Neuronal processes underlying rhythmic brain activity.

The neuroelectric activity of the brain provides a variety of instances of rhythmic events. The periodicity of such events ranges from milliseconds in the case of the firing of individual neurons t o circadian in the case of certain aspects of the "sleep" EEG. This paper will (be devoted t o a discussion of (i) methodological approaches to the detection and description of s6me of the shorter period rhythmic events, (ii) the nature of the underlying neuronal activity which generates the rhythmicity, and (iii) hints concerning the significance of such rhythmic activity for behavior. The apparent frequencies of the electrical activity of the brain are often functions of the technical capabilities of the devices which are used to make the recordings. For exemple, electrwncephalogrrams are usually made with amplifiers which exclude frequencies at both the high and low ends of the spectrum. Slow events (less than 1 Hz) and rapid events (above 50 Hz) are usually not recondd. Direct-coupled amplifiers with high frequency cutoffs in the kilohertz range, together with "non-polari-zable" glass micropipette recording electrodes permit a less restricted range of neuronal frequencies to be recorded. In recent years, these more sophisticated techniques have been applied t o recordings made in animals during "spontaneous" or trained behavior, as well as in "acute" p r q a-rations. (To a very limited extent, some of these techniques have been used in humans, see 1). By the use of microelectrode recordings and DC amplifiers, spontaneous and evoked rhythmic events in the cerebral cortex and in certain subcartical structures have been shown to be related t o synaptic processes in individual cerebral neurons. The precise form of