Mesolimbic interaction of emotional valence and reward improves memory formation

Animal studies suggest that dopaminergic neuromodulation is critical for hippocampal memory formation. Compatible with this notion, recent functional imaging evidence in humans showed that reward modulates the hippocampus-dependent formation of episodic memories through activation of areas belonging to the mesolimbic, dopaminergic system, including the ventral striatum and substantia nigra/ventral tegmental area (SN/VTA). However, the amygdala is also closely embedded within this mesolimbic circuitry with reciprocal connections to the SN/VTA, raising the possibility that emotionally valenced stimuli might also interact with hippocampal encoding through dopaminergic neuromodulation. By the same token, emotional processing in the amygdala,might be affected by reward-related processing in the mesolimbic system. In an event-related functional magnetic resonance imaging study, reward-related activity in the ventral striatum was enhanced by the concurrent presentation of emotionally positive but not emotionally negative stimuli. Emotional processing in the amygdala, on the other hand, was not affected by reward. One day after study, recollection of the positive stimuli was better when they were associated with reward at encoding as compared with unrewarded positive stimuli. The findings are compatible with the notion that the output of the reward system and memory formation in the hippocampus is influenced by positive emotional valence and suggest that the ventral striatum is a key structure for this modulation. (c) 2007 Elsevier Ltd. All rights reserved.