A. Ya. Kaplan

Analysis of EEG Structural Synchrony in Adolescents with Schizophrenic Disorders

A total of 39 healthy adolescents and 45 adolescents with schizophrenic disorders (mean age 12.3 years) were examined to study the EEG structural synchrony as reflecting temporal synchronization of the operational activity of neuronal networks. A significant decrease in the EEG structural synchrony was observed in the adolescents with schizophrenic disorders as compared to the healthy adolescents. The decrease was detected predominantly in the interhemispheric pairs of EEG derivations, as well as in the pairs related to the frontal, temporal (predominantly on the left), and right parietocentral regions. The findings provide evidence in favor of Friston’s hypothesis of disintegration of cortical electrical activity in schizophrenia and extend the hypothesis in that it is the operational synchrony of cortical activity that might suffer first in schizophrenia.

P300-based brain-computer interface: The effect of the stimulus position in a stimulus train

The most popular type of brain-computer interfaces (BCIs) are based on the detection of the P300 wave of the evoked potentials appearing in response to a stimulus chosen by the subject. In order to increase the speed of operation of these BCIs, it is possible to decrease the number of repeated stimulus presentations. It is associated with an increase in the relative importance of the response to the first stimulus in a train for correct recognition of the stimulus chosen. Event-related potentials (ERPs) in response to the first stimulus presentations are known to have their own specificity. Particularly, in many cases, the amplitude of the response to the first presentations is enhanced, which makes it very suitable for recognition in a BCI. However, this effect has not been studied to date. In this study, the ERPs recorded in healthy subjects in a standard BCI paradigm (n = 14) with ten presentations of stimuli or during triple-trial (n = 6) and single-trial (n = 6) presentations of stimuli in a modified BCI paradigm with moving objects have been analyzed. In both cases, first presentations of the target stimuli or single-trial presentation of the target stimulus were associated with higher amplitudes of ERPs. The opportunity to use specific differences between the responses to the first or single-trial presentations and the responses to later stimuli during their repeated presentations for improving high-speed operations in the P300-based BCI is discussed.

[Unconscious context control of visual perception of simple stimuli: a study using evoked potentials].

The effect of nonsemantic context on the perception of simple nonverbal visual stimuli has been studied in ten healthy volunteers by the event-related potential (ERP) method. The nonsemantic context was specified by the formation of a memory trace of a test visual stimulus via its repeated presentation without any instruction except gaze fixation. Then, this stimulus randomly alternated with control stimuli that did not form memory traces before their presentation. It has been found that an ERP in the interval 260–340 ms after presentation of a simple nonverbal stimulus significantly differs from the control ERPs. The results suggest that some stages of the processing of visual stimuli may be modified by nonsemantic context.

What Information Is Hidden in Chaotic Signals of Biological Systems

Applications of the Flicker‐Noise Spectroscopy (FNS) to analysis of electroencephalograms (EEG) are demonstrated. We present the double correlation function for the EEG measured in the C4 and O2 points for two patients — a healthy (“normal”) child and a sick Schizophrenia child. The drastic differences in the behavior of the two‐correlators manifest the information meaning of the similar dependences. We conclude that the FNS approach could be considered as a new instrument to early diagnostics of various brain diseases.

Depression of evoked potentials in rat thalamic ventro-basal complex and somatosensory cortex after reticular stimulation.

Experiments on unanesthetized rats immobilized with D-tubocurarine showed that electrical stimulation (100/sec) of the central gray matter and the mesencephalic and medullary reticular formation considerably depressed potentials in the somatic thalamic relay nucleus and somatosensory cortex evoked by stimulation of the forelimb or medial lemniscus. The mean threshold values of the current used for electrical stimulation of these structures did not differ significantly and were 70 (20–100), 100 (20–120), and 120 (50–200)μ A, respectively On comparison of the amplitude-temporal characteristics of inhibition of evoked potentials during electrical stimulation of the above-mentioned structures by a current of twice the threshold strength, no significant differences were found. Immediately after the end of electrical stimulation the amplitude of the cortical evolved potential and the postsynaptic components of the thalamic evoked potential was 50–60% (P<0.01) below the control values. The duration of this depression varied from 0.5 to 1 sec. An increase in the intensity of electrical stimulation of brain-stem structures to between three and five times the threshold led to depression of the presynaptic component of the thalamic evoked potential also. Depression of the evoked potential as described above was found with various ratios between the intensities of conditioning and testing stimuli.

