L. A. Zhavoronkova

Changes in the Nervous System in Chernobyl Nuclear Power Plant Accident Clean-Up Workers

health of the 1986–1987 Chernobyl nuclear power plant accident clean-up workers revealed time-dependent increases in impairments to physical and mental health [1]. Analysis of the histories of clean-up workers receiving inpatient treatment in the Department of Radiation Medicine of the Russian Scientific Center for Radiography showed that nervous system and mental diseases amounted to 20.6% of the total number of diseases and were second only to cardiovascular diseases [2]. Data from the Russian Interdisciplinary Expert Committee showed that neurological and mental diseases amounted to 24.9% [3]. Data from the Russian State Medical Dosimetric Register (RSMDR) indicate that the structure of invalidity among clean-up workers is quite stable: diseases of the circulatory system account for 39.2% of cases, those of the nervous system for 28%, mental illnesses for 9.3%, malignant tumors for 2%, and other diseases for 20.6%. This structure differed from the structure of invalidity among the working population of the Russian Federation, where the first three positions were occupied by circulatory diseases, malignant tumors, and trauma and poisoning. The proportion accounted for by diseases of the nervous and mental sphere in the structure of invalidity among clean-up workers was more than twice that in the general population of Russia. The aim of the present work was to characterize the features of nervous system pathology over time among Chernobyl nuclear power plant accident clean-up workers.

[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.

Effects of Including Stabilotraining in the Rehabilitation of Patients with Post-Traumatic Korsakov Syndrome

Complex investigations were performed in 10 patients with post-traumatic Korsakov syndrome (KS) and stabilographic and electroencephalographic (EEG) investigation results were assessed before and after rehabilitation using stabilotraining (ST) with feedback (7–12 sessions). Controls consisted of data from 18 healthy subjects. Before courses of ST, patients with KS showed maximal impairments in the cognitive (mnestic) sphere, which in terms of EEG data corresponded to maximum reductions in coherence in all frequency ranges in the frontal and parietal-occipital areas and between long diagonal pairs, i.e., between the left frontal and right parietal-occipital areas, this being clearest in the α range. After courses of rehabilitation with ST producing regression of KS, there was a tendency to normalization of stabilometric parameters, with stepwise increases in EEG coherence, especially in the α range: initially in the occipital-parietal-central areas of the right hemisphere and with subsequent increases in the central-frontal areas and then in the frontal areas, more so in the left hemisphere, corresponding to a tendency to normalization of the temporospatial organization of the EEG.

Interhemispheric EEG coherence during rehabilitation in patients after severe craniocerebral injury

Dynamic clinical and EEG examinations (78 observations) were carried out in 17 patients suffering from severe craniocerebral injury during the course of their rehabilitation. Successful recovery of functions to the point of social and family readaptation was reached in 61% of patients (group I), and in 39% of patients the results were poor (group II). The complex of EEG coherence parameters (six rhythmic bands, mean coherence levels for 26 intrahemispheric and 8 interhemispheric derivation pairs, and the asymmetry coefficient of the EEG coherence) was analyzed in patients in comparison with normal values (20 right-handers). The rehabilitation was most efficient in cases when a certain dynamic sequence of patterns of interhemispheric relations of the EEG coherence was observed. First, a stable formation of right-hemispheric dominance was observed (most expressed in the centrofrontal areas in the θ range). This asymmetry pattern was phenomenologically associated with the recovery of the emotional sphere and positive dynamics in the motor and autonomic spheres. Later on, formation of the left-hemispheric dominance of the EEG coherence was observed (in the frontotemporal areas in the α–β ranges. This pattern was associated with complication of the cognitive functions. In the most severe forms of brain damage, the rehabilitation process was accompanied by changes in the interhemispheric EEG coherence with the elements of “stealing” from one of the hemispheres, which was correlated with clinical dynamics. Different types of the dynamics of reactive changes in the EEG coherence were revealed in patients of the two groups: successive formation of a generalized and then local modally specific reaction to afferent stimuli was observed in group I, while the generalized type of reactivity persisted in group II until the end of rehabilitation. It is suggested that the different sequence of formation of the interhemispheric EEG coherence reflects the involvement of different brain regulation systems in different orders into the integrative activity, i.e., some specific features of the rehabilitation process.

