Short-term memory for food reward magnitude: the role of the prefrontal cortex

Memory for magnitude of reinforcement was assessed in rats using a go/no-go short-term memory paradigm. During the task's study phase rats were given a piece of cereal comprised of either 25 or 50% sugar. For all trials, one of the cereal types was designated positive, the other negative. On the ensuing test phase the rat was presented with an object which covered a food well. If a positive food reward was given during the study phase, a second food reward was placed beneath the object. No food reward was placed under the object if the study phase consisted of a negative food reward. Latency to object displacement was used as the measure of performance. Following the establishment of a significant difference between latency to approach the object with reward compared to latency to approach the object without reward, rats were given either agranular insular cortex, anterior cingulate cortex, pre- and infralimbic cortex or control lesions. Agranular insular cortex lesioned animals demonstrated a mild post-surgery impairment. Trials consisting of 10 and 20 s delays between the study and test phases were then introduced. Delays exacerbated the previous deficit of the agranular insular cortex lesion group, but had little effect on the other lesion groups. All animals transferred to a new set of cereals containing 25 and 50% sugar and exhibited taste preferences to sugar solutions of different concentrations. These results indicate that the agranular insular cortex may play an important role in the processing of affect-laden information within a prefrontal cortex short-term or working memory system.