Ž . International Journal of Psychophysiology 39 2001 241248 Gamma, alpha, delta, and theta oscillations govern cognitive processes Erol Bas ¸ ar a,b,  , Canan Bas ¸ ar-Eroglu c , Sirel Karakas ¸ b,d , Martin Schurmann a ¨ a Institute of Physiology, Medical Uni  ersity Lubeck, 23538 Lubeck, Germany ¨ ¨ b Tubitak Brain Dynamics Research Unit, Ankara, Turkey ¨ c Institute of Psychology and Cognition Research, 28334 Bremen, Germany d Institute of Experimental Psychology, Hacettepe Uni  ersity, Beytepe, Ankara, Turkey Abstract The increased interest in gamma oscillations, now widely regarded as functionally relevant signals of the brain, underlines the importance of the concept of event-related oscillations for bridging the gap between single neurons and neural assemblies. Taking this concept further, we review experiments showing that oscillatory phenomena such as alpha, theta, and delta responses to events are, just as the gamma band, strongly interwoven with sensory and cognitive functions. This review argues that selectively distributed delta, theta, alpha and gamma oscillatory systems act as resonant communication networks through large populations of neurons. Thus, oscillatory processes might play a major role in functional communication in the brain in relation to memory and integrative functions.  2001 Elsevier Science B.V. All rights reserved. Keywords: Delta; Theta; Alpha; Gamma oscillations; Sensory processing; Cognitive processing 1. Why this special issue A great change has taken place in Neuro- science. Brain scientists have recognized the im- portance of oscillatory phenomena and the func-  Corresponding author. Institute of Physiology, Medical University of Lubeck, Ratzeburger Allee 160, D-23538 Lubeck, ¨ ¨ Germany. Tel.: 49-451-500-4170; fax: 49-451-500-4171. Ž . E-mail address: erol.basar@deu.edu.tr E. Bas ¸ ar . tional EEG. This new development will not only govern improvements in Neuroscience within the next two or three decades, it will probably create the basic approach for the biophysical under- standing of brain machinery. At the beginning of the 1970s only few research scientists emphasized the importance of oscillatory brain activity. Now this branch of Neuroscience is rapidly growing. The reports in this special issue were collected from various laboratories by working with several colleagues from San Diego, Copenhagen, Van- 0167-876001$ - see front matter  2001 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 1 6 7 - 8 7 6 0 00 00145-8