One Brain, Two Operating Systems Fred H.GageGerdKempermannHongjunSongAdult Neurogenesis2008Cold Spring Harbor Laboratory Press673 pp., $135 hardcover

The continuous addition of neurons into the adult brain is a widespread phenomenon observed in many different animal species, ranging from invertebrates to humans. Several thousand papers have been written on adult neurogenesis since Joseph Altman discovered this phenomenon in 1962 at MIT, by a curious coincidence just a few hundred yards away from where this comment is being both written and published. There are two main reasons why adult neurogenesis has raised such great interest over the years. First, the persistence of neuronal addition into the mature brain suggests the possibility of harnessing this naturally occurring phenomenon toward replacing neurons lost to disease or injury. Unfortunately, the realization of these hopes has been modest at best, and the prospect of using adult neurogenesis toward brain repair remains a very distant possibility, with no clear direction for how to achieve this elusive goal. Second, adult neurogenesis represents an unexplained challenge to the traditional view of the brain as a static structure comprised of long-lived neurons, the stability of which was thought to be necessary for the long-term encoding of information. Given the size of the literature on the subject of neurogenesis, it would be convenient to have most of the existing information compiled in an easily accessible form. Adult Neurogenesis by Gage, Kempermann, and Song is a recently published book that fills this niche by covering many aspects of this intriguing phenomenon. The book, published by Cold Spring Harbor Laboratory Press, contains 30 independent chapters written by some 50 authors and provides a broad overview of the field. The book starts with a section that includes several chapters describing the methods most commonly used to study neurogenesis. I found this section particularly useful, since these chapters explained the techniques in a practical manner, also discussing the advantages and pitfalls of each method. The information presented in these chapters is very valuable, especially because methodological limitations are usually not discussed in a critical manner in papers or reviews. The book continues with a couple of sections describing in great detail the cellular process involved in the proliferation, migration, and differentiation of new neurons into the adult brain and the physiological processes that regulate the rates of neurogenesis. In recent years, a wealth of information has been accumulated on these matters, and these chapters provide a comprehensive survey of the topic. From here, the book deals with the perhaps most intriguing question in neurogenesis, its functional significance, specifically as it may relate to learning and memory. The role that adult neurogenesis may play in some disorders, such as depression and epilepsy, and the potential applications of adult neurogenesis for cell replacement in the brain are also discussed, and finally, there is a section dealing with the comparative and evolutionary aspects of neurogenesis, with chapters devoted to adult neurogenesis in the brains of fish, songbirds, humans, and wild populations of mammals. Despite being a multiauthor book, the different chapters are well integrated, with minimal repetition. I would have liked to have seen more discussion on the relevance of adult neurogenesis to behavior, especially in songbirds, where the correlation between adult neurogenesis and learning is particularly intriguing. Otherwise, the book is an authoritative source that provides wide coverage of the major topics of the field. Here, I briefly highlight some of the key pending issues regarding the functional relevance of adult neurogenesis discussed in the book and suggest some views on this process that hopefully would spark further discussion and experimentation.