The reflection of compensation processes in the structure of the EEG spatial-temporal relationships in patients with disordered brain regulatory mechanisms]

Studies of intercentral relations of electrical activity in the cerebral cortex of the patients with hypophysis tumours under the conditions of chronic (before operation) and acute (after tumour ablation, early post-operative period) influence of the focus on the regulatory brain systems allowed to reveal definite changes of spectral-coherent EEG characteristics, reflecting the functional state of the cerebral adaptive-compensatory apparatus. It has been shown that reciprocal character of changes of various forms of the brain electrical activity and their intercentral relations is one of manifestations of development of the processes of cerebral compensation. At the same time, global fall of the EEG intercentral relations indicating the disintegration of the cerebral functional connections, reflects a loss of CNS compensatory mechanisms. The revealed EEG-characteristics at the present time are applied in Burdenko Institute of Neurosurgery for diagnostic-prognostic estimation of the brain functional state in patients during pre- and post-operative period.     

Optimal structure of the connections of the electrical processes in the human cerebral cortex and its disorders in changes of state

In this paper the data are analyzed on the human EEG investigation. Significance is shown of parameters of correlative and spectral-coherent EEG functions for the estimation of the brain functional state of healthy people and patients with local cerebral lesions. In the norm, the parameter of the mean coherence is stable, its characteristics correspond to the optimum cortical tone, the most favourable for the performance of the cortical functions. In healthy people unstable, individual, different in different cortical areas changes of the spectrum details, coherence and phases reflect local processes, taking place at the optimum mean level of the coherence and form the cortical mosaic. These two sides of the intercentral relations of the electrical processes (optimum level of coherence and dynamic mosaic of connections of separate rhythms) reflect the most favourable conditions of the nervous processes development. In the brain pathology, different forms are noted of deviations from the system of intercentral relations and levels of coherence of cortical electrical processes.     

Intracerebral EEG functioning as a reflexion of the systemic brain organization in norm and pathology

The authors summarized the EEG findings and defined the nature of intercentral EEG relationships in different functional states of healthy subjects and patients with organic cerebral pathology based on coherence analysis. The EEG features typical of healthy subjects were identified: an anterior-posterior gradient of the mean coherence and the character of cortical-subcortical relationships in the anterior cerebral structures. Right- and lefthanded subjects showed the frequency and regional differences in EEG coherence, which reflected, mainly, specific intracortical relationships. Development and regression of pathologic signs in right- and lefthanded patients with organic brain lesions are thought to be determined by these differences. As distinct from cortical pathology, lesions of regulatory structures (diencephalic, brainstem, and limbic) were shown to produce more diffuse changes in intercentral relationships with a tendency to reciprocity. Intercentral relations, including their interhemispheric differences, varied with changes in the functional state of healthy subjects (increase and decrease in the level of functioning). A certain time course of changes in intercentral relationships was also revealed in patients with organic brain lesions during recovery of their consciousness and mental activity. Changes in the dominance of activity of individual regulatory structures are considered to be one of the most important factors that determine the dynamic character of EEG coherence.     

Changes in the brain spontaneous bioelectrical activity during transcranial electrical and electromagnetic stimulation

In order to study systemic brain reactions on transcranial electrical or electromagnetic medical stimulation and specify the neurophysiological criteria of its efficiency, comparative clinical and experimental examination was performed with the analysis of spontaneous bioelectric activity and behavioral or clinical parameters. We examined 6 patients with prolonged posttraumatic unconsciousness states treated with electrical stimulation and 17 intact Wistar rats subjected to electromagnetic stimulation of the brain. The effect of the transcranial stimulation was shown to depend on the initial level of the intercentral interactions of brain bioelectrical activity, estimated by the EEG coherence. Hypersynchronization of biopotentials as the main element of the brain reactivity can be the most useful for the rehabilitation of patients with cerebral pathology in cases of initially lowered level of the intercentral interactions in the absence of pathologically strengthened functional connections.     

