[Interhemispheric asymmetry of EEG rhythm connections during spontaneous awakenings after short sleep episodes during a monotonous psychomotor test]. / Mezhpolusharnaya asimmetriya svyazei ritmov EEG pri spontannykh probuzhdeniyakh posle kratkovremennykh epizodov sna pri vypolnenii monotonnogo psikhomotornogo testa.

OBJECTIVE: To study interhemispheric asymmetry (IHA) according to electroencephalography (EEG) data of a healthy person during cognitive awakening from the second stage of daytime sleep before restoring the performance of the psychomotor test. MATERIAL AND METHODS: In 23 healthy adult subjects, we studied IHA in the amplitude-amplitude interaction of EEG rhythms for 20 sec segments before spontaneous awakening determined by the moment the alpha-rhythm appearance on the EEG and the subsequent onset of psychomotor activity. The state of the subject during this period (in the initial stage of the so-called cognitive awakening preceding the behavioral awakening), when the person is unable to move, but is able to perceive external stimuli, is an experimental model for highlighting signs of conscious activity of patients when coming out of a coma. Wavelet transform was used to calculate the rhythmic characteristics of bioelectrical activity. The Kendall correlation coefficient served as a measure of rhythm interaction. RESULTS: IHA in the interaction of EEG rhythms is dynamic nature and formed by theta rhythm connections with alpha2- and beta-rhythms in the left brain hemisphere and delta-type connections in the right. CONCLUSION: Possibly, the greater activation of the left hemisphere is related to the retrieval of an instruction from memory, which subsequently allows to return to the activity interrupted by sleep.

[Sleep and neurophysiological correlates of consciousness activation upon awakening]. / Son i neirofiziologicheskie korrelyaty aktivatsii soznaniya pri probuzhdenii.

The authors discuss modern ideas about the neurophysiological mechanisms of awakening from sleep and the results of own EEG studies of the spatio-temporal dynamics of the activity of the cerebral hemispheres using the own experimental model for studying consciousness in the sleep-wake paradigm. This model is based on continuous execution of a monotonous psychomotor test performed lying down with eyes closed and allows observing several short-term sleep episodes during a 1-hour experiment, followed by spontaneous awakening and restoration of the psychomotor test. A necessary condition for the restoration of activity during spontaneous awakening is the emergence of the EEG alpha rhythm, the parameters of which determine the effectiveness of the restoration of the psychomotor test and, accordingly, the achievement of a certain level of consciousness, and therefore can be considered as a neurophysiological correlate of consciousness activation upon awakening. The considered experimental model of consciousness can be useful for analyzing the neurophysiological mechanisms of consciousness activation in patients with chronic impairments of consciousness and for searching for effective methods for the rehabilitation of such patients.

[Brain Organization of the Preparation for Visual Recognition in Preadolescent Children].

The brain organization of the process of preparation for the perception of incomplete images fragmented to different extents. The functional connections of ventrolateral and dorsoventral cortical zones with other zones in 10-11-year-old and 11-12-year-old children were studied at three successive stages of the preparation for the perception of incomplete images. These data were compared with those obtained for adults. In order to reveal the effect of preparatory processes on the image recognition, we also analyzed the regional event-related potentials. In adults, the functional interaction between dorsolateral and ventrolateral prefrontal cortex and other cortical zones of the right hemisphere was found to be enhanced at the stage of waiting for not-yet-recognizable image, while in the left hemisphere the links became stronger shortly before the successful recognition of a stimulus. In children the stage-related changes in functional interactions are similar in both hemispheres, with peak of interaction activity.at the stage preceding the successful recognition. It was found that in 11-12-year-old children the ventrolateral cortex is involved in both preparatory stage and recognition processes to a smaller extent as compared with adults and 10-11-year-old children. At the same time, the group of 11-12-year-old children had more mature pattern of the dorsolateral cortex involvement, which provided more effective recognition of incomplete images in this group as compared with 10-11-year-old children. It is suggested that the features of the brain organization of visual recognition and preceding preparatory processes in 11-12-year-old children are caused by multidirectional effects of sex hormones on the functioning of different zones of the prefrontal cortex at early stages of sexual maturation.

