The VTA is widely implicated in reward circuitry of the brain, in that stimuli with rewarding effect often promote the discharge of dopaminergic neurons in this region and consequently an instantaneous release of dopamine from the synaptic terminals.  The increase of dopamine normally associated with positive emotions has been well known to regulate various forms of learning and memory (e.g. stimulus-response association learning, reinforcement learning and working memory etc.).  However, it remains elusive how dopamine can influence the so called episodic memory that relies on the hippocampal formation.  Utilizing a combination of optogenetics, in vivo and in vitro electrophysiological techniques as well as behavioral tests, Prof. Mu’s team explored the role of dopamine in the dentate gyrus of the hippocampus and the underlying mechanisms.  By controlling electrical activities of dopaminergic neurons in the VTA with the optogenetic tool to mimic reward-induced dopamine release, they found that dopamine signals induced a long-term depression of cortical inputs to the dentate gyrus and diminished theta oscillations in this area.  In subsequent behavioral experiments, preexposure to a natural reward suppressed hippocampus-dependent memory formation, with an effective time window consistent with the duration of dopamine-induced changes of dentate activity.  This result indicates that dopamine in the dentate gyrus may impair postreward learning and reduce the interference of subsequent events, thereby allowing the preferential encoding of information received before reward into memory.  Overall, this study offers a new thought for studying regulation of hippocampus-dependent memory by dopamine.