Are cognitive processes manifested in event-related gamma, alpha, theta and delta oscillations in the EEG?

Gamma oscillations, now widely regarded as functionally relevant signals of the brain, illustrate that the concept of event-related oscillations bridges the gap between single neurons and neural assemblies. Taking this concept further, we review experiments concerning oscillatory responses to events (in the alpha, theta and delta ranges) as possible correlates of sensory and cognitive functions. It is argued that selectively distributed delta, theta, alpha and gamma oscillatory systems act as resonant communication networks through large populations of neurons, with functional relations to memory and integrative functions.