Roles of the Caudate Nuclei, Cerebellum, and Caudato-Cerebellar Interconnections in the Control and Coordination of Ballistic Food-Procuring Movements

We studied the roles of the cerebellum and caudate nuclei in the programming and control of ballistic movements. An experimental model of operant food-procuring movements of the rats was used; the activity of single neurons of the above structures was recorded in the course of these motor performances. To evaluate the impact of the cerebellar–caudate interaction on the process of control of the ballistic (centrally programmed) components of food-procuring motor performance, we also recorded modifications of the neuronal activity in one of the above-mentioned structures induced by electrical extrastimulation of another structure in the course of realization of the above components. It is demonstrated that the cerebellum and, in particular, its dentate nuclei are involved in the programming of ballistic food-procuring movements. Neurons of the caudate nuclei play a significant role in the immediate preparation for and subsequent current control of stereotyped ballistic movements. The high plastic properties of the cerebellar neurons manifested in the process of control of ballistic food-procuring movements are proved.     

Essential role for Csk upstream of Fyn and Yes in zebrafish gastrulation

Morphogenetic cell movements during gastrulation shape the vertebrate embryo bodyplan. Non-canonical Wnt signaling has been established to regulate convergence and extension cell movements that mediate anterior-posterior axis elongation. In recent years, many other factors have been implicated in the process by modulation of non-canonical Wnt signaling or by different, unknown mechanisms. We have found that the Src family kinases, Fyn and Yes, are required for normal convergence and extension cell movements in zebrafish embryonic development and they signal in parallel to non-canonical Wnts, eventually converging on a common downstream factor, RhoA. Here, we report that Csk, a negative regulator of Src family kinases has a role in gastrulation cell movements as well. Csk knock down induced a phenotype that was similar to the defects observed after knock down of Fyn and Yes, in that gastrulation cell movements were impaired, without affecting cell fate. The Csk knock down phenotype was rescued by simultaneous partial knock down of Fyn and Yes. We conclude that Csk acts upstream of Fyn and Yes to control vertebrate gastrulation cell movements.     

Alien hand syndrome: neural correlates of movements without conscious will

Background

The alien hand syndrome is a striking phenomenon characterized by purposeful and autonomous movements that are not voluntarily initiated. This study aimed to examine neural correlates of this rare neurological disorder in a patient with corticobasal degeneration and alien hand syndrome of the left hand.

Methodology/Principal Findings

We employed functional magnetic resonance imaging to investigate brain responses associated with unwanted movements in a case study. Results revealed that alien hand movements involved a network of brain activations including the primary motor cortex, premotor cortex, precuneus, and right inferior frontal gyrus. Conscious and voluntary movements of the alien hand elicited a similar network of brain responses but lacked an activation of the inferior frontal gyrus. The results demonstrate that alien and unwanted movements may engage similar brain networks than voluntary movements, but also imply different functional contributions of prefrontal areas. Since the inferior frontal gyrus was uniquely activated during alien movements, the results provide further support for a specific role of this brain region in inhibitory control over involuntary motor responses.

Conclusions/Significance

We discuss the outcome of this study as providing evidence for a distributed neural network associated with unwanted movements in alien hand syndrome, including brain regions known to be related to movement execution and planning as well as areas that have been linked to inhibition control (inferior frontal gyrus) and experience of agency (precuneus).     

Does the brain use sliding variables for the control of movements?

Delays in the transmission of sensory and motor information prevent errors from being instantaneously available to the central nervous system (CNS) and can reduce the stability of a closed-loop control strategy. On the other hand, the use of a pure feedforward control (inverse dynamics) requires a perfect knowledge of the dynamic behavior of the body and of manipulated objects. Sensory feedback is essential both to accommodate unexpected errors and events and to compensate for uncertainties about the dynamics of the body. Experimental observations concerning the control of posture, gaze and limbs have shown that the CNS certainly uses a combination of closed-loop and open-loop control. Feedforward components of movement, such as eye saccades, occur intermittently and present a stereotyped kinematic profile. In visuo-manual tracking tasks, hand movements exhibit velocity peaks that occur intermittently. When a delay or a slow dynamics are inserted in the visuo-manual control loop, intermittent step-and-hold movements appear clearly in the hand trajectory. In this study, we investigated strategies used by human subjects involved in the control of a particular dynamic system. We found strong evidence for substantial nonlinearities in the commands produced. The presence of step-and-hold movements seemed to be the major source of nonlinearities in the control loop. Furthermore, the stereotyped ballistic-like kinematics of these rapid and corrective movements suggests that they were produced in an open-loop way by the CNS. We analyzed the generation of ballistic movements in the light of sliding control theory assuming that they occurred when a sliding variable exceeded a constant threshold. In this framework, a sliding variable is defined as a composite variable (a combination of the instantaneous tracking error and its temporal derivatives) that fulfills a specific stability criterion. Based on this hypothesis and on the assumption of a constant reaction time, the tracking error and its derivatives should be correlated at a particular time lag before movement onset. A peak of correlation was found for a physiologically plausible reaction time, corresponding to a stable composite variable. The direction and amplitude of the ongoing stereotyped movements seemed also be adjusted in order to minimize this variable. These findings suggest that, during visually guided movements, human subjects attempt to minimize such a composite variable and not the instantaneous error. This minimization seems to be obtained by the execution of stereotyped corrective movements. Received: 18 February 1997 / Accepted in revised form: 29 July 1997     

