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The motor system relies on the recruitment of motor modules to perform various movements. Muscle synergies are the modules used by the central nervous system to simplify the control of complex motor tasks. In this paper, we aim to explore the primitive synergies to reflect different modes of coordination in upper limb motions. Muscle synergies and corresponding activation coefficients were extracted via non-negative matrix factorization from the electromyography signals of three basic and four complex upper limb motions in sagittal plane and coronal plane. Similarities of muscle synergies and activation coefficients between different tasks and different subjects were compared. Moreover, we used network theory to assess the coordination between multiple muscles and to elucidate the neural implementation of muscle synergies. The results showed that the combination of different sets of primitive muscle synergies can achieve complex motions in different planes. The muscle synergy network topology differed significantly between different tasks. We also demonstrated the potential of this study for the understanding of human motor control mechanism and implications for neurorehabilitation. [ABSTRACT FROM AUTHOR]

A motor action often involves the coordination of several motor synergies and requires flexible adjustment of the ongoing execution based on feedback signals. To elucidate the neural mechanisms underlying the construction and selection of motor synergies, we study prey-capture in anurans. Experimental data demonstrate the intricate interaction between different motor synergies, including the interplay of their afferent feedback signals (Weerasuriya 1991; Anderson and Nishikawa 1996). Such data provide insights for the general issues concerning two-way information flow between sensory centers, motor circuits and periphery in motor coordination. We show how different afferent feedback signals about the status of the different components of the motor apparatus play a critical role in motor control as well as in learning. This paper, along with its companion paper, extend the model by Liaw et al. (1994) by integrating a number of different motor pattern generators, different types of afferent feedback, as well as the corresponding control structure within an adaptive framework we call Schema-Based Learning. We develop a model of the different MPGs involved in prey-catching as a vehicle to investigate the following questions: What are the characteristic features of the activity of a single muscle? How can these features be controlled by the premotor circuit? What are the strategies employed to generate and synchronize motor synergies? What is the role of afferent feedback in shaping the activity of a MPG? How can several MPGs share the same underlying circuitry and yet give rise to different motor patterns under different input conditions? In the companion paper we also extend the model by incorporating learning components that give rise to more flexible, adaptable and robust behaviors. To show these aspects we incorporate studies on experiments on lesions and the learning processes that allow the animal to recover its proper functioning [ABSTRACT FROM AUTHOR]

The remarkable capacity of the speech motor system to adapt to various speech conditions is due to an excess of degrees of freedom, which enables producing similar acoustical properties with different sets of control strategies. To explain how the central nervous system selects one of the possible strategies, a common approach, in line with optimal motor control theories, is to model speech motor planning as the solution of an optimality problem based on cost functions. Despite the success of this approach, one of its drawbacks is the intrinsic contradiction between the concept of optimality and the observed experimental intra-speaker token-to-token variability. The present paper proposes an alternative approach by formulating feedforward optimal control in a probabilistic Bayesian modeling framework. This is illustrated by controlling a biomechanical model of the vocal tract for speech production and by comparing it with an existing optimal control model (GEPPETO). The essential elements of this optimal control model are presented first. From them the Bayesian model is constructed in a progressive way. Performance of the Bayesian model is evaluated based on computer simulations and compared to the optimal control model. This approach is shown to be appropriate for solving the speech planning problem while accounting for variability in a principled way. [ABSTRACT FROM AUTHOR]

