- the method of an electrophysiologic objective research of a functional condition of a brain based on graphic registration of its biopotentials;
- the section of an electrophysiology of the central nervous system studying the bioelectric processes connected with emergence of activity in structures of a brain with their transition from relative rest to the active, activated or brake state.
Data E. most widely use for the solution of the following main research and diagnostic objectives: establishments of localization patol. the center in a brain; differential diagnosis of organic and functional diseases of c. N of page; studying of mechanisms of epilepsy and identification at its early stages of epileptogenic focus in the absence of typical a wedge. symptoms of a disease; characteristics of reaction of activation of a cerebral cortex, and also orientation responses with assessment of stages of latency and duration of the periods of an after-effect of irritants both with the diagnostic purpose, and at various tests (e.g., at selection of the contingents of the persons steady against extreme conditions of their future production activity); during the definition of efficiency of the carried-out therapy (neurotropic, anticonvulsant and psychotropic drugs); for justification fiziol. harmlessness of effect of new anesthetics on c. N of page and determination of depth of an anesthesia in the course of an operative measure; estimates of reversible and irreversible changes of a brain on disturbance of biopotentials of a brain in the course of attenuation of its function and for the purpose of ascertaining of death of a brain (see).
In 1913 V. Pravdich-Neminsky for the first time by means of a string galvanometer registered various types of fluctuations of potentials of a naked brain of a dog, and also submitted their description and classification. In 1928 the German psychiatrist Berger (N. of Berger) for the first time wrote down biocurrents of a brain of the person, using as pickup electrodes of a needle, to-rye entered under a tendinous helmet of the head in frontal and occipital areas. Such way of assignment of biocurrents of a brain from the surface of the unimpaired skull was soon replaced with applying to head skin of plates from the depolarized material. This modification of assignment of biopotentials of a brain was included into a wedge, practice, having received the name of an electroencephalography; the curve of fluctuations registered at the same time biopo tentsial of a brain was called by the electroencephalogram (EEG). Berger established a regularity of rhythmic fluctuations of biopotentials of a cerebral cortex, gave the first classification of spontaneous rhythms of EEG of the person, described their features at rest and changes at a functional trial (opening of eyes of the examinee during record EEG). Further development E. as method of an electrophysiologic objective research and its implementation in neurologic, neurosurgical and psychiatric practice is connected with progress of electronics and development of multichannel highly sensitive electroencephalographs — the devices intended for registration of bioelectric processes in structures of a brain (see below).
Domestic electroencephalography as section of an electrophysiology of c. N of page developed in close connection with the general and experimental neurophysiology and at the beginning of the 50th it was not limited only to the description of a form of fluctuations of biopotentials of a brain, it is normal of their frequency and amplitude characteristics also at pathology. The initial stage of development of a clinical electroencephalography was characterized along with accumulation of the actual material about features of the general (diffusion) and local changes of EEG at various organic diseases and functional conditions of a brain of transition to studying of conditions of emergence of these or those forms of electric activity, mechanisms of generation of biocurrents of a brain, their communication with dynamic processes of excitement or braking in a cerebral cortex.
In the 60th broad development was gained by the so-called functional electroencephalography studying reactive changes of EEG in response to continuous and rhythmic afferent stimulation (light and sound irritations) for the purpose of identification of the center patol. activities, especially at tumoral and vascular diseases of a brain. In the same time researches of the local caused reactions of a brain at short-term irritations of a different modality and so-called nonspecific answers of bark were begun. On the basis of studying of the last it was established that the nature of the responses registered on EEG substantially is defined by a ratio of the vozbuzhdeniye coming to bark of cerebral hemispheres on specific (lemniskovy) and nonspecific (a reticular formation of a brain trunk) to afferent systems. At the same time in E. the direction of electrophysiologic studying of higher nervous activity of the person with the description of the difficult and mosaic neurodynamics accompanying process of elaboration of conditional reactions of the person was allocated is normal also at pathology.
In 60 — the 70th interest in direct registration of electric activity of subcrustal structures of a brain of the person by means of the electrodes implanted into a brain — the elektrosubkortikografiya (ESUBKOG) promoting studying of a role of deep formations of a brain in mechanisms of emotional reactions, etc. manifestations of mental activity of the person considerably increased.
Present stage of development clinical E. it is characterized by development of machine methods of quantitative assessment of frequency and amplitude and phase changes of biopotentials of a brain normal and at pathology. The mathematical analysis of EEG allows to reveal its features hidden at a usual visual estimate. In a crust. time by correlation analysis and calculation of ranges of coherence investigate coherence of separate rhythms in different areas of a cerebral cortex normal and at pathology (see. Analyzers of biopotentials )
Record of bioelectric processes in structures of a brain is made by means of an elekgroentsefalograf. It consists of the switch of assignments, the amplifier of the taken-away biopotentials, the chart recorder, the device calibration, structurally combined and put in the general case. Integral parts of the electroencephalograph are also electrodes (see), light and sound stimulators. There are different types of electrodes: the consignment notes which are pasted, the needle, kortikografichesky, implanted (long-term), multicontact probes and other. Apply the special electrodes brought through the nasal courses to a back wall of a nasopharynx to a research of biopotentials of a basal surface of a brain. The most convenient in a wedge. to practice laid on electrodes bridges are, to-rye strengthen on the head by means of rubber helmets grids. For the purpose of express diagnosis, e.g. at a severe craniocereberal injury, use needle electrodes. The electrodes applied to assignment of biopotentials of a brain from certain points of the head of the person have small transfer resistance (between an electrode and head skin), and also the small tension of polarization. They are made, as a rule, of the conducting metals having anticorrosive properties; usually use pure silver or its mix with silver chloride. The necessary contact during the overlaying of electrodes on head skin is created by a special electrode paste. The switch of assignments represents the mnogopozitsinonny switch. In a crust. time instead of mechanical switches of assignments is applied electronic (program)» to-rye allow to automate process of registration of biopotentials of a brain and to reduce time of record EEG. Sensitivity of electroencephalographs reaches 1 — 0,2 mm/mm. For ensuring such sensitivity in the frequency range of 0,5 — 100 Hz there are various devices suppressing external hindrances of a useful signal. For quantitative assessment of amplitude characteristics of EEG elekgroentsefalograf are built in by the device of calibration of sensitivity, amplitude of tension to-rogo is in range from 20 to 5000 mkv.
