Дата публикации: 29 августа 2021
Автор(ы): Alexander KONOVALOV →
Публикатор: Научная библиотека Порталус
Рубрика: ВОПРОСЫ НАУКИ →
Источник: (c) Science in Russia, №4, 2010, C.14-19 →
Номер публикации: №1630229892
Alexander KONOVALOV, (c)
Author: Academician Alexander KONOVALOV
AND THE BRAIN
by Academician Alexander KONOVALOV, Russian Academy of Sciences and Russian Academy of Medical Sciences, Director of Burdenko Research Institute of Neurosurgery, RAMS
This session of the Russian Academy of Sciences is devoted to one of the main and most intriguing problems of modern science-disclosure of mysteries of the brain. My aim here is to show how neurosurgery with its methods promotes solution of this problem. I also think it essential to formulate some tasks, which can be solved only by joint efforts of specialists representing different sciences. These efforts, focused on disclosure of innermost mechanisms of the brain, are particularly valuable, as they promote the progress in "Basic Sciences for Medicine"-a strategically important trend of research of the Russian Academy of Sciences.
The first thing we shall speak about here are modern diagnostic methods or, as we say now, neuro-visualization methods. The development of neurosurgery as a special science started from the time when it became possible to detect the location and structure of brain lesion. A number of diagnostic methods have been suggested by neurosurgeons. Unfortunately, these methods were mainly invasive and often traumatic.
Clinical application of two methods, providing ample information about the anatomy of the examined organ, more accurate than the picture in an anatomical
Magnetic resonance tractography of a patient with thalamic tumor.
atlas, became a revolution in medicine in general and primarily in neurology and neurosurgery. We mean computer-aided tomography, developed by Allan Cor-mack, an American physicist, and his British colleague Godfrey Hounsfield (Nobel Prizewinners of 1979) and magnetic resonance tomography (magnetic imaging, MRT), developed by Paul Lauterbur, American chemist, and Peter Mansfield, British physicist (Nobel Prizewinners of 2003).
The next step was made in recent years: visualization of the inner structure of the brain, its pathways, has become possible. Based on diffusion tensor magnetic resonance tomography, it is now possible to record the proton movement along nerve fibers and obtain their image by means of complex mathematical processing. This method (tractography) is important for more precise evaluation of brain involvement in tumors located in its deep structures, where its pathways are concentrated, in brain traumas (particularly severe ones), when these tracts suffer first of all, and in many other diseases.
Magnetic resonance tomography in the spectrogra-phy mode helps us to study biochemical processes in the brain. It is essential in circulatory disorders, inflammatory processes, tumors, when due to magnetic resonance spectroscopy it is possible to differentiate between malignant and benign tumors. Studies in this sphere are rapidly progressing. Not long ago, spectroscopy was based only on identification of hydrogen
protons, now we can carry out phosphorus spectroscopy in clinics, and in the near future carbon spectroscopy will be carried out using C-13 hyperpolarized isotope, which will allow to have an indepth glimpse of the cell.
Functional magnetic resonance tomography. Stimulation of the hand motor center during movement of the fingers.
The next extremely important achievement in diagnostics is functional magnetic resonance tomography, identifying the most significant brain regions. Due to experience gained throughout centuries, we know in which compartments of the brain the centers responsible for speech, hearing, visual perception, and motor activity are located. But one thing is to see all this in anatomical preparations or in atlases and quite different thing is to know the location of these centers in the patient. This problem is solved by means of functional MRT. This method is based on the fact that blood supply to brain areas, responsible for realization of a certain task, increases during performance of one or another. For example, during location of motor centers, specifically, of one of them, responsible for hand movements, the examined subject repeatedly bends and unbends fingers, as a result of which the bloodstream in the motor center of the hand increases and there develops a difference in the content of hydroxy-and deoxyhemoglobin (a paramagnetic) in comparison with other brain compartments. Changes in the signal are detected, mathematically processed, and on the tomograms we see the cortical motor area and other structures (the cerebellum), involved in realization of hand movements. The same method detects brain centers perceiving speech and visual signals, speech understanding centers, etc.
Functional magnetic resonance tomography is now widely used for diagnostics of mental diseases, in studies of drag effects on the brain functions. Valuable data on different roles of brain hemispheres (dominant and not dominant) in cognitive activity have been obtained during the last decade using this method. For example, we know now that the significance of the left hemisphere in maintenance of "intellectual well-being" increases with senescence.