In the companion paper utilizing a quantitative model of optimal motor coordination (Part I, Rand and Shimansky, in Exp Brain Res 225:55-73, ), we examined coordination between X and Y movement directions (XYC) during reaching movements performed under three prescribed speeds, two movement amplitudes, and two target sizes. The obtained results indicated that the central nervous system (CNS) utilizes a two-phase strategy, where the initial and the final phases correspond to lower and higher precision of information processing, respectively, for controlling goal-directed reach-type movements to optimize the total cost of task performance including the cost of neural computations. The present study investigates how two different well-known concepts used for describing movement performance relate to the concepts of optimal XYC and two-phase control strategy. First, it is examined to what extent XYC is equivalent to movement trajectory straightness. The data analysis results show that the variability, the movement trajectory's deviation from the straight line, increases with an increase in prescribed movement speed. In contrast, the dependence of XYC strength on movement speed is opposite (in total agreement with an assumption of task performance optimality), suggesting that XYC is a feature of much higher level of generality than trajectory straightness. Second, it is tested how well the ballistic and the corrective components described in the traditional concept of two-component model of movement performance match with the initial and the final phase of the two-phase control strategy, respectively. In fast reaching movements, the percentage of trials with secondary corrective submovement was smaller under larger-target shorter-distance conditions. In slower reaching movements, meaningful parsing was impossible due to massive fluctuations in the kinematic profile throughout the movement. Thus, the parsing points determined by the conventional submovement analysis did not consistently reflect separation between the ballistic and error-corrective components. In contrast to the traditional concept of two-component movement performance, the concept of two-phase control strategy is applicable to a wide variety of experimental conditions. [ABSTRACT FROM AUTHOR]

A quantitative model of optimal transport-aperture coordination (TAC) during reach-to-grasp movements has been developed in our previous studies. The utilization of that model for data analysis allowed, for the first time, to examine the phase dependence of the precision demand specified by the CNS for neurocomputational information processing during an ongoing movement. It was shown that the CNS utilizes a two-phase strategy for movement control. That strategy consists of reducing the precision demand for neural computations during the initial phase, which decreases the cost of information processing at the expense of lower extent of control optimality. To successfully grasp the target object, the CNS increases precision demand during the final phase, resulting in higher extent of control optimality. In the present study, we generalized the model of optimal TAC to a model of optimal coordination between X and Y components of point-to-point planar movements (XYC). We investigated whether the CNS uses the two-phase control strategy for controlling those movements, and how the strategy parameters depend on the prescribed movement speed, movement amplitude and the size of the target area. The results indeed revealed a substantial similarity between the CNS's regulation of TAC and XYC. First, the variability of XYC within individual trials was minimal, meaning that execution noise during the movement was insignificant. Second, the inter-trial variability of XYC was considerable during the majority of the movement time, meaning that the precision demand for information processing was lowered, which is characteristic for the initial phase. That variability significantly decreased, indicating higher extent of control optimality, during the shorter final movement phase. The final phase was the longest (shortest) under the most (least) challenging combination of speed and accuracy requirements, fully consistent with the concept of the two-phase control strategy. This paper further discussed the relationship between motor variability and XYC variability. [ABSTRACT FROM AUTHOR]

Type 1 Diabetes Mellitus is one of the most common illnesses found in children under the age of 18 as well as in young adults. Symptoms of this disease, including those with and without severe hypoglycemia, create abnormal blood glucose levels along with abnormal insulin levels. These abnormal chemical levels have been associated with neurocognitive deficits in memory, attention, motor skills, visuospatial abilities and executive functioning. In this paper, available literature on the central nervous system changes associated with the effects of insulin-dependent diabetes on school-aged children and young adults is reviewed. Implications for learning as well as a neurobiological cause of executive function deficits are discussed. [ABSTRACT FROM AUTHOR]

