity,1 which vary in prominence as the primary focus waxes and wanes, they have been referred to by some authors as "active" or "discharging" foci. Opposed to this have been the "inactive" or "quiescent" foci, characterized by areas of relatively low potential and associated with sizeable cortical processes, such as degenerative lesions, cysts, and cerebral gliosis.
Recognition of focal areas of low voltage, associated
Aird RB, Shimizu M. Neuropathological Correlates of Low-Voltage EEG Foci. Arch Neurol. 1970;22(1):75–80. doi:10.1001/archneur.1970.00480190079013
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