Lateralization of visuo-spatial function during masking in healthy subjects and in patients with chronic alcoholism

In healthy subjects and patients with chronic alcoholism, the ability to construct in mind geometric figures in conditions of masking was studied by means of recording the number of correct decisions, the reaction time and evoked cortical electrical activity. It has been found that solution of visual-spatial task of mentally constructing geometric figures is accomplished better if a figure-standard can be formed from the presented fragments. During solution of the visual-spatial task in norm the reaction time is shorter if the information comes "directly" to the right hemisphere. Such interhemispheric differences are not observed at chronic alcoholic intoxication. In patients with chronic alcoholism the late components of EPs N200 and P300 developed with a longer latency and lesser amplitude than in healthy subjects. The greatest depression of cortical activity is observed in the right hemisphere.     

Hemispheric lateralization of the visual-spatial function in chronic alcoholic intoxication in humans

A series of behavioural and electrophysiological parameters was recorded in subjects with chronic alcohol intoxication during solving of visual-spatial nonverbalized task. It is shown that in comparison with the healthy subjects, their reaction time (RT) of correct decisions was increased; it was more expressed when stimuli were presented in the left visual field, i.e., directly to the right hemisphere, and the number of correct reactions decreased at stimuli presentation directly to the left hemisphere. During repeated tests there were no changes in the number of correct reactions and RT value in the group with chronic alcohol intoxication. It is found that long-term taking of alcohol produces an increase of latency and decrease of the amplitude of the late positive wave P300, more pronounced in the right cerebral hemisphere.     

Solution of visuo-spatial tasks during masking

The images of two fragments of simple geometrical figures (square, triangle, etc.) were successively presented to healthy adult subjects in the left and right visual fields with the interval of 20, 80 and 380 ms; the subjects had to compare them mentally and decide whether they formed a geometrical figure. The correctness of reaction was controlled by a computer which lightened on the screen the word "correct" or "error". The number of correct decisions was significantly greater in response to the stimuli, forming a regular figure and increased with the increase of interstimuli interval. At the interval of 120 ms, when no regular figure could be formed from two fragments, the number of correct decisions was greater if the stimuli were presented in the left visual field. The reaction time did not depend on the hemisphere to which information was addressed; it was less in response to the stimuli forming a regular figure, and became shorter with the increase of the interstimuli interval.     

Lateralization of visual perception of letters during reverse masking

Identification by healthy subjects of single letters in conditions of backward masking was studied at lateralized presentation of stimuli. Both at dichoptic and unilateral presentations, the letters are identified better if they are presented in the left visual field, i.e. addressed "directly" to the right hemisphere. It is suggested that the data obtained result from the specificity of hemispheres' cooperation under difficult conditions of visual-spatial stage of information processing.     

Learning to differentiate microintervals of time using verbal feedback

Reaction time (RT) and the number of correct estimations of time microintervals (10 and 180 ms) between two visual stimuli were recorded in healthy subjects. It has been shown that 10 ms interval is better estimated when the stimuli are presented in the right visual field, i.e. when they are addressed directly to the left hemisphere. At the same time the number of correct estimations of 180 ms interval is greater and their RT is less when the stimuli are addressed directly to the right hemisphere. This points to different hemispheric mechanisms of time microintervals estimation. Study of the influence of different forms of verbal reinforcement on this learning has shown that after positive reinforcement (the word "good") the number of correct estimations is on average by 10% greater than after negative reinforcement (the word "error"). This may be connected with such processes as isolation and identification of erroneous reaction.     

Levels of consciousness and levels of activation

In the paper Pavlov's idea is used about "the bright spot of consciousness" as a zone of increased excitability which moves over the cerebral cortex. Zone of increased activation is revealed migrating from the frontal parts of the left hemisphere to the occipital parts of the right hemisphere. By means of various methods (record of amplitude and latency of the visual evoked responses, frequency and amplitude of the dominant rhythm, spectral-coherent analysis of the electroencephalogram) the activation of focus in the cerebral cortex was singled out, which moved, depending on the novelty, complication and degree of automatization of the task, from the frontal parts of the left hemisphere to the occipital parts of the right hemisphere. A parallel is drawn between Pavlov's hypothesis on the focus of consciousness as foci of increased brain activity, and revealed foci of activation. The conclusion is made about fluctuations of consciousness level as a factor which is in the basis of activation focus migration.     