[Relationships between the Flexibility of Cognitive Performance and the Response of Alpha-Rhythm in the Go/NoGo Task].

During the experiments, healthy subjects (n = 35) completed Go/NoGo task with a set towards the recognition of negative face expression; the visual stimuli were set in the middle of a 16-second-long interval between target (face) and triggering stimuli. The local changes in low-frequency alpha-oscillations in response to stimuli (desynchronization after a positive Go stimulus and synchronization after an inhibitory NoGo stimulus) take place in posterior frontal and anterior temporal lobes of the left hemisphere, i.e., in cortical areas directly involved in speech processes. In subjects with flexible set towards recognition, we observed synchronization of alpha-rhythm after inhibitory NoGo stimulus; in subjects with more stable set, this did not occur. Thus, we obtained new experimental data confirming that induced synchronization of alpha-oscillations reflects the enhancement of descending inhibitory control of the prefrontal cortex.

[Changes of the alpha-rhythm after introducing stimuli Go/NoGo in the context of experiments with a set to an angry face].

At healthy adults is (n = 35) in the middle of 16 second pauses between target (faces) and starting stimuli conditioning signals Go/NoGo. Lack of essential changes of flexibility of the set after introduction of an additional cognitive task is explained by enhansment of the induced synchronization of an alpha rhythm in time intervals between target, conditioning and starting stimuli. The increase of alpha potentials synchronization reflect the top-down inhibitory control suppressing effect of irrelevant factors, and that facilitating processing of significant information. In the range of time between NoGo and starting stimuli locally in a motor zone of cortex of only the left hemisphere (C3, FC3) the induced synchronization of low-frequency and especially high-frequency alpha rhythm is registered. One more experimental confirmation of the theory on the brake nature of this electrophysiological phenomenon is obtained. Used in physiology of the highest nervous activity of concept about internal or conditional inhibition is considered within the theory of top-down inhibitory control from prefrontal cortex.

[Functional organization of the cerebral cortex during preparation to recognition of incomplete linedrawings in 7-8 years-old children and adults].

Functional interaction between prefrontal, temporal and tempo-parieto-occipital zones during preparation to recognition of incomplete linedrawings were analyzed in adults (n = 26) and children of 7-8 years old (n = 20). The strength of cortico-cortical interactions was estimated with the imaginary part of the complex-valued coherence at the frequency of alpha-rhythm (Jα). The Jα value was analyzed in the following three experimental conditions which corresponded to different stages of preparation to visual recognition: nonspecific sustained attention in the period preceding the cue (C1); focused attention in the period preceding a not-yet-recognized target stimulus (C2) and focused attention prior the successfully recognized stimulus (C3). When sustained attention changed to focused attention toward a target stimulus Jα increased in adults but decreased in children. Comparing Jα in the subgroups of both adults and children that showed highest recognition scores helped to uncover the age-related pattern of rearrangement of the cortico-cortical functional interactions in alpha-rhythm. That pattern was found to be hemisphere-specific and different at different stages of preparation to recognition of incomplete linedrawings. In adults, the maximal Jα were found in the left hemisphere during the period preceding the recognition of a target stimulus. At this stage of the functional preparatory tuning, in adults, Jα in the left hemisphere was significantly greater than in children. In adults, Jα related to the right hemisphere attained the highest values when attention was directed to not-yet-recognized stimuli. These values were significantly higher than similar values measured in children. In children, Jα reached its highest value during sustained attention. The characteristic pattern of functional interactions among prefrontal, temporal and temporo-parieto-occipital cortices that observed in children of 7-8 years old during preparatory functional tuning for the recognition of incomplete linedrawings is considered to be an indication of relative immaturity of mechanisms of directed voluntary attention and working memory.

[The functional brain organization during preparation for recognizing incomplete images].

