Reproduction of tracking movements and target positioning of the forearm in humans in the absence of visual control

In 17 healthy volunteers, we studied movements of the forearm, which included episodes of positioning on the target level. The trajectory of the non-ballistic (relatively slow) movement looked like a double trapezium (flexion of the elbow joint from the state of full extension, 0 deg, positioning on the 50 deg level, further flexion to the limit angle of 100 deg, and a similar reverse sequence). The command trajectory and the trajectory of the realized movement were visualized with movements of cursors on a monitor in time/joint angle coordinates. We compared parameters of the tracking movements (in the presence of visual feedback) and their blindfold reproduction (with the complete absence of visual control). It was found that blindfold reproduction movements differ from sample tracking movements and their reproduction with partial limitation of visual control [16] in higher peak velocities and shorter durations, i.e., a trend toward conversion of such movements into ballistic ones was observed. Under conditions of elimination of visual control, movements that led to positioning were mostly hypermetric, i.e., positioning was usually accompanied by positive systematic errors (whose sign coincided with the direction of the preceding movement phase). The mean intragroup value of the systematic error of the first positioning (after flexion to the target level) was +6.73 ± 1.15 deg, while the respective mean for the second positioning (after extension to the same level) was +4.00 ± 1.31 deg. The nonlinear properties of stretch receptors of muscles whose activity provides the formation of a proprioceptive estimate of the joint angle are considered the crucial reason for systematic errors of blindfold positioning.Neirofiziologiya/Neurophysiology, Vol. 36, Nos. 5/6, pp. 393–404, September–December, 2004.This revised version was published online in April 2005 with a corrected cover date and copyright year.     

Positioning Errors in Simple Targeted Movements of the Forearm Realized in the Absence of Visual Control: Effects of Vibrational Stimulation of Antagonist Muscles

In 17 healthy subjects, we examined the characteristics of targeted movements of the forearm, flexion from the initial position of full extension taken as 0 deg to a 50 deg target angle in the elbow joint (flexor tests, FTs) and extension from the initial angle of 100 deg to the same target angle (extensor tests, ETs) with return to the initial positions. A standard movement (its trajectory corresponded to a simple trapezium) was performed under conditions of visual feedback (the value of the target angle and trajectory of the movement were visualized on the screen of a monitor); then, this movement should be reproduced by the subject (according to an acoustic signal) in the absence of visual control. Target-reaching test movements in the absence of visual feedback differed from the standard ones in a higher velocity. Blindfold reproduction of standard movements realized under kinesthetic control was accompanied in all subjects by noticeable positive systematic errors of targeted positioning (in the group, on average, 5.16 ± 0.55 and 4.83 ± 0.58 deg under FT and ET conditions, respectively). Vibrational stimulation of the muscles whose activity mainly provided the movement and positioning (m. biceps brachii in the FT cases and m. triceps brachii in the case of ETs) resulted in decreases of the errors of kinesthetic positioning; intragroup means of these errors were 2.55 ± 0.36 deg (FTs) and 2.26 ± 0.40 deg (ETs). The positioning errors demonstrated even greater decreases upon vibrational stimulation of the muscles, which were relatively inactive under conditions of the tests and underwent passive stretching in the course of the movements (m. triceps in FTs and m. biceps in ETs). Mean intragroup values of the errors in these cases were 0.46 ± 0.25 and 0.52 ± 0.31 deg, respectively. The nature of systematic positioning errors in the reproduction of targeted movements in the absence of visual control and the mechanisms underlying the influence of vibrational stimulation of the muscles involved in realization of these movements on the positioning errors under kinesthetic control are discussed.     

