[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.