Adult neurogenesis  Adult neurogenesis is the process in which neurons are generated from neural stem cells in the adult. This process differs from prenatal neurogenesis. In most mammals, new neurons are born throughout adulthood in two regions of the brain:  More attention has been given to the neurogenesis in the dentate gyrus than in the striatum. In rodents, many of the newborn dentate gyrus neurons die shortly after they are born, but a number of them become functionally integrated into the surrounding brain tissue. The numbers of neurons born in the human hippocampus remains controversial; some studies have reported that in adult humans about 700 new neurons are added in the hippocampus every day, while other studies show that adult hippocampal neurogenesis does not exist in humans, or, if it does, it is at undetectable levels. The role of new neurons in adult brain function thus remains unclear. Adult neurogenesis is reported to play a role in learning and memory, emotion, stress, depression, response to injury, and other conditions. Neural stem cells (NSCs) are the self-renewing, multipotent cells that generate the main phenotypes of the nervous system. Emerging evidence suggests that neural microvascular pericytes, under instruction from resident glial cells, are reprogrammed into interneurons and enrich local neuronal microcircuits. This response is amplified by concomitant angiogenesis. Planarian are one of the earliest model organisms used to study regeneration with Pallas as the forefather of planarian studies. Planarian are a classical invertebrate model that in recent decades have been used to examine neurogenesis. The central nervous system of a planarian is simple, though fully formed with two lobes located in the head and two ventral nerve cords. This model reproduces asexually producing a complete and fully functioning nervous system after division allowing for consistent examination of neurogenesis. The axolotl is less commonly used than other vertebrates, but is still a classical model for examining regeneration and neurogenesis. Though the axolotl has made its place in biomedical research in terms of limb regeneration, the model organism has displayed a robust ability to generate new neurons following damage . Axolotls have contributed as a bridge organism between invertebrates and mammals, as the species has the regenerative capacity to undergo complete neurogenesis forming a wide range of neuronal populations not limited to a small niche, yet the complexity and architecture is complex and analogous in many ways to human neural development.