[The Effects of Optokinetic Stimulation on Visual-Manual Tracking under Support-Proprioceptive Deprivation.]

To determine the effects of additional visual stimuli (retinal optokinetic stimulation - ROKS) on characteristics of the visual-manual tracking (VMT) without support and with decreased proprioceptive afferentation there was used a horizontal "dry" immersion. Altogether 18 subjects aged from 19 to 31 years participated in the study and they were submerged into the immersion bath from 5 to 7 days. There was evaluated performance of the VMT in tasks to pursue the jerky (saccadically) and smooth (linear, pendular and circular) movement of a point visual stimulus before, during and after immersion. Eye movements were recorded using electrooculography, hand movements - by ajoystick with a biological visual feedback (one of the two visible stimuli on the screen matched the current angle of thejoystick handle). Computerized visual stimulation programs were presented to subject using a virtual reality glasses with and without additional ROKS. We analyzed time, amplitude and velocity characteristics of the visual and manual tracking (VT and MT), including efficiency ratio (e) and gain (g) as ratios of respectively amplitudes and velocities of eyes/hand movements to the stimulus movement. Without ROKS efficiency ratio and gain of both VT and MT were significantly decreased in comparison with baseline during the whole immersion and up to the R + 3 day after. The most pronounced deterioration was observed in parameters of the VT. When using a "threshold" ROKS parameters of the VT and MT weren't changed before immersion, during and after immersion - they improved (on 1-5-7 days during immersion and on R + 3 day after there was a significant improvement of the VT and MT in comparison to same tests without ROKS). The greatest impact of the ROKS was observed in parameters of the VT. Evaluations of the vestibular function (VF) were performed before and after immersion using videooculography approach. We analyzed statical torsional otolith-cervical-ocular reflex (OCOR), dynamical vestibular-cervical-ocular reactions (VCOR) and vestibular reactivity (VR), spontaneous eye movements (SpEM). On R + 1 day after immersion in 28% of subjects there was found a significant decrease of the gain of OCOR (0.12 value in comparison to 0.25 baseline) with simultaneous significant increase of parameters of VCOR/VR. There was found a correlation between parameters of VT and MT, between VF and VT and no correlation between VF and MT. It was found that removal of the support and minimization of the proprioceptive afferentation has a greater impact-upon accuracy of the VT then accuracy of the MT. When using ROKS correlations between the studied parameters were not only preserved, but also intensified. The results obtained indicate the development of sensory deprivation (and afferent deficit) under the immersion exposure and the possibility of its correction with additional ROCKS.

[EFFECT OF REPEATED SPACE FLIGHTS ON OCULAR TRACKING].

The paper reports the results of studying the vestibular and ocular intersensory interactions and eye tracking function in 32 cosmonauts on maiden and repeated missions to the International space station. Mission duration ranged from 125 to 215 days. The cosmonauts were tested twice pre launch (baseline data collection) and on days R + 1/2, 4/5 and 8/9. Video oculography was used to test eye movements. It was found that in the majority of cosmonauts who had no experience of long-duration space missions the eye tracking function remained impaired significantly till R + 8/9. In cosmonauts who had already encountered with microgravity, obvious changes in eye tracking were observed on R + 1/2 only and, residual, on R + 4/5. On recovery, a new eye tracking strategy was acquired only by cosmonauts who had the first touch with spaceflight microgravity.

[VESTIBULAR FUNCTION AFTER REPEATED SPACE FLIGHTS].

Results of the vestibular function testing of 32 cosmonauts on return from repeated 125- to 215-day space flights (SF) on the International space station are presented. The cosmonauts were tested twice before flight (baseline data collection) and on days 1-2, 4-5 and 8-9 after landing. Electro- and video-oculography were used to register simultaneously eye and head movements. It was found that deadaptation following a repeated stay in long-duration SF takes statistically much shorter time. Most often, atypical vestibular disorders and changed patterns of the otolith-semicircular canal interaction are observed in cosmonauts who have made their maiden flights to microgravity.

[The effects of support-proprioceptive deprivation on visual-manual tracking and vestibular function].

