Varieties of inhibition: manifestations in cognition, event-related potentials and aging.

Inhibition and facilitation are the driving forces of selective attention. Some important and still unresolved conceptual issues with respect to facilitation and inhibition are: (a) are they separate processes with different neural substrates (b) what is their time course and (c) what is their temporal locus: do they operate at the level of early sensory, central or response-related selection processes? In this introductory article we present a overview of relevant experimental paradigms that are also (in part) reflected in the contributions of this special volume, and discuss the major behavioral and psychophysiological findings from which inhibitory processes have been inferred. The global pattern of the results indicates that there are multiple inhibitory systems and processes in the central nervous system that may be expressed in many different ways. Our overview of paradigms together with the aging-related literature leads us to propose a framework for conceptualizing inhibitory processes in terms of three distinct but interacting neural systems at the level of anterior and posterior cortices and the brain stem.