Positioning of the Human Forearm in Tracking Movements and Their Reproduction under Conditions of Limited Visual Control

In 14 healthy persons, we studied movements of the forearm with its positioning on a target level. A double trapezium was used as the command trajectory (flexion in the elbow joint from the state of full extension, 0°, with positioning on the level of 50 or 60° and further flexion to the 100° angle, and a similar reverse movement). We compared (i) tracking movements, when the subject tried to adequately reproduce the movement of the target along the command trajectory visualized on the monitor screen and obtained visual information about the performed movement (shifts of the second light point in time/joint angle coordinates), and (ii) reproduction of these movements under conditions of limitation of the visual feedback (when there was no information about the performed movement). Parameters of the tracking movements and of their reproductions (delays of initiation of the movement phases as compared with the command signal, durations of these phases, and angle velocities of the forearm movement), as well as the quality of positioning after oppositely directed movements, were compared. Positioning on the target level performed under proprioceptive control (when visual control was limited) was accompanied by systematic errors, whose sign in most test series performed by most subjects coincided with the direction of the preceding movement phase. The pattern of signs of systematic positioning errors after movements of opposite directions was quite individual (typical of a given subject) and demonstrated no dependence on the value of the extensor loading. Averaged intragroup systematic errors of positioning after movement phase 1 (flexion to the target level) and phase 3 (extension to the same level) under conditions of a minimum extensor loading (0.5-1.0 N · m) were 2.57° and 2.52°, respectively. When the loading was substantial (3.6-6.0 N · m), the respective errors were 3.85° and 3.48°. The nonlinear properties of muscle stretch receptors in the elbow flexors and extensors (responsible for the significant dependence of the parameters of afferent signals produced in these receptors on the movement prehistory) are considered the primary reason for systematic errors when positioning is performed exclusively under proprioceptive control. The influence of alpha-gamma co-activation in active muscles on the characteristics of the above signals is discussed.     

Coordination of the dynamic phases of EMG activity in human elbow flexors in the performance of targeted tracking movements

The EMG pattern in the elbow flexors during the performance of relatively slow (non-ballistic) targeted flexor and extensor movements with different velocities and amplitudes and subsequent fixation of a reached position was studied in healthy humans. Using a servocontrolled mechanostimulator, steady external loading was applied to the arm, which provided performance of the movements and their termination exclusively by the flexor activity, leaving the extensors passive. In all cases, even at very slow movements, EMG activity of the flexors at transition of the joint from one equilibrium state to another was shown to contain a clear dynamic phase followed by a phase of stationary activity. The level of the latter, generated during fixation of a reached position, was practically independent of the amplitude of a movement within the 0–60° range of the joint angles. Thus, the force developed by the flexors at the dynamic EMG phase became fixed when a new equilibrium joint position was reached and did not decrease in the course of a considerable drop in the efferent activity level, when the stationary phase of this activity began. The dynamic EMG phase included two components. The first component was related to leaving the equilibrium state with a certain acceleration, while the second component was probably involved in the velocity control and stoppage of the joint in a new equilibrium position. We suppose that retention of the joint in the equilibrium state is not provided exclusively by formation of a certain equilibrium level of efferent activity (as it is postulated by the equilibrium point hypotheses); it results from some coordinated modifications of the dynamic muscle activity that provide achievement of equilibrium in a certain position within a certain stage of the movement.     

The activity of abdominal stretch receptors during non-giant swimming in the crayfish<Emphasis Type="Italic"> Cherax destructor</Emphasis> and their role in hydrodynamic efficiency

Recordings were made from the nerve innervating the stretch receptors of the abdominal muscle receptor organs and slow extensor muscles of tethered crayfish, Cherax destructor, during so-called non-giant swimming. The stretch receptors were active during the flexor phase of swimming but the duration and pattern of activity varied from cycle to cycle. Their pattern of firing was modified by the activity of the large accessory neurons which make direct inhibitory synapses upon them. Neither the stretch receptors nor the accessory neurons were active during the extensor phase of the cycle. The timing and extent of tailfan movements during the period of stretch receptor activity were measured from video records before and after the stretch receptor nerves were cut in the second to fifth segments. The promotion of the tailfan during flexion was significantly delayed and the minimum angle to which the uropods were remoted at the end of flexion significantly larger in denervated animals. We propose that afferent information from the stretch receptors coordinates the timing and extent of tailfan movements according to variations in the positioning and movement of the abdominal segments such that the hydrodynamic efficiency of the tailfan is enhanced on a cycle by cycle basis during non-giant swimming.Abbreviations A# abdominal segment number - Acc accessory neuron - LUU large unidentified unit - MRO muscle receptor organ - NGS non-giant swimming - SEMN slow extensor motor neuron - SR stretch receptor neuron     

