[Show abstract][Hide abstract] ABSTRACT: Optimization of cognitive processing may depend on specific and distinct functions of the cortical cholinergic and noradrenergic systems. This investigation dissociates functions of cortical acetylcholine (ACh) and noradrenaline (NA) in arousal and visual attention by simultaneously measuring ACh and NA efflux in the rat prefrontal cortex during sustained attentional performance. The five-choice serial reaction time task was used to provide a continuous assessment of visuospatial attention. Previous studies using this task have established a critical role for the cortical cholinergic system in the detection of visual targets. However, selective lesions of the locus coeruleus noradrenergic system impair performance only when additional attentional demands are placed on the subject by distractors or temporally unpredictable targets. To test the hypothesis that the cortical noradrenergic system is particularly sensitive to novel task contingencies, we also assessed NA and ACh efflux in rats that been trained previously on the task but for whom the instrumental contingency coupling responding with stimulus detection and reward was abolished. Cortical ACh efflux showed a robust and task-related increase during established contingent performance. This response was significantly attenuated in noncontingent subjects, although it still exceeded pretask values. In contrast, NA efflux only increased transiently in contingent subjects after task onset but showed sustained elevations in noncontingent subjects on the first day when contingencies were changed. These data also implicate cortical ACh in aspects of attentional functioning but highlight a specific involvement of the cortical noradrenergic system in detecting shifts in the predictive relationship between instrumental action and reinforcement.
Full-text · Article · Aug 2001 · The Journal of Neuroscience : The Official Journal of the Society for Neuroscience
[Show abstract][Hide abstract] ABSTRACT: Recent studies have suggested a functional link between cortical cholinergic output and attentional task demands, whereby acetylcholine (ACh) release is regulated according to the outcome of ongoing behaviour. To explore this hypothesis we measured ACh efflux in the rat medial prefrontal cortex (mPFC) during between-session manipulations of the cognitive demands of an attentional task. Rats were trained to detect visual stimuli in a five-choice serial reaction time task (5-CSRTT) which involves sustained and divided attention. Following habituation to tethering and implantation with a microdialysis probe in the mPFC, rats were tested in the 5-CSRTT for three consecutive days, with different lengths of stimulus duration. During performance of the 5-CSRTT we measured robust, reproducible, task-related increases in ACh release in the mPFC across all sessions. Variations of the stimulus duration from the standard 0.5 s resulted in the predicted behavioural effects (reductions and increases in choice accuracy with 0.25 s and 5 s, respectively), but there was no evidence of either greater changes in ACh release in the more demanding condition or smaller changes in the less demanding condition. By contrast, in the session with 5-s stimulus duration there was a positive correlation between prefrontal cortical ACh efflux and the total number of trials completed. In summary, the present study shows that ACh efflux in the rat mPFC is increased during performance of a 5-CSRTT, but has found no evidence to support a specific relationship between cholinergic cortical output and attentional performance.
No preview · Article · Sep 2000 · European Journal of Neuroscience