Peculiarities of Activation of Muscles of the Shoulder Belt in Voluntary Two-Joint Movements of the Upper Limb

We studied coordination of central motor commands (СMCs) coming to muscles of the shoulder and shoulder belt in the course of single-joint and two-joint movements including flexion and extension of the elbow and shoulder joints. Characteristics of rectified and averaged EMGs recorded from a few muscles of the upper limb were considered correlates of the CMC parameters. Special attention was paid to coordination of CMCs coming to two-joint muscles that are able to function as common flexors (m. biceps brachii, caput breve, BBcb) and common extensors (m. triceps brachii, caput longum, TBcl) of the elbow and shoulder joints. Upper limb movements used in the tests included planar shifts of the arm from one spatial point to another resulting from either simultaneous changes in the angles of the shoulder and elbow joints or isolated sequential (two-stage) changes in these joint angles. As was found, shoulder muscles providing movements of the elbow with changes in the angle of the elbow joint, i.e., BBcb and TBcl, were also intensely involved in the performance of single-joint movements in the shoulder joint. The CMCs coming to two-joint muscles in the course of two-joint movements appeared, in the first approximation, as sums of the commands received by these muscles in the course of corresponding single-joint movements in the elbow and shoulder joints. Therefore, if we interpret the isolated forearm movement performed due to a change in the angle of the elbow joint as the main motor event, while the shoulder movement is considered the accessory one, we can conclude that realization of a two-joint movement of the upper-limb distal part is based on superposition of CMCs related to basic movements (main and accessory). Neirofiziologiya/Neurophysiology, Vol. 41, No. 1, pp. 48–56, January–February, 2009.     

Analysis of an optimal control model of multi-joint arm movements

 In this paper, we propose a model of biological motor control for generation of goal-directed multi-joint arm movements, and study the formation of muscle control inputs and invariant kinematic features of movements. The model has a hierarchical structure that can determine the control inputs for a set of redundant muscles without any inverse computation. Calculation of motor commands is divided into two stages, each of which performs a transformation of motor commands from one coordinate system to another. At the first level, a central controller in the brain accepts instructions from higher centers, which represent the motor goal in the Cartesian space. The controller computes joint equilibrium trajectories and excitation signals according to a minimum effort criterion. At the second level, a neural network in the spinal cord translates the excitation signals and equilibrium trajectories into control commands to three pairs of antagonist muscles which are redundant for a two-joint arm. No inverse computation is required in the determination of individual muscle commands. The minimum effort controller can produce arm movements whose dynamic and kinematic features are similar to those of voluntary arm movements. For fast movements, the hand approaches a target position along a near-straight path with a smooth bell-shaped velocity. The equilibrium trajectories in X and Y show an ‘N’ shape, but the end-point equilibrium path zigzags around the hand path. Joint movements are not always smooth. Joint reversal is found in movements in some directions. The excitation signals have a triphasic (or biphasic) pulse pattern, which leads to stereotyped triphasic (or biphasic) bursts in muscle control inputs, and a dynamically modulated joint stiffness. There is a fixed sequence of muscle activation from proximal muscles to distal muscles. The order is preserved in all movements. For slow movements, it is shown that a constant joint stiffness is necessary to produce a smooth movement with a bell-shaped velocity. Scaled movements can be reproduced by varying the constraints on the maximal level of excitation signals according to the speed of movement. When the inertial parameters of the arm are altered, movement trajectories can be kept invariant by adjusting the pulse height values, showing the ability to adapt to load changes. These results agree with a wide range of experimental observations on human voluntary movements. Received: 4 December 1995 / Accepted in revised form: 17 September 1996     

Peculiarities of Activation of the Upper Limb Muscles in Realization of Two-Joint Movements in Humans

In tests on humans, we recorded EMG activity from the muscles flexing and extending the forearm and shoulder in the course of realization of sequential single-joint and simultaneous two-joint movements of the upper limb. As was shown, the shoulder muscles m. biceps brachii and m. triceps brachii are involved in flexion/extension of both elbow and shoulder joints. Central commands sent to the above muscles in the course of a two-joint movement could be considered a superposition of the central commands coming to the same muscles in realization of the corresponding sequential single-joint movements with the same changes in the angles of the elbow and shoulder joints. External loadings applied in the direction of extension of the elbow and shoulder joints induced, in general, similar changes in coordination of the activity of muscles moving the forearm and shoulder under conditions of both single-joint and two-joint movements. These facts allow us to suppose that coordination of the muscle activity in two-joint movements depends to a greater extent on the forces influencing limb links than on the mode of realization of the movements (two sequential single-joint movements vs a two-joint movement corresponding to the above motor events).     

