For most of the past century the scientific consensus held that the adult human brain did not produce any new neurons... Recent work now suggests that one role may be to help the brain recover from traumatic brain injury.
Old and New Neurons Trade Roles to Aid Memory
Young granule cells help form new memories, but as they get older they switch roles to helping recall the past. Newer granule cells pick up the slack, taking on the role of helping to form new memories.