Customizing the parameter values of brain interface (BI) systems by a human expert has the advantage of being fast and computationally efficient. However, as the number of users and EEG channels grows, this process becomes increasingly time consuming and exhausting. Manual customization also introduces inaccuracies in the estimation of the parameter values. In this paper, the performance of a self-paced BI system whose design parameter values were automatically user customized using a genetic algorithm (GA) is studied. The GA automatically estimates the shapes of movement-related potentials (MRPs), whose features are then extracted to drive the BI. Offline analysis of the data of eight subjects revealed that automatic user customization improved the true positive (TP) rate of the system by an average of 6.68% over that whose customization was carried out by a human expert, i.e., by visually inspecting the MRP templates. On average, the best improvement in the TP rate (an average of 9.82%) was achieved for four individuals with spinal cord injury. In this case, the visual estimation of the parameter values of the MRP templates was very difficult because of the highly noisy nature of the EEG signals. For four able-bodied subjects, for which the MRP templates were less noisy, the automatic user customization led to an average improvement of 3.58% in the TP rate. The results also show that the inter-subject variability of the TP rate is also reduced compared to the case when user customization is carried out by a human expert. These findings provide some primary evidence that automatic user customization leads to beneficial results in the design of a self-paced BI for individuals with spinal cord injury. [ABSTRACT FROM AUTHOR]

Recent experiments on frogs and rats, have led to the hypothesis that sensory-motor systems are organized into a finite number of linearly combinable modules; each module generates a motor command that drives the system to a predefined equilibrium. Surprisingly, in spite of the infiniteness of different movements that can be realized, there seems to be only a handful of these modules. The structure can be thought of as a vocabulary of "elementary control actions". Admissible controls, which in principle belong to an infinite dimensional space, are reduced to the linear vector space spanned by these elementary controls. In the present paper we address some theoretical questions that arise naturally once a similar structure is applied to the control of nonlinear kinematic chains. First of all, we show how to choose the modules so that the system does not loose its capability of generating a "complete" set of movements. Secondly, we realize a "complete" vocabulary with a minimal number of elementary control actions. Subsequently, we show how to modify the control scheme so as to compensate for parametric changes in the system to be controlled. Remarkably, we construct a set of modules with the property of being invariant with respect to the parameters that model the growth of an individual. Robustness against uncertainties is also considered showing how to optimally choose the modules equilibria so as to compensate for errors affecting the system. Finally, the motion primitive paradigm is extended to locomotion and a related formalization of internal (proprioceptive) and external (exteroceptive) variables is given. [ABSTRACT FROM AUTHOR]

The purpose of this study was to explore the ability of the central nervous system (CNS) to organize synergies at two levels of a hypothetical control hierarchy involved in two-hand multi-finger prehension tasks with one or more persons participating in the task together. At the higher level of the hierarchy, the total force and moment of force produced on an object are distributed between the thumb and the virtual finger (an imagined finger with mechanical output equal to the involved fingers of the hand), while at the lower level the virtual finger action is distributed among the four fingers. We tested a hypothesis that the CNS is able to organize synergies at only one level of the hierarchy. The subjects held vertically one of the two handles, a narrow one and a wide one. They used the four fingers of the right hand opposed by the right hand thumb, the left hand thumb, the left hand index finger, the thumb of an experimenter, the index finger of an experimenter, or an inanimate object. Forces and moments of force produced by each digit were recorded. Indices of synergies stabilizing the mechanical output variables at each of the two levels were computed. Contrary to the expectations, force and moment of force stabilizing synergies were found at one or both levels of the hierarchy across all tasks. Unimanual tasks exhibited higher synergy indices compared to all tasks, while intrapersonal synergy indices were higher than those of interpersonal synergies. The results suggest that both feed-forward and feedback mechanisms may be used to create force and moment of force stabilizing synergies. We invoke the notion of chain effects and generalize it for relations among variance components related to stabilization of different mechanical variables. The reference configuration hypothesis offers a fruitful framework for analysis of prehension synergies. [ABSTRACT FROM AUTHOR]

