[Artificial Feedback for Invasive Brain-Computer Interfaces].

During the last two decades, considerable progress has been made in the studies of brain-computer interfaces (BCIs)--devices in which motor signals from the brain are registered by multi-electrode arrays and transformed into commands for articial actuators such as cursors and robotic devices. This review is focused on one problem. Voluntary motor control is based on neurophysiological processes which depend heavily on the afferent innervation of skin, muscles and joints. Thus, invasive BCI has to be based on a bidirectional system in which motor control signals are registered by multi-channel micro-electrodes implanted in motor areas, while tactile, proprioceptive and other useful signals are transported back to the brain through spatial-temporal patterns of intracortical microstimulation (ICMS) delivered to sensory areas. In general, the studies of invasive BCIs have advanced in several directions. The progress of BCIs with articial sensory feedback will not only help patients, but will also expand knowledge base in the field of human cortical functions.

[Quality of neuronal signal registered in the monkey motor cortex with chronically implanted multiple microwires].

Disconnection of central and peripheral parts of motor system leads to severe forms of disability. However, current research of brain-computer interfaces will solve the problem of rehabilitation of patients with motor disorders in future. Chronic recordings of single-unit activity in specialized areas of cerebral cortex could provide appropriate control signal for effectors with multiple degrees of freedom. In present article we evaluated the quality of chronic single-unit recordings in the primary motor cortex of awake behaving monkeys obtained with bundles of multiple microwires. Action potentials of proper quality were recorded from single units during three months. In some cases up to 7 single units could be extracted on a channel. Recording quality stabilized after 40 days since electrodes were implanted. Ultimately, functionality of multiple electrodes bundle makes it highly usable and reliable instrument for obtaining of control neurophysiologic signal from populations of neurons for brain-computer interfaces.

[Long-term recording of single unit activity and criteria for estimation of stability].

Stable single-unit recording in the brain of vertebrates allows to investigate processes underlying neural plasticity. In applied aspect long-term single-unit recording can be useful for development of invasive brain--computer interface. Here we propose a criterion for identification of neurons that were recorded for more than one day. Based only on the spike forms classification yields ambiguous result. Additional parameters (such as form of interspike interval histogram or certain parameters of that histogram) decreased misclassification probability considerably. Using proposed criterion we were able to identify 82 neurons that were recoded for more than one day. In extreme case activity of one neuron was observed for 94 days.

[Effect of 7-day dry immersion on the mechanisms of ocular saccadic movements generation].

To evaluate the impact of prolonged support deprivation on the mechanisms of ocular saccadic movement generation, four volunteers were tested on the eve of 7-d dry immersion and on the completion day. The task consisted of tapping random light stimuli emerging on the periphery of sensory screen. During testing, the head was kept in a fixed position. To tap stimuli, human subject was either to touch a respective spot on the screen with a finger with gaze shifting and fixation accompanying coordinated hand movement (1) or to press the mouse key after gaze fixation on stimulus (2). Movements of the eyes were registered and analyzed in the infrared frequency of 200 Hz. It is maintained that the similar impact of immersion on the peak saccade velocity-amplitude ratio no matter how stimuli were tapped suggests saccade acceleration after immersion in consequence of the direct effect of prolonged support deprivation.

[Effect of mechanic stimulation of foot support zones during 7-day dry immersion on alterations of ocular saccades kinematics associated with immersion].

Purpose of the investigation was to evaluate how daily sessions of mechanic stimulation (MS) of foot support zones applied to mitigate the effects of lack of support loading on the postural muscles influence ocular saccades during prolonged support deprivation. According to the experimental protocol, before and immediately after 7-day dry immersion, 4 control and 4 MC human subjects (experimental group) implemented the test of rapid blanking light target appearing on the visual field periphery. Eye motions were detected using infrared images obtained at 200 Hz. Analysis of normalized and consolidated data showed that MC of foot support zones moderated significantly alterations in ocular saccade kinematics associated with support load deprivation confirmed by recruitment of support afferentation in sensory input to mechanisms of ocular saccade generation.

[Neck-deep immersion effects on gaze fixation by primates].

Effects of load deprivation on gaze fixation were studies in two primates (Macaca mulatta) immersed neck-deep twice with a two-week interval. Gaze fixation was traced using electrooculography and measurement of head turn velocity in 5 hours since the beginning of immersion. Decrease of the maximum head velocity and vestibuloocular reflex gain in both animals were significantly higher in the second compared with the first period of immersion and the results of previous investigations with three primates repeatedly immersed chest-deep. During the second neck-deep immersion, loss of head velocity in both animals was accompanied by changes in the pattern of head movements toward the target that included emergence of a dual-wave velocity profile in one animal and noticeably earlier start of the head vs. saccade reaction in the other. To conclude, the longer load deprivation, the more profound changes in the memory-assisted central programming of eye-head movement coordination in the course of gaze fixation.

