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  • 1
    Electronic Resource
    Electronic Resource
    On the possibility of linear modelling the human arm neuromuscular apparatus (2000)
    Springer
    Biological cybernetics 82 (2000), S. 499-515 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract. 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004220050603
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  • 2
    Electronic Resource
    Electronic Resource
    Forearm postural control during unloading: anticipatory changes in elbow stiffness (1999)
    Springer
    Experimental brain research 124 (1999), S. 107-117 
    Details
    ISSN: 1432-1106
    Keywords: Key words Posture maintenance ; Bimanual unloading ; Joint stiffness ; Equilibrium angle ; Invariant characteristics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  In this study, the equilibrium-point hypothesis of muscle-torque generation is used to evaluate the changes in central control parameters in the process of postural-maintenance learning. Muscle torque is described by a linear spring equation with modifiable stiffness, viscosity, and equilibrium angle. The stiffness is considered to be the estimation of the central command for antagonist-muscle coactivation and the equilibrium angle to be the estimation of the reciprocal command for a shift of invariant characteristics of the joint. In the experiments, a load applied to the forearm was released. The subjects were instructed to maintain their forearm in the initial horizontal position. Five sessions of approximately twenty trials each were carried out by eight subjects. During two ”control” series, the load release was triggered by the experimenter. During three ”learning” series, the load supported by one forearm was released by the subject’s other hand. The elbow-joint angle, the angular acceleration, and the external load on the postural forearm were recorded. These recordings as well as anthropometric forearm characteristics were used to calculate the elbow-joint torque (which we called ”experimental”). Linear regression analysis was performed to evaluate the equilibrium angle, joint stiffness, and viscosity at each trial. The ”theoretical” torque was calculated using a linear spring equation with the found parameters. The good agreement observed between experimental and theoretical joint-torque time courses, apart from the very early period following unloading, argues in favor of the idea that the movement was mainly performed under a constant central command presetting the joint stiffness and the equilibrium angle. An overall increase in the stiffness occurred simultaneously with a decrease in the equilibrium angle during the ”learning” series in all the subjects. This suggests that subjects learn to compensate for the disturbing effects of unloading by increasing the joint stiffness. The mechanism possibly responsible for the presetting of the central control parameters is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002210050605
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  • 3
    Electronic Resource
    Electronic Resource
    The responses of pericruciate cortical neurones to distal forepaw electrical stimulation in the unanaesthetized, unrestrained cat (1986)
    Springer
    Experimental brain research 63 (1986), S. 474-486 
    Details
    ISSN: 1432-1106
    Keywords: Pericruciate cortex ; Cutaneous cortical afferents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Experiments were performed to examine the responses of cortical neurons in the pericruciate cortex to cutaneous afferent input from the distal forepaw. Ninty-nine cortical neurons responding to electrical stimulation of the forepaw were recorded from four cats. Their response latencies ranged from 6 to 23 ms. The units had cutaneous receptive fields which ranged in size from those restricted to one digit to those extending over the whole forelimb. They were recorded from area 4 and area 3. Intracortical microstimulation at the recording sites activated either the distal or proximal musculature of the forelimb. When the characteristics obtained from each recording site were examined as a group of features, a uniform population emerged which was significantly different from the rest of the sample. These units had 1) the shortest latency responses to distal forepaw electrical stimulation, 2) the shortest duration of evoked discharge, 3) the smallest distal cutaneous receptive fields. Such units were recorded at the border between areas 3 and 4, at sites which on microstimulation resulted in movements of the distal forepaw musculature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00237471
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  • 4
    Electronic Resource
    Electronic Resource
    Acquisition of co-ordination between posture and movement in a bimanual task (1989)
    Springer
    Experimental brain research 77 (1989), S. 337-348 
    Details
    ISSN: 1432-1106
    Keywords: Posture ; Movement ; Co-ordination ; Bimanual task
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The acquisition of co-ordination between posture and movement was investigated in human subjects performing a load lifting task. Sitting subjects held their left (postural) forearm in a horizontal position while supporting a 1 kg load via an electromagnet. Perturbation of the postural forearm position consisted of the load release triggered either by the experimenter (control) or by the subject voluntarily moving the other arm. In the latter case, the movement involved the elbow joint (load lifting (A), isometric force change at the wrist level (B), elbow rotation (C) and pressing a button with the wrist (D)) or the fingers (grip isometric force change). We recorded the maximal amplitude and maximal velocity of the rotation of the postural forearm, the EMG of the forearm flexors on both sides and the force exerted either by the load on the postural arm or by the isometric contraction of the moving arm. The maximal forearm angular velocity after unloading was known to be related to the level of muscle contraction before unloading. 