The hemispheric lateralization of the recognition of noisy visual stimuli in man

At tachistoscopic unilateral presentation of noisy visual stimuli and application of "yes-no" method in man predominance was found of the right hemisphere by the number and "yes" reaction time and of the left hemisphere by the number of responses "no". At verbal mnemic load preceding the presentation of visual patterns the left hemisphere asymmetry was observed by the number of "yes" responses and reactions time of both types. FMA was more clearly expressed in men in the first case and in women--in the second one. In more difficult conditions of recognition of several types of patterns, FMA was noticed mainly in women: initial left hemisphere advantage during the increase of the disturbance was changed to the right hemispheric one and appeared again. Preferential participation of the right hemisphere in singling out of the visual signal from noise is supposed. Possibility of the left hemispheric asymmetry manifestation was determined by the specificity and complexity of the visual task, by the level of the disturbance, presentation of competitive task and sexual composition of the group.     

The effect of masking in the human subject on the solving of a visual-spatial task

Images of two fragments of regular geometrical figures (square, triangle etc.) have been presented to 58 healthy persons successively with intervals of 20, 80, 120 and 380 ms. The subject must compare these fragments mentally, decide whether they form the standard figure and press a button by the right or left hand according to the instruction. At presentation of both fragments in one visual field, left or right, the number of correct responses is greater when they form the figure. The greater the interstimulus intervals, the greater the number of correct responses to stimuli forming and not forming the standard figure. At presentation of fragments in different visual fields, the number of correct decisions is the same, independently from forming the standard figure. The reaction time is shorter when exposing fragments forming the figure, independently from the way of their presentation; with prolongation of interstimulus intervals the reaction time decreases in all cases. The number of correct decisions is greater and the reaction time is shorter when the stimuli are presented in different visual fields.     

Event-related potentials during paired associate memory paradigm

We have studied event-related potentials (ERPs) during a visual paired association task with delayed discrimination in 10 normal right-handed subjects. After subjects completely memorized 4 pairs of figures during a learning period, they were presented with each cue (S1) and asked to judge whether the following figure (S2) formed one of the memorized pairs or not. A choice reaction task with delay was used for control in an attempt to identify brain activity specifically related to memory function. ERPs were recorded from 21 scalp electrodes and those occurring between the S1 and S2 presentation were analyzed. Two ERP components associated with memory function were identified in the difference waveform between the responses in the paired association task and those in the choice reaction task. One was a posterior positive component which appeared between 390 ms and 1100 ms after the S1 presentation and the other was a sustained frontal negative component which began at about 1100 ms after S1 and ended just before the S2 presentation. Both potentials were distributed predominantly on the scalp overlying the left hemisphere. It is postulated that the early posterior positive component may reflect retrieval of information from association memory, whereas the late frontal negativity may reflect retention of information in working memory.     

Sex Differences and Activity of the Left and Right Brain Hemispheres

The problem is reviewed of sex differences and the brain organization of the visual-spatial and verbal-cognitive functions both in adults and in the 5–15-year old children. Characteristic of men are the integral strategy of the face image recognition, specialization of the right hemisphere for visual-spatial functions, and the tonic inhibitory effect of the right hemisphere on the left one. Typical of women are the fragmented type of the image recognition, the equality of the brain hemispheres functions at the unfamiliar face recognition, and predominance of the left hemisphere by accuracy of the object localization in the visual field. It is possible that the general strategy of the recognition in women is not realized due to the right hemisphere submitted to the interfering effect of the left hemisphere. Analysis of sex differences in distribution of verbal functions shows that the capability for the verbal learning at the age of 5 years and older is higher in girls than in boys. Such capability seems to be accounted for by the superiority of the left hemisphere in girls in this type of its activity and by its earlier development and maturation. The phenomenon of semantic paralexia appearing more often in boys is accounted for by inclusion of lexical-semantic fields of the right hemisphere symmetric areas in the verbal-cognitive activity There are reasons to believe that the higher capability in girls for the verbal learning is mainly due to processes of the auditory-verbal integration within the limits of the left hemisphere, whereas this verbal ability in boys depends on the relative predominance of the interhemispheric connections.     