Voltage-gated sodium channel plays a critical role in pain sensation and has been considered as a potential target for the development of analgesic drug. Hainantoxin-III(HNTX-III) is a selective inhibitor of neuronal tetrodotoxin-sensitive voltage-gated sodium channels with similar selectivity for Nav1.7, 1.2 and 1.3 but not for Nav1.4 and Nav1.5 from the venom of the spider O. hainana. The aim of the present study is to investigate the analgesic effect of HNTX-III on inflammatory and neuropathic pain models. In the complete Freund's adjuvant (CFA) model and formalin model of inflammatory pain, HNTX-III produced reversal of hyperalgesia comparable with morphine, and in the spared nerve injury model of pain, HNTX-III inhibited allodynia compared with mexiletine. HNTX-III was also evaluated in a motor coordination assay to assess its propensity for central nervous system side effects, indicating it did not induce impairment of motor coordination. Our findings revealed that HNTX-III significantly alleviated chronic neuropathic pain and acute inflammatory pain and provided a potential template for analgesic drug design in future. [ABSTRACT FROM AUTHOR]

Motor learning is a process that extends beyond training sessions. Specifically, physical practice triggers a series of physiological changes in the CNS that are regrouped under the term 'consolidation' (Stickgold and Walker ). These changes can result in between-session improvement or performance stabilization (Walker ). In a series of three experiments, we tested whether consolidation also occurs following observation. In Experiment 1, participants observed an expert model perform a sequence of arm movements. Although we found evidence of observation learning, no significant difference was revealed between participants asked to reproduce the observed sequence either 5 min or 24 h later (no between-session improvement). In Experiment 2, two groups of participants observed an expert model perform two distinct movement sequences (A and B) either 10 min or 8 h apart; participants then physically performed both sequences after a 24-h break. Participants in the 8-h group performed Sequence B less accurately compared to participants in the 5-min group, suggesting that the memory representation of the first sequence had been stabilized and that it interfered with the learning of the second sequence. Finally, in Experiment 3, the initial observation phase was replaced by a physical practice phase. In contrast with the results of Experiment 2, participants in the 8-h group performed Sequence B significantly more accurately compared to participants in the 5-min group. Together, our results suggest that the memory representation of a skill learned through observation undergoes consolidation. However, consolidation of an observed motor skill leads to distinct behavioural outcomes in comparison with physical practice. [ABSTRACT FROM AUTHOR]

Proprioceptive sensory signals inform the CNS of the consequences of motor acts, but effective motor planning involves internal neural systems capable of anticipating actual sensory feedback. Just where and how predictive systems exert their influence remains poorly understood. We explored the possibility that spinocerebellar neurons that convey proprioceptive sensory information also integrate information from cortical command systems. Analysis of the circuitry and physiology of identified dorsal spinocerebellar tract neurons in mouse spinal cord revealed distinct populations of Clarke's column neurons that received direct excitatory and/or indirect inhibitory inputs from descending corticospinal axons. The convergence of these descending inhibitory and excitatory inputs to Clarke's column neurons established local spinal circuits with the capacity to mark or modulate incoming proprioceptive input. Together, our genetic, anatomical and physiological results indicate that Clarke's column spinocerebellar neurons nucleate local spinal corollary circuits that are relevant to motor planning and evaluation. [ABSTRACT FROM AUTHOR]