The walking-(and searching-) pattern generator of stick insects,a modular system composed of reflex chains and endogenous oscillators

Stick insects (Cuniculina impigra) possessing only one front leg with restrained coxa performed searching movements or walked on a treadband. The movements are described. Ablation, surgical manipulation or experimental stimulation of different sense organs (femoral chordotonal organ, campaniform sensilla on trochanter and femur basis, proprioceptors at the coxatrochanter joint) were performed, and the resulting changes in motor output were recorded. These experiments demonstrate that the walking- and searching-pattern generators cannot be separated, at least not for the movements investigated. This walking- and searching-pattern generator consists of central modules, each of which produces irregular alternation of the activity of motor neurones of antagonistic muscles of a single joint, and of reflex loops. At least some of these reflex loops are only present in the active animal. They are responsible either for the control of a single joint or for the coordination of the movements of separate joints. The performance of these reflexes does not only depend on the state of activity of the animal; some of them additionally seem to depend on the context signalled by other sense organs.     

Extrinsic flexor muscles generate concurrent flexion of all three finger joints

The role of the forearm (extrinsic) finger flexor muscles in initiating rotation of the metacarpophalangeal (MCP) joint and in coordinating flexion at the MCP, the proximal interphalangeal (PIP), and distal interphalangeal (DIP) joints remains a matter of some debate. To address the biomechanical feasibility of the extrinsic flexors performing these actions, a computer simulation of the index finger was created. The model consisted of a planar open-link chain comprised of three revolute joints and four links, driven by the change in length of the flexor muscles. Passive joint characteristics, included in the model, were obtained from system identification experiments involving the application of angular perturbations to the joint of interest. Simulation results reveal that in the absence of passive joint torque, shortening of the extrinsic flexors results in PIP flexion (80°), but DIP (8°) and MCP (7°) joint extension. The inclusion of normal physiological levels of passive joint torque, however, results in simultaneous flexion of all three joints (63° for DIP, 75° for PIP, and 43° for MCP). Applicability of the simulation results was confirmed by recording finger motion produced by electrical stimulation of the extrinsic flexor muscles for the index finger. These findings support the view that the extrinsic flexor muscles can initiate MCP flexion, and produce simultaneous motion at the MCP, PIP, and DIP joints.     

Movements of the Forearm and Shoulder Performed against the Gravitation Force: Target Positioning under Kinesthetic Control

In humans, we tested targeted movements of the forearm and shoulder performed in the vertical direction (in a parallel manner with respect to the sagittal plane). Movements were realized, first, with the possibility for visual control of the coincidence of the angle of the limb link axis vs the vertical and the target angle value (using an optic system and video recording), and, second, in the absence of the above control. Movements including flexion (i.e., movement against the gravitation force) – extension of the limb link with an individually selected convenient velocity were initiated and terminated according to the presentation of permissive sound signals; simultaneously, EMGs were recorded from a few muscles flexing and extending the elbow and shoulder joints. We analyzed systematic errors of target positioning of the forearm and shoulder in movements realized exclusively under kinesthetic control. In the case of isolated flexion of the forearm for a 90 deg target angle, such errors in all members of the examined group (n = 11) were positive. These errors were, on average, 8.1 ± 0.7 deg without loading and reached 11.2 ± 0.9 deg with introduction of a 10 to 30 N additional loading on the forearm. Isolated movements of the shoulder for a 70 deg target angle (performed without loading, with full extension of the forearm and its voluntary fixation) were accompanied by positive errors of 18.3 ± 1.1 deg, on average. Both the movements and positioning were performed due to changes in the levels of activity of the flexor muscles, with minimum involvement of the antagonists. The nonlinear properties of the receptor apparatus responsible for the formation of a kinesthetic estimate of the joint angle (first of all, of muscle spindles) are a fundamental reason for positive errors of target positioning of the limb links realized under kinesthetic control in the absence of the visual one.     