A biomechanical invariant of automated movement]

Trained arm movements and two-link arm dynamics and control of arm movements model are investigated. It is found that for these movements the component of the movements energy dissipations in the control force potential is invariable during the outer force actions.     

Impedance characteristics of a neuromusculoskeletal model of the human arm II. Movement control

The modulation of neuromusculoskeletal impedance during movements is analysed using a motor control model of the human arm. The motor control system combines feedback and feedforward control and both control modes are determined in one optimization process. In the model, the stiffness varies at the double movement frequency for 2-Hz oscillatory elbow movements and has high values at the movement reversals. During goal-directed two-degrees-of-freedom arm movements, the stiffness is decreased during the movement and may be increased in the initial and final phases, depending on the movement velocity. The stiffness has a considerable curl during the movement, as was also observed in experimental data. The dynamic stiffness patterns of the model can be explained basically by the α−γ coactivation scheme where feedback gains covary with motor control signals. In addition to the modulation of the gain factors, it is argued that the variation of the intrinsic stiffness has a considerable effect on movement control, especially during fast movements. Received: 14 October 1997 / Accepted in revised form: 18 May 1999     

Movement curvature planning through force field internal models

Human motion studies have focused primarily on modeling straight point-to-point reaching movements. However, many goal-directed reaching movements, such as movements directed towards oneself, are not straight but rather follow highly curved trajectories. These movements are particularly interesting to study since they are essential in our everyday life, appear early in development and are routinely used to assess movement deficits following brain lesions. We argue that curved and straight-line reaching movements are generated by a unique neural controller and that the observed curvature of the movement is the result of an active control strategy that follows the geometry of one’s body, for instance to avoid trajectories that would hit the body or yield postures close to the joint limits. We present a mathematical model that accounts for such an active control strategy and show that the model reproduces with high accuracy the kinematic features of human data during unconstrained reaching movements directed toward the head. The model consists of a nonlinear dynamical system with a single stable attractor at the target. Embodiment-related task constraints are expressed as a force field that acts on the dynamical system. Finally, we discuss the biological plausibility and neural correlates of the model’s parameters and suggest that embodiment should be considered as a main cause for movement trajectory curvature.     

Genetic relationship of catalepsy to penduliform movements and audiogenic epilepsy in rats

Within outbred Wistar stock, the pendulum movements are found to be inherited in what may be considered as a dominant mono- or oligogenic mode of inheritance with incomplete penetrance. This indicates that the albinism only permits the manifestation of the pendulum movements, which are also controlled by some other gene or genes. The pendulum movements show a positive genetic relation to catalepsy, although this relation is not strong: the proportion of animals with pendulum movements is 23% in the control population and 32% in F12-F16 bred for catalepsy (p less than 0.05). Within the latter, the proportion of animals with pendulum movements was 43% in the progeny of parents with phenotypically expressed catalepsy, and 29% in the progeny of phenotypically "normal" animals (p less than 0.01). The frequency of audiogenic seizures was 32% in the control population and 17% in F8-F16 bred for catalepsy (p less than 0.001). A genetic model is proposed to account for the paradoxical situation, where pendulum movements have a positive genetic relation both to catalepsy and audiogenic epilepsy, the catalepsy being at the same time negatively related to epilepsy.     

Optimal compensation for temporal uncertainty in movement planning

Motor control requires the generation of a precise temporal sequence of control signals sent to the skeletal musculature. We describe an experiment that, for good performance, requires human subjects to plan movements taking into account uncertainty in their movement duration and the increase in that uncertainty with increasing movement duration. We do this by rewarding movements performed within a specified time window, and penalizing slower movements in some conditions and faster movements in others. Our results indicate that subjects compensated for their natural duration-dependent temporal uncertainty as well as an overall increase in temporal uncertainty that was imposed experimentally. Their compensation for temporal uncertainty, both the natural duration-dependent and imposed overall components, was nearly optimal in the sense of maximizing expected gain in the task. The motor system is able to model its temporal uncertainty and compensate for that uncertainty so as to optimize the consequences of movement.     

