The Age of Olfactory Bulb Neurons in Humans

SummaryContinuous turnover of neurons in the olfactory bulb is implicated in several key aspects of olfaction. There is a dramatic decline postnatally in the number of migratory neuroblasts en route to the olfactory bulb in humans, and it has been unclear to what extent the small number of neuroblasts at later stages contributes new neurons to the olfactory bulb. We have assessed the age of olfactory bulb neurons in humans by measuring the levels of nuclear bomb test-derived 14C in genomic DNA. We report that 14C concentrations correspond to the atmospheric levels at the time of birth of the individuals, establishing that there is very limited, if any, postnatal neurogenesis in the human olfactory bulb. This identifies a fundamental difference in the plasticity of the human brain compared to other mammals.

► Carbon dating establishes cell turnover dynamics in the human olfactory bulb
► The yearly exchange rate of nonneuronal cells is 2.0%–3.4%
► Olfactory bulb neurons are as old as the individual
► <1% of olfactory bulb neurons are exchanged over 100 years in humans