The significance of interhemispheric asymmetry in the development of compensatory processes in the human brain

For more precise definition of the role of hemispheric interconnections in mechanisms of human CNS compensation the intercentral relations of the electrical activity of the left and right cerebral hemispheres were studied on physiological model of focal interhemispheric asymmetry. Spectral-coherent EEG characteristics of 36 patients with tumoral damage of one hemisphere were studied in condition of chronic (prior to operation) and acute (early terms of postoperative period) brain decompensation. In was shown that the reorganization of the structure of the EEG intercentral relations correlated with definite stages of CNS compensatory processes and that the character of hemispheric interconnections depended on the lateralization of the damage focus. The primary role was revealed of the degree of the left (dominant) hemisphere preservation in restoration of normal pattern of the interhemispheric asymmetry of the coherence of human brain electrical processes.     

Coherent analysis of the EEG during development of trace processes of the polarization dominant in the rabbit

By the method of spectral-correlation analysis, the dynamics was studied of changes in intercentral relations of electrical activity in the sensorimotor and premotor cortices of both cerebral hemispheres during formation, course, recovery and extinction of motor dominant created by a single action of DC anode in rabbits sensorimotor cortex. The motor dominant is capable to be preserved during the test for a long time after DC switching off and to recover in subsequent days under the action of testing stimuli. It should be noted that the recovery of the structure of intercentral relations of electrical brain activity, characteristic of dominant state, takes place much earlier than the motor "dominant" reaction.     

The role of cerebral regulatory structures in the formation of human EEG

This article generalizes the results of many years’ studies of the EEG of patients with tumorous lesions in the diencephalic, brainstem, and limbic structures, which fulfill the regulatory function in ensuring integral brain activity. The specific features of the inclusion of individual structures under investigation in the organization of the intra- and interhemispheric relations of cortical biopotentials were demonstrated against the background of diffuse changes in the biopotentials that reflect the systemic character of neurodynamic reorganizations when the regulatory brain structures are involved in the pathological process. This study expands the idea of the predominant functional connection of the diencephalic structures with the right hemisphere and brainstem structures with the left one with determination of the regional specific features of changes in the intrahemispheric EEG coherences. The distinguishing features of intercentral relations when the limbic structures are involved in the pathological process show similarity with the neurodynamic reorganizations in patients with lesions in both diencephalic and (even more so) brainstem structures. Universal elements were detected in the formation of integral adaptive reactions of the brain with lesions in its regulatory structures, which reflects their close functional interaction and makes it possible to consider them the individual links of an integral regulatory system. The study revealed reciprocal changes in various forms of electrical activity, which reflects reciprocation of interaction of individual regulatory structures. This is one of the EEG equivalents of the formation of adaptive-compensatory cerebral reactions. The specificity of influence of the studied regulatory structures are clearly seen in situations of their morphofunctional isolation observed during cerebral coma. In these conditions, when the cortex is functionally inactive, the authors demonstrated the dynamic character of changes in interhemispheric asymmetry, which reflects the dominance of individual links of the regulatory system playing the role of supreme regulator of life support of the body in critical states.     

Intercentral correlations in the cerebral cortex according to the EEG coherence index after restoration of consciousness and speech following prolonged coma

Power spectra and coherence function of EEG of various cortical areas of both hemispheres were analyzed in 9 patients with extremely protracted loss of consciousness. Five patients were in the state of posttraumatic apallic syndrome lasting for more than 4 years in one patient, and 4-9 months with successive lethal outcome in 4 patients. One patient for more than 2 years was in a state of areactivity to external signals. In 3 patients the process of recovery of consciousness and speech began in 1-2 months. At the apallic syndrome, only low-frequency EEG components were present in spectrograms, and the values of coherence function were sharply decreased. With recovering consciousness and speech, a gradual appearance of alpha-activity was observed as well as an increase of coherence values at the frequency of the alpha-rhythm. The recovery of intercentral EEG relations in the motor-verbal cortical area was shown to play a special role in further normalization of connections in the cerebral cortex.     