[Changes in ocular saccade kinematics after 7-day dry immersion].

To assess effects of long-term support removal on gaze control, 5 human subjects were tested for successful touch of a light target unpredictably emerging in the peripheral field of vision before and immediately after 7-d dry immersion. The test did not set time requirements to gaze fixation on target and motor task implementation. Ocular movements were registered with an infrared eye image analyzer at 100 Hz. Modification of the dependences of maximum velocity and duration of saccade toward the homolateral target on amplitude following immersion pointed to speeding-up of the saccadic eye movements.

[Water immersion effect on gaze fixation in primates].

Effects of support deprivation on gaze fixation were studied in Macacas mulatta immersed up to the sternum (two animals) and the neck (one animal) with the use of electrooculography and measurement of head motion velocity. Deterioration of gaze fixation parameters after five hours of sternum-high immersion was similar to what had been observed in experiments aboard the biosatellites, i.e. increased saccade amplitude and VOR gain, and decreased maximal head velocity. Five-hour neck-high immersion had a more pronounced effect on the head velocity and, besides, altered the pattern of head movement toward target. It can be surmised that support deprivation is one of the spaceflight factors impacting time and precision of gaze fixation. Water immersion of primates is an adequate model for studying mechanisms of the microgravity effects on coordination of eye and head movements toward gaze fixation.

[Effect of antiorthostatic hypokinesia and its combination with +Gz runs on the otolith regulation of cardiac rhythm in primates]. / Vliianie antiortostaticheskoi gipokinezii i ee sochetaniia s seansami uskoreniia +Gz na otolitovuiu reguliatsiiu serdechnogo ritma u obez'ian.

Amplitude of cardiac rhythm response to the otolith stimulus (AR-R), i.e. rapid reduction of the EKG R-R interval was determined in 24 Macacas mulatta before and after 28-d head-down (-6 degrees) immobilization (HDI). In two experimental series the animals were divided into 2 groups (control and CF) with 6 primates in each. In the HDI series-1, the CF animals were rotated on a centrifuge with a 3.62-m arm at 1.2 up to 1.6 +Gz for 30-40 minutes 4-5 times a week. In HDI series-2, the CF animals were rotated 30 min at 1.2 +Gz 2-3 times a week. In a day after HDI, AR-R was significantly reduced in both CF groups, which, when compared with EKG R-R intervals, suggests attenuation of equally parasympathetic and sympathetic influences on the heart. In 7 days since HDI, AR-R was close to baseline values in control primates on both series and CF primates in series-2, whereas in the CF group in series-2 AR-R exceeded baseline values. Significant differences in mean AR-R values in the control and CF groups in series-1 following 7 days after HDI point to the prophylactic effect of small but regular g-loads manifested in more rapid recovery of initial level of the cardiac rhythm regulation.

Cardiac rhythm responses to otolith stimulation of monkeys in microgravity.

Cardiac rhythm responses to otolith stimulation were investigated in two Bion 11 monkeys during flight (Z axis) and before and after flight (X axis). Cardiac rhythm responses were found to change in microgravity due to variations in the excitation of vestibular structures and vagal control of cardiac function.

The effect of microgravity on the autonomic nervous system of rhesus monkeys.

Gastric myoelectric activity and respiratory sinus arrhythmia of two monkeys flown on Bion 11 were investigated. During flight, vagal effects on cardiac and gastric function of the two animals varied differently: in one animal they decreased at an early flight stage and returned to the control level by the end of flight, whereas in the second monkey the trend was the opposite. The decrease was accompanied by space motion sickness symptoms.

Rhesus leg muscle EMG activity during a foot pedal pressing task on Bion 11.

Rhesus monkeys (Macaca mulatta) were trained to perform a foot lever pressing task for a food reward. EMG activity was recorded from selected lower limb muscles of 2 animals before, during, and after a 14-day spaceflight and from 3 animals during a ground-based simulation of the flight. Integrated EMG activity was calculated for each muscle during the 20-min test. Comparisons were made between data recorded before any experimental manipulations and during flight or flight simulation. Spaceflight reduced soleus (Sol) activity to 25% of preflight levels, whereas it was reduced to 50% of control in the flight simulation. During flight, medial gastrocnemius (MG) activity was reduced to 25% of preflight activity, whereas the simulation group showed normal activity levels throughout all tests. The change in MG activity was apparent in the first inflight recording, suggesting that some effect of microgravity on MG activity was immediate.

Head pitch movement and vestibular neuronal activity in response to otolith stimulation of monkeys in space.

Head pitch movement and vestibular neuronal activity of two Bion 11 monkeys exposed to otolith stimulation were investigated. During flight both parameters went through facilitation and inhibition followed by enhancement. The resultant data suggest involvement of the visual input in the above changes.

[Otolith-autonomic reactions in waking Macaca mulatta monkeys]. / Otolitovo-vegetativnye reaktsii u bodrstvuiushchikh obez'ian Macaca mulatta.