Influence of informational oversaturation on the quality of creative activity and spatial organization of EEG

The features of the spatial organization of bioelectric potentials in the cases of successful and unsuccessful creative imagination (refusal or poor quality of the product) under conditions of informational oversaturation. Two groups of subjects were compared: professionals (23 healthy students of the Department of Graphic Arts) and non-professionals (34 persons whose specialties were not linked with systematic visual imagination). During the experiments, the subjects were asked to mentally create a visual image based on two simple graphic elements, a right angle and a diagonal; after recording the EEG, they had to draw the image on paper and give it a title. The total number of elements exceeded 7 ± 2; hence, information processing at the conscious level was impossible, which caused the necessity of involving the mechanisms of unconscious information processing. The quality of the created product was evaluated with regard to the degree of success of performing the task and the features of spatial EEG organization. The EEG was recorded from 24 scalp sites of a subject using a SIT-EEG portable telemetric device. In the case of the successful performance of the task by professionals, the parameters of spatial organization of bioelectric potentials, i.e., spatial synchronization (linear processes) and spatial disorder (non-linear process) were strengthened compared to the base-line level in the frontal temporal areas of the right hemisphere and parietal occipital areas of the left hemisphere. Conversely, in the nonprofessionals, these parameters increased in the frontal temporal areas of the left hemisphere and parietal occipital areas of the right hemisphere. In the case a task was not successfully performed by the professionals, the spatial disorder of bioelectric potentials increased in all the cortical areas; in the nonprofessionals, only weak changes were observed. In all situations, the groups differed also in the parameters of coherence (Coh), spectral power (Sp) of bioelectric potentials, and informational energy, which reflects the level of expenditure of the brain’s energy for information processing. The evidence obtained is interpreted in terms of electroencephalographic correlates of successful task performance by professionals and nonprofessionals, i.e., their creative imagination under the conditions of informational over-saturation.     

Dynamic spatial coding within the dorsal frontoparietal network during a visual search task

To what extent are the left and right visual hemifields spatially coded in the dorsal frontoparietal attention network? In many experiments with neglect patients, the left hemisphere shows a contralateral hemifield preference, whereas the right hemisphere represents both hemifields. This pattern of spatial coding is often used to explain the right-hemispheric dominance of lesions causing hemispatial neglect. However, pathophysiological mechanisms of hemispatial neglect are controversial because recent experiments on healthy subjects produced conflicting results regarding the spatial coding of visual hemifields. We used an fMRI paradigm that allowed us to distinguish two attentional subprocesses during a visual search task. Either within the left or right hemifield subjects first attended to stationary locations (spatial orienting) and then shifted their attentional focus to search for a target line. Dynamic changes in spatial coding of the left and right hemifields were observed within subregions of the dorsal front-parietal network: During stationary spatial orienting, we found the well-known spatial pattern described above, with a bilateral hemifield representation in the right hemisphere and a contralateral preference in the left hemisphere. However, during search, the right hemisphere had a contralateral preference and the left hemisphere equally represented both hemifields. This finding leads to novel perspectives regarding models of visuospatial attention and hemispatial neglect.     

Interhemispheric asymmetry in rats differentiating figures by size

Motor alimentary conditioned reflex was elaborated in Wistar line rats to presentation of various pairs of figures, those of larger area serving as positive signals. In tests on animals with intact brain and with unilateral hemispheric cortical inactivation, new pairs of figures were used besides basic stimuli. The level of analysis in testing experiment was lower than normal: by 5.6% at intact brain, by 16.4%--at right hemisphere inactivation, by 36.4%--at left hemisphere inactivation. Elimination of the left hemisphere produced prolongation of the conditioned reaction time, signs of frustration and aftereffect. In conditions of right hemisphere inactivation the level of discrimination of figures depended on their specific properties and the side of presentation. Conclusion is made on dominating role of the left hemisphere in analysis of abstract and concrete characteristics of visual stimuli, in control of temporal, spatial and emotional characteristics of reactions in situations when considerable abstraction and distinguishing of generalizing invariant sign "more-less" is necessary for elaboration of the conditioned reflex.     

Changes of Motor and Sensory Asymmetries in Highly Trained Athletes

Data about peculiarities of organization of motor control and brain functional asymmetry pattern in highly trained judo wrestlers are presented. It has been shown that in athletes the right hemisphere is predominant in processing of both speech and visual-spatial information, while high competition results in wrestlers with left-side stand correlates with prevalence of the left hemisphere in speech perception. It is suggested that high sport results in wrestlers are due to formation of novel long-term skills, reorganization of motor control, and interhemispheric interaction.     