A Brain-Machine Interface for Control of Medically-Induced Coma

Medically-induced coma is a drug-induced state of profound brain inactivation and unconsciousness used to treat refractory intracranial hypertension and to manage treatment-resistant epilepsy. The state of coma is achieved by continually monitoring the patient''s brain activity with an electroencephalogram (EEG) and manually titrating the anesthetic infusion rate to maintain a specified level of burst suppression, an EEG marker of profound brain inactivation in which bursts of electrical activity alternate with periods of quiescence or suppression. The medical coma is often required for several days. A more rational approach would be to implement a brain-machine interface (BMI) that monitors the EEG and adjusts the anesthetic infusion rate in real time to maintain the specified target level of burst suppression. We used a stochastic control framework to develop a BMI to control medically-induced coma in a rodent model. The BMI controlled an EEG-guided closed-loop infusion of the anesthetic propofol to maintain precisely specified dynamic target levels of burst suppression. We used as the control signal the burst suppression probability (BSP), the brain''s instantaneous probability of being in the suppressed state. We characterized the EEG response to propofol using a two-dimensional linear compartment model and estimated the model parameters specific to each animal prior to initiating control. We derived a recursive Bayesian binary filter algorithm to compute the BSP from the EEG and controllers using a linear-quadratic-regulator and a model-predictive control strategy. Both controllers used the estimated BSP as feedback. The BMI accurately controlled burst suppression in individual rodents across dynamic target trajectories, and enabled prompt transitions between target levels while avoiding both undershoot and overshoot. The median performance error for the BMI was 3.6%, the median bias was -1.4% and the overall posterior probability of reliable control was 1 (95% Bayesian credibility interval of [0.87, 1.0]). A BMI can maintain reliable and accurate real-time control of medically-induced coma in a rodent model suggesting this strategy could be applied in patient care.     

Cerebral Oxidative Metabolism and Blood Flow During Acute Hypoglycemia and Recovery in Unanesthetized Rats

Abstract: Progressive neurological depression leading to coma was produced in unanesthetized rats at a constant level of hypoglycemia induced by insulin. High-energy phosphate concentrations in brain remained normal during hypoglycemic lethargy, but ATP declined by 6% during stupor and by 40% during coma that was characterized by an isoelectric EEG. Cerebral blood flow (CBF) remained normal during hypoglycemia whereas the cerebral metabolic rates for oxygen (CMRo₂) and glucose (CMR_glucose) decreased by 45 and 73%, respectively, indicating oxidation of nonglucose fuels. A plot of CMRo₂ and CMR_glucose versus plasma glucose indicated increasing oxidation of alternate substrates (elevated CMRo²/CMR_glucose) at plasma glucose concentrations below 2.5 mm . The cerebral uptake of β-hydroxybutyrate increased during hypoglycemic stupor and its complete oxidation could account for the CMRo₂ in excess of glucose utilization. Brain ammonia, a byproduct of amino acid metabolism, reached a level during hypoglycemic coma sufficient to produce coma in normoglycemic animals. The rate and degree of recovery after glucose administration depended on the duration of hypoglycemia and the pretreatment neurological state of the animal. Following 10 min of glucose infusion, ATP levels that were modestly depressed in stuporous rats recovered fully, paralleling the animals' apparently full neurological recovery. Rats that had been in hypoglycemic coma for 1 min or less fully recovered high-energy phosphate concentrations in brain. However, when normalization of plasma glucose was delayed for more than 1 min of coma, the CMRo₂ remained depressed, CBF decreased to 40% of control, and high-energy substrates failed to normalize. In keeping with the depression of oxidative metabolism and blood flow, neurological function and the EEG remained abnormal even after 1 h of glucose infusion. The findings suggest that irreversible brain injury may develop within the first minutes of hypoglycemic coma.     

Cortico-hippocampal relation of electrical activity during a motor polarization dominant in rabbits

By the method of spectral-coherent analysis, the intercentral relations were studied of the electrical activity of the sensorimotor and premotor cortices and of CAs field of the dorsal hippocampus of both hemispheres during the motor polarization dominant, created by the action of the direct current on the rabbits sensorimotor cortical area. The formation was shown of a new structure of the intercentral relations of electrical activity of the sensorimotor cortex and CA3 of the dorsal hippocampus. It should be noted that the dominant optimum and its inhibition are characterized by different interhippocampal relations: at the optimum a low range of the theta-rhythm is highly coherent while at the activation of "the non-dominant" hemisphere--a high range.     

