1 Adult Neurogenesis: A Prologue

New ideas pass through a series of stages from initial rejection to skepticism, to reluctant acceptance (without true belief in its importance), to a final casual acknowledgment of the obvious. It is fair to say that the acceptance of the idea that new neurons are generated in the adult brain of all mammals has been a slow process, and along the way, the idea has been met with skepticism and resistance. It is still not yet casually accepted as obvious. Rather, adult neurogenesis remains in the stage of reluctant acceptance, without a clear understanding of its importance, but the search for its function is in full gear. Joseph Altman’s original observations in the 1960s were met with significant reservation, as were attempted confirmations by a handful of investigators in the next 20 years. Somehow, Fernando Nottebohm and Steve Goldman’s observation of neurogenesis in the brains of adult canaries was received more positively but—because it took place in birds—was not considered as much of a threat to the prevailing belief (often even termed “dogma”) that there are no new neurons in the adult mammalian brain. Why this resistance to the capacity of the adult brain to generate new neurons? It was well accepted that other systems, like blood, liver, and skin, could generate new cells, so why not the brain? The most straightforward explanation is that the brain is not just any organ. At a philosophical and metaphysical level, the brain is thought to be the place where the...