Neural representations of limb movement kinematic parameters are common among central nervous system structures involved in motor control, such as the interpositus nucleus of the cerebellum. Much experimental evidence indicates that neurons in the interpositus may encode limb kinematic parameters both during active, voluntary actions and during limb motion imposed passively, which entrains only sensory afferents. With respect to the sensory processing of information related to movement kinematics, we show that interpositus neuronal activity can parse out the directional from the scalar component (i.e., the movement speed) of the velocity vector. Moreover, a differential role for the anterior and posterior portion of interpositus in encoding these parameters emerged from these data, since the activity of the posterior interpositus was specifically associated to changes of movement speed. Limb movement representations in the interpositus nucleus may be instrumental for the control of goal-directed movements such as shaping hand during grasping or precise foot placement during gait. Finally, we discuss the idea that sensory information about the movement kinematics contribute to both feedback and anticipatory processes for limb movement control. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the contralateral motor overflow in children during single-finger and multi-finger maximum force production tasks. Forty-five right handed children, 5–11 years of age produced maximum isometric pressing force in flexion or extension with single fingers or all four fingers of their right hand. The forces produced by individual fingers of the right and left hands were recorded and analyzed in four-dimensional finger force vector space. The results showed that increases in task (right) hand finger forces were linearly associated with non-task (left) hand finger forces. The ratio of the non-task hand finger force magnitude to the corresponding task hand finger force magnitude, termed motor overflow magnitude (MOM), was greater in extension than flexion. The index finger flexion task showed the smallest MOM values. The similarity between the directions of task hand and non-task hand finger force vectors in four-dimensional finger force vector space, termed motor overflow direction (MOD), was the greatest for index and smallest for little finger tasks. MOM of a four-finger task was greater than the sum of MOMs of single-finger tasks, and this phenomenon was termed motor overflow surplus. Contrary to previous studies, no single-finger or four-finger tasks showed significant changes of MOM or MOD with the age of children. We conclude that the contralateral motor overflow in children during finger maximum force production tasks is dependent upon the task fingers and the magnitude and direction of task finger forces. [ABSTRACT FROM AUTHOR]

The cerebellum is a key-actor in motor control. Attempting to extract the motor codes underlying the organization of movement and the rules of signal processing applied by the cerebellar modules has been and remains a major goal for many researchers worldwide. There is an impressive body of evidence showing that the cerebellar pathways influence basic aspects of movement control including: anticipation, timing of motor commands, sensorimotor synchronization, sensorimotor associations and tuning of the magnitudes of muscle activities. The cerebellum contains more neurons than any other part of the brain and is considered as an extremely powerful machine for deciphering information. In this issue, we have gathered scientists working on the field of motor control to provide an overview of recent advances in our understanding of the contribution of this remarkable circuitry in the elaboration and shaping of motor commands. [ABSTRACT FROM AUTHOR]

Besides its known importance for motor coordination, the cerebellum plays a major role in associative learning. The form of cerebellum-dependent associative learning, which has been examined in greatest detail, is classical conditioning of eyeblink responses. The much advanced knowledge of anatomical correlates, as well as cellular and molecular mechanisms involved in eyeblink conditioning in animal models are of particular importance because there is general acceptance that findings in humans parallel the animal data. The aim of the present review is to give an update of findings in humans. Emphasis is put on human lesion studies, which take advantage of the advances of high-resolution structural magnetic resonance imaging (MRI). In addition, findings of functional brain imaging in healthy human subjects are reviewed. The former helped to localize areas involved in eyeblink conditioning within the cerebellum, the latter was in particular helpful in delineating extracerebellar neural substrates, which may contribute to eyeblink conditioning. Human lesion studies support the importance of cortical areas of the ipsilateral superior cerebellum both in the acquisition and timing of conditioned eyeblink responses (CR). Furthermore, the ipsilateral cerebellar cortex seems to be also important in extinction of CRs. Cortical areas, which are important for CR acquisition, overlap with areas related to the control of the unconditioned eyeblink response. Likewise, cortical lesions are followed by increased amplitudes of unconditioned eyeblinks. These findings are in good accordance with the animal literature. Knowledge about contributions of the cerebellar nuclei in humans, however, is sparse. Due to methodological limitations both of human lesion and functional MRI studies, at present no clear conclusions can be drawn on the relative contributions of the cerebellar cortex and nuclei. [ABSTRACT FROM AUTHOR]