Intercentral EEG relationships in regressive and chronic post-traumatic Korsakoff syndrome.]

Dynamic EEG study of patients with posttraumatic Korsakoff's syndrome (KS) with the application of complex analysis methods revealed a complicated pathological structure of the intercentral relations of cortical electrical activity. The interhemispheric EEG coherence between symmetrical frontal cortical areas are sharply reduced, while the intrahemispheric coherence are increased in comparison with the normal values. The proposed technique of segregation of statistically homogeneous spectro-coherent characteristics made it possible to reveal the earlier intercentral EEG relations formed by stable and variable coherence spectra. The structure formed by the stable and variable coherence spectra in KS differs from that reflected in the mean coherence levels. During the KS regression, the EEG coherence between the right and left frontal areas increased to the normal level, and the variable spectra are revealed. In the chronic KS syndrome, the pathological intercentral relations persist, while the variable relations in the frontal areas are absent. A reduction of pathologically decreased intrahemispheric coherence selectively revealed in the right hemisphere during the KS regression and formation of variable relations in this hemisphere point to a leading role of the right hemisphere in development of compensatory processes in KS. The reciprocal relations between the intra- and interhemispheric coherence and coherence dynamics in the theta rhythm suggest that pathological activity in the basal diencephalic structures plays an important role in formation of the pathological EEG pattern in KS.     

Cerebral responses of healthy humans to rhythmic transcranial magnetic stimulation of different intensities

The effect of rhythmic transcranial magnetic stimulation (rTMS) of different intensities (single superthreshold rTMS more intense than 1.2 T and subthreshold one with an intensity of 70–80% of the motor threshold) of sagittal premotor cortical areas on the human functional activity was estimated in eight volunteers on the basis of combined EEG, neuropsychological, and hemodynamic examinations. The objectives of the study included the selection of the frequency of activating stimulation and revision of the objective EEG criteria of rTMS efficiency. It has been demonstrated that analysis of the EEG response to photostimulation at different frequencies is efficient in selecting the rTMS frequency. The EEG coherence is one of the most informative characteristics of the rTMS effect on central neurodynamics. The functional effects of stimulation (activating or inhibitory) have been shown to depend on the initial level of intercentral coherent relationships It has been found that rTMS of the sagittal premotor cortex causes definite changes in the functional activity of a healthy brain different from those caused by placebo. These changes are greater in the left hemisphere (in the form of intrahemispheric changes in coherence and depend on the stimulation intensity (superor subthreshold) and the initial state. The vascular factor has been shown to play an important role in the formation of cerebral responses to rTMS.     

Asymmetry of the bioelectrical activity of the human brain at different levels of consciousness

Asymmetry of different human EEG indices was studied at different levels of consciousness. Subjects' self-reported changes in the content of consciousness: the intensity and quality of involuntary mental processes served as indicator of the level of consciousness. It was shown that a certain profile of EEG asymmetry corresponded to each the observed level of consciousness. In active state of consciousness, the connections in the high-frequency bands: beta-2 and gamma, were more pronounced in the left hemisphere of the brain. At the same time, transition of the focus of coherent connections to the right hemisphere was characteristic of the state of inhibition of "internal speech". The interhemisphere dynamics of autospectra amplitude and foci of coherent connections supports the notion that the character of interhemisphere asymmetry of the brain bioelectrical activity depends on its functional state.     

Electroencephalographic correlates of individual features of the mental efficiency of adolescents

Evident correlations of spatial-temporal organization of the electrical brain activity with individual features of the mental working capacity were revealed in juveniles by the methods of analysis of spectra power density and of coherence function of rhythmic EEG components. EEG in juveniles with a low working mental capacity is characterized by hypersynchroneity, monofrequency, low reactivity of alpha-rhythm and high level of generalized spatial synchronization. Juveniles with high level of mental working capacity are characterized by regional specificity of the main EEG rhythm, the presence of the local dynamic foci of interconnected activity. It is suggested that the correlation of mechanisms of controlled local and non-specific generalized cortical activity is one of the main factors, determining the individual specificity of mental ability.     

