G. N. Boldyreva

Electroencephalographic Intercentral Interaction as a Reflection of Normal and Pathological Human Brain Activity

The authors summarized EEG findings and defined the nature of the intercentral EEG relationships in different functional states in healthy subjects and patients with organic cerebral pathology, based on a coherence analysis. Similar EEG characteristics in healthy individuals were identified: an anterior-posterior gradient of average coherence levels, the type of cortical-subcortical relationships in anterior cerebral structures. Right- and left-handed individuals showed frequent and regional differences in EEG coherence, which mainly reflected specificity of intracortical relationships. Development and regression of pathology in right-and left-handed individuals with organic brain lesions were thought to be caused by these differences. Lesions of regulatory structures (diencephalic, brain stem and limbic structures) provoked a more diffused kind of changes of intercentral relationships, in contrast to cortical pathology. These changes tended to reciprocate. The dynamic nature of intercentral relationships and their interhemispheric differences was revealed when changing functional states of the brain (increase and decrease of functional level) in healthy individuals and patients with organic cerebral pathology in the process of conscious and psychic activity restoration. Changing activity predominance of certain regulatory structures was considered one of the most important factors determining the dynamic nature of EEG coherence.

[fMRI-EEG study of healthy human brain responses to functional loads].

The functional magnetic resonance imaging (fMRI) and EEG responses to identical functional (visual and motor) loads have been compared in ten healthy subjects with the use of individual structural MRIs of the brain. It has been established that an increase in the coherence of the EEG α waves corresponds mostly to the zone of the fMRI response (as a +BOLD reaction). Reactive rearrangements, according to the data of fMRI and, particularly, EEG studies, are characterized by pronounced interindividual variation, which increases along with the functional test complexity. The fMRI responses have shown a greater locality and closer dependence on the modality of presented stimuli than EEG rearrangements, which underline the systemic character of brain response to functional loads. The −BOLD response accompanying the local +BOLD effect is more generalized, without distinct topographic referencing to the functional load modality; it conforms most of all to the decrease in the EEG’s coherence.

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.

Individual variation of fMRT responses to eye opening, motor, and speech tests in healthy subjects

Functional magnetic resonance imaging (fMRI) was used to study the variation of functional changes that arise in the brain in response to similar tests in healthy subjects. The approach was assumed to demonstrate diverse individual strategies of achieving the same external (behavioral) response via different brain mechanisms and to identify the factors responsible for the diversity. Hemodynamic (fMRI) responses to activation of attention while opening the eyes or performing motor (consecutively moving the fingers of the right and left hands) and speech (mentally repeating the months of the year or the days of the week in the backward order) tests were determined in 21 healthy subjects aged 21–30 years, including 14 males and 7 females. A variation in fMRI responses was observed, i.e., three or four types of reactive hemodynamic changes were seen in the same test in the group, the prevalence of each type varying from 40 to 10% in one test. The responses showed distinct gender differences, and their specifics depended on the nature of the functional test. In motor and speech tests performed with the eyes closed, the fMRI responses in the females were more specific and local than in the males. In motor tests, the fMRI responses of the males compared with the females were characterized by a greater involvement of the frontal regions, which are responsible for regulatory functions. In the activation test (eye opening), the fMRI responses were more diffuse in the females and more local in the males.

Structural-Functional Characteristics of Brain Functioning on Performance and Imagination of Motor Tasks in Healthy People (EEG and fMRI studies)

Bioelectrical (EEG) and hemodynamic (fMRI responses) reactions of the brain to motor tasks for the right and left hands and imaginary performance of those tasks were studied in 15 healthy right-handed subjects (21–39 years old). In real movements, the main fMRI response was recorded in the central gyri of the contralateral (to the working hand) hemisphere. Activation zones were also seen in the supplementary motor area and the ipsilateral hemisphere of the cerebellum. The corresponding EEG showed increases in the coherence of the high-frequency alpha and beta frequencies in the activated hemisphere. Imagination of movements produced fMRI reactions which were highly variable in terms of extent and topography; weakening of responses was seen in the motor zone and cerebellum, with increased activation of subcortical structures in the parietal associative zones. Changes in the EEG in this situation were very variable; there were increases in the coherence of high-frequency alpha and beta oscillations, in the right hemisphere. Changes in spectral power were similar in real and imaginary movements and consisted of increases in the power and mean frequency of beta oscillations not confined to the activated hemisphere but also appearing in the left hemisphere. These reflected the nonspecific component of the responses.

EEG correlates of the states of visual and auditory attention in healthy subjects

In order to determine more accurately the EEG markers of different types of attention (AT) of a healthy adult, 14 young healthy subjects (aged 18–30 years) were subjected to spectral coherent analysis of the electrical activity of the brain in the baseline state and during activation of different forms of AT (the orienting response to the sound tone and opening of the eyes, involuntary and voluntary visual AT). In the last two cases, specially developed computer-aided techniques were used. The quantitative differences in the states were assessed on the basis of nonparametric (the Mann-Whitney test) and parametric (Student’s t test) statistics. In three subjects, EEG and fMRI comparisons of the brain response to opening of the eyes were made. It was shown that the activation of different forms of AT in healthy subjects is accompanied by considerable diffuse nonspecific changes in the EEG spectral coherent characteristics (a decrease in the average spectral frequency and power, as well as in coherence) in combination with more local, more often oppositely directed shifts in the region of the cortical representation of the working analyzer. Complex systemic rearrangements of the brain activity involving all components of the activating system, as well as the specifics of different forms of AT connected with the rearrangement of activity between its divisions, are reflected in the diffuse changes of intercentral interaction. For example, marked reactivity of the symmetrical frontopolar (Fp1-Fp2) and the anterotemporal (F7-F8) cortical areas with unidirectional maximum shifts during voluntary AT is likely to reflect the responses of the frontothalamic component of the activating system. The reciprocity of the behavior of interhemispheric frontopolar and temporal relationships seems to be determined by the activity of its different components: frontothalamic and hippocampal. The local component of the EEG response to opening of the eyes in the form of increased α coherence in the occipital areas is coupled with increased oxygenation of blood in the cortical representation of the visual analyzer (the +BOLD effect of the fMRI response).

