Electrogenesis of Slow Potentials of the Brain
The occurrence of slow fluctuations down to 0 Hz in the spectrum of EEG waves has been known since the early days of electroencephalography, when the bioelectric activity of the brain was recorded by means of galvanometers (cf. Brazier, 1963; O’Leary & Goldring, 1976). However, such measurements were frequently distorted by uncontrollable artifacts due, for instance, to changes in electrode potentials or in skin resistance. As a result, the origin and functional significance of slow potential fluctuations in the cerebral cortex attracted little attention for rather a long time, and only a few decades later did essential improvements in the available technical equipment lead to more intense studies on the problem (cf. O’Leary & Goldring, 1964). The observed “slow” bioelectric phenomena were most often labeled “slow potentials,” “ultraslow oscillations,” or “steady (standing, sustained) potentials.” A common feature of all these fluctuations in the frequency range between approximately 0.5 and 0 Hz is that they can reliably be recorded only by means of DC amplifiers. To avoid confusion, it has therefore been proposed that the potential changes in question be referred to as “DC potentials” (Caspers, 1974). This term will be used also in this paper, and the following presentation will not be restricted to the origin of slow potentials encountered in definite experimental situations, but will deal with the problem on a more general basis.
KeywordsDepression Cage Shrinkage Acetylcholine Crosscorrelation
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