Neuroplasticity and neurogenesis
Olfactory neurons can grow back
A nerve that grows back
Almost nothing in the adult nervous system regenerates. A neuron lost in the spinal cord is not replaced. The olfactory epithelium is a rare exception: it renews itself throughout life.
The reason is where it sits. Olfactory neurons are open to the outside and meet the same air as the lungs: viruses, dust, solvents. A cell built like that wears out quickly, and evolution gave the tissue its own repair shop.
That repair shop is the basal cells lying deep in the epithelium. They divide and mature into new olfactory neurons. In 2020 a single-cell analysis of human olfactory mucosa confirmed that the mechanism operates in adult humans, not only in laboratory animals.
Why regeneration alone is not enough
Growing a cell is half the task. A new neuron has to send its axon through the openings in the cribriform plate and connect to the right glomerulus in the olfactory bulb: the place where the brain expects that particular component of an odour.
This is where the difference lies between "the cells recovered" and "smell came back". If the connection was made cleanly, the odour is perceived as before. If it was made with errors, the signal arrives but is read wrongly, and the familiar starts smelling foreign. That is parosmia.
It is also why recovery often comes in waves rather than smoothly: some odours return, then distortions appear, then they gradually fade.
Where training fits in
Training does not speed up the division of basal cells — it has no influence there. It works on the second half of the task: the connecting.
The nervous system tunes its connections by use: what is used regularly is strengthened, what is unused weakens. A regular, deliberate, repeated stimulus gives the system grounds to refine, over and over, which input belongs to what. That is neuroplasticity in its most practical sense — not "the brain can do anything", but "connections reorganise under load".
This makes the shape of the protocol clear. Regularity is needed because tuning proceeds through accumulated repetitions. Different odour categories are needed because different channels have to be tuned. Length is needed because rewiring is a matter of months, not days.
Honestly about expectations
A capacity to regenerate is not a guarantee. Some people recover fully, some partially, some not at all. With age the repair capacity of the epithelium declines, and if the bulb itself or the pathways are damaged, regeneration at the periphery does not help.
The point of training is not a promise. It shifts the odds in your favour and gives you something to do instead of waiting. That is not nothing when the timescale is months.
Sources
- Durante M. A. et al. Single-cell analysis of olfactory neurogenesis and differentiation in adult humans. Nature Neuroscience, 2020. PubMed — confirmation that the olfactory epithelium renews itself in adults.
- Whitcroft K. L. et al. Position paper on olfactory dysfunction: 2023. Rhinology, 2023. PubMed — which smell disorders respond to what.