A simulation study of a programme generator for centrally programmed fast two-joint arm movements: responses to single- and double-step target displacements

From earlier experimental results we concluded that a sudden displacement of a target causes the internal representation of the target to shift gradually from the first to the second target location. This internal target is used as an input to the motor programme generator. The aim of the present simulation study is to investigate whether the CNS can programme fast arm movements towards the internal representation of the target without taking into account velocity-dependent mechanical interactions between the upper arm and forearm and velocity-dependent biomechanical properties of the muscles. The simulations of single- and double-step responses show that on the basis of the assumptions mentioned above, movement trajectories and velocity profiles are in fair agreement with experimental results. However, at the end of fast arm movements a stiffness and viscosity control is needed to halt the movement at the target location.     

Characterization of different decomposition stages of biowaste using FT-IR spectroscopy and pyrolysis-field ionization mass spectrometry

The decomposition stage and stabilization of organic matter in biowaste (mixture of yard waste and kitchen waste), originating from an open windrow process, were investigated using Fourier transform infrared (FT-IR) spectroscopy and pyrolysis-field ionization mass spectrometry (Py-FIMS). These investigations provided detailed information about chemical constituents and their behavior during the composting process. The chemical compounds were classified by their molecular signals in Py-FIMS. Multivariate statistical analysis revealed, that during the composting process, the group containing lipids, fatty acids and other chemical compounds with aliphatic skeletons changed the most. Corresponding with Py-FIMS findings changes were observed in absorbance bands of infrared spectra that reflect this group of organic compounds: the aliphatic methylene bands at 2925 and 2850cm^-1, the band of C=O vibrations of carboxylates at 1640cm^-1, the O=H in-plane bend of carboxylic acids, the CO₂ stretch of carboxylates and the CH₂ group of alkanes at around 1430cm^-1. During decomposition these bands decreased up to a steady level that indicated stabilization. The band at 1260–1240cm^-1 that can be assigned to the C=O stretch of carboxylic acids or to the C=N stretch of amides and the band of aromatic amines at 1320cm^-1 disappeared completely. The nitrate band at 1384cm^-1 appeared at a later stage of the composting process. The relative increase of chemical compounds like moieties of lignin, humic acids and tannins in the composted material contributed to the aromatic C=C band at around 1640cm^-1.     

Characteristics of dynamic postural reactions in the locust hindleg

Summary The use of the locust (Schistocerca americana) hindleg in postural control was examined in animals that stood on a repeatedly swayed vertical substrate. Myograms were recorded from leg muscles and the angle of the femoro-tibial joint was monitored photographically. Two discrete strategies were observed,; in compensatory reactions the hindleg was held in place, while in flexion reactions, the leg was moved, most often to complete flexion of the femoro-tibial joint. Tightly coupled, rhythmic bursting occurred in the flexor and levator muscles of the leg during compensatory reactions. Bursting was initiated repeatedly when the substrate was being pulled away from the animal. Bursting was correlated with subsequent decreases in the rate of change of the femorotibial joint angle. Compensatory and flexion reactions occurred preferentially in different ranges of joint angles: most often, compensatory reactions occurred in the midrange, while flexion reactions were elicited in the extremes of joint angle. These differences may be due to the mechanical advantages of the tibial muscles and the leg may be moved to full flexion because of a locking mechanism of the flexor muscle tendon. These reactions are compared with known reflexes of hindleg proprioceptors and contrasted with similar responses of vertebrates.     