The functional interaction between prefrontal cortex and other cortices was analyzed during the pre-stimulus period in the task in which human subjects (n = 36) were asked to recognize a set of incomplete images of different degree of fragmentation. The imaginary part of the complex-valued coherency was used to measure a strength of inter-area coupling at the alpha-rhythm frequency. Based on the analysis of individual responses the two equal sub-groups (n = 13) showing the lowest and highest recognition scores were extracted from the whole group of subjects. It is shown that the pattern of the functional cortico-cortical interactions as well as the direction of its' changes differ in the two sub-groups. In those subjects who successfully solve the cognitive task, the changes in functional connectivity indices in the situation of focused attention are most pronounced in the right hemisphere if stimulus-to-come would not be recognized. Period preceding recognized stimulus is characterized by the increased cortico-cortical coupling in the left hemisphere. In that sub-group, the values of imaginary part of alpha-coherency show the growth in both hemispheres when the period of focused attention is compared against the period of nonspecific attention. On the contrary, the similar comparison for the sub-group of the least successful subjects shows the imaginary coherency decreases in both hemispheres. These results suggest the constructive role of the alpha-rhythm in functional assembling the prefrontal cortex during the period that precedes the recognition of incomplete images.

[Brain organization of recognition of fragmented pictures in subjects who show different levels of the task performance success].

We studied the behavioral and EEG changes in healthy adults during the recognition of fragmented pictures presented in a series beginning with a low fragmentation level up to the complete figure. Our sample was divided into two groups according to the recognition success. The first group had a small amount of mistakes. The other group had a significantly higher amount of mistakes as compared to the first group; this group had a lower reaction time and recognition threshold (i.e. the fragmentation level at which the object became recognizable). The ERP analysis showed the statistical dependence between the recognition success and the involvement of the frontal and caudal cortical areas. As compared to the second group, in the first one we found no significant association between the recognition process and both early and late ERP components in the dorsolateral prefrontal cortex; we found the increase of sensory-specific components P1 and P2 in caudal areas. These results support the hypothesis of the impact of the prefrontal cortex on the successfulness of recognition of fragmented pictures.

[Induced synchronization of alpha rhythm in the time intervals between the visual stimuli at different degrees of set flexibility].

In healthy adults (n = 35) was used the model the set study of recognition angry facial expression. The load on working memory by extending the interstimuli time up to 16 sec between the target (facial image) and starting (spot light) stimuli does not lead to a significant slowdown of switching of the set. Differences in the magnitude of the induced synchronization of the alpha rhythm in interstimulus period obtained in the subjects with the change in recognition of emotional facial expressions and the subjects "without errors". At the last group synchronization is clearly more pronounced. The implementation of successive cognitive acts is modulated by selective attention, whichis evident in the level of changes the induced synchronization/desynchronization of alpha range potential. The proposed mechanism "inhibitory control" provides the flexibility of cognitive processes by suppressing effect on cortical processes irrelevant factors during interstimulation pauses. This "protective" mechanism, we believe due to little effect of the loading on working memory.

[Development of mechanisms of recognition fragmented images at the preschool and early school ages].

Psychophysical and electrophysiological indices of recognition of incomplete objects with progressive increasing of fragments, were studied in children of three age groups: 5-6, 7-8 and 9-10 years old. It is shown that most pronounced change in the effectiveness of recognition takes place between 5-6 and 7-8 years of age. In the group of children of 5-6, neither significant influence of the recognition process on ERP was found in the prefrontal cortex nor any significant growth of the Nd component was observed over extrastriate cortex. However, in the extrastriate cortex, the amplitude N170-200 component that reflects sensory analysis and encoding extracted features did increase. In the majority of children of this age, the immaturity of the prefrontal cortex manifest itself in the deficit of inhibitory control that results in the tendency to give the impulsive responses and make numerous errors. In children of 7-8, successful recognition is accompanied by the growth of the amplitude of N100 and N250 components over the prefrontal cortex and the growth of NcI component over the extrastriate cortex. In these children, when compared to the children of 5-6, a significant reduction, is observed in the error rate and the recognition threshold. By the age of 9-10 years, the growing role of the prefrontal cortex shows in greater gain in the Nd amplitude and the later ERP component that correspond to cognitive operations related to the recognition process. The results of the study point to the qualitative difference in the mechanisms of recognition between pre-school children and the younger school-children. At the age of 5-6, recognition is carried out on the basis of integration of sensory signs of objects. Since the 7-8 age, in recognition of fragmented images major role belongs to the prefrontal cortex, with its participation search of possible analogs of object in memory and the object identification is carried out.

[Development of function of the recognition of angry face expression in children of 5-11 years old].

