Paradox of pattern separation and adult neurogenesis: A dual role for new neurons balancing memory resolution and robustness

•Memory involves a competition between pattern separation and pattern completion.•Adult-born dentate granule cells act as broad input integrators and network sparsifiers.•Adult neurogenesis permits the dynamic regulation of memory resolution and robustness. Hippocampal adult neurogenesis is thought to subserve pattern separation, the process by which similar patterns of neuronal inputs are transformed into distinct neuronal representations, permitting the discrimination of highly similar stimuli in hippocampus-dependent tasks. However, the mechanism by which immature adult-born dentate granule neurons cells (abDGCs) perform this function remains unknown. Two theories of abDGC function, one by which abDGCs modulate and sparsify activity in the dentate gyrus and one by which abDGCs act as autonomous coding units, are generally suggested to be mutually exclusive. This review suggests that these two mechanisms work in tandem to dynamically regulate memory resolution while avoiding memory interference and maintaining memory robustness.