To be or not to be: Adult neurogenesis and psychiatry

The recent discovery that neurons are born throughout life in specific brain regions has caused explosive interest in the possible involvement of adult neurogenesis in a host of psychiatric conditions. Neurogenesis in the subgranular zone of adult hippocampus dentate gyrus has received the greatest attention to date, since it is highly regulated. In general, several types of deleterious conditions (e.g. stress, drug addiction, advanced age) are associated with reduced neurogenesis in the adult hippocampus, while palliative conditions (e.g. enriched environment, voluntary exercise, antidepressant treatments) are associated with enhanced neurogenesis. The major limitation in the field today is the lack of direct evidence for an important role of the newly born neurons in hippocampal function. This review provides an overview of preclinical research relating adult neurogenesis to psychiatric disorders, with an emphasis on how such research can provide insight into the functional role of adult neurogenesis. Given that another limitation in the field is a lack of consensus on what constitutes a newly born cell or a newly born neuron, we also provide an overview of the technical challenges facing the field, and suggest guidelines for defining cytogenesis and neurogenesis. In general, we suggest that an improved understanding of adult hippocampal neurogenesis could shed light onto the neurobiological mechanisms underlying certain psychiatric conditions, and might even lead to the development of novel treatments for these disorders.