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.

Role of the visual afferent stream in recovery of the postural control in different periods after craniocerebral injury

A comprehensive posturographic (PG), electroencephalographic, and clinical examination was performed during rehabilitation in 17 patients (mean age 27.5 ± 7.4 years) who had suffered a severe craniocerebral injury (SCCI). Of these, nine were examined soon after the SCCI and eight, in the period of remote consequences of the SCCI. The patients were compared to a control group of 18 healthy subjects (mean age 27.8 ± 12.2). The PG studies showed that, in the healthy subjects, the amplitude of sway of the common center of pressure (ACCP) in the absence of the visual control was higher than with the eyes open. The ACCP was higher in the sagittal than in the frontal plane and decreased during optokinetic stimulation. In the control group, rhythmic photostimulation produced a local increase in interhemispheric EEG coherence in symmetrical occipital and parietal cortical areas. In the patients examined early after the SCCI with the eyes open, the ACCP was higher than in the healthy subjects, especially in the frontal plane. The ACCP did not decrease in the Romberg posture and increased during optokinetic stimulation. In these patients, rhythmic photostimulation was accompanied by a generalized increase in mean interhemispheric EEG coherence as compared to the resting level. In the remote period after the SCCI, the PG and EEG responses to a decrease or an increase in the visual afferent stream proved to be inverted: the patients stood better with the eyes closed than with them open and photostimulation produced a decrease in EEG coherence in the occipitoparietal areas of the cortex. The results confirmed a greater efficiency of rehabilitation in the early period after the SCCI. Thus, specific PG and EEG reactions were observed in the SCCI patients at different stages of recovery. The generalized reactivity and “infantile” features of the EEG and PG rearrangements characteristic of the early period after the SCCI were considered to be a favorable prognostic sign for the recovery of the integrative brain activity and postural control of a patient. The inversion of the reactions in the remote period after the SCCI testified to limited possibilities of the recovery of the impaired functions and was indicative of a pathological type of compensatory rearrangements.

EEG Markers of the Stabilotraining Effect during the Rehabilitation of Patients with Posttraumatic Korsakoff's Syndrome

Nine patients with posttraumatic Korsakoff syndrome (KS) were examined before and after a rehabilitation course of feedback stability training (ST) using EEG, posturographic and clinical tests (with the FIM and Mayo Portland scales used for estimation). During 7 to 12 sessions, the patients tried to perform static and motor tasks. A group of 18 healthy subjects were examined to provide standard parameters. The results demonstrated a disturbed spatiotemporal EEG pattern in patients with KS before ST in the form of a reduced coherence for short derivation pairs (intrahemispheric, interhemispheric, and diagonal ones) in frontal and parietooccipital areas. Analysis of specific EEG rhythms demonstrated the maximum decrease in coherence in the α band (with the aforementioned regional specificity) and for long diagonal pairs (between the left frontal and right parietooccipital areas). The ST course was accompanied by KS regression (according to clinical scales and posturographic study); an original increase in EEG coherence, especially that of α waves, was recorded in the occipitoparietal and central frontal areas of the right hemisphere; a subsequent increase in coherence of the frontal areas in both hemispheres was observed. Late after the ST course, further positive changes were characteristic of the EEG spatiotemporal pattern. However, comparison with standard data suggested incomplete recovery of various coherence parameters: hypertrophied coherence in intrahemispheric pairs and still reduced values in interhemispheric derivations. This EEG pattern suggested incomplete KS regression, which was confirmed by clinical data.