THE CEREBRAL-CORTEX OF THE RAT AND VISUAL ATTENTIONAL FUNCTION - DISSOCIABLE EFFECTS OF MEDIOFRONTAL, CINGULATE, ANTERIOR DORSOLATERAL, ANDPARIETAL CORTEX LESIONS ON A 5-CHOICE SERIAL REACTION-TIME-TASK

Dissociable effects of bilateral excitotoxic lesions of different regi ons of the rat neocortex, including medial prefrontal and anterior cin gulate cortices, were investigated in a five-choice serial reaction ti me task that provides several indices of the accuracy and speed of att entional function. Whereas medial prefrontal cortical lesions impaired performance of the task as revealed by a reduction in choice accuracy , an increase in the latency to respond correctly to the visual target and enhanced perseverative responding, lesions of the anterior cingul ate cortex specifically increased premature responding. By contrast, l ateral frontal cortical lesions did not significantly disrupt baseline performance of the task, but rather increased the latency to respond correctly to the visual target during various behavioral manipulations , for example, when the length of the intertrial interval was varied u npredictably and during interpolation of distracting bursts of white n oise. Lesions of the parietal cortex failed to disrupt any aspect of t ask performance investigated. These behavioral effects in the five-cho ice task were compared with the effect of these same lesions on acquis ition and retention of a one-trial passive avoidance task. The main fi nding from this paradigm was that lesions of the lateral frontal corte x produced a significant disruption to the retention of passive avoida nce, which stands in marked contrast to the successful retention obser ved by animals of the other lesion groups. In addition, this pattern o f results reveals that the ''disinhibitory'' effect of cingulate corte x lesions are relatively specific to the five-choice attentional task. Finally, the results of the present study are compared with the findi ngs of previous experiments using the five-choice task, which have exa mined the effect of selective manipulations of the ascending noradrene rgic, cholinergic, dopaminergic, and serotonergic projections. In part icular, the deficits in attentional function observed following cholin ergic lesions of the nucleus basalis magnocellularis appear to be attr ibutable to cholinergic denervation of the medial frontal cortex. Thes e results are discussed in terms of the role of parallel distributed n eural systems within the neocortex that mediate continuous attentional performance in the rat.