Beobachtungen zu Biologie und Verhalten des Gro?en Kragenlaubenvogels (Chlamydera nuchalis)

Zusammenfassung Von Mai bis Juli 1969 wurde im Gebiet von Darwin und Arnhemland (Northern Territory, Australien) Biologie und Verhalten vonChlamydera nuchalis studiert.28 Lauben wurden gefunden. Einzelheiten des Laubenbaues und der hierzu verwendeten Materialien werden beschrieben. Das muß etwa 4–5000 Zweige zum Laubenplatz schaffen; die Wände der Laube bestehen aus etwa 1400 bis 1840 Zweigen.Die zur Ausschmückung der Laube verwendeten Gegenstände umfaßten Molluskenschalen, Knochen, Glasstückchen, Steine und kleine glänzende Metallobjekte. Das Gesamtgewicht des Laubenschmuckes betrug 6,6 bis 12,1 kg. Größe und Gewicht der Einzelobjekte schwankten zwischen 4–10 mm und 0,2–1,2 g bzw. 73 × 36 mm und 40 g. Ihre Gesamtzahl liegt zwischen 5000 und 12 000. Bevorzugt werden weiße und graue Objekte; auch grüne Glasstückchen wurden gefunden.Die Technik des Laubenbaus, die ausschließlich das ausführt, wird beschrieben. Der Rohbau nimmt etwa 3 Wochen in Anspruch, doch werden im Anschluß daran dauernd neue Objekte eingetragen. Anzeichen für das Ausmalen der Laube wurden nicht gefunden. Während der Balz singt das intensiv auf Bäumen oder am Boden. Die einzelnen Balzphasen werden beschrieben. Während des Höhepunktes versucht das durch Sprünge im Kreis das an der Laube zu halten. Begattung wurde außerhalb der Laube nahe dem Ausgang beobachtet. Offensichtlich hat ein mehrere während einer Balzperiode. Während der Balz wird die Laube dauernd ausgebessert und ihr Schmuck neu arrangiert.

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On the biology and behaviour of the Great Grey Bower Bird(Chlamydera nuchalis)

Summary From May to July, 1969 the author observed in the region of Darwin and Arnhem Land (Northern Territory, Australia) the biology and behaviour of the Great Grey Bower Bird.28 bowers were found, in three cases the building process was observed. Bower-building starts with cleaning up an area of 210 to 95 cm and with forming a 7.5 cm thick mat of small twigs intertwined in all directions. The walls are made of uniform twigs the measurements of which are on an average 29.2 mm in length and 2.4 mm in thickness at the lower end. A wall consists of 700 to 920 twigs placed parallel to each other (1400 to 1840 twigs on the two walls). The carries 4000 to 5000 twigs to the site of the bower. The paper gives the measurements of the bower and its orientation towards cardinal points.The bower is completed by a collection of ornaments which consists of land and sea shells of the generaXanthomelon, Venus andTelescopium, bone and glass fragments, stones (almost exclusively quartzite and limestone), and small pieces of glossy metal objects, tin seals etc. The lowest total weight of all objects collected was 6.2 kg, the highest was 12.1 kg. The size and weight of the objects varies between 4 to 10 mm and 0.2 to 1.2 g and 73 by 36 mm and 40 g respectively.Their total number was established at 5000 to 12000.Chlamydera nuchalis prefers white and grey objects with the exception of glass of which also green fragments were found. Some objects were experimentally painted blue, red, black, yellow and green. The discarded them successively and threw them out of the bower.The paper describes the technique of bower-building which is carried out solely by the . It takes the bird three weeks to finish the construction in the rough, but even afterwards the systematically continues to complete the bower, adding a growing number of ornamental objects. During the display period, however, a rebuilt a bower, which had been destroyed, within 2.5 days. The activities observed are shown in the table. Bower Birds may carry, on an average, 90 twigs and 28 glass fragments per hour to the bower. The bower wall painting behaviour ofChlamydera maculata andPtilonorhynchus violacaeus was not observed inChlamydera nuchalis. No traces of painting were found in any of the bowers observed. The author found an interesting behaviour pattern in two who stuck pieces of food into the cracks in the walls. This behaviour strikingly resembles that of passerines feeding their young.During the display period the sings ardently either on trees or on the ground. Display consists of alluring manifestations of the , including nape-crest presentation and bounds. At the bower, the shows the some objects on the opposite side of the passage, and after bowing and raising his head, he turns it so that the nape is directed toward the , and presents to her its lilac crest. During the culminating phase of display the attempts, by circling in leaps, to keep the at the bower. Mating was observed outside the bower, next to its exit. A apparently has several females during the display period. Also during display the rearranges and completes the bower.

