Our recent understanding that neural stem cells are resident in the adult brain raises questions about the potential role of neurogenesis in neurological disorders and in age-related cognitive decline. If neurogenesis would indeed decline with aging then perhaps small molecule modulators of neural stem cell differentiation would find application as therapeutic agents to treat or prevent cognitive decline. We have studied the effects on human neural stem cell differentiation of some known small molecule modulators of neurogenesis and also of some carotenoids dietary antioxidants. Changes to neural stem cell differentiation and cell fate induced by these small molecules will be reported.