The method is rapidly developing with software becoming more sophisticated. Clinical use of potent 3-7 T magnets is starting. I am sure, and it is not at all a fantasy, that very soon we shall be able to see the course of this or that thinking process, the solution of intellectual problems in the brain.
We must mention also some other important research methods here, for example, positron emission tomography and magnetic encephalography. One of the first attempts to use the latter method for studies of brain functions was undertaken about 30 years ago at Kurcha-tov Institute of Nuclear Energy (now called RSC "Kurchatov Institute"). Unfortunately the research was later stopped and the results were not materialized in appropriate devices. In this connection we count on collaboration with Academician Yuri Gulyaev and his team (V. Kotelnikov Institute of Radiotechnology and Electronics, Russian Academy of Sciences). They have suggested devices recording changes in magnetic fields of the heart, and at present we are developing an original variant of magnetic encephalographer.
I should like to emphasize that these methods are extremely important for the development of neuropsychology. One of the founders of this science was a brilliant Russian psychologist, Member of the USSR Academy of Pedagogical Sciences Alexander Luriya (1902-1977). Unfortunately, our priorities in this sphere of knowledge are now lost to some extent. And the neuropsychologists now have to restore the prestige of Russia in this field by using modern potentialities.
The next problem I should like to mention is methods for studies of blood supply to the brain. The applied (clinical) significance of these methods cannot be overestimated. Leaving out details, I should like to emphasize that cerebrovascular disorders are one of the main causes of mortality and disability of the pop-
The "mould" of the vascular system of the brain (a); three-dimensional computer angiography of the brain (b).
ulation. Every year about 400,000 patients become victims of a stroke, which is mainly a result of malfunction of blood supply to one or another brain region.
And here I have to mention universally known facts: in contrast to other organs, the brain has no energy reserves. All it needs for work (primarily oxygen and glucose) is delivered by the bloodstream. If it stops even for 5-7 minutes, brain cells die. This explains a paradox: the organ constituting approximately 1.5 percent of body weight consumes 20 percent of oxygen, 20 percent of blood flowing in its vessels.
It is very important that today clinic physicians can detect changes in cerebral circulation with high precision. These methods include studies of brain tissue perfusion, which, carried out directly after the emergency development, helps identify the brain region with deranged bloodstream. The most important information can be obtained also by magnetic resonance spectroscopy. Characteristic metabolic shifts are detected in the ischemic zone; these shifts can be monitored in a dynamic range.
It is extremely important for neurosurgeons to unite the entire available information in a three-dimensional image of at least a zone of special interest, if not of the whole brain. Research in this direction is carried out in collaboration with the Design Bureau of Information and Measuring Systems (Dubna, Moscow Region).
One more important problem is how to use the obtained information during an operation, to make it effective and safe at the same time. One of such approaches is intraoperating navigation. It consists in the following: during the operation the surgeon compares the position of his instruments, located by infrared pickups, with the available results of computer and magnetic resonance tomography, angiography, and other studies. This navigation system is already used in the design of modern surgical microscopes.
Registration of bioelectric activity in certain brain regions and stimulation of one or another zone also facilitate the orientation in brain structures. This approach is particularly important for operations on the brainstem, where the most significant vital functions are concentrated. The recovery method is used after operations near speech zones. The gist of this method is the following: in the course of the most important moment, when the neurosurgeon manipulates near the speech centers (the so-called Broca's Center), the patient is awakened and it becomes possible to speak with him.
Due to the improvement of operation methods, operations are carried out in the zones, which were considered prohibited not long ago: on the brainstem, hypothalamic area, and some other regions. This necessitates studies of the role of these structures. For example, removal of a tumor of the hypothalamus and the third ventricle. Such interventions can result in a striking improvement of endocrine metabolic functions and in their serious disorders (which are often inevitable, as the centers regulating the metabolic and endocrine processes are concentrated in the hypothalamic area). Evaluation of such surgical aggression, prevention and treatment of its untoward aftereffects is a problem, which can be solved only by mutual efforts of endocrinologists, pathophysiologists, and biochemists.
The so-called "functional neurosurgery" is one of the most interesting and important (for providing new
Resection of a large tumor involving the hypothalamus and third ventricle (a-before and b-after tumor resection).
information) trends of research. Such interventions are intended to normalize or improve the brain function in epilepsy, stubborn painful syndromes, and parakineses.