At children 5-6, 7-8 and 10-11 years on model of cognitive set are revealed age features of influence of last experience on perception of a face expression. At children of 5-6 years rigid set on an angry face was experimentally formed: at a testing stage show set-shifting caused large number of erroneous recognition of face expression of perseverative type (assimilative illusions). Plasticity of the set raises in 7-8-year age and considerably the number of assimilative illusions decreases. On 10-11 years sets doesn't differ essentially from adult people on plasticity and a ratio of number of assimilative and contrast illusions. Changes of spatial synchronization of electric potentials teta- and alpha ranges of frequencies in all age groups it is observed generally at a stage of formation of set. On all age groups strong correlation between bioelectric data and features of the set on a face expression is revealed. These data supports the hypothesis that cortiko-hippocampal and fronto-thalamic functional systems of integration of a brain activity participate in the organization of a set on an emotional face expression and provide cognitive flexibility.

[Theta and alpha-band EEG spatial synchronization under the conditions of visual set, formed to an angry face expression. A study of 5-11-year-old children].

EEG coherence in theta and alpha bands during set-forming and set-shifting was studied in 5-6-year-old (n=18) and 10-11-year-old (n=25) children. Set was formed to visual stimuli (facial photos with emotionally negative expression). Younger children displayed smaller coherence values, especially in the right hemisphere, than older ones. We also revealed differences in theta and alpha band coherence in cases of a rigid and a plastic set. For example, EEG-coherence values were smaller when cognitive processes were relatively rigid (i.e., in a case of a slower set-shifting). A strong correlation between electrophysiological and behavioral data supports the hypothesis that cortico-hippocampal and fronto-thalamic brain integration systems participate in facial expression recognition and provide cognition flexibility.

[Cognitive control in recognition of emotionally negative face in 5-10-year-old children].

We used the experimental model of cognitive visual set, designed by D.N. Uznadze, to study the influence of previous experience on emotional face expression recognition in pre-school (6.1 +/- 0.3 years) and elementary school (10.5 +/- 0.1 years) children. Our results suggest that the ability to form a cognitive set to an angry face expression develops in ontogenesis in strong concordance with functional maturation of prefrontal cortex that takes place at the age of approximately 10 years. At this age children display almost the same level of set plasticity and a similar kind of erroneous perceptions during set actualization as grown-ups. Children of younger age (6.1 +/- 0.3 years) display more perceverative erroneous perceptions, or assimilative illusions (probably of a priming origin), than the above mentioned groups. We consider this to be a result of a more strong influence of previous experience in their case.

[Neurophysiological mechanisms of recognition fragmented images in 5 to 6-year-old children].

Behavioral indices and ERP parameters were analyzed in 5-6 years old children who were shown a previously unseen set of fragmented drawings of familiar objects. Within this set, each object was represented by a series of drawings of different degree of fragmentation. It is found that children of 5-6, when compared to 7-8 years old children, are capable to recognize less fragmented drawings. In these children, no increase was found in N350-400 prefrontal negativity and late positive complex, otherwise a typical feature of mature recognition involving executive control. A comparison of ERP for recognized vs. unrecognized stimuli showed a significant increase in P300 and N400 amplitude over the right occipital area. A key feature of children of this age is a lack of significant difference between ERP to recognized vs. unrecognized stimuli over extrastriatal cortex (T5/T6) which is the crucial structure for recognition of fragmented objects via integration of their sensory features. The data we obtained suggest that both executive control immaturity and insufficient involvement of the ventral visual system constitute a specifics of recognition in children of 5-6.

[EEG spatial synchronization at different set stages in 8-year-old children with different levels of selective attention fronto-thalamic system maturity].

Visual cognitive set was studied in two groups of 8-year-old children: with normal development of fronto-thalamic system (FTS) (n = 21) and with functional immaturity of this system (n = 29). In most of the children with the FTS-immaturity a formed visual set was rigid. EEG was recorded from the frontal, central, temporal, parietal and occipital regions, and coherence function in theta-, alpha- and beta-bands was analyzed. The most vivid differences between two groups of children were revealed at the set actualization stage. If the set was a plastic one, the value of coherence function between frontal and dorsal areas was higher in children with FTS-immaturity, than in "normal" ones. In the group with FTS-immaturity the dependence of coherence function on the set's plasticity was more vivid, than in children without FTS-immaturity. In all children with a rigid set value of coherence function was higher during set formation, actualization and extinction, than at resting condition with eyes opened. In the group with FTS-immaturity the coherence of theta-band considerably increased at the set actualization stage, mainly in the right hemisphere. We consider this to be the evidence of a comparatively bigger role of cortico-hippocampal system and implicit episodic memory the set shifting. Probably these processes compensate the FTS-dysfunction and make a set more plastic.

