  The aim of this study was to estimate the number of new cells and neurons
added to the dentate gyrus across the lifespan, and to compare the rate of
age-associated decline in neurogenesis across species. Data from mice (Mus
musculus), rats (Rattus norvegicus), lesser hedgehog tenrecs (Echinops
telfairi), macaques (Macaca mulatta), marmosets (Callithrix jacchus), tree
shrews (Tupaia belangeri), and humans (Homo sapiens) were extracted from twenty
one data sets published in fourteen different papers. ANOVA, exponential,
Weibull, and power models were fit to the data to determine which best
described the relationship between age and neurogenesis. Exponential models
provided a suitable fit and were used to estimate the relevant parameters. The
rate of decrease of neurogenesis correlated with species longevity r = 0.769, p
= 0.043), but not body mass or basal metabolic rate. Of all the cells added
postnatally to the mouse dentate gyrus, only 8.5% (95% CI = 1.0% to 14.7%) of
these will be added after middle age. In addition, only 5.7% (95% CI = 0.7% to
9.9%) of the existing cell population turns over from middle age onwards. Thus,
relatively few new cells are added for much of an animal's life, and only a
proportion of these will mature into functional neurons.

Neurons and Cognition;Applications