The chart recorder of the electroencephalograph has several speeds of the movement of paper, use speeds of 15, 30 and 60 mm/sec. more often. Effective width of record shall not exceed 20 mm. In electroencephalographs apply peryevy and jet an ink pitchfork of record, and also thermal zvpis on a special paper strip. The frequency filters intended For restriction of a strip of EEG within 15, 30, 75 Hz enter the device of an elekgroentsefalograf.
On number of channels of record EEG electroencephalographs happen 8-, 16-and 32-channel. The greatest use in medical practice was received 8-also by 16-channel devices installed for convenience of operation on mobile carts. With pomoshchyo additional sensors, prefixes, the built-in blocks elekgroentsefalograf allow to register also other electrophysiologic parameters — the electrocardiogram, the electromyogram, curves of breath, etc.
Improvement of electroencephalographs goes on the way of automation of their management and implementation of processing of EEG by means of the micro COMPUTER and microprocessors. Results of inspection of the patient at the same time receive in a digital or alphabetic form with the conclusion according to the diagnosis (see Analyzers of biopotentials).
Except elekgroentsefalograf, apply elektroentsefaloskopa to a research of biopotentials of a brain — the devices allowing to investigate at the same time biocapacities of many areas of c. N of page. On the screen of an electron-beam tube of an elektroentsefaloskop spacing of biopotentials can be observed on change of brightness of a beam according to a sign and intensity of bioelectric potential in each point of assignment.
Record EEG is made in the sacred and soundproofed placement for leveling of orientation responses of the examinee on influence of external factors. Modern electroencephalographs are supplied with special filters for suppression of network aimings of current therefore the cameras, screened from electric hindrances, which were earlier used for record EEG are optional.
Inspected depending on weight of a state during record EEG is in situation reclining in a special convenient chair or lies on a couch with a little raised head restraint. Before an electroencephalography of inspected warn that the procedure of record EEG is harmless, painless, no more than 20 — 25 min. proceed that it is necessary to close eyes, to relax muscles of a trunk, extremities, necks and face muscles.
Fixing of pickup electrodes on the head is made according to the international scheme (fig. 1) in which the base points of imposing of electrodes having certain designations and corresponding to specific areas of a surface of a brain are presented: frontal — F3, F4, nizhnelobny — F7, F8, frontal and polar — Fp1, Fp2, central — C3, C4, parietal — P3, P4, occipital — O1, O2, front and back temporal — T3, T4 and T5, T6, sagittal — Pz, Cz, Fz. Electrodes establish symmetrically in relation to the centerline of the head so that distances between the next electrodes on both sides were identical. The indifferent electrode more often imposed on a lobe of an ear is designated a letter A. The electrodes located on the right half of the head designate even counts, on left — odd. In clinical E. use schemes of assignments with the reduced quantity of electrodes (10 — 12). Distinguish two ways of assignments: bipolar, at Krom record EEG is carried out from two active electrodes, and monopolar when one active electrode, and the second — indifferent. Before installation of electrodes skin on the head is degreased (wipe with mix of alcohol, ether and acetone) that provides a normal amount of transfer resistance.
In a crust. time is recognized that registration only of EEG of rest (background, spontaneous EEG) is insufficiently informative for assessment of indistinctly expressed local disturbances and definition of activity patol. the center anyway influencing biocapacities of the neighboring and remote areas of cerebral hemispheres. For the purpose of identification patol. activities on EEG at clinical E. use a number of methodical receptions. To them tests treat with opening and closing of eyes during record EEG, and also exteroceptive irritations rhythmic or continuous light and a sound, proprioceptive and vestibular irritations. Other functional trials are the hyperventilation, dark adaptation, a dream and a deprivation (deprivation) of a dream. The choice of this or that functional trial for the purpose of specification of a ratio of focal and all-brain disturbances at patients decides on local damages of a brain by a condition of the patient, and also specific objectives of a research.
But to modern representations, EEG registered through the unimpaired covers of the head is the total, average bioelectric activity of a brain caused by synchronous activity of a set of neurons. By consideration of theoretical questions E. it is necessary to distinguish an origin of electric activity of a brain and an origin of rhythmics of biopotentials of bark and subcrustal educations (see. Bioelectric potential ). Existence of constant regular rhythmics on EEG testifies against the assumption that on EEG independent activity of the neural populations which are near the pickup electrode is registered. Total EEG represents organized oscillatory process, in Krom visually and especially accurately in the automatic machine analysis it is possible to allocate regular frequency components.