Synchronization of EEG theta and alpha rhythms in an unconscious set to the perception of an emotional facial expression.

Coherence functions in cortical electrical potentials in the theta (4-7 Hz) and alpha ranges (8-13 Hz) recorded during the formation and testing stages of a visual set to facial images bearing an emotional expression (an angry face) were studied in healthy adult subjects (n = 35). Differences in the spatial synchronization between theta and alpha potentials were seen, especially in rigid forms of the set, in which cases of erroneous perception of facial expressions were seen with contrast and assimilative illusions. This group of subjects (n = 23) showed increases in theta potentials between the dorsolateral areas of the frontal cortex (the orbitofrontal cortex) and the temporal area in the right hemisphere. A mechanism is proposed for the development of visual illusions. Analysis of the coherence functions of cortical potentials in the theta and alpha ranges generates a "window" which can be used to study the operation of the two functional systems integrating brain activity, i.e., the corticohippocampal and frontothalamic, in the perception of a facial expression. The frontothalamic system is associated with more diffuse types of cortical activation, especially in its anterior areas. The theta rhythm system evidently facilitates integration of the frontal cortex with the temporal area in the right hemisphere and the connections of the latter with the parietal and central zones in both hemispheres.

[Visual set and shifting of selective attention in 8-year-old children with EEG-signs of immaturity of fronto-thalamic and brainstem activating systems].

Visual set (by D.N.Uznadze) was studied in three groups of 8-year-old children: children with EEG-signs of immaturity of fronto-thalamic activation system; children with a deficit of non-specific activation from mesencephalic reticular formation; children with normal development of these systems (control group). Children with a deficit of non-specific activation split in two groups: one group was similar to the control group in set-forming, set-shifting and response time dynamics; another group haven't displayed a set actualization stage and had a considerably bigger response time during attention shifting. Children with immaturity of fronto-thalamic system, when compared to the control group, had considerably more contrast illusions at set-testing stage and considerably bigger response time during attention shifting at set actualization stage. These data suggest a participation of fronto-thalamic system in set-forming and set-shifting.

Relationship between the plasticity of a set to an emotional facial expression and the load on working memory.

The effects of increasing the loading on working memory (by introduction of an additional cognitive task into the experimental context) on the recognition of an emotional facial expression using a visual set model were studied in healthy adult humans. A relationship was found between the plasticity of the cognitive set to an emotional facial expression and working memory: increases in the load on memory slowed set substitution when the situation changed. The set became more rigid, as indicated by an increase in the number of trials showing erroneous assessments of facial expressions, i.e., contrast and assimilative illusions, at the test stage of the experiment. The role of internal states in the increase in the number of erroneous assessments of emotional facial expressions when working memory was loaded is discussed.

Spatial organization of cortical electrical activity at different stages of a visual set in preschool and early school age.

Parameters of the formation of a visual nonverbal set and the rate of its replacement with a new set were compared in children of three age groups: 5-6, 6-7, and 9-10 years. The vast majority of subjects (27 of 30 preschool children and 42 of 43 third-grade children) showed clear set effects. Age-related differences in set plasticity and the dynamics of reaction times to test stimuli were observed. The set was more rigid in children aged 5-6 years than in older children. Differences in the dynamics of the spatial organization of alpha and theta activity were seen in the anterior areas of the cortex at different stages of the set in children of different age groups. Analysis of cortical potentials coherence functions and behavioral parameters led to the hypothesis that the frontothalamic selective attention system and the corticohippocampal connection system responsible for the cortical processing of new visual information and episodic memory function are involved in organizing the visual set. A critical age (from six to seven years) was identified in the formation of plastic types of visual nonverbal sets.