The hippocampal formation is traditionally viewed as having a feed-forward,unidirectional circuit organization which promotes propagation of excitatory processes.While the substantial forward projection from hippocampal CA1 to the subiculum has been very well established,accumulating evidence supports the existence of a significant back-projection pathway comprised of both excitatory and inhibitory elements from the subiculum to CA1.Based on these recently updated anatomical connections,such a back projection could serve to modulate information processing in hippocampal CA1.In this talk,I will present new circuit mapping and functional studies of the non-canonical subicular projections to CA1.New insights into this understudied pathway will improve our understanding of how the subiculum interacts with CA1 to regulate hippocampal circuit activity and learning and memory behaviors.