     

The taxonomic significance of the trunk limbs of the chydoridae (Cladocera)

Summary The differences in the structure of the trunk limbs allow to outline three sections of Chydoridae (see table I and fig. 1), coinciding with the sections distinguished according to the structure of the head pores.

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Chydoridae (Cladocera)

Chydoridae (. ), , .

     

Interferon-γ (IFN-γ) and interleukin-2 in the generation of lymphokine-activated killer cell cytotoxicity — IFN-γ-induced suppressive activity

Summary Incubation of human lymphocytes with recombinant interleukin-2 (rIL-2) results in the generation of lymphokine-activated killer (LAK) cells capable of lysing a wide variety of tumor cells. The present study was undertaken to examine the effect of recombinant interferon (rIFN-) on LAK cell cytotoxicity generated from different peripheral blood mononuclear cell (PBMC) subpopulations. When unseparated PBMC were stimulated by rIL-2 and rIFN-, the latter induced a transient enhancement after 2 days followed by a suppression of LAK cell cytotoxicity at day 6. Enhancement of LAK cell cytotoxicity was moderate and inconstant, whereas the inhibition was strong and observed with all the donors tested. This suppression was not associated with a decrease in the [³H]thymidine uptake. PBMC depleted of adherent cells were more sensitive to the stimulation by rIL-2 and the induced cytotoxicity was not modified by rIFN-. Monocyte-enriched plastic-adherent cells, when incubated with rIL-2 and rIFN-, became cytotoxic after 2–3 days of culture and inhibited LAK cell activity after 5–6 days. Collectively, our results suggest that rIFN- affects LAK cell cytotoxicity through the activation of plastic-adherent, monocyte-rich, cells which modulate natural killer cells, first in a positive, then in a negative way.     

Optimal task performance of antagonistic muscles

Movements against a variety of loads are relatively invariant in form. These movements are controlled in general by antagonistic groups of muscles. In this paper optimal control strategies are computed for coupling antagonistic muscles so as to minimize deviations from a desired trajectory. Simulations are presented for linear and nonlinear decision functions linking control of the two muscles for a variety of movements in a way that may be compared with experimental observations.This work was partly supported by the Natural Sciences and Engineering Research Council of Canada Grant NSERC OGP-4345 and by the Medical Research Council of Canada Grant MRC PG-47 through the University of Alberta     

The Study of Intramuscular Nerve Distribution Patterns and Relative Spindle Abundance of the Thenar and Hypothenar Muscles in Human Hand

Background

The intramuscular nerve distribution and relative spindle abundance of the human hand have not been well defined, although this is important in guiding hand surgery.

Methods

Forty human hands were dissected and subjected to modified Sihler’s stain and haematoxylin and eosin stain to investigate intramuscular nerve distribution and relative spindle abundance, respectively.

Results

The flexor pollicis brevis (FPB), adductor pollicis (AP), and abductor digiti minimi (ADM) contain separate nerve compartments. Neural anastomoses were observed in the thenar and hypothenar muscles, including the Y-like, O-like, H-like, and U-like appearance. We found that U-like neural anastomoses may be the characteristic of the opponens muscles. The relative spindle abundance was the greatest in the opponens muscles which may coordinate fine movements.

Conclusion

Except for the two opponens muscles, the rest of the thenar and hypothenar muscles could be used as whole muscle or half-muscle donors for muscle transplant. Our nerve map of the hand offers valuable guidance for hand reconstruction.     