To determine the effects of support and proprioceptive afferentation on characteristics of the visual-manual tracking (VMT) we used a model of weightlessness - horizontal "dry" immersion. Altogether 30 subjects who stayed in immersion bath from 5 to 7 days were examined to evaluate the accuracy of VMT in tasks to pursue the jerky (saccadically) and smooth (linear, pendular and circular) movement of a point visual stimulus. Examinations were performed before, during and after immersion using electrooculography (to record eye movements) and a joystick (to record hand movements) with a biological visual feedback - one of the two visible stimuli on the screen matched the current angle of the joystick handle. Computerized visual stimulation programs were presented to subject using a virtual reality glasses. We analyzed time, amplitude and velocity characteristics of the visual and manual tracking (VT and MT), including efficiency ratio (eVT and eMT) and gain (gVT and gMT) as ratios of respectively amplitudes and velocities of eyes/hand movements to the stimulus movement. eVT was significantly decreased in comparison with baseline all the time while subject lied in the immersion bath and until R+4 day after immersion, eMT was significantly decreased only on I-1 and I-3 days in immersion. gVT significantly differed from baseline only on I-3 and I-6 days in immersion and R + 1 day after immersion. We found no significant changes in gMT. Evaluations of the vestibular function (VF) were performed before and after immersion using videooculography approach. We analyzed statical torsional otolith-cervical-ocular reflex (OCOR), dynamical vestibular-cervical-ocular reactions (VCOR), spontaneous eye movements (SpEM), the accuracy of perception of subjective visual vertical (SVV). After immersion 47% of subjects had significant decrease of OCOR with a simultaneous significant increase of VCOR on 37% of subjects as well as significant changes in accuracy of perception of SVV which correlated with changes in OCOR. We found correlation between characteristics of the VT and MT, between characteristics of the VF and VT and found no correlation between VF and MT. It was found that removal of the support and minimization of the proprioceptive afferentation has a greater impact upon accuracy of the VT then accuracy of the MT.

[Effect of a real and simulated weightlessness on characteristics of the static torsional otolith-cervical-ocular reflex].

To determine the role of the support-proprioceptive factor in the functioning of the vestibular system, in particular the static torsional otolith-cervical-ocular reflex (OCOR), comparative OCOR studies with videooculography recording were performed after a 7-day "dry" horizontal immersion (16 immersion subjects) and after a prolonged (126 to 195 days) exposure to weightlessness (14 ISS cosmonauts). For the first time it was demonstrated that minimization of the support and propripceptive afferentation may results in an inversion or absence of the static torsional OCOR and the development of a positional nystagmus with an inverted reflex. A comparative OCOR data analysis of cosmonauts and immersion subjects has revealed similarity of responses. However, changes in OCOR after immersion were noted in only 60% of subjects, while after space fight, 90% of cosmonauts showed them. Post-flight changes were more frequent, marked and long-lasting.

[Visual-manual tracking during 5-day dry immersion].

Level dry immersion (DI), a model of the physiological effects of microgravity, support deprivation, minimization of muscle activity and proprioceptive afferentation specifically, was used to determine the effects of low proprioceptive, tactile and support afferentation on visual-manual tracking. Hand-eye motor coordination was tested in 13 subjects in 5-d DI who tracked jerky and smooth (linear and pendulum-like horizontal and vertical, circular clockwise and counterclockwise) motions of point visual stimulus. Binocular electrooculography was used to register ocular movements and a joystick with a biological visual feedback to register manual motor acts (1 of 2 stimuli on the screen showed the actual joystick inclination). Computerized stimulation was provided with the help of virtual goggles. Evaluated parameters were latent and total reaction time, amplitude and velocity of eye and hand movements, coefficients of effectiveness (amplitudes ratio) and gain (velocity ratio). Testing was performed before DI, after 3 hours in DI, on DI days 3 and 5, during the first hours and in 3 days after DI (all subjects) and on post-DI days 5-7 (4 subjects). It was demonstrated that support deprivation and minimization of proprioceptive afferentation affect ocular tracking to a larger degree than accuracy of the manual motor act of following the visual stimulus. Manual tracking by all subjects was found more accurate than visual and did not alter significantly during tests sessions; on the contrary, visual tracking accuracy altered noticeably as in the course, so after DI.