EEG is characterized by such main indicators as frequency, amplitude and a phase of fluctuations. For treatment fiziol. it is normal of value of these or those changes of EEG and at pathology it is important to estimate a form of biopotentials, their stability, spatio-temporal parameters.
In EEG the main allocate the following fiziol. rhythms with frequency ranges: 1 — 3 Hz — the delta (θ); 4 — 7 Hz — a theta (θ); 8 — 13 Hz — an alpha (α); 14 — 20 Hz — low a beta (βн); 20 — 30 Hz — high a beta (β); over 30 Hz — scale (γ) (fig. 2). Besides, are known registered in certain conditions of rolandicheskiya, or a mu (μ)-, and a kappa (κ) - rhythms, frequency to-rykh is in limits and-diaiazona.
The most characteristic, the main in EEG of the healthy person is the α-rhythm having amplitude in the range of 45 — 70 mkv, two-phase character and a sinusoidal form. The α-rhythm has the greatest expressiveness in occipital, occipitotemporal and occipitoparietal areas of a brain in a condition of the relative rest inspected at the closed eyes and relaxation of muscles. At 75 — 90% of healthy faces the α-rhythm is dominating, at other healthy faces it can have the reduced amplitude and not exceed expressiveness of other frequency components. Opening of eyes during registration EEG, short-term photoirritation cause an accurate desynchronization test of a α-rhythm, to-ruyu called blockade or a depression of a α-rhythm earlier. In a crust, time these changes of a α-rhythm are called reaction of the activation resulting from disturbance of synchronism of work of nervous elements of a brain in response to influence of any external or internal factor (fig. 3). Existence or lack of reaction of activation, degree of its expressiveness during irritation and a recovery rate of an initial α-rhythm after cancellation of an irritant (or during the closing of eyes) are used in the diagnostic purposes, and also in expert practice as objective criterion of reactivity of c. N of page.
Normal on EEG, except a α-rhythm, also other frequency components, more frequent and slower, than a α-rhythm come to light.
The beta rhythm has the frequency of 14 — 30 Hz and amplitude in the range of 15 — 20 mkv. This rhythm in the central and frontal regions of cerebral hemispheres is most expressed. It reflects the activated condition of subcrustal educations and a cerebral cortex. During registration of EEG at autokinesia of the right or left extremities of the examinee or visualization of this autokinesia by it, especially at record from an open surface of a brain, i.e. at record of an elektrokortikogramma (EKOG), shows changes of amplitude of a beta rhythm and a α-rhythm in front departments of cerebral hemispheres. And changes of a beta rhythm are more expressed, than the desynchronization of a α-rhythm occurring at the same time. At reirritation of esodic nerves amplitude of a beta rhythm increases by 2 — 3 times, the α-rhythm will be disorganized, the condition patholologically of steady hyper activation of subcorticocortical bonds develops (irritation). Such type of diffusion changes of EEG is observed at hyperkinesias, pain syndromes, in the period of an exacerbation of cerebral hypertensia, etc.
The theta rythm has the frequency of 4 — 7 Hz, amplitude does not exceed it amplitude of a α-rhythm. At healthy the theta rythm is shown from two parties in the form of short-term episodes of hl. obr. in front areas of hemispheres. It reflects activity of median and trunk formations of a brain and changes in process of age maturing of cortical and trunk bonds towards decrease in amplitude and duration of manifestation on EEG. At defeat of underlying structures of a brain amplitude of a theta rythm increases to 400 — 500 mkv that reflects a condition of excessive, permanent initiation of formations of a brain trunk and decrease in actually cortical akivnost.
The delta rhythm has the frequency of 1 — 3 Hz and amplitude which is not exceeding amplitude of a theta rythm at adults. Existence in EEG of waves of a delta rhythm indicates decrease in level funktsional activities of bark, e.g. at a drowsy state, exhaustion. Normal delta waves are registered quickly, diffuzno, in all assignments; at inclusion of irritations of any modality the delta rhythm is replaced by a α-rhythm. At organic expressions, e.g. at tumors of a brain, a delta wave are registered locally in a zone of the bark surrounding patol. the center, at irritation they do not disappear, and are slowed down, amplitude of fluctuations at the same time increases. Changes of a delta rhythm at irritations even more emphasize a zone local patol. changes on EEG or EKOG.
Normal in total EEG at 12-15% of examinees it is possible to manufacture a so-called rolandichesky rhythm, or a mu rhythm. It has the frequency of 8 — 12 fluctuations in 1 sec. and amplitude 40-60 mkv. The rolandichesky rhythm differs from a α-rhythm in topography and a form. It is registered preferential in the field of the central (rolandovy) furrow of cerebral hemispheres, has the form of arc-shaped, single-phase fluctuations of potential, to-rye do not change at photoirritations and are desynchronized at a muscular exercise (compression of a brush in a fist, etc.).
The kappa rhythm on the frequency range (8 — 12 Hz) matches a α-rhythm. It is registered in temporal areas of a brain at an intellectual tension when the α-rhythm in other areas of hemispheres is suppressed. Believe that α-, mu - and a kappa rhythms belong to one category of rhythmic activity of bark, they, apparently, are similar by origin and connected with activity of thalamic structures (see. Thalamus ).