We studied the coordination of arm and wrist motion in a task requiring fine control of hand orientation. Subjects were instructed to reach and grasp one of two targets positioned in the frontal plane at various orientations. The task was performed under three target conditions: fixed orientation, predictably perturbed orientation, and randomly perturbed orientation. For fixed target orientations, the hand began to rotate to the required orientation from the beginning of the reach. Hand peak supination angles scaled linearly with target orientations. The trajectories of hand/arm joint angles also had a one-to-one relationship with different target orientations. These demonstrate that target orientation is a constraint on the hand/arm final orientation, a control variable to be specified in advance by the central nervous system (CNS). Under perturbation conditions, subjects were still able to complete the task smoothly. In the early trials of the predictable perturbation, the hand rotated first to the original target orientation and then corrected for the final target orientation. Initial corrections occurred about 200 ms after the onset of perturbation. This latency decreased as the subjects adapted to the perturbation, and the hand orientation trajectory shifted to match the unperturbed trajectory for the final orientation. By contrast, we observed no clear changes in orientation trajectory under the randomly perturbed conditions. These suggest that feedback control is important to the execution of the movement, but that the CNS tends to optimize feedforward planning rather than feedback correction when the disturbance information is predictable. [ABSTRACT FROM AUTHOR]

The purpose of the study was to develop a model of force variability for a fast action performed by a multi-effector system and to verify it for multi-finger quick force production. The experiments involved quick isometric contractions to different target force levels using different finger combinations. Force variance calculated over sets of trials for a multi-finger force production task showed non-monotonic single-peak profiles of force variance with a peak at a time between the times of the maxima of the force rate and of the total force. When analyzed in the four-dimensional space of finger forces, the variance peak was mostly expressed in the direction of the force rate, and was absent in the directions orthogonal to it. The non-monotonic time profile of the force variance could be reproduced by a model of force production, which assumes that each finger force profile is based on a template function scaled in duration and magnitude with two parameters assigned prior to each trial with some variability. The model allows decomposition of the force variance into two fractions related to variability in setting the magnitude and duration scaling parameters. The former fraction changes monotonically with time, while the latter shows a transient peak in the middle of the action. The model was able to reproduce experimental variance time profiles across conditions with the total error of under 8%. The results demonstrate, in particular, that fast multi-finger actions may show transient changes in motor variability in certain directions of the finger force space, particularly in the direction of the first force derivative, without any task-specific coordinating action by the controller. These findings require a reconsideration of some of the conclusions drawn in recent studies on the structure of motor variability in redundant multi-effector systems. [ABSTRACT FROM AUTHOR]

In the present study, we investigated the influence of external force manipulations on movements in different directions, while keeping the amplitude invariant. Subjects (n=10) performed a series of cyclical anteroposterior, mediolateral, and oblique line-drawing movements (star drawing task) with their dominant limb in the horizontal plane. To dissociate kinematics from the underlying patterns of muscle activation, spring loading was applied to the forearm of the moving limb. Whereas spring loading of the arm resulted in considerable changes in the overall amount of muscle activation in the elbow and shoulder muscles, invariance was largely maintained at the kinematic level. Subjects produced the required movement directions and amplitudes of the star drawing largely successfully, irrespective of the force bias induced by the spring. These observations demonstrate motor equivalence and strengthen the notion that the spatial representation of drawing movements is encoded in the higher brain regions in a rather abstract form that is dissociated from the concrete muscle activation patterns underlying a particular movement direction. To achieve this goal, the central nervous system shifted between two or more muscle grouping strategies to overcome modulations in the interaction among posture-dependent (joint stiffness), dynamic (inertial), and elastic (spring) torque components in the joints. Spring loading induced general changes in the overall amount of EMG activity, which was largely muscle but not direction specific, presumably to represent the posture-dependent biasing force of the spring. Loading was mainly shown to increase muscle coactivation in the elbow joint. This indicates that the subjects tended to increase stiffness in the elbow to compensate for changes in the spring bias forces in order to minimize trajectory errors. Changes in muscle grouping of the shoulder antagonists were mainly a consequence of movement direction but were also affected partly by loading, presumably reflecting the influence of dynamic force components. Taken together, the results confirmed the hypothesis that changes of movement direction and direction of force in the end-effector generated specific sets of muscle grouping to overcome the dynamic requirements in the joints while keeping the kinematics largely unchanged. This suggests that directional tuning in muscle activity and changes in muscle grouping reflects the formation of appropriate internal models in the CNS that give rise to motor equivalence. [ABSTRACT FROM AUTHOR]