[Computerized methods for therapy and rehabilitation of patients suffering dizziness and balance disorder].

A new computerized method is proposed for correction and inhibition of unfavorable illusory (vertigo), vestibular-oculomotor (nystagmus), and vestibular-postural (balance) responses. This method allows to teach the subject to block generalization of an afferent signal to effector mechanisms of the central nervous system by developing a fixational reflex, utilizing a delayed biofeedback. Three variant ofthis method were employed, depending on the kind of stimulation programs aimed at inducing abnormal responses of a certain sensory modality (visual, vestibular or combined). The study involved 36 subjects divided into 3 equal groups one of which had been taught by a visual or vestibular technique, and the last one by a combined. Each group included approximately equal numbers of subjects with vestibulopathies of an organic (peripheral or central) or psychogenic origin. It was demonstrated that the method proposed allows, with the help of computerized stimulation programs, to provoce abnormal illusory and vestibular-optooculomotor responses in the subject, and inhibit them with the help of development of a fixational reflex. Patients were taught using three various variants of the method. A subsequent comparative analysis of results obtained has shown dependence of their effectiveness on the level of disturbance in the vestibular system: the visual variant of correction was the most effective for subjects with peripheral vestibulopathia; for subjects with central vestibulopathia, the vestibular variant was more effective; the combined variant of correction was the most effective for subjects with psychogenic vestibulopathia.

[Computer-aided techniques for the treatment and rehabilitation of patients suffering vertigo and balance disorders].

A new computerized method is proposed for the correction and elimination of undesirable illusory sensations (dizziness), vestibulo-oculomotor (nystagmus), and vestibulo-postural (imbalance) reactions. The method allows to teach the subject about how to avoid generalization of afferent signals over the effector mechanisms in the central nervous system by developing a fixational reflex employing delayed biological feedback for the assessment of efforts being exerted (self-control of training results). Three variants of application of this technique were evaluated depending on the type of stimulation software intended to induce illusory and oculomotor reactions of a defined sensory modality (visual, vestibular or combined). The study involved 30 subjects divided into three groups. They had been taught using the visual (group 1), vestibular (group 2) or combined (group 3) methods. Each group was comprised of an approximately equal number of subjects with vestibulopathies of either peripheral or central origin. The study demonstrated that the proposed approach allows to invoke, with the use of a computer stimulation software, abnormal illusory and vestibulo-oculomotor responses and inhibit them by developing the adequate fixational reflex. Comparative analysis of the results obtained by teaching the patients with the help of the three different methods revealed the dependence of their effectiveness on the level of disturbances in the vestibular system. The visual method of correction proved to be especially efficacious for the patients with peripheral vestibulopathy, and the vestibular methods for the patients with central vestibulopathy. Patients with combined peripheral and central vestibulopathy required the choice of training modalities (either visual or vestibular) on an individual basis.

[A computerized method for the combined evaluation of otoneurological and non-pharmacological correction of vestibulo-sensory and oculomotor disturbances].

Methodology and a new <> hard/software complex (HSC) have been developed jointly by the Institute of Biomedical Problems, <> and <> Companies to be used in vestibulometric, otoneurological, and psychophysiological tes-ting with synchronous registration and in the analysis of head movements, various types of nystagmus, and all forms of visual pursuit. The complex is intended for the expert/diagnostic evaluation, prognosis, and monitoring of the vestibular function, intersensory interactions, and eye pursuit movements as well as for teaching correction and elimination of unfavourable perceptive and vestibular-sensorimotor responses by developing a fixation reflex during exposure to visual and dynamic stimuli. The <> HSC was tested during pre- and post-flight observation of astronauts, under simulated and clinical conditions, as well as in monitoring the functional status of athletes engaged in various sports. The study has demonstrated that the use of special computerized stimulation programs allowing (by irritating visual and vestibular sensory inputs) to produce perceptive and sensorimotor responses provides a promising tool for the evaluation of the state of the vestibular and related sensory systems, stability of static and dynamic spatial orientation in the presence of separate and combined visual and vestibular stimuli or without them.

