[The Features of Saccadic Reactions to a Consequent of Visual Stimuli in Healthy Subjects and Patients with Schizophrenia].

We studied the features of cognitive functions of attention and decision making in 18 healthy subjects and 15 patients with schizophrenia with the use of pairs of two short visual stimuli (double step). In the group of patients with schizophrenia, we observed a higher number of errors and higher frequency of modified saccadic pattern--two saccades to each stimulus instead of only one saccade to the second stimulus. In these patients, the latency period of the first saccade was shorter, while the latency period of a single saccade to the second stimulus was longer as compared with healthy subjects. The lateral differences in the saccade latency in schizophrenic and healthy subjects are opposite. The data provide an evidence of disorders in the cognitive control and prognostic processes of saccade programming in schizophrenic patients.

[Saccade latency and pattern of saccade response in the experimental scheme "double step"].

To investigate the decision-making process at the saccade programming we used modification of the "double step" experimental scheme, in which two short stimuli are presented successively in the opposite semifields (puls overshoot--scheme). The dependence of saccades to visual stimuli number, responses pattern (two saccades, or a single saccade to the second stimulus) and the value of saccade latency from the first stimulus duration (150 or 50 ms), the spatial stimuli arrangement and the individual characteristics of the subjects was shown. The findings suggest the relationship of attention and decision making processes at saccade programming and indicate to the possible influence of prognostic processes on the saccadic response "pattern" at the expectation period in the experimental "double step" scheme.

Specific Aspects of Eye Movement Reactions as Markers of Cognitive Control Disorders in Patients with Obsessive-Compulsive Disorder (Review).

Multiple studies in patients with obsessive-compulsive disorder (OCD) became the basis for revealing selective attention, inhibitory control, and working memory impairments, which correlates with an imbalance in the activity of the cortico-striatal-thalamic-cortical circuit associated with maintenance of cognitive control functions. Patients with OCD often demonstrate changes in the parameters of target-oriented eye movement reactions being a consequence of a possible impairment of the cognitive control neurophysiological framework. This review summarizes and analyzes data on cognitive control disorders in OCD obtained with eye movement recording techniques. It was established that the most often used are smooth pursuit eye movements tasks, memory-guided saccades, and anti-saccadic tasks. Data on smooth pursuit eye movements tasks and memory-guided saccades are contradictory, although they partially confirm selective attention and working memory impairment. Most studies on the anti-saccadic task identified impaired inhibitory control in patients with OCD. Similar disorders in form of increased latency and higher error rate in anti-saccades were also noted in the patients' first-degree relatives, which allows considering such disorders as manifestations of the endophenotype associated with the underlying risk of OCD. Future confirmation of these results in experiments using complex anti-saccadic tasks with images of various modalities (taking into account the increased anxiety in patients with OCD as the disorder basis) might contribute to validation of the OCD-specific markers.

[Cortical potentials evoked to response to a signal to make a memory-guided saccade].

The difference in parameters of visually guided and memory-guided saccades was shown. Increase in the memory-guided saccade latency as compared to that of the visually guided saccades may indicate the deceleration of saccadic programming on the basis of information extraction from the memory. The comparison of parameters and topography of evoked components N1 and P1 of the evoked potential on the signal to make a memory- or visually guided saccade suggests that the early stage of the saccade programming associated with the space information processing is performed predominantly with top-down attention mechanism before the memory-guided saccade and bottom-up mechanism before the visually guided saccade. The findings show that the increase in the latency of the memory-guided saccades is connected with decision making at the central stage of the saccade programming. We proposed that wave N2, which develops in the middle of the latent period of the memory-guided saccades, is correlated with this process. Topography and spatial dynamics of components N1, P1 and N2 testify that the memory-guided saccade programming is controlled by the frontal mediothalamic system of selective attention and left-hemispheric brain mechanisms of motor attention.

[Initiation potential of the brain cortex before memory-guided saccades].

Longer latency and duration of memory-guided saccades and their lower amplitude compared with visually-guided saccades testify to the slower programming of the former. Lateral distinctions in the latencies and durations of memory-guided and visually-guided saccades can reflect leading role of the right hemisphere in programming memory-guided saccades and leading role of the left hemisphere in programming visually-guided saccades. Topography and spatiotemporal dynamics of presaccadic potentials P-1 and N-1 within the last 100 ms of latent period suggest that the mechanisms of final stage of the programming of memory-guided and visually-guided saccades are different. Shorter latencies of the presaccadic P-1 and N-1 prior to memory-guided saccades testify to acceleration of the initiation of the memory-guided saccades. The acceleration of the initiation period of memory-guided saccades suggest that deceleration of memory-guided saccade programming occurs at the stages preceding saccade initiation.

[Attention and eyes movement. Structure of oculomotor system, phenomenology and saccade programming].

In the review modern conceptions of the brain organization of visiomotor system are given. They based on neurophysiological and clinical researches which show reflection of attention processes at various levels of this system. Phenomenological data of saccadic eyes movements and existing models of saccade programming, which expressed on the basis of studying of saccades latent periods variation in different conditions of visual stimulation, are presented. Theoretical ideas of saccade programming stages according to "bloc" model of saccade programming are given. On the basis of literature data and own researches various views at the nature of "Gap-effect" and the express-saccades as a reflections of attention contribution in saccade programming are shown.

