DISSOCIABLE EFFECTS OF ANTERIOR AND POSTERIOR CINGULATE CORTEX LESIONS ON THE ACQUISITION OF A CONDITIONAL VISUAL-DISCRIMINATION - FACILITATION OF EARLY LEARNING VS IMPAIRMENT OF LATE LEARNING

Two experiments investigated the effects of quinolinic acid induced le sions of the anterior and posterior cingulate cortices on the acquisit ion and performance of a conditional visual discrimination (CVD) task, in which rats were required to learn a rule of the type: ''If lights are flashing FAST, press the right lever; if SLOW press left''. In Exp eriment 1, animals with lesions of the anterior cingulate cortex (ANT group) demonstrated a significant enhancement in learning during the e arly stages of task acquisition. Conversely, animals with lesions of t he posterior cingulate cortex (POS group) were impaired in learning du ring the later stages of acquisition. There were no significant differ ences between the ANT and POS groups on the performance of the task wh en either variable inter-trial intervals or reduced stimulus durations were imposed. In Experiment 2, the specificity of the lesion effects for processes operative during the early and late stages of learning w as tested. Animals were trained to a criterion of 70% correct choices on two consecutive sessions prior to lesioning, and subsequently allow ed to continue to acquire the task to the mean asymptotic performance level of 85% correct choices on two consecutive sessions. Animals of t he POS group were impaired in learning during this later stage of task acquisition, thus replicating the pattern of results obtained in Expe riment 1. The animals in Experiment 2 were then tested following a 30- day retention interval and during extinction (removal of sucrose from the magazine). The extinction test revealed an impairment in the abili ty of animals in the ANT group to omit lever responses in the absence of reinforcement. These results indicate that the anterior and posteri or cingulate cortices are functionally dissociable, and suggest that t hey may form part of complementary, but competing, learning and memory systems.