[Visual-manual tracking and vestibular function during 7-day dry immersion].

The seven-day DI experiment provided an opportunity to study the effects of decreased proprioceptive, tactile and support afferentation on the vestibular function and visual-manual tracking. Before and after immersion, six subjects participated in videooculographic evaluation of the static torsion otolith-cervicoocular reflex (OCOR) in response to head inclination at 30 degrees in the frontal plane and dynamic vestibular-cervicoocular reactions to head longitudinal rotations at 0.125 Hz. In addition, the hand-eye motor coordination of tracking a jerky (sinusoidal) or smooth (linear) movement of point targets along the horizontal or the vertical was evaluated based on the data of electrooculography and records of manipulations with the joystick during immersion. The computerized test was performed in virtual spectacles dsplaying images of visual stimuli and hand motor acts. Computed parameters included latent reaction time, amplitude, speed and time of eye and hand movements, and gains of optooculomotor reactions and manual tracking as a ratio of eye/hand to visual stimulus speed. Testing was fulfilled before the experiment, in 3 hrs. of immersion, on days 3 and 6 of staying in the bath, in the initial hours after immersion, and on day 3 of recovery. It was shown that removal of support and minimization of proprioceptive afferentation had a profound effect on the ocular tracking rather than hand pursuance of visual stimulus. Accuracy of manual tracking was better comparing with the eye tracking in all the subjects. This was the first time when we observed changes in the peripheral vestibular system in two out of 6 subjects, i.e. inversion of static torsion OCOR and positional nystagmus on the background of converted reflex which did not mar the parameters of oculo-manual tracking.

Static and dynamic vestibulo-cervico-ocular responses after prolonged exposure to microgravity.

The vestibular function was investigated in 13 Russian crew members of the ISS missions on days 1(2), 4(5), and 8(9) after prolonged exposure to microgravity (126 to 195 days). The static torsional otolith-cervico-ocular reflex was studied, as well as the dynamic vestibulo-cervico-ocular responses, vestibular reactivity, and spontaneous oculomotor activity using videooculography (VOG) and electrooculography (EOG) for simultaneous recording of eye movements. On days 1-2 of return to the gravity (R+1-2), the cosmonauts were found to increase the spontaneous oculomotor activity (floating eye movements, both typical and atypical forms of spontaneous nystagmus, square wave jerks, gaze nystagmus) with the head held in the vertical position. The otolith function during static head inclinations to the right or left shoulder at 30 degrees was suppressed as determined by the inversion or absence, or reduction by half of the amplitude of torsional compensatory eye counter-rolling and the vestibular reactivity during head yaw movements at 0.125 Hz was increased as revealed by a lowered threshold and an increased intensity of vestibular nystagmus. The pattern, depth, dynamics, and velocity of the vestibular function recovery varied with individual participants in the investigation. However, the suppressed otolith functioning in the period of readaptation to the normal gravity was, as a rule, accompanied by an exaggerated vestibular reactivity.

[Studies of the eye tracking function in changed sensory conditions with new soft- and hardware and computer tests].

The new soft- and hardware is intended to specifically test the eye-tracking profession in order to diagnose and monitor the ocular and related sensory systems. Oculography is used to investigate different forms, including spontaneous and evoked, of visual tracking by computer stimulation of the sensory inputs. The system validation was a part of the pre- and post-flight examination of Russian spacecrew members, and protocol of the 7-d dry immersion. As a result, demonstrated was a considerable degradation of the precision and velocity, and extension of time parameters after long-duration missions with differentiation of concurrent peripheral vestibular disturbances and central structural changes. Throughout the period of immersion, the parameters displayed diverse changes which rendered distinction between baseline and experimental data impossible. Comparative analysis of the post-flight and experimental data showed that the most marked deviations in the eye tracking function were peculiar to cosmonauts on return from long-duration space flight.

[Effect of long-term microgravity on the vestibular function].

