[FREQUENCY-TEMPORAL STRUCTURE OF HUMAN ELECTROENCEPHALOGRAM IN THE CONDITION OF ARTIFICIAL HYPOGRAVITY: DRY IMMERSION MODEL].

Frequency-temporal electroencephalogram (EEG) reactions to hypogravity were studied in 7 male subjects at the age of 20 to 27 years. The experiment was conducted using dry immersion (DI) as the best known method of simulating the space microgravity effects on the Earth. This hypogravity model reproduces hypokinesia, i.e. the weight-bearing and mechanic load removal, which is typical of microgravity. EEG was recorded by Neuroscan-2 (Compumedics) before the experiment (baseline data) and at the end of day 2 in DI. Comparative analysis of the EEG frequency-temporal structure was performed with the use of 2 techniques: Fourier transform and modified wavelet analysis. The Fourier transform elicited that after 2 days in DI the main shifts occurring to the EEG spectral composition are a decline in the alpha power and a slight though reliable growth of theta power. Similar frequency shifts were detected in the same records analyzed using the wavelet transform. According to wavelet analysis, during DI shifts in EEG frequency spectrum are accompanied by frequency desorganization of the EEG dominant rhythm and gross impairment of total stability of the electrical activity with time. Wavelet transform provides an opportunity to quantify changes in the frequency-temporal structure of the electrical activity of the brain. Quantitative evidence of frequency desorganization and temporal instability of EEG wavelet spectrograms may be the key to the understanding of mechanisms that drive functional disorders in the brain cortex in the conditions of hypogravity.

Transformation of the kinematic characteristics of a precise movement after a change in a spatial task.

The central mechanism of motor programming was studied using a model of precise horizontal flexion of the arm at the elbow joint. Training was performed in the dark to ensure that formation of the motor program was based predominantly on the use of proprioceptive afferentation. The target was not demonstrated before training: subjects determined the angle of arm flexion during training, the moment at which the target position was reached being identified by a brief LED flash. Subjects had to perform the movement as quickly and accurately as possible. The amplitude, speed, and accuracy of the movement were measured in real time. The ten subjects were divided into two groups for initial training to precise movements, using two different protocols: flexion of the elbow to 70 degrees and to 55 degrees . At the second stage of the experiment, each subject's initial target position was suddenly changed (from 70 degrees to 55 degrees and vice versa). Training was continued until a stable accuracy in the new conditions was achieved (with errors of no more than 5% of the specified amplitude). The nature of the transformation in the kinematics of the precise movement in response to the change in the single task parameter illuminated the fundamental principle of organization of the supraspinal motor command for movements of this type. For both specified flexion amplitudes, the ratio between the acceleration and deceleration phases of the movement were identical during the period of skill fixation. On average, 70% of the total amplitude of flexion was accounted for by the acceleration phase and 30% by the deceleration phase. Adaptation of the precise movement to changes in the specified horizontal elbow flexion angle (i.e., re-achievement of the required movement accuracy in the changed conditions) during rearrangement was completed by inversion of these values. According to the results of previous studies, the most informative measure for analysis of the dynamics of the controlling central command was the acceleration of the movement. In terms of current concepts of the mechanism of motor control, the acceleration plateau can be regarded as mirroring long-term depression--the voltage plateau in Purkinje cells and motoneurons. Data processing involved calculation of the integral acceleration in both phases of the movement in relation to the angle of flexion (phase plots). These data underlie our understanding of the mechanism of transformation of movement kinematics responsible for the formation of a new central command.

[Transformation of kinematic characteristics of a precise movement after change in a spatial task].

Brain mechanisms of motor programming were studied with the use of the model of learning precise horizontal elbow flexion. To exclude visual control and make learning to be based, predominantly, on proprioception, experiments were carried out in darkness. The target position was not demonstrated beforehand. Subject (S) had to find an adequate angle of flexion during training with a short light-diode flash which marked the moment of target reaching. Ss were asked to perform a precise horizontal elbow flexion as fast as possible. Movement amplitude, velocity and acceleration were on-line recorded. Ten Ss were divided in two groups. The first group was initially trained to make the precise movement with the preset amplitude of 70 degrees and the second group had to perform similar movement with the amplitude of 55 degrees. Each S was trained to the moment of acquisition of a stable skill (within the 5% error of preset flexion amplitude). After that the target position was unex pectedly changed (from 70 for 55 degree or visa verse). This work was a continuation of our earlier search for a mathematical hypothesis most correctly explaining the central mechanism of motor learning. The dynamics of kinematic characteristics of learning in our experiments fitted well to A. Barto and J. Houk's "Cerebellar Model of Timing and Prediction". A comparison of a computer simulation of this model to the learning characteristics allowed us to make some refinements of the model very important for data analysis possible under conditions of noninvasive investigations. The analysis of acceleration dynamics not considered by the authors of the model made it possible to identify this index with the "pulse phase" similar to the period of LTD of Purkinje cells (the key mechanism of the model). We took such an interpretation as principal in our analysis of experimental data. We analyzed integrals of positive and negative acceleration which made it possible to gain a deeper insight into the physiological mechanism of a replacement of one central command by the other as a consequence of change in spatial task conditions.

[Motor learning with the minimal involvement of visual afferentation]. / Dvigatel'noe obuchenie pri minimal'nom uchastii zritel'noi afferentatsii.