Activation of the Shoulder-Belt and Shoulder Muscles in Two-Joint Arm Movements Performed in Humans with the Action of Opposite Loadings

In tests on four volunteers, we examined coordination of central motor commands (CMCs) controlling slow two-joint movements of the arm within the horizontal plane. Current amplitudes of EMGs recorded from six muscles of the shoulder belt and shoulder and subjected to full-wave rectifying and low-frequency filtration were considered correlates of these commands. In particular, we studied the dependence of coordination of CMCs on the direction of an external force applied to the distal forearm part. As was found, coordination of CMCs significantly depends on the direction of the force flexing the elbow joint. According to our observations, EMGs of definite muscles in the case of performance of a two-joint movement can, in a first approximation, be presented as linear combinations of the EMGs recorded in the course of separate sequential single-joint movements under conditions of shifting the reference point of the hand toward the same point of the operational space as that in the two-joint movement. These data can be interpreted as confirmation of the principle of superposition of elementary CMCs in the performance of complex movements of the extremity.     

On the possibility of linear modelling the human arm neuromuscular apparatus

It has been widely claimed that linear models of the neuromuscular apparatus give very inaccurate approximations of human arm reaching movements. The present paper examines this claim by quantifying the contributions of the various non-linear effects of muscle force generation on the accuracy of linear approximation. We performed computer simulations of a model of a two-joint arm with six monarticular and biarticular muscles. The global actions of individual muscles resulted in a linear dependence of the joint torques on the joint angles and angular velocities, despite the great non-linearity of the muscle properties. The effect of time delay in force generation is much more important for model accuracy than all the non-linear effects, while ignoring this time delay in linear approximation results in large errors. Thus, the viscosity coefficients are rather underestimated and some of them can even be paradoxically estimated to be negative. Similarly, our computation showed that ignoring the time delay resulted in large errors in the estimation of the hand equilibrium trajectory. This could explain why experimentally estimated hand equilibrium trajectories may be complex, even during a simple reaching movement. The hand equilibrium trajectory estimated by a linear model becomes simple when the time delay is taken into account, and it is close to that actually used in the non-linear model. The results therefore provide a theoretical basis for estimating the hand equilibrium trajectory during arm reaching movements and hence for estimating the time course of the motor control signals associated with this trajectory, as set out in the equilibrium point hypothesis. Received: 17 February 1999 / Accepted in revised form: 22 October 1999     

A model of handwriting

The research reported here is concerned with hand trajectory planning for the class of movements involved in handwriting. Previous studies show that the kinematics of human two-joint arm movements in the horizontal plane can be described by a model which is based on dynamic minimization of the square of the third derivative of hand position (jerk), integrated over the entire movement. We extend this approach to both the analysis and the synthesis of the trajectories occurring in the generation of handwritten characters. Several basic strokes are identified and possible stroke concatenation rules are suggested. Given a concise symbolic representation of a stroke shape, a simple algorithm computes the complete kinematic specification of the corresponding trajectory. A handwriting generation model based on a kinematics from shape principle and on dynamic optimization is formulated and tested. Good qualitative and quantitative agreement was found between subject recordings and trajectories generated by the model. The simple symbolic representation of hand motion suggested here may permit the central nervous system to learn, store and modify motor action plans for writing in an efficient manner.     