Response priming tasks reveal huge reaction time (RT) costs when invalidly prepared movements have to be reprogrammed after the imperative response signal. Yet, possible brain correlates of motor reprogramming have rarely been examined. The present experiments were designed to ascertain the brain correlates associated with motor reprogramming by combining the recording of event-related brain potentials (ERPs) with a spatiotemporal source-localisation approach. In two experiments either valid or invalid advance information about direction (experiment 1) and about direction and response hand (experiment 2) was provided. RTs showed considerable motor reprogramming costs in invalid trials. In both experiments reprogramming effects were reflected in ERP difference waveforms in terms of a centroparietally distributed negative and a frontal positive deviation. Source localisation of these ERP difference waveforms indicated brain activity in medial higher-order motor regions. Present findings accord with the assumption that the human pre-supplementary motor area plays an important role in motor reprogramming. [ABSTRACT FROM AUTHOR]

The question of whether the final arm posture to be reached is determined in advance during prehension movements remains widely debated. To address this issue, we designed a psychophysical experiment in which human subjects were instructed to reach and grasp, with their right arm, a small sphere presented at various locations. In some trials the sphere remained stationary, while in others (the perturbed trials) it suddenly jumped, at movement onset, to a new unpredictable position. Our data indicate that the final configuration of the upper limb is highly predictable for a given location of the sphere. For movements directed at stationary objects, the variability of the final arm posture was very small in relation to the variability allowed by joint redundancy. For movements directed at "jumping" objects, the initial motor response was quickly amended, allowing an accurate grasp. The final arm posture reached at the end of the perturbed trials was neither different from nor more variable than the final arm posture reached at the end of the corresponding stationary trials (i.e. the trials sharing the same final object location). This latter result is not trivial, considering both joint redundancy and the motor reorganization imposed by the change in sphere location. In contrast to earlier observations, our data cannot be accounted for by biomechanical or functional factors. Indeed, the spherical object used in the present study did not constrain the final arm configuration or the hand trajectory. When considered together, our data support the idea that the final posture to be reached is planned in advance and used as a control variable by the central nervous system. [ABSTRACT FROM AUTHOR]

In this study, a piece of embryonic tissue from the raphe nucleus was transplanted into the spinal cord below the lesion 1 month after transection. Two months later the recovery of hindlimb motor function in rats which had received a transplant of neural tissue (ST rats) was much better than in spinal control animals without the graft (SC rats). Analysis of the electromyographic (EMG) activity showed that the timing of muscle activity during locomotor-like movement of hindlimbs in ST rats was more regular than in SC rats. In SC rats the relationships between EMG burst duration (soleus, tibialis anterior) and step cycle duration were significantly altered. The restoration of hindlimb motor function of ST rats was also reflected in the better interlimb coordination during locomotor-like hindlimb movements. The results of several behavioural tests demonstrated that the responses to stimulation of various receptors, such as tactile or proprioceptive, in ST rats were more complex than in SC rats. Additionally, unlike in SC animals, in ST rats long-lasting spontaneous episodes of air stepping movement of hindlimbs accompanied by a relatively high amplitude of EMG activity were obtained. These results confirm that grafted embryonic raphe nuclei which contain serotoninergic cells are likely to increase the excitability of neuronal circuitry in the injured spinal cord. Moreover, transplantation of embryonic raphe nuclei encourages the recovery of hindlimb motor function in adult rats even when the grafting is carried out several weeks after spinal cord injury. [ABSTRACT FROM AUTHOR]

