DO CORTICAL AND THALAMIC BIOELECTRIC OSCILLATIONS HAVE A FUNCTIONAL-ROLE - A BRIEF SURVEY AND DISCUSSION

This paper first briefly describes rhythmic bioelectric oscillations t hat can be recorded from the neocortex (particularly in cats). This de scriptive section is followed by a review of the mechanisms whereby th ese rhythms are generated, and a section in which we try to go beyond the purely correlative aspect and discuss the possible functional role of synchronized oscillations in thalamo-neocortical channels. Based o n the literature data, it seems that two distinct and opposite roles c an be attributed to these oscillations: either to lower the level of a wareness,such as in slow wave sleep, when these oscillations are wides pread on the neocortex; or to contribute to perceptual processing, whe n these rhythms are more localized and possibly of a higher frequency. Electrocortical (ECoG) rhythmical activities have been known and desc ribed since the early days of electrophysiological explorations of the human and animal brain. Surprisingly though, little importance has ge nerally been attached to these oscillatory activities, except as indic ators of sleep stages in animals and humans and, in the case of the al pha rhythms (the first rhythm to be discovered in the thirties by Hans Berger), of a certain state of 'relaxation' in humans. Despite the we ll-accepted fact that the human alpha rhythm evidently occurs during w aking (even if it is in a 'relaxed' state), the idea has curiously pre vailed that the waking ('aroused') state in general is mostly characte rized by low voltage fast ('desynchronized') activity It is only more recently that some studies have suggested a functional importance of a variety of regular oscillatory activities that can be recorded from t he neocortex and/or from a variety of thalamic nuclei not only in the sleeping but also on the waking, behaving animal. This review consider s possible reasons indicating that these rhythmical activities are mor e than just epiphenomena. Our analysis is essentially restricted to th e cat, with only a very quick glance at other species.