Organization of spontaneous electrical activity in the neocortex.

Publisher Summary This chapter discusses the intrinsic organization of cortical activity. There is a general agreement about several aspects of the cortical bioelectrical organization. It is admitted, for instance, that electroencephalography (EEG) waves are related chiefly to postsynaptic potentials generated in pyramidal cells. These potentials are of a long-lasting type, particularly the inhibitory ones. It is unlikely that changes in glial membrane potential act as a generator for the usual EEG waves. Except in certain situations, intracellular recordings do not show a general relationship between the polarity of EEG waves and, respectively, the depolarization or hyperpolarization of the cortical neurons. However, by taking into account action potential discharges during spontaneous EEG activity, it becomes possible to demonstrate a clear-cut statistical relationship between several types of waves and elementary cellular phenomena. This relationship is preserved in an experimentally isolated cortical gyrus and has also been established for the human cortex. The presence of an EEG wave implies synchronous and largely homogenous activity in a population of pyramidal cells. The amplitude of the wave is related then to the number of neurons simultaneously invaded by the same postsynaptic phenomenon. Another property of a given EEG wave is to occupy a definite surface area of the cortex. This involvement of a cortical sector may be virtually simultaneous, or else a small delay can separate the occurrence of the wave in different cortical regions. Mechanisms underlying cortical slow wave synchronization are located at least partially within the cortex itself, although the role of thalamic nuclei is firmly established for other types of rhythmic bioelectric activities.

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