Age-related specificity of the frontal and temporoparietal cortex activation levels in three-to seven-year-old children

The results of studies on the specificity of formation of the frontal and temporoparietal cortex activation levels in children aged three, four to five, and six to seven years with a normal development of higher mental functions and speech are summarized. The parameters of the stable millivolt-range potential recorded from the head surface were used for this purpose. The results obtained are compared with published data on the specificity of the morphological and functional organization of the brain and the level of development of the slow information control system estimated on the basis of EEG parameters at the same ages. The estimation of the contribution of the brain superslow information control system by one of the basic parameters of state makes it possible to determine, in quantitative terms, (1) the characteristics of the formation of activation levels of cerebral systems involved in the regulation of the resting state, higher mental functions, and speech at different stages of ontogeny; (2) (on the basis of the stable-potential variance) the degrees of freedom of the activation levels of the cerebral systems studied, which determine their regulatory capacity at different ages; and (3) the degree of development of the system-forming mechanisms combining all these systems into an integrated whole at a certain stage of ontogeny (from six to seven years of age).     

A psychophysiological approach toward the problem of consciousness

Psychophysiological analysis of the relationship between the level of consciousness and the brain activation permitted an identification of three levels of consciousness at the transition from wakefulness to sleep. A change in the intensity and quality of involuntarily mental processes served as an index of the level of consciousness according to subjects' self-reports. It was found that a certain EEG profile corresponds to each level of consciousness under study. Data obtained showed that the lowest level of activation corresponds to a state in which a subject notes an inhibition of "internal speech", "failure of thoughts". At this case the dynamics of the EEG high frequency rhythm changes which is possibly related to the mechanism of transmission of cognitive information.     

Use of EEG-based Adaptive Biocontrol in Correcting Neurological Patients' Functional State

This article deals with changes in the EEG amplitudes and frequencies, spatial distribution of the main EEG rhythms, and structure of the interconnections between various zones of the hemispheric cortex in neurological patients before and after adaptive biocontrol sessions aimed at normalizing their state. The authors discuss the strategy and tactics of adaptive biocontrol with regard for the individual disorders of EEG parameters. Purposeful voluntary modification of the structure of interzonal relations leads to the rearrangement of intercentral connections and contributes to the cessation of pathological states; neurological symptoms completely disappear in most of the patients. It is concluded that if the parameters of purposeful EEG regulation are selected properly, taking into account individual rearrangements, adaptive biocontrol may be used more widely in rehabilitation.     

脑死亡与脑昏迷脑电信号的复杂度研究

脑死亡诊断是有关病人生死的重要问题.许多国家都把脑电平坦列为脑死亡诊断的基本条件,但研究发现并非所有的脑死亡患者均表现为脑电平坦,同时脑昏迷患者在部分情况下也会表现出脑电平坦的现象,从而有可能在临床中造成误判.C0复杂度判断指标能够利用脑电信号中的复杂度特性帮助临床诊断中对于脑死亡和脑昏迷状况的鉴别.运用C0复杂度算法对22位脑死亡和脑昏迷病例进行分析实验,可以发现脑死亡脑电信号的复杂度明显高于脑昏迷脑电信号的复杂度.实验表明C0复杂度可以用来有效地区分脑死亡和脑昏迷脑电信号,具有潜在的重要临床价值.     

The reflection of different levels of the regulation of human brain activity in spectrally coherent EEG parameters]

On the basis of clinico-anatomo-electroencephalographic studies it was shown, that in early terms of cerebral trauma, at gross disturbances of the cortical functions and safety in some cases of only vital regulation, the parameters of the EEG stability or variability are of distinct information value for estimation of the functional state of patients. It was established, that changes of stability of the frequency, power, and coherent EEG characteristics correlate with different parameters of changes of the structural-functional brain organization. At this stage the greatest connection with the disease outcome reveals the EEG coherence parameters of the cortical symmetrical points reflecting the state of predominantly median formations and general brain reactions to traumatic action. In the process of restoration of disturbed neuromental functions priority prognostic significance is acquired by parameters of intrahemispheric coherence as well as by frequency-regional properties of interhemispheric asymmetry of coherence of the brain electrical processes, characterizing functional features of the lesion focus.