A model of control of the movement of the multiarticular extremity

A model for coordinated execution of multijoint goal-directed limb movements is suggested from the following principles. (1) Central control signals for a single limb joint are individually formed, proceeding from its ability to bring the limb nearer to the target and leaving control signals directed simultaneously to other joint out of account. The joints thereby behave as a set of Tsetlin's abstract automata [11], each functioning independently and guided by a common, collective effect. (2) Neither levels of muscle activation, nor force and kinematic variables are directly specified by the command signals. They only modify the system's parameters that affect equilibrium joint positions, and thus make the limb to move to the goal. A concrete model based on the above principles is described and its behavior is compared with actual goal-directed movements in man and spinal frogs. Various control strategies for multiarticular movements in living organisms are discussed.     

An interference effect of observed biological movement on action

It has been proposed that actions are intrinsically linked to perception and that imagining, observing, preparing, or in any way representing an action excites the motor programs used to execute that same action. There is neurophysiological evidence that certain brain regions involved in executing actions are activated by the mere observation of action (the so-called "mirror system;" ). However, it is unknown whether this mirror system causes interference between observed and simultaneously executed movements. In this study we test the hypothesis that, because of the overlap between action observation and execution, observed actions should interfere with incongruous executed actions. Subjects made arm movements while observing either a robot or another human making the same or qualitatively different arm movements. Variance in the executed movement was measured as an index of interference to the movement. The results demonstrate that observing another human making incongruent movements has a significant interference effect on executed movements. However, we found no evidence that this interference effect occurred when subjects observed a robotic arm making incongruent movements. These results suggest that the simultaneous activation of the overlapping neural networks that process movement observation and execution infers a measurable cost to motor control.     

Optimal control of antagonistic muscle stiffness during voluntary movements

This paper presents a study on the control of antagonist muscle stiffness during single-joint arm movements by optimal control theory with a minimal effort criterion. A hierarchical model is developed based on the physiology of the neuromuscular control system and the equilibrium point hypothesis. For point-to-point movements, the model provides predictions on (1) movement trajectory, (2) equilibrium trajectory, (3) muscle control inputs, and (4) antagonist muscle stiffness, as well as other variables. We compared these model predictions to the behavior observed in normal human subjects. The optimal movements capture the major invariant characteristics of voluntary movements, such as a sigmoidal movement trajectory with a bell-shaped velocity profile, an N-shaped equilibrium trajectory, a triphasic burst pattern of muscle control inputs, and a dynamically modulated joint stiffness. The joint stiffness is found to increase in the middle of the movement as a consequence of the triphasic muscle activities. We have also investigated the effects of changes in model parameters on movement control. We found that the movement kinematics and muscle control inputs are strongly influenced by the upper bound of the descending excitation signal that activates motoneuron pools in the spinal cord. Furthermore, a class of movements with scaled velocity profiles can be achieved by tuning the amplitude and duration of this excitation signal. These model predictions agree with a wide body of experimental data obtained from normal human subjects. The results suggest that the control of fast arm movements involves explicit planning for both the equilibrium trajectory and joint stiffness, and that the minimal effort criterion best characterizes the objective of movement planning and control.     

无眼动条件下中文阅读的研究

设计了计算机控制的中文阅读材料的不同显示方式,并对各种阅读过程中的徙动波形进行记录和分析。实验结果表明,无眼动的阅读速度较正常有眼动高,分别为853字/分和640字/分。通过固定窗口显示方式和知动窗口显示方式条件下中文阅读的比较,排除了强迫阅读的因素,说明有无眼动是产生阅读速度差异的主要原因;根据以上实验结果,可得出结论,在有眼动的情况下,除了saccade抑制影响阅读和识别外,主要的因素在于高级中枢对位置信号的处理,眼动的驱动控制及运动过程影响了高级中枢对阅读内容和识别内容的解码速率。无眼动阅读的速度主要受到高级中枢解码速率和记忆的影响,而不是周边视觉系统的限制。实验结果还表明,在无眼动的情况下,周边信息对阅读不仅不起帮助作用,反而起到干扰作用。     

Form and function in lacertilian knee and mesotarsal joints; a contribution to the analysis of sprawling locomotion

The structure and function of the knee and mesotarsal (ankle) joints in lizards with normally developed limbs is described. It is shown that the knee joint is strictly of the hinge type, but is asymmetrical, resulting in a mesial inflexion of the long axis of the crus relative to that of the femur. The mesotarsal joint is a complex screw joint which permits conjunct rotatory movements of the crus on the pes, as well as flexion-extension. These movements are mediated by interlocking control surfaces on either side of the joint, and are an external expression of the geometry of these surfaces. The morphology of these joints, and the movements they permit are evaluated with reference to the movements of the limb segments during retraction.     