Effect of Tendon Vibration on Hemiparetic Arm Stability in Unstable Workspaces

Sensory stimulation of wrist musculature can enhance stability in the proximal arm and may be a useful therapy aimed at improving arm control post-stroke. Specifically, our prior research indicates tendon vibration can enhance stability during point-to-point arm movements and in tracking tasks. The goal of the present study was to investigate the influence of forearm tendon vibration on endpoint stability, measured at the hand, immediately following forward arm movements in an unstable environment. Both proximal and distal workspaces were tested. Ten hemiparetic stroke subjects and 5 healthy controls made forward arm movements while grasping the handle of a two-joint robotic arm. At the end of each movement, the robot applied destabilizing forces. During some trials, 70 Hz vibration was applied to the forearm flexor muscle tendons. 70 Hz was used as the stimulus frequency as it lies within the range of optimal frequencies that activate the muscle spindles at the highest response rate. Endpoint position, velocity, muscle activity and grip force data were compared before, during and after vibration. Stability at the endpoint was quantified as the magnitude of oscillation about the target position, calculated from the power of the tangential velocity data. Prior to vibration, subjects produced unstable, oscillating hand movements about the target location due to the applied force field. Stability increased during vibration, as evidenced by decreased oscillation in hand tangential velocity.     

Modulation of the soleus muscle H reflex caused by ballistic voluntary arm movements in humans

In healthy humans, we studied the influence of conditioning voluntary arm movements on the H reflex induced by transcutaneous stimulation of the tibial nerve and recorded from the soleus muscle. We examined the effects of flexion and extension of the forearm, as well as of finger clenching performed with the maximum rate. Conditioning arm movements were self-induced or realized upon presentation of a visual signal (light flash). We found that the pattern of changes in the H reflex is determined by the position of the subject’s body in the course of tests. The ipsilateral arm flexion in the elbow joint in the standing position resulted in depression of the H reflex lasting about 100 msec from the beginning of the movement, while the effect observed in the lying position (on the couch with the feet hanging free in the air) looked like a facilitation of the reflex lasting about 100 to 200 msec. The direction and dynamics of modifications of the H reflex under conditions of the use of different conditioning movements (forearm flexions/extensions and finger clenching of the ipsilateral arm, as well as contralateral forearm flexions in the elbow joint) were rather similar. We also showed that the observed facilitation of the H reflex began earlier than the voluntary arm movement (40 to 50 msec prior to the beginning). We hypothesize that these conditioning influences result from the action of central motor commands and represent the factor related to anticipatory postural rearrangements. Such rearrangements are directed toward the maintenance of equilibrium of the body in the course of a future movement. These commands depend significantly on the spatial position of the subject’s body. Neirofiziologiya/Neurophysiology, Vol. 40, No. 2, pp. 147–154, March–April, 2008.     

Winching up heavy loads with a compliant arm: a new local joint controller

A closed kinematic chain, like an arm that operates a crank, has a constrained movement space. A meaningful movement of the chain’s endpoint is only possible along the free movement directions which are given implicitly by the contour of the object that confines the movement of the chain. Many technical solutions for such a movement task, in particular those used in robotics, use central controllers and force–torque sensors in the arm’s wrist or a leg’s ankle to construct a coordinate system (task frame formalism) at the local point of contact the axes of which coincide with the free and constrained movement directions. Motivated by examples from biology, we introduce a new control system that solves a constrained movement task. The control system is inspired by the control architecture that is found in stick insects like Carausius morosus. It consists of decentral joint controllers that work on elastic joints (compliant manipulator). The decentral controllers are based on local positive velocity feedback (LPVF). It has been shown earlier that LPVF enables contour following of a limb in a compliant motion task without a central controller. In this paper we extend LPVF in such a way that it is even able to follow a contour if a considerable counter force drags the limb away along the contour in a direction opposite to the desired. The controller extension is based on the measurement of the local mechanical power generated in the elastic joint and is called power-controlled relaxation LPVF. The new control approach has the following advantages. First, it still uses local joint controllers without knowledge of the kinematics. Second, it does not need a force or torque measurement at the end of the limb. In this paper we test power-controlled relaxation LPVF on a crank turning task in which a weight has to be winched up by a two-joint compliant manipulator.     