Comprehensive computerized oculomotor testing was used to investigate the vestibular function in 9 Russian members of ISS crews 3-9 on days 1 (2), 4 (5) and 8 (9) of return from long-term stay in microgravity (126 to 195 days). The vestibular function was assessed by the static otolith-cervical-ocular reflex, dynamic otolith-cervical-ocular reactions, vestibular reactivity, and spontaneous oculomotor activity. The postflight investigations revealed functional disorders in the peripheral (an increased vestibular reactivity, absent or damped otolith-cervical-ocular reflex), and central (spontaneous typical and atypical nystagmus, gaze nystagmus) vestibular analyzer. The pattern and extent of vestibular disorders after long-term exposure in microgravity were individual by character; however, some of the vestibular reactions, including disappearance or considerable damping of the static otolith-cervical-ocular reflex, exaggerated vestibular reactivity and spontaneous eye movements, displayed consistency.

[Computerized method of objectification of dizziness and vertigo and differential diagnostic of vestibulopathies].

OBJECTIVE: To create a complex computerized method of objectification of dizziness and vertigo, and differentiation of vestibulopathies of various geneses using electrooculography approach that allows to record and analyze spontaneous, vestibular- and visually-induced eye movements, with the following classification (discriminant) analysis of the results obtained. MATERIAL AND METHODS: The study involved 69 patients of different sex and age complained of dizziness, vertigo and disequilibrium, and 64 healthy men. Based on the results of clinical examination, patients were divided into three groups: patients with peripheral vestibulopathy, patients with central vestibulopathy and patients with psychogenic vestibulopathy. Electrooculography was performed using the hardware-software complex (HSC) "OCULOSTIM-CM". RESULTS AND CONCLUSION: Significant diagnostic parameters based on the recognition and analysis of spontaneous, vestibular- and visually-induced eye movements were coefficients of efficacy and increased frequency of fixation saccades and smooth pursuit with- and without retinal optokinetic stimulation. We developed the algorithm and complex computerized method for differentiation of different types of vestibulopathy.

Orientation illusions in spaceflight.

Investigations of spontaneous illusory reactions were carried out during space-flights of various durations by ANKETA questionnaires (104 cosmonauts). From a total of 104 cosmonauts, 24, in addition, used a dictaphone to record a verbal description of the illusions and their sensations on tape. Analysis of data generated by ANKETA and the tapes thus recorded have shown that during adaptation to weightlessness, 98% of cosmonauts have noted the occurrence of various illusions of orientation (coordinate and kinetic): illusions pertaining to their position or illusions of self- and surround-motion. The development of spatial orientation illusions during and after flight is not limited to certain individuals, but is a general response of the sensory system to microgravity. These responses differ to some extent among individuals in severity, nature, time and duration of occurrence, and the dynamics of the process. Perceptual disorders may occur even if the cosmonaut feels well and experiences no anomalous autonomic reactions. The nature of spatial illusions was determined by the role and relative contribution of various types of sensory input to spatial orientation. After completion of the initial stage of adaptation to weightlessness, the perceptual disorders disappear. However, spontaneous illusory reactions were often observed after 50 days of exposure to weightlessness. The adaptation process during long-term spaceflight had an undulating course, in which adaptation and de-adaptation alternated. A classification of weightlessness illusions is proposed.

Vestibular function and sensory interaction in space flight.

The vestibular system and vestibulo-visual interaction were examined in 11 astronauts by the electrooculographic (EOG) method during short- and long-term flights on days 2, 3, 5, 9, 22, 50, 164, and 169 (experiments OPTOKINES and LABYRINTH). In space (flight days 2 and 3), they showed enhanced spontaneous vertical nystagmus, and disorders of tracking of vertical and diagonal movements of the stimulus which improved after active head movements. Early increasing of the reactivity of the cupulo-endolymphatic system (flight days 2-3) was replaced after 5 days of flight with a reduction of the vestibular function and an increase of the significance of the visual input in the formation of oculomotor responses to combined vestibulo-optokinetic stimulation. The type of spontaneous ocular reaction and vestibular stimulation of oculomotor activity under the conditions of weightlessness represented, on one hand, the general responses of sensory systems to weightlessness and, on the other hand, specificity of integrating and adaptive processes.

