Adult neurogenesis: basic concepts of signaling.

Findings over the past decades demonstrating persistent neurogenesis in the adult brain have challenged the view of a fixed circuitry in normally functioning brain and raised hopes for self-renewal following brain injury. In addition to providing insights for repair, studying adult neurogenesis may improve our understanding of embryonic development assuming that fundamental mechanisms are similar. It is argued here, using examples of cell:cell communication, that parallels can be drawn between adult and embryonic neurogenesis. Paradoxically, cell:cell communication in neurogenic regions resembles that in a mature neuroglial network. This suggests that differences in the integrative properties of cells and the extracellular matrix molecules may constitute a neurogenic environment or "niche". While reasons for persistent adult neurogenesis in humans remains obscure, recent findings regarding the environmental and activity-driven control of neurogenesis reinforce the original concept of a role for neurogenesis in motor memory formation and refinement of information processing.