Ventral hippocampal CA1 and CA3 differentially mediate learned approach-avoidance conflict processing

The ventral hippocampus is thought to play a key role in the resolution of approach-avoidance conflict, a scenario that arises when stimuli with opposing valences are present simultaneously. Little is known, however, about the contributions of specific hippocampal sub-regions in this process, a critical issue given the functional and anatomical heterogeneity of this structure. Using a non-spatial cue-based paradigm in rats, we found that transient pharmacological inactivation of ventral CA1 produced an avoidance of a conflict cue imbued with both learned positive and negative outcomes, whereas inactivation of the ventral CA3 resulted in the opposite pattern of behavior, with significant preference for the conflict cue. In contrast, dorsal CA1- and CA3-inactivated rats showed no change in conflict behavior. Our findings provide important insight into the functions and circuitry of the ventral hippocampus by demonstrating that the ventral CA1 and CA3 subserve distinct and opposing roles in approach-avoidance conflict processing.