A gamma rhythm call fluctuations of potentials of a cerebral cortex with a frequency more than 30 Hz and with an amplitude of fluctuations 8 — 12 mkv. Frequency of a γ-rhythm varies in the range from 30 to 100 Hz. Natural changes of a γ-rhythm are noted at different types of cerebration. At usual ink record EEG the γ-rhythm does not manage to be revealed, special processing of EEG is necessary for its detection.
On EEG are sometimes shown so-called over slow potentials, duration to-rykh it is measured seconds and even in tens of seconds. Superslow potentials, pe-visible, play a role in correlation of activity of different departments of a brain, in their «sonastroyka» at elaboration of new temporary bonds. On the ordinary electroencephalographs which are not supplied with amplifiers of a direct current it is almost impossible to write down superslow potentials through covers of a skull.
At different forms of functional activity of a brain is normal, and also at morbid and borderline cases complex assessment of EEG is necessary. At the same time it is important to consider not only expressiveness of separate rhythms, but also ratios of their frequency and amplitude indicators and spacing. In a crust. time widely is implemented the mathematical analysis of EEG with use of the COMPUTER which allows to carry out frequency assessment of total EEG and to express the power of each rhythm in quantitative indices (fig. 4).
Changes of EEG at various functional conditions of a brain. Picture EEG of the healthy person with accurate domination and - a rhythm, synchronization of electric activity can be received only in strictly certain conditions when inspected is in a condition of relative rest or the so-called weakened wakefulness: he lies or sits blindly, in the dark, sound irritations are excluded, muscles of a body are relaxed. In this state inflow of afferent impulses to c. the N of page is minimum that causes synchronous activity of neural ensembles of a thalamus and cerebral cortex and is shown on EEG in the form of dominating, arranged and - a rhythm. Strengthening or weakening of external or internal irritations changes picture EEG. Record EEG in a condition of active wakefulness is made in the same conditions (see above), but with presentation inspected a number of tasks, napr, on a short-term memory, tension of attention, with dominance of emotional loading of a positive or negative sign. On EEG at the same time there is a desynchronization of cortical rhythmics quite often with dominance of fluctuations of beta range, emergence a kappa rhythm in temporal assignments. However these ratios between the level of functional activity of bark and rhythms of EEG shall not be treated simply as mental activity of the person of direct reflection on total EEG, as we know, does not find. Further complex electrophysiologic and psychophysiological researches are necessary for disclosure of an electrophysiologic picture of active wakefulness.
Manifestation fiziol. changes of functional activity of a brain the condition of a dream is. A dream (see) unlike patol. states represents completely and quickly reversible process. The Elektroentsefalografichesky picture of a dream is heterogeneous. The phase of a slow dream is characterized by disappearance and - a rhythm, emergence of slow activity, expressiveness a cut increases in process of deepening of a dream, and also specific EEG-phenomena — so-called sleepy spindles, K-complexes. The phase of a REM sleep is shown by dominance of low-amplitude activity and so-called sawtooth categories with a frequency - 4 — 6 Hz. Emergence of sleepy spindles on EEG removed in conditions of both a physiological, and narcotic dream is treated as reflection of activity of talamokortikalny bonds; emergence of slow waves is connected with the bulbar synchronizing system, and fast-wave paradoxical phasa of a dream — with the ascending activating system of a mesencephalon. There are instructions on the fact that expressiveness of phases and stages of a dream on EEG depends on a condition of emotsiogenny subcrustal structures and on the nature of corticofugal influence of bark on nonspecific systems of a brain.
Unlike fiziol. the dream connected with cycle variations fiziol. functions of an organism, and the anesthesia caused by the purposeful dosed influences of narcotic substances, a lump (see) is the state caused patol. the process leading to dysfunction of the activating ascending system of a brain trunk and as a result to disturbance of consciousness. Fluctuations of extent of disturbance of consciousness are shown by various EEG-patterns (the sequence of certain forms of fluctuations) arising in process of deepening of coma. At a coma the basic is elektrofiziol. a research of reactivity of a brain on external irritations. Data of EEG gain important diagnostic and predictive value only in combination with assessment nevrol. disturbances.
According to EEG, allocate 4 stages of a coma. The first stage which is clinically shown a sopor, confusion of consciousness on EEG is usually characterized by disorganization and - a rhythm and emergence a theta - and delta waves with an amplitude of 50 — 70 mkv.
The second stage clinically is followed by loss of consciousness, but safety of reactions to intensive external irritations. On EEG in this stage a theta wave (5—6 in 1 sec.) also delta waves (2 — 3 in 1 sec.) with an amplitude up to 150 — 200 mkv, becoming frequent to 7 — 8 in 1 sec. in response to afferent irritations prevail generalized.
The third stage differs in lack of vegetative and electrophysiologic reactions to external influences. In this stage on EEG delay of rhythmics to 0,5 — 2 fluctuations in 1 sec. continues. Further decrease in amplitude diffuzno of widespread slow waves without regional distinctions and signs of mezhpolusharny asymmetry is observed that demonstrates deepening of coma.
The fourth stage is characterized not only by falloff of amplitude of slow forms of activity, but also emergence of the menacing electrophysiologic symptoms — the periods of so-called electric silence of a cerebral cortex. In this stage of gross violations of functions of c. the N of page needs to write down EEG at big strengthening (to 3 mkv/mm).