Linear combinations of nonlinear models for predicting human–machine interface forces

 This study presents a computational framework that capitalizes on known human neuromechanical characteristics during limb movements in order to predict human–machine interactions. A parallel–distributed approach, the mixture of nonlinear models, fits the relationship between the measured kinematics and kinetics at the handle of a robot. Each element of the mixture represented the arm and its controller as a feedforward nonlinear model of inverse dynamics plus a linear approximation of musculotendonous impedance. We evaluated this approach with data from experiments where subjects held the handle of a planar manipulandum robot and attempted to make point-to-point reaching movements. We compared the performance to the more conventional approach of a constrained, nonlinear optimization of the parameters. The mixture of nonlinear models accounted for 79±11% (mean ±SD) of the variance in measured force, and force errors were 0.73 ± 0.20% of the maximum exerted force. Solutions were acquired in half the time with a significantly better fit. However, both approaches suffered equally from the simplifying assumptions, namely that the human neuromechanical system consisted of a feedforward controller coupled with linear impedances and a moving state equilibrium. Hence, predictability was best limited to the first half of the movement. The mixture of nonlinear models may be useful in human–machine tasks such as in telerobotics, fly-by-wire vehicles, robotic training, and rehabilitation. Received: 20 October 2000 / Accepted in revised form: 8 May 2001     

Effect of cold stimulation of the arm fingers on the spectral/coherent EEG characteristics in humans

Examination of modifications of EEG in humans induced by cold stimulation of the arm fingers showed that the EEG frequency composition noticeably depended on this thermal influence (in the relaxed state with no movements or during realization of voluntary cyclic movements by the fingers of another arm). In the resting state, cold stimulation mostly induced intensification of the delta activity, while, when coinciding with the performance of voluntary movements, it also resulted in increases in the powers of oscillations of the alpha1 and beta1 ranges. The structure of changes in the coefficients of coherence under the influence of cooling also depended on the conditions of testing (in the resting state or during motor activity). Therefore, the effect of tonic cold stimulation on the interaction between synchronizing and desynchronizing cerebral systems and interrelations between different cortical zones was modified under conditions of realization of a motor function. Neirofiziologiya/Neurophysiology, Vol. 40, No. 3, pp. 268–270, May–June, 2008.     

Kinematic invariants during cyclical arm movements

It has been observed that the motion of the arm end-point (the hand, fingertip or the tip of a pen) is characterized by a number of regularities (kinematic invariants). Trajectory is usually straight, and the velocity profile has a bell shape during point-to-point movements. During drawing movements, a two-thirds power law predicts the dependence of the end-point velocity on the trajectory curvature. Although various principles of movement organization have been discussed as possible origins of these kinematic invariants, the nature of these movement trajectory characteristics remains an open question. A kinematic model of cyclical arm movements derived in the present study analytically demonstrates that all three kinematic invariants can be predicted from a two-joint approximation of the kinematic structure of the arm and from sinusoidal joint motions. With this approach, explicit expressions for two kinematic invariants, the two-thirds power law during drawing movements and the velocity profile during point-to-point movements are obtained as functions of arm segment lengths and joint motion parameters. Additionally, less recognized kinematic invariants are also derived from the model. The obtained analytical expressions are further validated with experimental data. The high accuracy of the predictions confirms practical utility of the model, showing that the model is relevant to human performance over a wide range of movements. The results create a basis for the consolidation of various existing interpretations of kinematic invariants. In particular, optimal control is discussed as a plausible source of invariant characteristics of joint motions and movement trajectories.     

Relations between the errors of targeted movements and inexactitude of visual perception of space

Errors of targeted movements of the arm to the places of presentation of light targets (in darkness) were studied in healthy subjects kept in a vertical position or laying on their backs. An error along theY axis (corresponding to the longitudinal body axis) changed its sign depending on the body orientation with respect to the gravitation vector. In the vertical position, the arm shifted to the feet at the movement’s termination, while in the laying position it shifted to the head. AnX error showed no dependence on the position of the body in space. The errors reached their maxima in the absence of visual control, but became two-three times smaller when the tested subject could observe the position of an indicator (light diodes) fixed on the end of the index finger (or of a pointer rod). When the spatial positions of targets were reconstructed according to verbal “indications”, the amplitudes ofX andY errors appeared similar to those at real movements (indication under visual control). In this case, the sign ofY errors also depended on the body orientation, but their direction was opposite. We suppose that systematicY errors at the targeted arm movements are determined not only by an antigravitation component of the motor program, but also by shifting of a sensory visual estimations of the spatial target position.     