Amongst motor control and learning models, "A Cerebellar Model of Timing and Prediction" of A. Barto and J. Houk is the most interesting and physiologically well-grounded. Developing D. Marr's "The Theory of Cerebellar Cortex", this model proposed the important role in motor learning of the ability of Purkinje cells to change their activity level by the dendritic bistability mechanism. The aim of this investigation was to verify this idea in experiments with human learning of precise elbow flexion. The unsupervisual method of learning was used in order to guarantee the principal role of proprioception in training. The experiments were carried out in darkness to exclude the vision control. Subjects were asked to perform a precise horizontal elbow flexion as fast as possible and repeat this action from 30 to 50 times up to the point of complete movement acquisition (stable movement with the error in the range of 5% of a given flexion amplitude). The target point (a given angle of the horizontal elbow flexion) was not presented to the subjects in advance. Reaching the target point was indicated by a short light flash. During training, subjects learned to hit target point with the given precision. Kinematic characteristics of the movement (time change of elbow flexion angle, velocity, and acceleration) together with EMG of the flexor and extensor were recorded. The obtained results were in good agreement with J. Houk and A. Barto's hypothesis. Analysis of changes in the kinematic characteristics in the course of training revealed an asymmetric velocity profile and a fragmentary shape of acceleration profile at the beginning of learning. In the course of training, the acceleration profile transformed into biphasic curve with a single change in polarity. Thus, it acquired a characteristic shape of a plateau. Correspondingly, to the end of training, the character of the asymmetry of the velocity profile changed. No correlation was observed between the velocity parameters and movement precision. These features essentially distinguish the motor reactions under study from the common visuomotor coordinations. It is suggested that the amplitude and duration of the acceleration plateau reflect the intensity and time of inhibition of the descending activity of Purkinje cells as a result of bistability (in accordance with Houk and Barto's hypothesis).

[Psychosomatic evaluation of primates with the use of a psychomotor testing system]. / Issledovaniia psikhosomaticheskogo sostoianiia obez'ian v ékstremal'nykh usloviiakh s ispol'zovaniem psikhomotornoi testovoi sistemy.

The higher nervous system reactions of rhesus monkeys to the head-down tilt (HDT, 28 d, -5 degrees) and preventive centrifugation were evaluated with the use of a computerized psychological testing system (PTS). Prior to HDT, the primates elaborated conditioned instrumental food-obtaining reflexes by playing computer games. Drilled to perform PTS tests to the best of their ability, the animals were to fulfill two PTS tests of increasing complexity in HDT. Test results were used to determine the dynamics of primates' cognitive function and the psychological state. The investigation consisted of two series with two groups of monkeys in each series. Twelve animals of each group (10 had skill in performing the PTS tests) were distributed into 2 subgroups. Every other day one of the subgroups was exposed to centrifugation at 1 to 2.5 g. In the first series, 10 monkeys worked on the simplest test, i.e. spotting a static object. All animals showed interest in the computer game, and played a lot and successfully during HDT. In the second series, the animals were challenged with a more difficult test of following a moving object with the cursor. Based on the analysis of experimental data, a significant variability in achievement and emotional behavior of the primates should be attributed to different types of the nervous system.

Certain methods of biomechanical description of various postural adjustment patterns during motoric learning in dogs.

Methods for the biomechanical description of spatial displacements of the center of mass of quadruped animal (dog), developed by the authors on the basis of an assessment of the vertical constituents of support pressures, as well as methods for the assessment of the postural adjustment pattern (coefficient of diagonality), are presented in this paper. The results are presented of an investigation of the role of the motor cortex in the accomplishment of the postural adjustment pattern of dogs, reorganized during learning, in the performance of an instrumental movement.

[Methods for the biomechanical description of different patterns of postural rearrangement in the motor learning of dogs]. / Nekotorye sposoby biomekhanicheskogo opisanii razlichnykh patternov perestroiki pozy pri dvigatel'nom obuchenii u sobak.

The biomechanical description of spatial transfer of quadruped center of gravity is elaborated on the basis of analysis of vertical components of support pressures. The methods of evaluation of posture reconstruction pattern (coefficient of diagonally at all) are presented. The role of motor cortex in postural pattern reorganization in the process of learning in dogs is investigated by mean of this methods.

[Vitamin A and lipid peroxidation: effect of retinol deficiency]. / Vitamin A i perekisnoe okislenie lipidov: vliianie nedostatochnosti retinola.

The effect of alimentary vitamin A deficiency on some parameters of lipid peroxidation (LPO) in young rats was studied. It was found that under vitamin A deficiency the content of diene conjugates in liver homogenates and microsomes diminishes, whereas that of malonic aldehyde in small intestinal mucosa, liver and testis homogenates is unaffected. However, the malonic aldehyde production in liver homogenates and microsomes decreases after 60 min incubation at 37 degrees C without addition of prooxidants. At the same time, enzymatic NADPH-dependent and nonenzymatic ascorbate-dependent LPO in liver microsomes of vitamin A-deficient rats does not change significantly. The decrease of LPO intensity in vitamin A-deficient animals may be due to the reduced content in liver microsomes of the main LPO substrates, i.e., arachidonic and linoleic acids, as well as to the decrease of cytochrome P-450 level in rat liver.