Use of methods of the mathematical analysis of EEG, in particular studying of the intercentral relations by calculation of coherence, allows to find a mismatch between areas of a brain in the third stage a ladle and their functional dissociation in the fourth stage.
Due to the achievements of resuscitation and transplantology there was a problem of objectification by means of different methods of process of attenuation of functions of a brain and the fact of death of a brain (see). One of the main criteria of death of a brain is electric silence of a cerebral cortex, at Krom on all assignments of EEG, mono - and bipolar, the line of record matches an isoelectric straight line, and the spontaneous and caused electric activity of a brain is absent. At the same time record EEG should be made at the maximum strengthening of the registering system of the device. Electric silence is one of reliable signs of death of a brain only when at the same time are absent nevrol. manifestations of function of a brain trunk and a cerebral cortex (see the Apallichesky syndrome), sharp intoxication and a hypothermia of a brain is excluded. For ascertaining of the fact of death of a brain of EEG it is necessary to register it is continuous, long (not less than 30 min.) at rest and not less than 10 min. at action of light, sound and pain stimulations. The visual analysis of EEG is insufficient for definition of death of a brain especially as carrying out functional loads in the course of record EEG at so heavy patients is very complicated, and sometimes it is almost impossible. In such cases of EEG are subject to the mathematical analysis.
Changes of EEG at damages of a brain at various levels. Strict nosological specificity of the frequency making EEG and reactive changes of total EEG at certain diseases of c. the N of page is absent. However it does not exclude need of studying of elektroentsefalografichesky syndromes, in a varying degree characteristic of damage of a brain at the certain levels and for his nek-ry diseases.
At localization patol. the center on a surface of hemispheres or near a surface of cerebral hemispheres of EEG it is characterized by the expressed mezhpolusharny asymmetry with decrease in amplitude and - a rhythm and dominance of delta waves on the party of defeat; existence patol. activities in a zone of the bark surrounding patol. the center (a perifocal zone), is more often in the form of the local delta waves (3 — 4 in 1 sec.) increasing at functional loads, especially at record of biopotentials from an open surface of a brain (fig. 5). Registration of electric activity of bark from an open surface of cerebral hemispheres during neurosurgical operations for tumors of a brain showed that EEG and EKOG reflect at pathology not destructive processes in brain fabric, and changes of reactivity of those structures, to-rye are not destroyed, but patholologically changed and continue to function at the reduced level of activity. At researches EKOG of a zone of the bark surrounding a tumor of a brain it was established that the tumor of a brain electrically is inert (from it rhythmics of biopotentials is not taken away) while in the zone of a cerebral cortex surrounding it the local medlennovolnovy activity called by the center of pathological activity is registered. In cases when on background EEG focal changes are absent or are expressed indistinctly, simultaneous registration of reactions of different areas bark in response to the same irritation helps to reveal patol. activity at tumors, abscesses, hematomas and epileptogenic focus at epilepsy. At localization patol. the center near a surface of parencephalons normal picture EEG meets much less often (5 — 10%), than at other localizations patol. center.
At localization of the center in korkovopodkorkovy departments of hemispheres of EEG it is characterized by polymorphism, variability that is explained by influence patol. the center on subcrustal structures and their bonds with a cerebral cortex, and also gradual involvement in patol. process of specific and nonspecific afferent systems of a brain.
Distinctive feature of EEG during the involvement in process of subcrustal nuclear structures is expressiveness of a bilateral theta rythm (4 — 7 in 1 sec.), periodic emergence of paroxysmal flashes of high-amplitude fluctuations in θ-or Δ-ranges, the trunk and thalamic structures reflecting symptoms of irritation is preferential in the frontal central regions. The more deeply local subcrustal process is located in a parencephalon, the less it is broken and - a rhythm and the more so paroxysmal forms of activity are expressed. Disturbance of reaction of activation (a depression of an alpha rhythm) is more expressed on the party patol. center.
Patol. the processes which are localized in basal and diencephalic area of a brain do not cause certain local changes of biopotentials at assignments them from a surface of hemispheres. Influencing the diencephalic, median and basal educations participating in genesis and - and θ-rhythms, patol. the centers of basal and diencephalic localization cause on EEG first of all disturbances of the space organization of rhythmic forms of activity of a brain. The most characteristic indicator of dysfunction of c. the N of page at the verkhnestvolovy and diencephalic levels serves emergence on EEG of paroxysmal flashes of the bilateral synchronized activity (in and - and θ-ranges)))))))))) which is most expressed in the frontal and central departments of hemispheres.
At localization patol. the center in the field of a back cranial pole the nature of changes of EEG is defined first of all by direct influence of process on median structures of a brain, to-rye functionally combine formations of a myelencephalon, a varoliyev of the bridge, a mesencephalon, a thalamus and a gipotalama sa, nek-ry mediobazalny formations of limbic system. At nizhnestvolovy localization the pro-mass is noted a wide spread occurance patol. activities on all areas of a brain. Bilateral pathological activity can be shown by paroxysmal flashes and to be constantly dominating.
At localization patol. the center in a cerebellum at adult patients safety of frequent cerebellar potentials (18 — 30 Hz) is observed die assignment from a normal hemisphere of a cerebellum and, on the contrary, their reduction in a zone patol. center (e.g., tumors). Insufficient use of a method of record of electric activity a hemisphere of a cerebellum — elektrotserebellogramma (ETsG) in a wedge. to practice is explained by complexity and morbidity of the manipulations connected with introduction of needle electrodes under a periosteum of scales of an occipital bone. Therefore for objective assessment of existence or lack of primary defeat of cerebellar structures the method of registration of electric activity of hemispheres of a cerebellum through the unimpaired covers of a skull is perspective, to - ry was not widely adopted yet.