The aim was to determine a technique and parameters to test the otolith-autonomous reflex responses in conscious monkeys. The study involved 8 Macacas mulatta weighing 3 to 5 kg with subcutaneously pre-implanted electrodes to record ECG, rheopneumogram, and myoelectric activity of the stomach. The animals were seated in primate couches in which their bodies were softly restrained whereas their heads were restrained rigidly with plastic rings mounted on the cranium. Subsiding motion of a flat-parallel swing with the proper period of 3 s and starting amplitudes 20 cm (0.08 g) and 40 cm (0.16 g) exerted vestibular stimulation along the interaural axis. The monkeys responded to stimulation by altering the external breathing, myoelectric activity of the stomach, and cardiac rhythm. The highest reproducibility and individual steadiness featured cardiac reactions manifested by 2 waves of HR acceleration sequel to reflex-driven changes in the activity of the sympathetic and parasympathetic components of the autonomous nervous system. Data of the study attested the feasibility of testing the otolith-autonomous reflex responses in conscious monkeys with moderate stimulation in controlled experiments.

[Effects of isolated and combined effects of a constant magnetic field and antiorthostatic hypokinesia on central hemodynamics in rats]. / Vliianie izolirovannogo i kombinirovannogo deistviia postoiannogo magnitnogo polia i antiortostaticheskoi gipokinezii na tsentral'nuiu gemodinamiku u krys.

The effect of a constant magnetic field on central circulation of rats was investigated during their exposure to antiorthostatic hypokinesia. Circulation parameters were measured by impedance rheoplethysmography. It was found that 3-hour exposure to a 0.4 T magnetic field did not produce a significant effect on central circulation, whereas exposure to hypokinesia caused substantial changes which included decreases of heart rate, stroke volume and cardiac output. During a combined exposure to a constant magnetic field and antiorthostatic hypokinesia, the magnetic field exerted a beneficial effect on central circulation.

[Activation of respiratory sinus arrhythmia in monkeys during space flight]. / Aktivatsiia respiratornoi sinusovoi aritmii u obez'iany v kosmicheskom polete.

During the first day in space the rhesus monkey, called Vernyi, flown on Cosmos-1667 showed higher values of the daytime, night, and daily respiratory sinus arrhythmia (RSA) when compared to those observed before launch and before or the first day of a simulation study. During orbital flight, the mean daily value of RSA was in the range 13.08-16.00 beats/min. In the simulation study, this parameter increased from 4.68 beats/min during the first day to 15.16 beats/min on the 6th day. The mean RSA values during days 1 through 3 were significantly higher in real than in simulation flight. Analysis of rheopneumograms revealed a correlation between respiration parameters and RSA variations. In space, there was no correlation between RSA and HR, which was reported in the simulation study (r = -0.625). Assuming that RSA is a noninvasive indicator of parasympathetic control over cardiac rhythm, it can be postulated that the primate body adapted to microgravity via activation of parasympathetic mechanisms controlling the heart function.

[Hemodynamics in monkeys in the initial period of adaptation to weightlessness]. / Gemodinamika u obez'ian v nachal'nom periode adaptatsii k nevesomosti.

Using pre-implanted electrodes and transducers, arterial pressure and linear blood flow velocity in the common carotid artery of the rhesus-monkey Gordyi were measured during his space flight on a Cosmos biosatellite and ground-based control experiments. As compared to the prelaunch level, blood pressure remained unchanged, blood flow velocity increased significantly and blood flow resistance in the area decreased during the first hours after insertion into orbit. During subsequent flight days mean daily values of blood pressure increased and blood flow returned to the baseline level, although they showed distinct day-night variations. Daily variations of blood flow velocity and its ratio to cardiac output gave evidence that the circulation system of the rhesus-monkey under study rapidly adapted to microgravity conditions.

[Features of changes in blood pressure and blood flow in the common carotid artery of monkeys exposed aboard the biosatellite Cosmos-1514]. / Osobennosti izmeneniia arterial'nogo davleniia i krovotoka v basseine obshchei sonnoi arterii u obez'iany, éksponirovannoi na biosputnike "Kosmos-1514".

Preflight the rhesus-monkey Bion was implanted with sensors and transducers to measure blood pressure and linear flow velocity in the common carotid artery and to compare these parameters with central circulation. At the early flight stage blood pressure increased, blood flow decreased and resistance in the area grew. The last change can be regarded as a compensatory reaction that can provide rapid adaptation of regional circulation to changes in systemic circulation. At later flight stages blood pressure showed distinct circadian oscillations and blood flow, a significant increase when compared to the ground-based 36-hour control study. Regulatory mechanisms of the cardiovascular system changed to the greatest extent on flight day 2. This manifested as a decrease of the amplitude of circadian oscillations of the above circulation parameters. Signs of cardiovascular adaptation to the effects of microgravity were discerned on flight days 3 to 5.