[Attention and eye movements in human: psychophysiological concepts, neurophysiological models and EEG correlates].

A review. Recently published articles concerning the problem of attention are discussed, the most popular psychophysiological concepts and neurophysiological models of attention are described, and correlation of spatial attention and saccadic eyes movements is shown. The evidence for reflection of attention mechanisms and saccade preparation in intensity and topography of the visual evoked potentials and event-related potentials is given. On the basis of the results obtained by the authors and literature data, the contribution of attention to preparation of a saccade and its programming is shown. Different kinds of attention are reflected in a complex of EEG potentials of various duration and polarity. The analysis of parameters and topography of these potentials can serve a tool for investigation of the attention mechanisms.

[Human fast negative EEG potentials before express saccades].

Fast negative EEG potentials preceding fast regular saccades and express saccades were studied by the method of backward averaging under conditions of monocular stimulation of the right and left eye. "Step" and "gap" experimental paradigms were used for visual stimulation. Analysis of parameters of potentials and their spatiotemporal dynamics suggests that, under conditions of the increased attention and optimal readiness of the neural structures, express saccades appear when the previously chosen program of the future eye movement coincides with the actual target coordinates. We assumed that the saccade latency decreases at the expense of the involvement of the main oculomotor areas of motor and saccadic planning in its initiation; an express saccade can be initiated also by means of direct transmission of the signal from the cortex to the brainstem saccadic generator passing by the superior colliculus. Moreover, anticipating release from the central fixation and attention distraction are necessary for the successful initiation of an express saccade.

[Positive potentials ot the human brain in the latent presaccadic period under conditions of stimulation of the leading and nonleading eye].

We used backward averaging method to study fast positive presaccadic EEG-potentials under conditions of the monocular stimulation of the leading and nonleading eye. Two schemes of the visual stimulus presentation ("no gap" and "overlap") were used. In the "no gap" condition, potential P1 dominated in the hemispere ipsilateral to a saccade direction. In the "overlap" condition, when the gaze was fixed at the central point, foci of this potential were localized in the sagittal derivations or in the same sites as in the "no gap" conditions. Irrespective on the stimulation scheme, the P2 foci were localized in the hemisphere contralateral to a saccade direction. We assume that the fast positive potentials involve both activation and inhibition processes in visuomotor structures and can be also associated with cognitive presaccadic processes (such as fixation disengage, attention lateralization and a preliminary extraction of motor programs from memory).

[Lateralization of saccadic latency during monocular presentation of stimuli to a leading and non-leading eye]. / Lateral'nye razlichiia v velichine latentnykh periodov sakkad pri monokuliarnom pred"iavlenii stimulov s "perektytiem" v vedushchii i nevedushchii glaz.

Saccadic latencies were studied in ten healthy subjects. Peripheral targets were presented monocularly to a leading and nonleading eyes in the right and left hemifields. SS (single step) and OVERLAP (200 ms) schemes of visual stimulation were used. Under OVERLAP conditions, the saccadic latency was longer by 30-39 ms and the number of long-latency saccades was higher than under SS conditions, especially in subjects with mixed asymmetry profiles. In the majority of subjects with right asymmetry profile, the latencies of saccades during stimulation of the leading eye were by 12 ms shorter than during stimulation of the nonleading eye, and the latencies of right saccades were by 24 ms shorter than that of the left saccades independently of the stimulated eye. The obtained results explain some characteristic features of hemyspheric asymmetry in organization of saccadic movements.

[The effect of the visual stimulation of the leading and nonleading eye on the value of the saccadic latency period and on the peak latency of rapid presaccadic potentials]. / Vliianie zritel'noi stimuliatsii vedushchego i nevedushchego glaza na velichinu latentnogo perioda sakkady i latentnost' pika bystrykh presakkadicheskikh potentsialov.

Visual targets were presented monocularly to the leading and nonleading eyes. The complex of rapid positive and negative potentials was studied using the reverse summation from the onset of saccades. The latencies of saccades and peak latencies of the averaged presaccadic potentials were measured. The dependence of the saccade latencies and peak latencies of the complex of potentials on stimulation of the leading or nonleading eye and saccade direction was not simple and was largely determined by the individual profile of asymmetry. It is suggested that during stimulation of the leading eye the processes of attention fixation and switching as well as of the space visual processing are faster than during stimulation of the nonleading eye. Thus, the leading role of the right eye is reflected not only in fixation processes but also in movement anticipation.

[Fast positive cortical potentials of the human cerebral hemispheres to visual stimuli evoking saccades]. / Bystrye pozitivnye potentsialy kory bol'shikh polusharii golonogo mozga cheloveka na zritel'nye stimuly, vyzyvaiushchie sakkady.

The EEG was recorded in 7 healthy subjects aged 20-25 years according to the International 10-20 System in the frontal and parietal derivations (F3, F4, Pz, P3, P4) during the saccades related with the visual stimuli. A complex of fast (positive and negative) event-related potentials was recorded in response to visual stimulation before the saccade onset. The amplitude and spatial distribution of these potentials depended on the saccade latency, order of stimuli presentation, personality of a subject etc. The results suggest that the early positive potentials observed in the saccade latent period reflect the activation of the cortical structures which participate in programming and initiation of saccades.