Changes of biopotentials of a brain have diagnostic value at tumors of a brain, and also at vascular or posttraumatic focal processes (a hematoma, a heart attack of a brain, a bruise of a brain). So, by means of EEG patol. activity in a zone of a tumor decides at 80 — 85% ball on tumors of a brain. At vascular processes and a craniocereberal injury owing to diffusion changes on EEG reflecting trunk and all-brain reactions, the local pathological center comes to light only at certain stages of process in 50 — 60% of observations.
In a crust. time in clinical practice a computer tomography (see the Tomography computer), methods of radio isotope diagnosis are used (see) and ultrasonic diagnosis (see), giving rather exact information on localization, the sizes and character patol. center, existence and sizes of a perifocal zone of hypostasis, sizes of cerebral cavities, etc. In this regard clinicodiagnostic value E. gradually decreases. However E. remains by an irreplaceable method of a research at diagnosis and control of treatment of epilepsy (see), at the solution of problems of the functional neurosurgery directed to correction of the hyper activated structures of a brain at hyperkinesias (see) and pain syndromes (see Bol).
The Elektroentsefalografichesky syndrome at epilepsy differs in certain types of the convulsive activity which is shown acute high-amplitude categories, complexes peak — a slow wave or an acute wave — a slow wave. The complex peak — a slow wave is an electrographic phenomenon, pathognomonic for epilepsy. Its manifestation reflects typical epileptogenic neurodynamics in the form of excessive synchronous excitement bigger, than normal, quantities of populations of neurons, with their subsequent transition to a brake state. AA. quite often allows to differentiate true epilepsy with paroxysmal syncopal states, to reveal the epileptogenic center and to specify its localization, to define type of epileptic seizures (local, bilateral, generalized). Achievements of experimental physiology in disclosure of function of a reticular formation of a brain trunk and limbic educations promoted improvement of electrophysiologic diagnosis of the epileptogenic center in subcrustal (basal and diencephalic, mediobazalny and deep and temporal) structures of a brain. From in what zones of a brain populations of epileptogenic neurons concentrate, the possibility of differentiation of secondary bilateral epilepsy from primary depends. In recent years idea of pathological epileptic systems with difficult hierarchy of links is formulated: epileptic neuron — the epileptic center — epileptic system, sharply changing activity of all brain. Repeated assignments of biopotentials by means of the electrodes implanted in a brain reveal epileptogenic focus in underlying structures, at the same time epileptic categories can be defined a long time only within limbic system and thereof not to be shown on records EEG through covers of the head. At concentration of epileptogenic neurons within one area the most effective is surgical treatment of epilepsy, in the presence of the epileptic centers in several areas of a brain — treatment by means of the multiple electrodes implanted into a brain (see Epilepsy). Different types of epileptic activity can be differentiated during the use of methods of functional provocation. Bilateral and synchronous flashes of slow waves without combination to acute categories at test with a hyperventilation at adults are an indicator of dysfunction of trunk systems of a brain, but not proyav a leniye of epilepsy. Identification on EEG of epileptic activity in nek-ry cases can be promoted by dark adaptation, a night dream (its medlennovolnovy phase), and also a deprivation of a dream within one-two nights. The sleep deprivation provokes the general synchronization of brain potentials that favors to identification hidden in the awake condition of epileptic activity.
The vascular diseases of a brain which are not followed by the expressed ischemia of brain fabric do not cause essential changes on EEG. At an idiopathic hypertensia diffusion disorganization and - a rhythm and emergence of low-amplitude acute and slow potentials are considerably expressed only at late stages of a disease. At brain strokes data of EEG help to define character patol. process (a hemorrhagic or ischemic stroke) to specify localization patol. center (cortical stroke or deep, subcrustal). Expressiveness of changes of EEG at fibrinferments and stenoses of the main arteries of the head depends on extent of disturbance of cerebral circulation and opportunities of collateral circulation. Apply functional trials with short-term crossclamping of one or two arteries to detection of the hidden deficit of blood supply of a brain (sleepy or vertebral), at the same time the zone of the steadiest local disturbances of biopotentials of a brain comes to light.
At patients with aneurisms of vessels of a brain without intracraneal hemorrhages of change of EEG are absent or are unstable and expressed indistinctly. At hemorrhage owing to a rupture of aneurism of vessels of a brain of EEG allows to specify whether hemorrhage is subarachnoidal or intracerebral, whether there was a rupture of a vessel at a konveksitalny surface of hemicerebrums or on its basis.