1. In the control situation, repetition of the imposed unloading test resulted in a progressive reduction in the maximal forearm rotation without any decrease in the maximal velocity. The amplitude and duration of the unloading reflex were found to increase in parallel. These results suggest that an adaptive mechanism took place which increased the gain of the unloading reflex loop and reduced the mechanical effect of the perturbation. This mechanism was found to come into play not only in the control situation but also in other paradigms where the perturbation was expected by the subjects. 2. A decrease in both maximal amplitude and velocity of forearm rotation together with a weak “anticipatory” deactivation of the forearm postural flexors was observed when the unloading was caused by an elbow movement (situations A, B, C) which indicates that a feedforward postural control took place. An interlimb coordination was built up and stabilized after 40–60 trials. Pressing a button with the wrist (weak force and displacement) was a less effective means of inducing an anticipatory control of the flexors of the postural forearm, which indicates that the intensity of the central control plays a role in the building up of the coordination. 3. A distal grip action exerting either weak (100 g) or a high (1 kg) force was able to reduce the maximal amplitude of the forearm rotation, but not the maximal velocity, which indicates that an improved reflex action takes place, but not a feedforward anticipatory postural control. 4. It is concluded that both feedback and feedforward phasic postural controls play a role in the stabilization of the forearm position when a postural perturbation is caused by a voluntary movement. The acquisition of the feedforward postural control depends on the central command per se rather than on the resulting movement parameters. In addition, proximal joints are more appropriate for building up the coordination than the finger joints.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00274991
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  • 5
    Electronic Resource
    Electronic Resource
    Role of the sensorimotor cortex in postural adjustments accompanying a conditioned paw lift in the standing cat (1989)
    Springer
    Experimental brain research 78 (1989), S. 588-596 
    Details
    ISSN: 1432-1106
    Keywords: Motor cortex ; Conditioned movement ; Posture ; Balance control ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The role of the sensorimotor cortex in the postural adjustments associated with conditioned paw lifting movements was investigated in the cat. Cats were trained to stand quietly on four strain gauge equipped platforms and to perform a lift-off movement with one forelimb when a conditioned tone was presented. The parameters recorded were the vertical forces exerted by the paws on each platform, the lateral and antero-posterior displacements of rods implanted on the T2, T12, L5 vertebrae as well as their rotation, and the EMG of triceps and biceps of both forelimbs. Before lesion, the postural adjustment consisted of a “nondiagonal” pattern where the CG was displaced laterally inside the triangle formed by the three remaining supporting limbs. Here a lateral bending of the thoracic column toward the supporting forelimb could be observed. The associated EMG pattern consisted of an early activation of the triceps lateral head in the moving limb which was probably responsible for the body displacement toward the opposite side, and a late biceps activation associated with the lift. In the supporting forelimb, a coactivation of the biceps and triceps was usually present. After contralateral sensorimotor lesion, the conditioned lifting movements were lost for 4–15 days after the lesion, before being subsequently recovered. The same lateral CG displacement and bending of the back was seen after lesion as before, which indicates that the goal of postural adjustment was preserved. However, the means of reaching it were modified. In most of the intact animals, the CG displacement was achieved in one step, whereas in the animals with lesions, the displacement was made either according to a slow ramp mode or in a discontinuous manner involving several steps. The mechanisms responsible for this disturbance are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00230246
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  • 6
    Electronic Resource
    Electronic Resource
    Coordination between posture and movement in a bimanual load-lifting task: is there a transfer? (1996)
    Springer
    Experimental brain research 109 (1996), S. 450-456 
    Details
    ISSN: 1432-1106
    Keywords: Posture ; Movement ; Bimanual coordination ; Motor learning ; Learning transfer ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The present experimental series was designed to test the possibility that an anticipatory postural adjustment learned during the performance of a bimanual load lifting task may be transferred between the upper extremities. Eight seated subjects were asked to maintain horizontally one forearm (postural arm) loaded with a 1kg load, which was fixed to the arm by means of an electromagnet. The unloading was triggered either by the experimenter pressing a switch (control) or by the subjects making a voluntary movement with their other arm (moving arm). In the latter case, the subject lifted a 1-kg load resting on a force platform with the moving hand, and the switching off was triggered when the force level reached a threshold of 0.5 kg. The maximum amplitude (MA) and the maximum velocity (MV) of the postural forearm elbow joint rotation occuring after the unloading were measured at each trial. The learning process was estimated by performing a regression analysis on each series of trials, using an exponential model, and from the intercept of the regression curve with the ordinate. 1. During the original learning session (three series of 20 trials), a decrease in MA and MV was found to occur both within the series and between the series during a session. 2. After the initial learning session, the sides of the postural and moving arm were interchanged to test whether any transfer had occurred. The first series of trials in the second session (transfer) and the last series of trials in the original learning session were compared and found to be significantly different in terms of the intercept (seven subjects in the case of MA, five subjects in the case of MV) and the slope (five subjects), indicating a lack of transfer. 3. The data recorded during the second transfer learning session indicated that learning occurred in all eight subjects in the case of MA and in six subjects in the case of MV. It was observed that the original learning session did not facilitate the second one. 4. The lack of transfer of the anticipatory postural adjustment observed in this task is discussed with reference to the data in the literature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00229629