Detection of isoenergetic discreteness in various rhythmic movements

It has been found that phasic trajectories were composed of some few elliptical segments during rhythmic movements of human forearm at the elbow. The control program of the movement was shown to be realised as piece constant functions of two control parameters depending on boundary conditions in junctions of the elliptical segments. The control process at the interval between junctions is characterized by an energetic functional being invariant in respect to the trajectories of movements.     

Electrical activity of the lateral hypothalamus related to food-procuring movements of rats

On freely moving albino rats we demonstrated that, when fast food-procuring movements are performed, the mass electrical activity of the lateral hypothalamus (LH) is suppressed 1.6–2.0 sec before the movement beginning recorded with a photoelectrical device. Videorecording of the movements and recording of the spike activity of LH units showed that the latter are activated 1.0–0.1 sec before the movement initiation. The LH is considered a motivation-related structure, which serves as a source providing an increase in the excitability of the structures involved in the control of food-procuring movements and, further on, supporting this increased excitability. The LH is also a component of the mechanisms providing formation of the motor program. The role of the LH in the ensemble of motor centers, which organize and control voluntary movements, is discussed.     

Role of the lateral hypothalamus and prefrontal cortex in organization of voluntary movements

Roles of the lateral hypothalamus and prefrontal cortex in organization and control of automatized food-procuring movements were studied in rats under conditions of unrestrained behavior with the use of video- and photorecording techniques, destruction of the brain structures, and recording of single neuron impulse responses. The lateral hypothalamus is considered a link in the control system for food-procuring movements, which provides formation of the motor program. The role of the prefrontal cortex is regarded as related to programing and initiation of food-procuring movements and current control of efficiency of their performance. Positions of the lateral hypothalamus and prefrontal cortex within an ensemble of the motor centers, which organizes voluntary movements, are discussed.     

Neural basis of learning new movements: evolution of classical concepts

According to classical consepts, the role of the motor cortex in performance of skilled movements of distal parts of extremities is confined to control of appropriate motoneurons by the "point-to-point" principle. However, much evidence of plasticity of the motor cortex and its active role in motor learning appeared in last decade. Fos-gene expression in the motor cortex was found to accompany learning a skill. Strengthening of horizontal pathways in layers II-III was revealed, and cholinergic input to tese layers was found to be important. The imaging data show that activity of the motor cortex increases during motor practice as well. This raises the question of specificity of the motor cortex in the motor learning per se. During acquisition of new movements some previously used synergies prevent the necessary coordination from being learned, so they must be suppressed in the process of motor learning. Investigations of central mechanisms of coordination interference in humans are still at the beginning. However, there are some animal models of reorganization and suppression of interfering synergies. The reorganization and suppression of coordination preventing realization of a new movement is shown to be a specific function of the motor cortex. After automation of new synergies the cortical control is still present, as distinct from the learned movements, which do not require suppression of interfering synergies. However, it does not mean that the conscious control of the performance is still present.     

Examination of the λ equilibrium point hypothesis when applied to single degree of freedom movements performed with different inertial loads

 One of the theories of human motor control is the λ Equilibrium Point Hypothesis. It is an attractive theory since it offers an easy control scheme where the planned trajectory shifts monotionically from an initial to a final equilibrium state. The feasibility of this model was tested by reconstructing the virtual trajectory and the stiffness profiles for movements performed with different inertial loads and examining them. Three types of movements were tested: passive movements, targeted movements, and repetitive movements. Each of the movements was performed with five different inertial loads. Plausible virtual trajectories and stiffness profiles were reconstructed based on the λ Equilibrium Point Hypothesis for the three different types of movements performed with different inertial loads. However, the simple control strategy supported by the model, where the planned trajectory shifts monotonically from an initial to a final equilibrium state, could not be supported for targeted movements performed with added inertial load. To test the feasibility of the model further we must examine the probability that the human motor control system would choose a trajectory more complicated than the actual trajectory to control. Received: 20 June 1995 / Accepted in revised form: 6 August 1996