SELECTIVE ROLES FOR HIPPOCAMPAL, PREFRONTAL CORTICAL, AND VENTRAL STRIATAL CIRCUITS IN RADIAL-ARM MAZE TASKS WITH OR WITHOUT A DELAY

The hippocampus, the prefrontal cortex, and the ventral striatum form interconnected neural circuits that may underlie aspects of spatial co gnition and memory. In the present series of experiments, we investiga ted functional interactions between these areas in rats during the per formance of delayed and nondelayed spatially cued radial-arm maze task s. The two-phase delayed task consisted of a training phase that provi ded rats with information about where food would be located on the maz e 30 min later during a test phase. The single-phase nondelayed task w as identical to the test phase of the delayed task, but in the absence of a training phase rats lacked previous knowledge of the location of food on the maze. Transient inactivation of the ventral CA1/subiculum (vSub) by a bilateral injection of lidocaine disrupted performance on both tasks. Lidocaine injections into the vSub on one side of the bra in and the prefrontal cortex on the other transiently disconnected the se two brain regions and significantly impaired foraging during the de layed task but not the nondelayed task. Transient disconnections betwe en the vSub and the nucleus accumbens produced the opposite effect, di srupting foraging during the nondelayed task but not during the delaye d task. These data suggest that serial transmission of information bet ween the vSub and the prefrontal cortex is required when trial-unique, short-term memory is used to guide prospective search behavior. In co ntrast, exploratory goal-directed locomotion in a novel situation not requiring previously acquired information about the location of food i s dependent on serial transmission between the hippocampus and the nuc leus accumbens. These results indicate that different aspects of spati ally mediated behavior are subserved by separate, distributed limbic-c ortical-striatal networks.