Quantization of human motions and learning of accurate movements

This paper presents a mathematical model for the learning of accurate human arm movements. Its main features are that the movement is the superposition of smooth submovements, the intrinsic deviation of arm movements is considered, visual and kinesthetic feedback are integrated in the motion control, and the movement duration and accuracy are optimized with practice. This model is consistent with the jerky arm movements of infants, and may explain how the adult motion behavior emerges from the infant behavior. Comparison with measurements of adult movements shows that the kinematics of accurate movements are well predicted by the model. Received: 15 May 1997 / Accepted 5 December 1997     

Karyotypes of three somaclonal variants and wild plants ofAllium tuberosum by bicolor FISH

Using the fluorescence in situ hybridization (FISH) technique, we conducted karyotype analyses to identify the lost chromosomes in three somaclonal variants obtained from tissue culture of wildAllium tuberosum (2n = 4X = 32). The three lost chromosomes of the At29 variant (2n = 29) were all chromosome 2, the two for At30 (2n = 30) were chromosomes 7 and 8, and At31 was missing chromosome 2. Chromosome compositions of these variants were confirmed as being fixed lines during two years of greenhouse cultivation. The bicolor FISH technique, involving both 5S and 18S–5.8S–26S ribosomal RNA genes as probes, was used to assign chromosomal locations and to confirm whether the lost chromosomes contained any rRNA markers. The 5S rRNA gene signals in all variants as well as the wild type were detected as two sets, one on the intercalary region of the short arm of chromosome 3, the other on the intercalary region of the long arm of chromosome 6. One 18S–5.8S–26S rRNA gene site on the secondary constriction included a flanking satellite and terminal region on the short arm of chromosome 8. Signals of the 18S–5.8S–26S rRNA gene in At30 showpd in only three chromosomes, indicating that one of the lost chromosomes was chromosome 8. Overall, three marker chromosomes were established by FISH, using rRNA multigene families.     

Chromosomal distribution of 18S-25S rDNA in four <Emphasis Type="Italic">Lupinus</Emphasis> species visualized by fluorescence <Emphasis Type="Italic">in situ</Emphasis> hybridization

The number and position of 18S–25S rDNA sites in 4 selected Lupinus species are reported for the first time. L. atlanticus, L. subcarnosus and L. paniculatus had two rDNA loci, while L. albus exhibited only one loci. Among these 4 species, all of them exhibited one large pair of strong signals that extends from the short arm to a NOR on a chromosome satellite. L. atlanticus, L. subcarnosus, L. paniculatus had one more locus of 18–25S rDNA, but a pair of weak hybridization signals were observed in L. paniculatus when 18S–25S rDNA was used as probe. The results are discussed in terms of the evolutionary relationships among these species.     

Chromosomal polymorphism of ribosomal genes in the genus Oryza

The genes encoding for 18S–5.8S–28S ribosomal RNA (rDNA) are both conserved and diversified. We used rDNA as probe in the fluorescent in situ hybridization (rDNA-FISH) to localized rDNAs on chromosomes of 15 accessions representing ten Oryza species. These included cultivated and wild species of rice, and four of them are tetraploids. Our results reveal polymorphism in the number of rDNA loci, in the number of rDNA repeats, and in their chromosomal positions among Oryza species. The numbers of rDNA loci varies from one to eight among Oryza species. The rDNA locus located at the end of the short arm of chromosome 9 is conserved among the genus Oryza. The rDNA locus at the end of the short arm of chromosome 10 was lost in some of the accessions. In this study, we report two genome specific rDNA loci in the genus Oryza. One is specific to the BB genome, which was localized at the end of the short arm of chromosome 4. Another may be specific to the CC genome, which was localized in the proximal region of the short arm of chromosome 5. A particular rDNA locus was detected as stretched chromatin with bright signals at the proximal region of the short arm of chromosome 4 in O. grandiglumis by rDNA-FISH. We suggest that chromosomal inversion and the amplification and transposition of rDNA might occur during Oryza species evolution. The possible mechanisms of cyto-evolution in tetraploid Oryza species are discussed.     