Features of EEG at a craniocereberal injury are defined by its weight. At a slight craniocereberal injury generally unstable changes of EEG indicating not rough irritation — an irritation of bark of a great brain are observed. These changes disappear within the first two months after an injury. At an injury of average and heavy degree on EEG not only changes and - a rhythm, but also pathological activity in Δ-, θ-ranges come to light.......... Intracranial hematomas (subdural or epidural) are shown by mezhpolusharny asymmetry of biopotentials of bark with emergence on 5 — the 8th day after an injury of local slow pathological waves. Chronic subdural and epidural hematomas do not cause essential changes on EEG in most of patients, only at 7 — 10% of patients noticeable local disturbances are registered. In the acute period after an injury into the forefront disturbances of functions of trunk and diencephalic departments of a brain quite often act, to-rye are shown on EEG by bilateral flashes pointed alpha and theta rythms. At a severe craniocereberal injury the slow polymorphic waves which almost are not changing at external irritations prevail. At the severe craniocereberal injury which is followed by coma (see Côme), the electroencephalography helps to diagnose a possible hematoma and to predict extent of recovery of activity of a brain after the EEG loudspeaker. At an ultraboundary coma of EEG serves as method of objective assessment of weight of a condition of sick and irreversible fading of life activity of a brain, at a cut so-called zero EEG (electric silence of a brain) is registered.
At patients with a slight injury and a moderately severe injury at happy ends in the remote period of EEG it is completely normalized. At a severe injury it is recovered normal and - a rhythm and reaction of activation, local disturbances considerably smooth out, but completely do not disappear. Quite often at E. posttraumatic epileptic activity of bark comes to light (acute waves, nicknames, complexes peak — a slow wave) that can serve as the indication to purpose of preventive anticonvulsant therapy even at absence at sick convulsive attacks and paroxysms.
Elektroentsefalografichesky syndromes at inflammatory diseases of a brain — arachnoidites (see) are, as a rule, characterized by rather easy diffusion changes of EEG in the form of decrease in amplitude and irregularity and - a rhythm, and also dominance of more frequent fluctuations. At arachnoidites of optiko-hiazmalny localization diffusion manifestations of an irritation of bark come to light in basal assignments of EEG by means of a nasopharyngeal electrode more accurately. More noticeable changes of EEG with the advent of slow waves demonstrate development of more crushing organic lesion of a brain. At encephalitis (see) and arakhnoentsefalita all-brain pathological slow waves (1 — 4 Hz) with epileptic categories and flashes bilateral Δ-and θ-fluctuations are registered.......... At most of such patients on EEG signs of involvement in patol come to light. process of trunk and median formations of a brain. In the residual period of inflammatory diseases of c. the N of page extent of changes of EEG depends on degree and character of the residual phenomena, usually they correlate with nevrol. symptomatology.
In the last decades for studying of various forms of pathology of a brain use not only EEG, but also registration of so-called evoked potentials, to-ruyu carry out through covers of the head by means of automatic electronic devices (neuroaveragers) allowing to allocate weak signals from noise of background (spontaneous) fluctuations of biopotentials. Evoked potentials are registered in the form of a characteristic complex of fluctuations of potential in projective and other zones of a cerebral cortex in response to single short irritations light, a sound, etc. (fig. 6).
At the first stages of formation of a method of registration of evoked potentials their late components arising with stage of latency of 120 — 250 ms after inclusion of an irritant were studied. Early components of evoked potentials, on modern representations, are connected with the lemniskovy fast-carrying-out projective system, with specific thalamic kernels and talamokortikalny projections. Later components of evoked potentials are caused by carrying out excitement on slowly carrying out fibers, to-rye switch to the nonspecific thalamic kernels connected with kernels of a reticular formation and a limbic complex. The circle of the issues resolved by means of a method of registration of evoked potentials is wide. It includes assessment of a condition of sensitivity of afferent systems during the studying of problems of perception and processing of information for the purpose of diagnosis of peripheral and central damages of a brain. The method of registration of evoked potentials gains the increasing value in studying of psychophysiological problems of perception of signals of the environment on a different emotional background, in disclosure of mechanisms of memory and attention, and also in questions of psychiatry.
Multiple records of evoked potentials at 12 — 16-channel assignments reveal a mosaic of local reactions in the healthy and struck hemisphere. At registration of EKOG from an open brain more accurately, than at registration of EEG through covers of the head, change of evoked potentials in a perifocal zone of a tumor, and also in a zone of the intracerebral center is shown. Despite broad development of researches by method of evoked potentials in the field of clinical neurophysiology, still there are no settled principles of diagnostic use it with the indication of the choice of the most effective criteria in the analysis of specific and nonspecific evoked potentials at patients with organic and functional forms of diseases of a brain.
The last decade was marked by development of the so-called capacities of the remote field which are taken away from the surface of the head, but generated by trunk educations in response to sound click. Extremely weak signals and rather bystry fluctuations of trunk potentials demand for their detection and registration of use of the special equipment. Fiziol. value of various components of acoustical trunk evoked potential, a possibility of their correlation with certain kernels and conduction paths in a brain trunk are in a stage of studying. At hemilesion of a brain trunk accurate asymmetry of trunk evoked potentials with their reduction on the party of defeat is expressed. The most noticeable narushenya components of trunk evoked potentials are observed at posttraumatic comas.
In the long term development clinical E. comparison of the bioelectric and electromagnetic processes arising in a brain at various functional conditions of the healthy and sick person is represented effective.
Broader use of mathematical methods of the analysis of an ECG for the purpose of the quantitative characteristic of the intercentral bonds and their reorganizations at a research of generalized and local reactions in combination with opportunities of stereotaxic and telemetric methods will allow to open in the future fiziol. origins and fixing patol. states at various diseases of a brain. In this regard issues of diagnosis of diseases of a brain by means of EEG will be resolved at the new methodological level.
