Adult Neurogenesis in Mammals and Nonmammals

processes as dentate gyrus neurogenesis is in mammals, i.e. by learning and cognitive stimulation. Thus, his paper does not acknowledge the existence of evidence that neurogenesis in widespread areas of the nonmammalian brain is subject to the same processes as neurogenesis in the dentate gyrus of mammals. For example, enriched environments enhance adult neurogenesis in nonmammals, just as Kempermann and others have shown in extensive studies of mammals [e.g., Kempermann et al., 1997; Nilsson et al., 1999; van Praag et al., 1999]. Mountain chickadees that live in the wild, where the environment is presumably richer, show more neurogenesis in the hippocampus than those that live in a laboratory setting [LaDage et al., 2010], and mountain chickadees that live in the laboratory and are allowed to cache seeds show more adult neurogenesis than those prevented from caching seeds [LaDage et al., 2010]. Painted turtles exposed to an enriched environment show more adult neurogenesis in the telencephalon, including the homologue of the hippocampus, the medial cortex, compared to those housed individually in tanks with little opportunity for stimulation [Powers and Hanusch, 2012]. After exposure to an enriched environment, there was an increase in the numIn a recent article in Nature Reviews Neuroscience , Kempermann [2012] proposed that adult neurogenesis in the dentate gyrus of mammals may function differently from the adult neurogenesis seen in the brains of nonmammals and, rather than representing a vestigial function compared to the widespread neurogenesis seen in nonmammals, is a co-opting of that process for a new purpose in mammals, namely the ability to adapt to a wide range of environments. He cites rats and humans as examples of species that possess that adaptability, species that are found in every ecological niche on earth. He correctly states that the dentate gyrus is not present in nonmammals in its mammalian form and hypothesizes that, with its appearance, a new ability to adapt developed. This ability varies among mammals, according to his hypothesis, with animals like bats and dolphins, who have limited or no neurogenesis in the dentate gyrus, showing less adaptability in their behavior than rats or humans. This thesis is an interesting one, which will require much more data than are currently available to test, as Kempermann acknowledges. He does not discuss, however, data showing that adult neurogenesis in nonmammals is influenced by the same Published online: May 25, 2013