Olfactory neurons are not restored, scientists say
Last reviewed: 23.04.2024
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Unlike animals, neurogenesis in an adult goes not in the area of the brain that delivers new neurons to the olfactory tract, and there and only where the command center of memory and training is located.
A person is born with a fixed set of olfactory neurons, according to the Neuron magazine, researchers from the Karolinska Institute (Sweden). Not long ago this statement would have been a model of banality, but since neurogenesis in the mature brain was discovered, it is believed that the olfactory neurons are renewed throughout life.
At least this is the case for all mammals - except, as is now known, a person.
Neurogenesis in the mature brain is concentrated in two zones - in the hippocampus, responsible for learning and memory, and in the subventricular zone of the walls of the cerebral ventricles. Animal studies have shown that neurons formed in the subventricular zone migrate to the olfactory tract and are inserted into the olfactory bulb. The person clearly confirmed only the formation of neurons in the hippocampus, about the second focus of neurogenesis, the data were uncertain.
Scientists from the Karolinska Institute tried to trace the appearance of new neurons with the help of a radiocarbon method. According to their data, an extremely small number of new nerve cells can appear in the olfactory tract of the human brain, if they appear there at all. To replace at us only 1% of olfactory neurons, it is necessary to wait a hundred years - while in rodents half of olfactory neurons is updated for a year.
However, the authors of the work specify that they could see only those neurons that are embedded in the olfactory ways. That is, in principle, neurogenesis in the subventricular zone in humans can occur, only the nerve cells are sent therefrom not at all into the olfactory tract. Or such cells in general can die right after birth. It is possible that because of the switched off (or improperly working) neurogenesis, a person has lost the ability to smell as sharply as animals. And here, of course, it would be very interesting to repeat the same experiments, but with professional "sniffers": perfumers, cooks, wine merchants, sommeliers. It is known, for example, that in rodents the newborn olfactory cells die quickly, if the animal does not exercise in the sense of smell, does not feel new smells. Perhaps we are doing exactly the same, and updating olfactory neurons occurs in those who really need them.
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