Localization of cortical lesions of the human brain and features of recognition of emotional expression

The quantity of correct and erroneous identifications of human emotions was compared according to their intonational and mimical cues in the group of healthy persons (31 persons) and in the group of patients with lesions of different cortical parts of the left and right cerebral hemispheres (54 patients). It was established that the intactness of the temporal parts of both hemispheres is important for non-verbal recognition (choosing of appropriate photograph by the observer) of emotions by mimics. Correct verbal identification of emotions by mimics requires the integrity of the fronto-parietal parts of the left hemisphere while verbal identification of emotional intonation needs the intactness of the fronto-parietal parts of the right hemisphere. The significance of the temporal areas (especially of the right hemisphere) increases in case when the emotional colouring of the presented verbal communication does not coincide with its contents.     

Asymmetry of the cerebral hemispheres during comparison of paired visual stimuli

In conditions of tachistoscopic presentation of visual stimuli, healthy (male and female) right-handed subjects carried out a paired comparison of the stimuli presented unilaterally and in the center of the visual field. In case of recognition of images of words and objects, the number of correct answers and motor reaction time usually did not significantly differ at two interstimuli intervals (1 and 10 s). In comparing images of faces, there also were no differences by the number of reactions, and the reaction time was less at the intervals of 1 s. The left hemisphere dominated at the identification of words and female faces, the right one--at the recognition of male faces. When the right visual field was stimulated images of various classes were recognized more differentially than at the stimulation of the left visual field. The male subjects had more prominent interhemispheric differences than the females. The increase of the interstimuli interval from 1 to 10 s brought to a weakening of the functional interhemispheric asymmetry and decreasing of the differences between the male and female subjects. The obtained data show that in the processes connected with short-time memory, functional interhemispheric asymmetry is basically formed at the initial stages of the information processing.     

The discrimination of time microintervals by emotionally excitable personalities

Function of time microintervals estimation was studied in emotionally excitable subjects (23 persons) as well as learning of this function by means of positive and negative reinforcements--words "good" and "error"--and interhemispheric relations. In excitable subjects, discerning is disturbed of short pauses between the visual stimuli, especially of 10 ms pause, presented in the right visual field. Deficit of learning of the intervals discerning is noted by reaction time parameter. There is no advantage of the left hemisphere in discerning the 10 ms pause from 60 ms, which is observed in healthy people.     

The role of feedback in the dynamics of functional asymmetry of brain hemispheres in man

Reaction time, number of correct evaluations of time microintervals, and P300 wave were studied in healthy adult subjects. The role is shown of feedback stimuli in training of a subject to discriminate short intervals and in changes of interhemispheric functional relations. These relations change in the course of training as a result of lateralized activation of the left hemisphere. Training with informative feedback is more efficient in the left hemisphere. The right hemisphere in lesser extent than the left one is subject to correcting influence of the feedback. In this sense the former is more autonomous.     

Reflection of the type and successfulness of the cognitive activity in the human EEG: application of nonlinear methods in psychophysiology

The information processing by the human brain was studied in two types of cognitive activity: solving a visual-spatial task and a verbal task. One of the Wechsler tests represented a visual-spatial task, whereas a speed-reading was used as a verbal task. A correlation dimension calculated from the EEG time series, was shown to depend on individual capabilities. Subjects with a higher correlation dimension in frontal brain areas executed more successfully the spatial task.     

Cross-modal individual recognition in domestic horses (Equus caballus) extends to familiar humans

It has recently been shown that some non-human animals can cross-modally recognize members of their own taxon. What is unclear is just how plastic this recognition system can be. In this study, we investigate whether an animal, the domestic horse, is capable of spontaneous cross-modal recognition of individuals from a morphologically very different species. We also provide the first insights into how cross-modal identity information is processed by examining whether there are hemispheric biases in this important social skill. In our preferential looking paradigm, subjects were presented with two people and playbacks of their voices to determine whether they were able to match the voice with the person. When presented with familiar handlers subjects could match the specific familiar person with the correct familiar voice. Horses were significantly better at performing the matching task when the congruent person was standing on their right, indicating marked hemispheric specialization (left hemisphere bias) in this ability. These results are the first to demonstrate that cross-modal recognition in animals can extend to individuals from phylogenetically very distant species. They also indicate that processes governed by the left hemisphere are central to the cross-modal matching of visual and auditory information from familiar individuals in a naturalistic setting.