Electroencephalography at children. Age features of EEG are caused by process of an ontogeny of electric activity of various areas of bark in process of maturing of the morfofunktsionalny organization of a brain. At certain stages of this process there are essential changes in a frequency range of EEG and spacing of biopotentials that is connected with a geterokhronnost of maturing of bark and subcrustal areas with various extent of participation of these structures in formation of EEG at children of different age. Record EEG at children is made in a condition of a dream and wakefulness, apply a special helmet to imposing of electrodes.
The type inherent to the healthy newborn during wakefulness is found from 36th week of pre-natal development. Since this period of EEG gains continuous character, it is synergistic in both hemispheres. Low-amplitude waves with a frequency of 1 — 2 and 3 — 4 Hz without interruption in any of areas are registered.
In certain cases during wakefulness flat EEG is registered, amplitude of fluctuations does not exceed a cut 10 mkv. In the period of a neonatality distinctions of EEG of a dream and wakefulness are established. In the period of activity at newborns the continuous medlennovolnovy activity modulated by slow rhythms is defined. In a phase of a quiet dream continuous wave activity is registered.
At the age of 6 weeks the organized slow rhythm (sleepy spindles) in the central regions of a brain appears during a quiet dream. At children at the age of 3 months on EEG the expressed rhythmic activity in the range of 3 — 5 Hz prevailing in occipital and parietal departments of bark of cerebral hemispheres and blocked at light stimulation is noted. Frequency and stability of this rhythm progressively increase, reaching 6 — 7 Hz by the end of the first year of life.
At the age of 6 — 8 months on EEG in a condition of a somnolence the theta rythm with a frequency up to 4 Hz appears vysokoamplitudiy (75 — 200 mkv). By the end of the first year of life recurrence of circadian rhythms of wakefulness and various phases of a dream is finalized. The delay of formation of EEG-patterns during the specified age periods testifies to deviations during normal development of a brain.
At the age of 1 — 3 years further increase of frequency of the main rhythm of EEG of quiet wakefulness is noted, the edge is reached by 7 — 8 Hz, and amplitude increasing to 80 mkv. Expressiveness of these fluctuations decreases in front departments of bark of cerebral hemispheres, it is minimum in frontal departments of cerebral hemispheres. Waves of fluctuations with a frequency of 6 — 8 Hz alternate the groups of high-amplitude fluctuations with a frequency of 3 — 4 Hz which are most expressed in front departments of hemispheres. In all registered areas existence of fluctuations with a frequency of 18 — 25 Hz is noted. Individual variations of EEG at children at the age of 1 — 3 years are more considerable, than on the first year of life.
At the age of 4 — 6 years big individual variability of EEG also remains. In one cases the rhythmic fluctuations with the dominating frequency of 6 — 7 Hz which are preferential expressed in occipital departments of bark in others become the leading type of electric activity of a brain — fluctuations a theta range of more low frequency (4 — 6 Hz) which are preferential expressed in perednetsentralny departments of bark have considerable specific weight. They often are registered in the form of bilateral generalized flashes, to-rye have periodic character, have high amplitude (to 80 — 100 mkv) and are preferential expressed in temennotsentralny areas of bark. There can be also transition types of EEG.
At the age of 7 years domination of fluctuations with a frequency of 8 — 10 Hz in occipital area comes to light. In the central EEG cortical regions has polymorphic character. Electric activity of bark of occipital shares prevails over electric activity of the central departments of amplitude in all frequency range. In EEG the bilateral complexes of high-amplitude slow waves registered at earlier age remain. Domination both in occipital, and in the central regions of bark of fluctuations with a frequency of 8 — 12 Hz is characteristic of children of 8 — 9 years. Amplitudes of these fluctuations are significantly higher in bark of occipital shares.
At the age of 10 — 12 years against the background of the alpha rhythm dominating in all cortical areas, to-ry it is uneven on the frequency (8 — 12 Hz) and amplitude, significant increase in expressiveness of a slow component of a range of EEG is noted, it is preferential in the central cortical area, connected, apparently, with activation of diencephalic area in the prepubertatny period. Bilateral generalized flashes of paroxysmal activity since this stage of ontogenesis are not registered any more.
By 14 years stabilization of the main rhythm of electric activity in all areas of bark of cerebral hemispheres is observed. Frequency and - a rhythm, characteristic of the adult — 8 — 12 Hz is established, and frequencies of the upper bound of a range are prevailing. Differences from EEG of the adult are expressed in nek-rum dominance at a number of children of slow fluctuations that reflects functional changes of c. the N of page connected with puberty. By 16 — 17 years of EEG gains character stable, inherent to this individual.
EEG is widely used in children's neurologic clinic for the purpose of diagnosis various patol. states and for control of treatment. At epilepsy and epileptiform syndromes on EEG paroxysmal activity in the form of monomorphic medlennovolnovy flashes, typical complexes of waves (peak — a wave) and single or multiple pinnacled potentials can be found. These categories can be single or in the form of series and are registered in all or in separate assignments. At infantile spasms at children of early age polymorphic paroxysmal activity — a so-called hypsarrhythmia can come to light almost constant high-amplitude (to 600 — 700 mkv). At other organic lesions of the central nervous system on EEG resistant mezhpolusharny asymmetry of fluctuations of biopotentials or the general disorganization of a rhythm can be observed. In many cases data of EEG help to localize the center of defeat.
Indicators of EEG at any disease shall be correlated to the given clinical inspection and anamnestic data.
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