The “efferent copy” hypothesis in saccadic programming in cats

Eye movements were investigated in cats while following a visual target. Wire coils implanted into the eyes served as transducers; the animal was placed in a revolving magnetic field (the magnetic search coil technique). The linear nature of amplitude-velocity relationships in saccadic eye movements was demonstrated. With combined head and eye movements, slope of plot was unrelated to maximum velocity of head movement over the entire test range (of up to 250 deg/sec); saccades decelerated when the head was immobile. Duration of gaze shift rose as it increased in amplitude. Amplitude of gaze was found to depend on head velocity. Experimentally obtained data on the interaction between head and eye movements when combined in following a target may be interpreted from the aspect of a mechanism operating to suppress saccadic signals by an efferent copy signal for head movement.M. V. Lomonosov State University, Moscow. Translated from Neirofiziologiya, Vol. 20, No. 5, pp. 631–637, September–October, 1988.     

A model of visually-guided smooth pursuit eye movements based on behavioral observations

We report a model that reproduces many of the behavioral properties of smooth pursuit eye movements. The model is a negative-feedback system that uses three parallel visual motion pathways to drive pursuit. The three visual pathways process image motion, defined as target motion with respect to the moving eye, and provide signals related to image velocity, image acceleration, and a transient that occurs at the onset of target motion. The three visual motion signals are summed and integrated to produce the eye velocity output of the model. The model reproduces the average eye velocity evoked by steps of target velocity in monkeys and humans and accounts for the variation among individual responses and subjects. When its motor pathways are expanded to include positive feedback of eye velocity and a switch, the model reproduces the exponential decay in eye velocity observed when a moving target stops. Manipulation of this expanded model can mimic the effects of stimulation and lesions in the arcuate pursuit area, the middle temporal visual area (MT), and the medial superior temporal visual area (MST).     

Dependence between the parameters of dynamic and stationary segments of the EMG activity in the elbow joint muscles and the joint angle during realization of targeted movements in cats

In experiments on cats we studied the pattern of EMG activity recorded from the flexors and extensors of the elbow joint and related to realization of flexor targeted operant movements of the forearm. The levels of stationary EMG activity generated by the flexors at a stabilized equilibrium position of the joint demonstrated no correlation with the values of joint angles. We suppose that this feature depends on manifestation of the hysteresis effects of muscle contraction. A target position was attained mostly due to the dynamic phases of muscle activity. The respective patterns of the movement-related activity of synergic muscles significantly differed; separate components related to leaving an equilibrium state with a certain acceleration and attaining a presettled equilibrium joint angle could be differentiated in this activity. Final positions of the forearm could be significantly different at equal levels of the stationary EMG activity generated during stabilization of these positions; they depended on specificities in the time course of dynamic phase of the activity (in particular, on the time of activity decay to a stationary level). We conclude that the movement of a limb link from one equilibrium position to another is mostly controlled via coordination of the dynamic phase of muscle activity.     

Effect of muscle fatigue on target positioning of the human forearm under conditions of restriction of visual control

We studied movements of the forearm within the limits of 0 deg (full extension)-flexion to a 100 deg angle in the elbow joint-a reverse movement with episodes of target positioning at an intermediate target level (50 deg). The standard trajectory and trajectory of the performed movement were visualized by movements of cursors on the screen of a monitor in joint angle vs time coordinates. Systematic errors of blindfold (kinesthetic) positioning (after removal of the visual feedback informing the subject on the characteristics of the performed movement) observed under control conditions and after realization of a fatigue-inducing series of flexions/extensions of the forearm with a high loading were compared. It was found that the development of fatigue evoked no fundamental changes in the pattern of systematic errors of kinesthetic positioning. Both considerable prevailing of positive systematic errors within the examined group, their high interindividual variability, and (in most cases) patterns of signs of errors after reaching the target level by movements of opposite directions typical of the given subject were preserved. Mean intragroup values after the development of fatigue demonstrated some trend toward a decrease, but these changes did not reach the significance level. Possible mechanisms of the influence of muscle fatigue on the process of target positioning of a limb link realized exclusively under proprioceptive control are discussed. Neirofiziologiya/Neurophysiology, Vol. 38, Nos. 5/6, pp. 432–439, September–December, 2006.