Novelty and dopaminergic modulation of memory persistence: A tale of two systems

Adaptation to the ever-changing world is critical for survival, and our brains are particularly tuned to remember events that differ from previous experiences. Novel experiences induce dopamine release in the hippocampus, a process which promotes memory persistence. While axons from the ventral tegmental area (VTA) were generally thought to be the exclusive source of hippocampal dopamine, recent studies have demonstrated that noradrenergic neurons in the locus coeruleus (LC) co-release noradrenaline and dopamine in the hippocampus, and that their dopamine release boost memory retention as well. Here, we propose that the projections originating from the VTA and the LC belong to two distinct systems that enhance memory of novel events. Novel experiences that share some commonality with past ones (‘common novelty’) activate the VTA and promotes semantic memory formation via systems memory consolidation. In contrast, experiences that bear only minimal relationship to past experiences (‘distinct novelty’) activate the LC to trigger strong initial memory consolidation in the hippocampus resulting in vivid and long-lasting episodic memories