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  • 7
    Electronic Resource
    Electronic Resource
    Diminution and reversal of eye movements induced by local stimulation of rabbit cerebellar flocculus after partial destruction of the inferior olive (1978)
    Springer
    Experimental brain research 33 (1978), S. 139-141 
    Details
    ISSN: 1432-1106
    Keywords: Inferior olive ; Cerebellum ; Flocculus ; Rabbit ; Eye movement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary After the dorsal cap and adjacent ventrolateral outgrowth regions of the inferior olive had been chronically destroyed in the rabbits, the eye movements evoked by local stimulation of the flocculus were reduced in amplitude and reversed in direction, indicating that the inhibition by flocculus Purkinje cells of vestibulo-ocular relay neurons could no longer be actuated by the stimulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00238801
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  • 8
    Electronic Resource
    Electronic Resource
    Postural forearm changes induced by predictable in time or voluntary triggered unloading in man (1985)
    Springer
    Experimental brain research 60 (1985), S. 330-334 
    Details
    ISSN: 1432-1106
    Keywords: Posture ; Unloading reflex ; Voluntary movement ; Anticipatory postural reaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Human subjects sitting in a chair were asked to maintain their right forearm in a horizontal position in half supination. The forearm was loaded with a constant weight of one kilogram. Vertical force at the wrist level, angular position of the elbow and EMG activity of biceps, brachio-radialis and triceps muscles were recorded. Unloading was tested under four different conditions, the first two having been used in a previous study (Hugon et al. 1982): (A) Voluntary unloading by the subject's other hand. An “anticipatory” deactivation of the load bearing forearm flexors is observed preventing the elbow rotation of that arm. (B) Unpredictable passive unloading. This results in an upward forearm rotation which provokes the classical “unloading reflex”. Two new conditions were tested in the present paradigm: (C) Imposed unloading predictable in time (tone signal preceding unloading by a fixed interval). (D) Unloading being actively triggered when the subject presses a key. Under the two latter conditions, no anticipatory deactivation of the flexor supporting muscles preceding the onset of unloading as in situation A was observed. During the first 120 ms after the onset of unloading, the forearm rotation was the same as in situation B (unpredictable passive unloading). Thereafter, the rotation was smaller in some subjects, apparently due to an ameliorated reflex action. It is concluded that temporal information concerning the precise time of the unloading or the triggering of the load release by a voluntary movement (key press) was not by itself able to induce the anticipatory deactivation of the forearm flexors that was seen with a coordinated voluntary release of the load by the contralateral arm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00235928
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  • 9
    Electronic Resource
    Electronic Resource
    Biomechanical and electromyographical comparison of two postural supporting mechanisms in the cat (1982)
    Springer
    Experimental brain research 45 (1982), S. 38-44 
    Details
    ISSN: 1432-1106
    Keywords: Posture ; Movement ; Biomechanic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 1. Two patterns of postural support accompanying single limb movements in the cat, diagonal and non-diagonal, were studied to determine the differences underlying their elaboration. 2. Markers were implanted in selected vertebrae at the T1, T12 and L5 levels to measure movements of the vertebral column during both types of supporting reaction. Electromyographic activity of a hind-limb extensor, the triceps surae, was recorded bilaterally. 3. The diagonal pattern was characterized by an approximately bipedal stance, most of the animal's weight being supported by one forelimb and the diagonally opposite hindlimb. This postural support was observed to accompany single limb movements evoked by an unexpected perturbation. The back remained relatively rigid and no rotation at any level was observed. The center of gravity moved very little. The triceps of the loaded hindlimb was activated, while that of the unloaded limb decreased in activity. Both these myographic changes preceded force changes in the homonymous limbs, indicating that the postural supporting response was probably a response of all the limbs acting in concert, and not the result of individual loading or unloading of the various limbs. 4. The non-diagonal pattern exhibited shifts in weight restricted to one half of the body (i.e. forelimbs for a forelimb lift). This pattern of support was seen when learned limb movement was performed. There was a marked lateral flexion of the vertebral column rostral to the T12 level, producing a lateral displacement of the center of gravity. During a forelimb movement, no reciprocal myographic changes were seen in the hindlimb triceps muscles. The functional significance of these differences between the two patterns is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00235761
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