It has now been demonstrated for the first time that the brains of people who can no longer smell still respond to odours and the act of sniffing. In such situations, it may still be possible to train the sense of smell.
These findings come from research by the Smell and Taste Centre, run by Wageningen University and the Gelderse Vallei hospital, in partnership with researchers from the University of Graz. The study was published in Human Brain Mapping. The researchers used data on patients whose olfactory sense was fully or partially impaired. They examined whether and how these people’s brains responded to odours and to sniffing odourless air.
First they determined the degree to which the sense of smell had been affected, using an odour test. Then the researchers used functional MRI to get a picture of the activity of the neural networks in the brain. The results were surprising. When the patients were exposed to an odour, the researchers saw activation not just in the brain’s odour network but also in the cerebellum and the visual network.
Research leader Sanne Boesveldt says this is the first study that shows there is any brain activity at all in people without a sense of smell and that it involves more than one neural network. ‘The interesting thing is that we don’t just see brain activity when the patients are exposed to smells but also when they sniff odourless air.’ According to Boesveldt, the findings are an indication that training in smelling and sniffing could also help people who have completely lost their sense of smell.
‘If there is still activity in the brain, that suggests the relevant nerve routes are still intact,’ concludes Boesveldt. ‘And that presents possibilities for training.’ Given the observed effect of sniffing on brain activity, she speculates that training in sniffing could help achieve at least partial recovery of the sense of smell. At present, doctors only use olfactory training for people with a partly impaired sense of smell.