Characterisation of arm microvibration recorded on an accelerometer

Microvibration (MV) of the freely hanging and firmly supported lower arm was studied (n = 8) using two accelerometers, one located over muscle tissue (brachioradialis muscle) and one over bony tissue (processus styloideus). Measurements were made in the completely relaxed arm (REST), during arterial occlusion (CUFF) and during mild handgrip (GRIP), first with the arm relaxed and hanging beside the chair and then repeated with the arm supported in a special rest. At REST, ballistocardiac forces were identified as the driving mechanism for the regular MV pattern, whereas actions of local pulse waves (CUFF) could be excluded. During GRIP irregular MV, related to the contraction process, became superimposed on both signals. The MV at REST was sensitive to arm position. In the freely hanging state, when the arm was family coupled to the trunk, ballistocardiac body motion was present over bony tissue, producing a low damped 7–13 Hz resonant response over muscle tissue. In the supported state, the arm became isolated from body motions. Nevertheless, ballistocardiac forces reached the arm, producing smaller oscillatory responses over bone and muscle tissue. Regionally produced MV (GRIP) was not sensitive to arm position, but the spectrum content in the 7–13 Hz region was very similar to REST. From these results it would appear, that a low damped 7–13 Hz resonance process exists in relaxed muscle tissue, which physiologically becomes stimulated by cardiac and muscle forces. From the close relationship of the simultaneous MV waveforms in the supported arm, evidence for mechanical coupling between bone and muscle tissue is given. Accepted: 15 October 1996     

Changes in the spectral power and coherence of the EEG alpha rhythm in humans performing grasp efforts by the right and left arm

We compared changes in the EEG indices in healthy dextral volunteers performing static force grasps by the arm. Three test modes were used: (i) performance of two successive grasps by the dominant (right) arm (test A), (ii) performance of two successive grasps by the subdominant (left) arm (test B), and (iii) performance of the grasps first by the right arm and then by the left arm (test C). Fourteen, six, and nine persons took part in tests A–C, respectively. In the course of grasps performed by the right and left arms, bilateral increases in synchronization within the alpha 1 and alpha 2 ranges were frequently observed in occipital regions in both the first and repeated grasps (P < 0.05). Consecutive grasps by the right arm were accompanied by clear desynchronization in a few anterior and central leads. Alpha 2 desynchronization was observed in both realizations of the left-arm grasps (test B) performed by some subjects, but intragroup modifications were not significant in this case. The coherence coefficients of the alpha 2 rhythm in most cases increased for symmetric leads from the right and left hemispheres in the course of grasps by both the right and left hands. The effect of intensification of interhemisphere links was manifested in the anterior and central cortical regions; this fact showed that interhemisphere interaction increases in the course of the static effort. Changes in the coherence coefficients for the alpha 2 range in the performance of the grasp efforts by the right arm and the left arm were most clear in the posterotemporal (P = 0.02), parietal (P = 0.05), and anterofrontal (P = 0.06) lead pairs. Thus, we demonstrated the dependence between the side of performance of the muscle effort in the mode close to isometric and lateralization of the EEG modifications. Neirofiziologiya/Neurophysiology, Vol. 38, No. 3, pp. 235–238, May–June, 2006.     

Is a virtual trajectory necessary in reaching movements?

The mass-spring model of limb control was extended to two-joint arm movements in the horizontal plane and tested against kinematic data from human subjects. Two versions of the model were compared in order to test the idea that the equilibrium position of the hand moves along a virtual trajectory as demonstrated in single-joint arm movements (Bizzi et al. 1982, 1984; Latash and Gottlieb 1991). In the peripheral version, the equilibrium position was shifted abruptly, while the torques generated at the joints are gated by rise-time functions. In the central version, the equilibrium position was updated gradually according to a predefined trajectory. The paths and tangential velocity profiles of the hand generated by these two versions were compared to Morasso's (1981) experimental data. The central version generally performed better throughout the workspace except in certain special directions. Moreover, its paths exhibited more stability as the movement speed was varied.