fMRI-EEG assessment of cerebral reactivity to motor tasks in patients with brain tumor

A comprehensive study with the assessment of reactive responses to motor tasks was performed in nine patients with a tumor localized in the frontal divisions of the brain using two methodological approaches: functional magnetic resonance imaging (fMRI) and EEG. The data obtained were compared to the results of a similar study on 12 healthy subjects. It was established that cerebral pathology was associated with disorders of functional specialization and an increase in the diffuse component of reactivity. The fMRI responses were characterized by greater intactness compared to the EEG parameters of reactive changes. These features are especially marked when an afferent stimulus is sent to the damaged hemisphere. The characteristics of the involvement of individual EEG bands in the formation of motor responses and changes in the fMRI response topography are determined by the degree of cerebral dysfunction reflected by the pattern of baseline EEG reorganization and the severity of the motor defect. The predominant increase in the coherence of slow rhythms in the damaged hemisphere irrespective of the target of the afferent stimulus in patients with severe cerebral dysfunction reflects the dominant formation of a pathological focus and is indicative of a greater, compared to healthy subjects, involvement of deep brain structures in the reactive process, which is confirmed by the fMRI data.

Atypical Forms of Cerebral α-Activity in the Case of Lesions in Regulatory Structures of the Human Brain

The results of the EEG study of patients with tumor lesion of diencephalic (29 subjects) and limbic (25 subjects) structures with the focus on the analysis of structural and functional organization of α activity have been summarized. It has been found that diencephalic structure dysfunction is accompanied by disorder of α-rhythm spatial organization in the form of generalization or translocation of its focus to the frontal regions of the cerebral cortex. Distinctive features of “diencephalic” type alteration of α rhythm are determined by predominant integration of the thalamic or hypothalamic structures into the pathological process. Involvement of the limbic structures, especially at early stages of the disease, induces increase in α-rhythm intensity in the temporal region of the affected hemisphere. The nature of the response of the EEG pattern to the functional stress allows identifying it as a “hippocampal α rhythm”. Implementation of the automatic methods of analyzing plays an important role in the identification of these specified pathologic forms of the α rhythm that are often invisible during visual assessment. Detected atypical forms of α rhythm facilitates the interpretation of hemispheric asymmetry of the EEG in patients with cerebral pathology.

fMRI responses of the brain during active and passive movements in left-handed subjects

The hemodynamic (magnetic resonance imaging, fMRI, 3T) brain responses were studied in 15 left-handed healthy subjects performing active and passive movements of the dominant and non-dominant hands. Group and individual fMRI responses to the motor load were analyzed. It was found that, during the active movements of dominant and non-dominant hands, the main activation cluster appeared in the preand postcentral gyrus of the contralateral hemisphere and which topographically similar during active and passive movements. The activation cluster of greater volume was identified in these areas; the response was more diffused during the non-dominant hand movements in comparison with the dominant hand. During passive movements, the cortical activation clusters of a smaller volume in comparison with the active movements were found, which was expressed most clearly during the performance of non-dominant hand movements and could reflect the weakening of the control from the cortical structures in these conditions.

P312 fMRI analysis of the human brain’s neuroplasticity as a basis of movement disorders compensation after traumatic brain injury

Severe traumatic brain injury (STBI) is nearly always comes with movement disorders. Objectives Comparison of cerebral structural-functional control of movement’s opportunity and implementation in healthy volunteers and patients with various degrees of hemiparesis after STBI. Methods Observation groups: 28 patients with SOBI (main) and 17 healthy volunteers (control). 3T fMRI recorded at rest and passive right hand finger clenching (by experimenter). Individual and group analysis of Sensorimotor resting-state network and motor fMRI responses was carried out by FSL software (ICA algorithm), SPM8 and CONN. Topography and volume activated brain regions as well as brain connectivity between them were determined. Results At STBI in the majority cases without hemiparesis or with its mild degree, neuroanatomy of the rest-state sensorimotor network and “passive” motor fMRI response are close to normal. However with an increase of hemiparesis expression we have seen an asymmetric reduction of sensorimotor resting-state network and more diffuse “passive” fMRI response - with activation of nonspecific to movement brain structures: frontal and temporal cortex, cerebellar vermis and others. Discussion A comparison of the passive movement’s functional anatomy in STBI with motor system topographic anatomy indicates a variability in movement disorders compensation mechanisms based on the possible inclusion of different “functional doublers”, such as fronto-pontinus conduction tract as well as occipito–temporopontinus. This hypothesis confirmed by comparative analysis of brain connectivity within different neuroanatomical motor tracts in healthy volunteers and patients with STBI. Conclusions The retrieved data can be useful to develop individualized neurorehabilitation programs of post-traumatic motor disorders. Supported by RFFI 115-36-01038.