Abstract

1. Introduction

2. The construct "arousal"

3. Functions of brainstem afferents

4. Conclusions

References

Discussion
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Numerous experiments, using a variety of behavioral paradigms for the assessment of different aspects of attention, have concluded that the integrity of cortical cholinergic inputs is required for the detection, selection and processing of stimuli and associations. Furthermore, decreases and increases in activated cortical acetylcholine (ACh) release are associated with bidirectional changes in sustained or divided attentional performance. Moreover, increases in the demands on attention, but not changes in related non-cognitive variables, are correlated with increases in cortical ACh efflux. The hypothesis that cortical cholinergic inputs mediate attentional abilities appears to be in conflict with the more traditional notions that cortical cholinergic inputs represent a rostral extension of the ascending 'arousal' systems. Neuropharmacological studies from our laboratories suggest that noradrenergic inputs permit glutamatergic inputs from forebrain areas to potently stimulate basal forebrain cholinergic neurons via NMDA receptors. However, once the cholinergic neurons are stimulated via NMDA receptors, noradrenergic inputs do not further modulate the activity of this projection. Additional data and speculations suggest that noradrenergic inputs may gate the excitability of basal forebrain cholinergic corticopetal projections in situations requiring the biased processing of novel or stress-like stimuli, or stimuli with strong affective qualities. These data provide the basis for the development of specific hypotheses about the interactions between the defined cognitive functions of basal forebrain cholinergic inputs and the more global modulatory mechanisms mediated via brainstem afferents of these neurons. Supported by PHS Grants NS32938, MH57436, NS37026 and MH01072.

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Presentation Number SAsarter0163
Keywords: Basal forebrain, Attention, Acetylcholine, Noradrenaline, Arousal