Abstract. Reaching movement is a Fast movement towards a given target. The main characteristics of such a movement are straight path and a bell-shaped speed profile. In this work a mathematical model for the control of the human arm during ballistic reaching movements is presented. The model of the arm contains a 2 degrees of freedom planar manipulator, and a Hill-type, non-linear mechanical model of six muscles. The arm model is taken from the literature with minor changes. The nervous system is modeled as an adjustable pattern generator that creates the control signals to the muscles. The control signals in this model are rectangular pulses activated at various amplitudes and timings, that are determined according to the given target. These amplitudes and timings are the parameters that should be related to each target and initial conditions in the workspace. The model of the nervous system consists of an artificial neural net that maps any given target to the parameter space of the pattern generator. In order to train this net, the nervous system model includes a sensitivity model that transforms the error from the arm end-point coordinates to the parameter coordinates. The error is assessed only at the termination of the movement from knowledge of the results. The role of the non-linearity in the muscle model and the performance of the learning scheme are analysed, illustrated in simulations and discussed. The results of the present study demonstrate the central nervous system's (CNS) ability to generate typical reaching movements with a simple feed forward controller that controls only the timing and amplitude of rectangular excitation pulses to the muscles and adjusts these parameters based on knowledge of the results. In this... [ABSTRACT FROM AUTHOR]

Over the expanse of evolutionary history, humans, and predecessor Homo species, ran to survive. This legacy is reflected in many deeply and irrevocably embedded neurological and biological design features, features which shape how we run, yet were themselves shaped by running. Smoothness is a widely recognised feature of healthy, proficient movement. Nevertheless, although the term 'smoothness' is commonly used to describe skilled athletic movement within practical sporting contexts, it is rarely specifically defined, is rarely quantified and remains barely explored experimentally. Elsewhere, however, within various health-related and neuro-physiological domains, many manifestations of movement smoothness have been extensively investigated. Within this literature, smoothness is considered a reflection of a healthy central nervous system (CNS) and is implicitly associated with practiced coordinated proficiency; 'non-smooth' movement, in contrast, is considered a consequence of pathological, un-practiced or otherwise inhibited motor control. Despite the ubiquity of running across human cultures, however, and the apparent importance of smoothness as a fundamental feature of healthy movement control, to date, no theoretical framework linking the phenomenon of movement smoothness to running proficiency has been proposed. Such a framework could, however, provide a novel lens through which to contextualise the deep underlying nature of coordinated running control. Here, we consider the relevant evidence and suggest how running smoothness may integrate with other related concepts such as complexity, entropy and variability. Finally, we suggest that these insights may provide new means of coherently conceptualising running coordination, may guide future research directions, and may productively inform practical coaching philosophies. [ABSTRACT FROM AUTHOR]

Evidence has emerged that suggests a link between motor deficits, obesity and many neurological disorders. However, the contributing genetic risk factors are poorly understood. Here we used the Collaborative Cross (CC), a large panel of newly inbred mice that captures 90% of the known variation among laboratory mice, to identify the genetic loci controlling rotarod performance and its relationship with body weight in a cohort of 365 mice across 16 CC strains. Body weight and rotarod performance varied widely across CC strains and were significantly negatively correlated. Genetic linkage analysis identified 14 loci that were associated with body weight. However, 45 loci affected rotarod performance, seven of which were also associated with body weight, suggesting a strong link at the genetic level. Lastly, we show that genes identified in this study overlap significantly with those related to neurological disorders and obesity found in human GWA studies. In conclusion, our results provide a genetic framework for studies of the connection between body weight, the central nervous system and behavior. [ABSTRACT FROM AUTHOR]

The article discusses the research which suggests that achieving such balance is no minor achievement but instead it involves a sophisticated process of sensorimotor coordination. Accordingly, spring-like properties of muscles, local spinal interneuronal reflexes and the systems throughout the central nervous system (CNS) are all combined to produce an appropriate compensation. In the study, cats were first trained to stand on four separate force plates.