MODULATION OF COGNITIVE-PROCESSES BY TRANSSYNAPTIC ACTIVATION OF THE BASAL FOREBRAIN

Each of the neurotransmitter-specific afferents to the basal forebrain (BF) carry different types of information which converge to regulate the activity of cholinergic projections to telencephalic areas. Brains tem monoaminergic and cholinergic inputs are critical for context-depe ndent arousal. GABAergic afferents are gated by a variety of ascending and descending systems, and in addition provide an intrinsic control of BF output excitability. Corticofugal glutamatergic inputs represent reciprocal connections from sites to which BF afferents project, and carry information about the current level of cortical processing inten sity and capacity. Peptidergic inputs arise from hypothalamic sources and locally modulate BF output as a function of motivational and homeo static processes. The significance of these afferent systems can be st udied by examining the behavioral consequences of infusion into the BF of drugs that act on the specific receptor systems. Although traditio nal analyses suggest that the BF has many behavioral functions that ca n be subdivided regionally, an analysis of studies employing transsyna ptic approaches lead to the conceptualization of the BF as having a un iform function, that of maximizing cortical processing efficiency. The BF is conditionally active during specific episodes of acquisition an d processing of behaviorally significant, externally-derived informati on, and drives cortical targets into a state of readiness by reducing interference and amplifying the processing of relevant stimuli and ass ociations, thus allowing for more efficient processing. This paper des cribes the transsynaptic approach to studying BF function, reviews the neurobiological and behavioral consequences of altering neurotransmit ter-specific inputs to the BF, and explores the functional significanc e of the BF.