A woman without olfactory bulbs did not lose her sense of smell: how and why do people manage to live normally without important parts of the brain

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A woman without olfactory bulbs did not lose her sense of smell: how and why do people manage to live normally without important parts of the brain
A woman without olfactory bulbs did not lose her sense of smell: how and why do people manage to live normally without important parts of the brain
Anonim

Researchers have discovered in the girl an amazing anomaly - the absence of olfactory bulbs with a preserved sense of smell. Let's try to figure out why this is possible and how the brain copes with the need to "replace" problem areas.

Left - MRI of a normal brain; on the right - MRI of the brain of a girl without olfactory bulbs

We used to think that "nerve cells do not regenerate." Of course, many have heard about the compensatory capabilities of the brain, post-stroke rehabilitation, and maybe even that, in fact, new neurons appear in our entire life. But the human brain is a box with such surprises that sometimes it is impossible to imagine, but you can only see and look for an explanation for them.

A patient with a twist - or rather, without

An article by Israeli scientists from the Weizmann Institute recently published in the journal Neuron explores a kind of scientific mystery.

The authors of the work initially studied a completely different field: they wanted to know how the sense of smell is involved in intergender relations and what is its role in finding a partner. The brains of each participant in the experiment were scanned using MRI.

Suddenly, in one of the images, the researchers found no olfactory bulbs. But this was not striking: in the world, every ten thousandth person suffers from anosmia. However, people with anosmia have no sense of smell at all or almost completely. But the 29-year-old participant in the experiment, whose data baffled scientists, turned out to be an excellent "sniffer". She passed all the tests, showed the usual picture of the activity of the necessary parts of the cerebral cortex and generally lived remarkably, not at all suspecting that her olfactory system was at least in some way abnormal.

Just in case, the authors turned to fellow engineers from the University of Melbourne. They suggested that the fault could be a defect or inaccuracy of the MRI. However, the new methods have confidently shown that there are no bulbs.

What's the catch

The olfactory bulbs are an indispensable (until now thought) part of our olfactory system in the brain. This is a paired organ: two such bulbs consisting of neurons are located in the region of the intracranial cavities of the nose. The chemoreceptors in the nose capture the molecules of volatile substances, send a signal through the olfactory nerve to the bulbs, where it is processed, and then transmitted to the subcortical centers and, finally, to the temporal region, where the cortical olfactory center of the brain is located.

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The absence of bulbs effectively cuts this multi-step path. However, the fact is obvious: there is a girl, there is a sense of smell, there are no bulbs. To check whether this is a unique case, the scientists examined several more women of the same age, as an additional factor determining left-handedness ("patient zero" was left-handed). On the ninth attempt, they found another girl of the same kind. Subsequently, after examining 1113 more people, scientists found three women with a similar anomaly. None of the five hundred surveyed men had such a problem. Perhaps, in some way, such a superpower is related to gender, perhaps, given its rarity, at least one such man will be found in a larger sample.

How could this possibly be? This case is incredible, scientists shrug their shoulders in shock - or not?

The researchers have not yet found an iron explanation for the mechanism of the phenomenon, as well as the reasons for its appearance, only recorded its existence.But the most likely option is neuroplasticity, which can literally work wonders.

Brain-Proteus: what is neuroplasticity

For a long time, it was assumed that the human brain is formed in utero, completes its development in childhood, and remains structurally unchanged in adulthood. Modern research has shown that this is not the case. Throughout life, the brain remains changeable and plastic.

Neuroplasticity, that is, the ability of the human brain to change under the influence of new experience, includes not only the ability to repair neural connections damaged by damage, form new ones, or strengthen existing ones during learning.

Recent studies show that the brain is able to grow significant volumes of new neurons in its various departments, and if it is impossible to completely replace the lost, it can “reassign” one group of neurons to perform the functions of another. Moreover, examples of the possibilities of such “substitutes” sometimes boggle the imagination.

Man does not use 90% of his brain

This phrase was incredibly popular 10-20 years ago, during the heyday of various pseudoscientific techniques that promised to unleash the intellectual abilities of everyone and grow a genius out of any solitaire manager in the workplace. However, science knows cases in which this expression is close to the truth. Sometimes - downright "not some fact, but the pure truth!"

The most common examples are post-stroke rehabilitation. Children who had suffered a stroke did not differ in their mental abilities from their peers, and the functions of the affected areas of the left hemisphere, which are responsible for speech, were fully able to perform the symmetrical areas of the right. But there are also more striking examples.

