DISSOCIABLE EFFECTS OF AMPA-INDUCED LESIONS OF THE VERTICAL LIMB DIAGONAL BAND OF BROCA ON PERFORMANCE OF THE 5-CHOICE SERIAL REACTION-TIME-TASK AND ON ACQUISITION OF A CONDITIONAL VISUAL-DISCRIMINATION

The aim of the present study was to investigate the role of the cholin ergic innervation of the cingulate cortex in visual attentional functi on and acquisition of a visual conditional discrimination task. Follow ing AMPA pha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid) lesi ons of the vertical limb diagonal band of Broca (VDB) which provides t he main cholinergic projection to cingulate cortex, animals were not s ignificantly impaired on the 5-choice serial reaction time task. This task, which provides a continuous performance test of visual attention , has previously been shown to be sensitive to AMPA lesions of the nuc leus basalis magnocellularis (nbM). In contrast to the results obtaine d for visual attentional function, lesions of the VDB did significantl y affect the acquisition of a visual conditional discrimination. While showing a significant facilitation in the early learning stage of acq uiring this task animals with lesions of the VDB were significantly im paired during the late stages of learning this task. This late learnin g deficit was not the result of the animals being unable to learn the task due to the presence of the lesion throughout task acquisition as the results of a second experiment revealed that when animals were pre -trained to 70% accuracy on the task and then lesioned, the impairment in late learning was still apparent. In light of the results presente d in the accompanying paper (Bussey et al., Behav. Brain Res., 1996), these results suggest that the early learning effects may be due to ch olinergic denervation of the anterior cingulate cortex while the late learning effects may be due to denervation of the posterior cingulate cortex. Taken together with previous work indicating a role for the nb M cholinergic system in visual attentional function, these results sug gest a role for the cholinergic innervation of the cingulate cortex in conditional learning but not for continuous attentional performance.