At first these interventions were mainly destructive: transection of pathways, destruction of certain nuclear structures of the brain. The accuracy of insertion of an appropriate instrument deep into the brain is validated by a stereotaxic surgery. By using a stereotaxic device fixed on the patient's skull and calculations based on computer-aided or magnetic resonance tomography, the instruments can be inserted in one or another brain compartment with very high (up to 1-2 mm) precision. In the last decade the electrostimulation method, allowing to modulate the malfunction, replaced the destruction of brain structures. Operations of this kind are particularly effective in Parkinson's disease, which is, unfortunately, rather frequent.
An electrode, connected to the subcutaneously placed receiving device, is inserted into one of the deep subcortical structures (for example, the posterior lateral nucleus of the thalamus*, pallidum**). A program of electric stimulation, effective for the patient, is chosen. If indications for the intervention are strictly observed, such operation can result in elimination of the limb tremor, reduction of the muscle tone, and expansion of functional potentialities of the patient. No less beneficial results can be attained in other diseases leading to parakineses, forced muscle spasm, the so-called torsion spasm***. I should like to mention here the important contribution of Russian scientists of the 1970s-1990s, including Academician Natalya Bekhtereva and Academician Georgy Kryzhanovsky, to understanding of the mechanisms of stubborn pains, forced (involuntary) movements, and other disorders of the nervous activity.
The mechanisms of regulation of movements, pain perception, development of epilepsy are extremely intricate. Disorders in the neurotransmitter metabolism often underlie the pathogenesis, for example, in Parkinson's disease. These mechanisms can be disclosed only by mutual efforts of neurophysiologists, pharmacologists, and a number of other specialists.
One of the problems to which I should like to draw your attention is brain regeneration. Up to recent time it was universally assumed that nerve cells did not regenerate. And only the studies of recent years have demonstrated that new stem cells, replacing a part of dead cells, are constantly emerging in the hippocampus and paraventricular zone of the brain.
The stem cells and their probable role in regeneration of damaged brain structures is one of the most intriguing and, presumably, promising trends. On the other hand, this problem remains experimental, and there are still no real grounds for application of stem cells in clinical neurosurgery.
In conclusion I should like to mention, at least in brief, the problem of prosthetic repair of lost functions,
* The thalamus is a brain area responsible for redistribution of information from organs of senses (except olfaction) to the cerebral cortex.-Ed.
**The pallidum is a part of the cerebral lentiform nucleus. It is a component of the extrapyramidal system involved in the regulation of movements, maintenance of the muscle tone and posture.-Ed.
*** Torsion spasm is a chronic progressive disease, characterized by peculiar changes in the muscle tone, which leads to emergence of pathological postures.—Ed.
which is one of the prospective trends, and certain progress has already been achieved—for example, prosthetic repair of lost hearing caused by damage of sound-perceiving cells in the cochlea. The device for improving hearing ability in such cases consists of an external part, transforming the sounds of different frequency into electric signals. The latter are transmitted to an electrode of a special design: it is inserted into the cochlea and directly stimulates the nerve terminals. This method is effective and is widely used in many countries, including Russia.
The possibility of restoring (at least partially) perception of sounds, when the acoustic nerves are damaged for one or another reason, is an interesting problem for neurosurgeons. In such cases direct stimulation of the acoustic nuclei in the brainstem is used almost in all countries, and the results are in some cases encouraging.
Similar studies are carried out in case of loss of vision. In such cases they stimulate the retina, optic nerves, and occipital cortex.
Attempts to transform electric potentials of the motor cortex into electric pulses are undertaken to activate external devices capable of reproducing to some extent the function of the hand.
I intended to show in this article the important achievements of recent years, which permit to understand how the brain works and, on the basis of this knowledge help patients. The interest to the mechanisms of its work is increasing, and we can hope that many of its mysteries will be disclosed. However, I am afraid, we shall never cognize the most concealed thing: how the material processes become ideal, how the brain work transforms into consciousness.
I am grateful to the staff members of our Institute, who participated in preparation of this article: Academician Valery Kornienko, Russian Academy of Medical Sciences, David Pitskhelauri, Igor Pronin and Vladimir Shabalov, Drs Sc. (Med.), and Dmitry Samborsky, designer-artist.
Опубликовано на Порталусе 29 августа 2021 года
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