So, in the summer, doctors in the Moscow region discovered a man without a left cerebral hemisphere. At all. In the MRI scans, you can see the empty space at this place. According to the doctors, to whom the patient was admitted with ischemia, he lived like this all his life, up to 60 years, but did not know about his peculiarity. Development did not go so well in utero, but the rest of the brain was able to compensate for the missing part. The man did not show any problems with motor skills, vision or psyche; moreover, he studied quite successfully and worked as an engineer for many years.

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But minus one hemisphere is not the limit for neuroplasticity. This is proved by a Frenchman, who in 2007 was diagnosed with the destruction of 90% of the cerebral cortex. Since childhood, the man suffered from hydrocephalus, which led to such devastating consequences. However, neither he nor his family knew about the changes taking place, and by the age of 44, the patient was worried about only a slight weakness in one of the limbs.

Even his IQ was not lowered to the level of mental retardation, despite the fact that all higher psychological activity of a person is associated with the functioning of the cortex. Nevertheless, an ordinary civil servant (yes, he coped with his duties quite well) successfully dispensed with the remains of the cortex, the brain stem and the cerebellum.

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The brain is able to cope not only with the loss of parts of the cortex. Thus, a Chinese woman who lived a normal life, gave birth to two children and experienced only minor motor impairments, became a valuable patient for scientists. It turned out that she had lived all her life without a cerebellum at all.

All these cases show that although brain injuries or abnormalities in its development are dangerous and often lead to sad consequences, there are no irreplaceable parts of the brain. For literally any part of the brain, if a person is lucky, a kind of "acting" can be found.

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How does it even work

What neuroplasticity can do sounds like magic. But this is not more magic than any other process taking place in our body, if you look at it in detail from the point of view of science.

In general, the brain is a fairly stable system with a certain margin of safety.Without this, we would not have been able to survive. The brain maps us completely: everything we do, every skill or part of the body has its "representation" in the form of neural pathways and neurons connected to each other. The higher the activity, the more this representation, and the less time we spend, for example, training some skill, the weaker the connections become.

During life, the neurons included in such structures are partially updated, while the circuit itself is preserved. As a child, we grow up to a thousand new neural connections per second. After this period of highest receptivity, it is time for neuronal (synaptic) pruning. The brain seeks to make the schemes of interaction of neurons in network representations as simple as possible. The number of synapses and neurons in these ligaments tends to the optimal minimum, cutting off the excess through the elimination of synapses. This process opposes the constantly emerging new connections between neurons and their groups during the learning process. Simply put, without pruning, our brain would turn into a huge messy tangle of connections, ineffective both for processing information and in terms of energy balance. By constantly maintaining a balance between creating connections and breaking them, the brain has the ability, if necessary, to find new ways for the functioning of suddenly broken parts.

For example, post-stroke rehabilitation techniques are based on these properties of the brain. If the patient is forced to try to use a limb whose control center in the brain is damaged, he activates the remaining parts of this system, which are looking for "workarounds."

By communicating with neurons that are suitable for their functions, the structure tries to re-assume its usual form, as much as possible. The more original neurons survived and the more “replacement teachers” around them, the easier and more complete the function will be restored.

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In addition, the younger a person is at the moment when the brain needs to invent a new way of functioning of some part of it, the greater the chances of success. With congenital defects, such a restructuring is prepared even in utero. In the case of the French patient, the destruction in his brain, although it was incredibly extensive and began, most likely, after 14 years, but it happened slowly, which gave time for the brain to rebuild slowly.

Let's return to the mystery of women who can smell, although in theory they have nothing. Let's try to summarize: is it really about neuroplasticity?

What could have given such an effect? One of the options is genetic abnormalities, possibly sex-linked, in which the olfactory bulbs are reduced so that the olfactory information goes in a roundabout way.

The other is good old neuroplasticity. Perhaps other systems in the regions and structures of the brain associated with the sense of smell were able to create ensembles that replaced all functions of the bulbs without losing the quality of life. As we have seen, history knows not such cases.

Thirdly, there is a chance that we have an incomplete or fundamentally wrong idea of ​​the entire apparatus of the human olfactory system. If there is evidence of this, the authors of the original article, of course, will acquire the laurels of scientists who have changed an entire branch of science. This (undoubtedly flattering for them) scenario, however, is hardly possible. Not all animal studies of the olfactory system can be replicated in humans, primarily from an ethical point of view. Still, it is well mapped, and, most likely, we are talking about two other probabilities.

Well, do not discount the fact that there is still a chance (albeit very small) of a simple mistake. The bulbs can be simple or very small or extremely atypical. Organ transposition is not a rare case, and sometimes it happens that a patient, for example, has a tooth growing in his nose.So, perhaps, while the scientific world is trying to come up with a beautiful explanation for a unique phenomenon, the bulbs peacefully live their lives somewhere in the backyard of the neighboring brain region and do not worry about anything.

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