Neurogenesis: remembering all or forgetting some.

Research over the last 20 years has begun to elucidate the importance of adult neurogenesis in cognition. Three studies recently asked what might be happening to memories formed before neurogenesis in the hippocampus (Akers KG, Martinez-Canabal A, Restivo L, Yiu AP, De Cristofaro A, Hsiang HL, Wheeler AL, Guskjolen A, Niibori Y, Shoji H, Ohira K, Richards BA, Miyakawa T, Josselyn SA, Frankland PW. Science 344: 598-602, 2014; Epp JR, Silva Mera R, Köhler S, Josselyn SA, Frankland PW. Nat Commun 7: 10838, 2016; Kodali M, Megahed T, Mishra V, Shuai B, Hattiangady B, Shetty AK. J Neurosci 36: 8112-8122, 2016). These studies found conflicting results: running (which increases neurogenesis) induced forgetting in two studies, but there was no difference in memory retrieval after exercise in another. To reconcile these studies, one must understand the processes behind memory maintenance and recall and consider context, species, and other factors.