CORTICAL ACETYLCHOLINE AND PROCESSING CAPACITY - EFFECTS OF CORTICAL CHOLINERGIC DEAFFERENTATION ON CROSSMODAL DIVIDED ATTENTION IN RATS

The effects of 192 IgG-saporin-induced lesions of the corticopetal cho linergic neurons of the basal forebrain on divided attention were asse ssed in rats. Divided attention was measured using an operant version of the crossmodal divided attention paradigm. This task utilized the p ropositional response rules of visual and auditory conditional discrim inations. Presentation of only visual or only auditory stimuli constit uted performance under the condition of modality certainty. Conversely , the presentation of a randomized sequence of all possible stimuli re presented the condition of modality uncertainty and was hypothesized t o tax processing capacity. A single session was composed of two unimod al blocks of trials (20 trials each), followed by a bimodal block of 6 0 trials. Animals were extensively trained in this task and baseline p erformance was characterized by high response accuracy (> 80%) in both conditions. Compared to unimodal trials, the response latencies in th e bimodal block of trials were 160 ms longer. The lesion of the cholin ergic system increased the response latencies exclusively under the co ndition of modality uncertainty. The extent of the lesion-induced decr ease in cortical cholinergic fiber density correlated highly with the differences between uni-and bimodal response latencies. These results demonstrate a lesion-induced decrease in processing capacity and a pre servation of response accuracy at the cost of response latency, i.e., a speed-accuracy tradeoff. Cortical acetylcholine is suggested to medi ate the regulation and allocation of processing resources. (C) 1997 El sevier Science B.V.