Neurophysiological foundations and practical realizations of the brain–machine interfaces in the technology in neurological rehabilitation

The brain–computer interface (BCI) technology, based on the registration and interpretation of EEG, has recently become one of the most popular developments in neuroscience and psychophysiology. This is due not only to the intended future use of these technologies in many areas of practical human activity, but also to the fact that BCI is a completely new paradigm in psychophysiology, which allows testing hypotheses about the possibilities of the human brain to the development of skills of interaction with the outside world without the mediation of the motor system, i.e., only with the help of voluntary modulation of EEG generators. This paper examines the theoretical and experimental basis, the current state, and the prospects of development of training, communicational, and assisting complexes based on BCI to control them without muscular effort on the basis of decoding mental commands detected in the EEG of patients with severely impaired speech and motor system.

Late negativity in visual evoked potentials in humans to changes in the topology of simple nonverbal stimuli

Late negativity arising in evoked potentials to semantic mismatching of sequentially presented stimuli is usually linked with verbal or symbolic representations of stimuli during the process of perception. The present studies showed that the late negativity characteristic of semantic mismatch arises even in the context of non-symbolic and nonverbal stimuli, for example, stimuli consisting of four points differing only in terms of topology or angular size. Distraction of attention from the test stimuli completely eliminated the late negativity effect. It is suggested that any stimulus composition can have semantic (meaning) and formal (shape, pattern) descriptions which, when stimuli are compared using the oddball paradigm, result in various levels of the N400 component depending on the amount of attention paid to the stimuli themselves.

The complex of unsaturated fatty acids eikonol optimizes human cognitive activity

The effects of eikonol, a preparation containing polyunsaturated fatty acids omega-6/omega-3 in a ratio close to the optimal for humans, were tested in a psychophysiological study involving 42 subjects. A dietary vegetable oil served as control. In the sensorimotor testing of the operational, type, the subjects were supposed to memorize three reference two-digit numbers during a short time so as to decide on presentation of the test number whether the latter was present among the reference numbers. The subject was presented 480 test samples with randomly selected numbers before and after the intake of eikonol. The course of eikonol for 30 days exerted a statistically significant positive effect on all the subjects. Individual features in the subjects’, response to eikonol were noted, i.e., in about 50% of them, the effect of eikonol was manifested by only a decreased number of wrong answers, whereas, in the rest of subjects, this effect was observed simultaneously with an increased number of right answers. As compared with the effects of the oil, the positive effect of eikonol on the parameters of operational activity of humans appeared to be much more pronounced and affected twice as many subjects tested. Possible prospects of the use of eikonol for optimization of cognitive processes in humans with an individual selection of the dosage and regimen are discussed.

The Efficiency of the Brain-Computer Interfaces Based on Motor Imagery with Tactile and Visual Feedback

In this study we compared tactile and visual feedbacks for the motor imagery-based brain–computer interface (BCI) in five healthy subjects. A vertical green bar from the center of the fixing cross to the edge of the screen was used as visual feedback. Vibration motors that were placed on the forearms of the right and the left hands and on the back of the subject’s neck were used as tactile feedback. A vibration signal was used to confirm the correct classification of the EEG patterns of the motor imagery of right and left hand movements and the rest task. The accuracy of recognition in the classification of the three states (right hand movement, left hand movement, and rest) in the BCI without feedback exceeded the random level (33% for the three states) for all the subjects and was rather high (67.8% ± 13.4% (mean ± standard deviation)). Including the visual and tactile feedback in the BCI did not significantly change the mean accuracy of recognition of mental states for all the subjects (70.5% ± 14.8% for the visual feedback and 65.9% ± 12.4% for the tactile feedback). The analysis of the dynamics of the movement imagery skill in BCI users with the tactile and visual feedback showed no significant differences between these types of feedback. Thus, it has been found that the tactile feedback can be used in the motor imagery-based BCI instead of the commonly used visual feedback, which greatly expands the possibilities of the practical application of the BCI.

Variability of the EEG Autocorrelation Structure in Adolescents with Schizophrenia Spectrum Disorders

Quantitative analysis of changes in the autocorrelation structure of EEG short segments (in the range of several seconds) was performed in healthy adolescents (n = 39) and adolescents with schizophrenia spectrum disorders (n = 39). The variability of the EEG autocorrelation structure was shown to be higher in patients with the greatest trend in the frontal leads. It is suggested that psychopathology of the schizophrenia spectrum is accompanied by a break in the mutual determination of cortical neural networks with predominant localization of this process in the frontal areas of the brain cortex.