["Noise" in brain electrical activity. I. Basic research findings, cognitive processes]

For those who use electrophysiological methods the "neuronal noise" generated by the nervous system is well known and is usually regarded as an annoying phenomenon. Compared to this aperiodic signal, a much larger body of information has been accumulated to that which can be defined by oscillatory peaks in the conventional spectral plots both regarding basic research and also related to its role in cognitive processes. In this review the most important theoretical and technical aspects (types of noise, the generation mechanism and measurement of the so-called pink noise, stochastic resonance, importance of noise in synchronization processes) are discussed. After considering observations regarding neuronal noise the most important investigations related to the role of noise in cognitive processes are reviewed.