Microgravity effect on the vestibulo-ocular reflex is dependent on otolith and vision contributions.

BACKGROUND: We studied whether microgravity influences horizontal and vertical vestibulo-ocular reflex (VOR), and what the otolith contributes to VOR in the absence of gravity, in six cosmonauts during and after space missions. METHOD: VOR was elicited by active yaw and roll head movement at a frequency of about 0.2 Hz. RESULTS: The various individual quantitative changes (increase, decrease, and left-right asymmetry) found in the horizontal VOR evoked by yaw head movements during the adaptation period to microgravity suggested central reprogramming of mechanisms controlling VOR; i.e., a non-specific effect of microgravity on VOR. At the same time, horizontal and vertical VOR's were recorded during roll head movements, which were not obvious before flight. In the consmonaut who participated in a long-term flight, the increased activity of vertical canals turned to unidirectional (downward) eye movements, independent of the head movement direction, lasting during the whole mission. These VOR changes probably resulted from the absent adequate otolith stimulation and reduced otolith influence upon semicircular canal function. CONCLUSIONS: Thus, a specific effect of microgravity on VOR was observed during roll head movements, when the interaction between semicircular canals and otoliths should be more pronounced, mainly in the vertical plane. The stability of the "space" pattern of interactions in the readaptation period depended on the time spent in microgravity. We suggest that in visual-vestibular interactions revealed in VOR evoked by head movements with open eyes, vision dominates when a conflict arises between "space" and "terrestrial" patterns of sensory interactions.

Space motion sickness: phenomenology, countermeasures, and mechanisms.

A summary of the incidence of Space Motion Sickness (SMS) in 27 Soviet cosmonauts who flew on missions varying from 2-185 d in the Salyut-6/Soyuz vehicle complex is presented. A questionnaire indicated that 88% (24) of the cosmonauts developed some type of "illusionary sensations" while 44% (12) presented some degree of SMS. The SMS countermeasures used in flight included an antihistaminic drug, pneumatic cuffs applied to the thigh region, application of lower body negative pressure, a head cap that restricted head movement while simultaneously providing force stimulus to the cervical antigravity muscles, and finally the use of an insole counterpressure device that added pressure to the sole of the foot.

The role of gravitation-dependent systems in visual tracking.

The effects of prolonged microgravity conditions on the performance of visual tracking functions such as fixational rotations of the eyes (saccades), smooth tracking of linear and curved movements of a foveal point stimulus, and following a vertical pendulum-like movement of foveoretinal optokinetic stimuli were studied. Experiments were performed on 31 cosmonauts in freefall conditions, in ten cases followed by additional studies after a cycle of head movements and in 14 after resting. These experiments showed that while intrinsic visual functions were retained in microgravity conditions, there were decreases in the precision and speed measures of all types of visual tracking (fixational rotations of the eyes, smooth tracking) and, in some cases, complete degradation of the smooth tracking reflex, an increase in the time taken to fix the gaze on a target (by factors of 2 or more), and decreases in the frequency of stimulus tracking. During the initial period of adaptation to the altered gravitational conditions and periodically during prolonged flight, the system of smooth visual tracking was found to undergo a transition to a strategy of saccadic approximation, in which gaze tracks the movement of the target using a set of macro- or microsaccadic movements. These impairments, seen in virtually all the cosmonauts, resulted from vestibular deprivation (functional deafferentation of the otolith input) in conditions of weightlessness, while in cosmonauts conceptualizing space on the basis of perceiving the positions of the feet and head additionally showed support-tactile deprivation.

Modifications of spontaneous oculomotor activity in microgravitational conditions.

Investigations on spontaneous oculomotor activity were carried out prior to and after (five cosmonauts) and during space flight (two cosmonauts) on the 3rd, 5th and 164th days of the space flight. Recording of oculomotor activity was carried out by electrooculography on automated data acquisition and processing system "Zora" based on personal computers. During the space flight and after it all the cosmonauts with the eyes closed or open and dark-goggled showed an essential increase of the movements' amplitude when removing the eyes into the extreme positions especially in a vertical direction, occurrence of correcting saccadic movements (or nystagmus), an increase in time of fixing reactions.