Coordination Of Limb Movements Research Articles

Hierarchical generative modelling for autonomous robots

Humans generate intricate whole-body motions by planning, executing and combining individual limb movements. We investigated this fundamental aspect of motor control and approached the problem of autonomous task completion by hierarchical generative modelling with multi-level planning, emulating the deep temporal architecture of human motor control. We explored the temporal depth of nested timescales, where successive levels of a forward or generative model unfold, for example, object delivery requires both global planning and local coordination of limb movements. This separation of temporal scales suggests the advantage of hierarchically organizing the global planning and local control of individual limbs. We validated our proposed formulation extensively through physics simulation. Using a hierarchical generative model, we showcase that an embodied artificial intelligence system, a humanoid robot, can autonomously complete a complex task requiring a holistic use of locomotion, manipulation and grasping: the robot adeptly retrieves and transports a box, opens and walks through a door, kicks a football and exhibits robust performance even in the presence of body damage and ground irregularities. Our findings demonstrated the efficacy and feasibility of human-inspired motor control for an embodied artificial intelligence robot, highlighting the viability of the formulized hierarchical architecture for achieving autonomous completion of challenging goal-directed tasks.

Multimodal spatial-temporal feature representation and its application in action recognition

目的 在人体行为识别研究中，利用多模态方法将深度数据与骨骼数据相融合，可有效提高动作的识别率。针对深度图像信息数据量大、冗余度高等问题，提出一种通过获取关键时程信息动作帧序列降低冗余的算法，即质心运动路径松弛算法，并根据不同模态数据的特点，提出一种新的时空特征表示方法。方法 质心运动路径松弛算法根据质心在相邻帧之间的运动距离，计算图像差分后获得的活跃部分的相似系数，然后剔除掉相似度高的帧，获得足以表达行为的关键时程信息。根据图像动态部分的变化特性、人体各部分在运动中的协同性和局部显著性特征构建一种新的时空特征表示方法。结果 在MSR-Action3D数据集上对本文方法的效果进行验证。在3个子集中进行交叉验证的平均分类识别率为95.743 2%，分别比Multi-fused，CovP3DJ，D3D-LSTM（densely connected 3DCNN and long short-term memory），Joint Subset Selection方法高2.443 2%，4.763 2%，0.343 2%，0.213 2%。本文方法在使用完整数据集的扩展实验中进行交叉验证的分类识别率为93.040 3%，具有很好的鲁棒性。结论 实验结果表明，本文提出的去冗余算法在降低冗余后提升了识别效果，提取的特征之间具有相关性低的特点，在组合识别中具有良好的互补性，有效提高了分类识别的精确度。;Objective Human body motion-related recognition has been developing in the context of computer vision and pattern recognition like auxiliary human-computer interaction，motion analysis，intelligent monitoring，and virtual reality. To obtain two-dimensional information for its behavioral recognition，conventional motion behavior recognition is mainly used the RGB image sequence captured by RGB camera. To improve the ability to detect short-duration fragments，current feature descriptors for RGB image sequences are employed to characterize human behavior，such as histogram of oriented gradient（HOG），histogram of optical flow （HOF），and a three-dimensional feature pyramid. Some researchers are focused on the feature that image depth is insensitive to ambient light since RGB images are oriented to behavior image sequences of objects in terms of two-dimensional information. The depth information of the image is coordinated with the features of RGB image to describe the related behavior. Human behavior recognition-relevant multi-modal method can be used to fuse depth data and skeleton data，which can improve the recognition rate of action effectively. Recent depth map is widely used in relevant to human behavior recognition. But，the collection of depth information data is required to be optimized because of time complexity of feature extraction and space complexity of feature storage. To resolve the problems，we develop an algorithm to optimize frames of the depth map and resource consumption. At the same time，a new representation of motion features is facilitated as well according to the motion information of the centroid. Method First，the temporal feature vector is used in terms of depth map sequence-extracted time sequence information. The centroid motion path relaxation algorithm is used to realize depth image de-duplication and de redundancy，and the skeleton map-extracted spatial structure feature vector from are spliced to form the spatio-temporal feature input. Next，spatial features are extracted in terms of the original skeleton points coordinates-spliced three-channel spatial feature map. Finally，the fusion probability of spatio-temporal features and spatial features is used for classification and recognition. Our centroid motion path relaxation algorithm is focused on the optimization of redundant information，the time complexity of feature extraction，and the space complexity of feature storage. For the skeleton data，the global feature of motion direction is proposed to fully reflect the integrity and coordination of limb movements. The extracted features are concatenated to obtain the spatio-temporal feature vector，and they can be fused and enhanced through the original coordinates of skeleton points-built three-channel spatial feature map. Its effectiveness is verified on the MSR-Action3D dataset. Result The experimental setting 1 demonstrate that it is 0. 826 0% higher than the depth motion map（DMM）-local binary pattern（LBP）algorithm，1. 015 2% higher than DMM-CRC（collaborative representation classifier），3. 450 1% higher than gradient local auto correlation（DMM-GLAC） algorithm，0. 605 8% higher than EigenJoint algorithm，and 0. 605 8% higher than space-time auto correlation of gradient （STACOG）algorithm is 10. 624 5% higher. After removing redundancy，the result of experimental setting 1 is 0. 126 1% higher as well. The cross-validation on experimental setting 2 show that the average classification and recognition rate in the three subsets is 95. 743 2%，2. 443 2% higher than multi-fused method，4. 763 2% higher than CovP3DJ method，0. 343 2% higher than D3D-LSTM method，and 0. 213 2% higher than joint subset selection method. For the overall data set，it is 2. 030 3% higher than low latency method，0. 240 3% higher than combination of deep models method，and 2. 340 3% higher than complex network coding method. The experimental setting 2 illustrates that the average classification recognition rate of cross-validation in three subsets is 95. 743 2%，and the classification recognition rate of the complete dataset is 93. 040 3%. Conclusion Our algorithm proposed can improve the recognition effect based on redundancy-optimized，and the featuresextracted have lower correlation mutually，which can improve the accuracy of classification recognition effectively.

Integrated analysis of gait parameters and gene expression profiles in a murine model of subarachnoid hemorrhage.

Gait analysis has been widely used to examine the behavioral presentation of numerous neurological disorders. Thorough murine model evaluation of the subarachnoid hemorrhage (SAH)-associated gait deficits is missing. This study measures gait deficits using a clinically relevant murine model of SAH to examine associations between gait variability and SAH-associated gene expressions. A total of 159 dynamic and static gait parameters from the endovascular perforation murine model for simulating clinical human SAH were determined using the CatWalk system. Eighty gait parameters and the mRNA expression levels of 35 of the 88 SAH-associated genes were differentially regulated in the diseased models. Totals of 42 and 38 gait parameters correlated with the 35 SAH-associated genes positively and negatively with Pearson's correlation coefficients of >0.7 and <-0.7, respectively. p-SP1453 expression in the motor cortex in SAH animal models displays a significant correlation with a subset of gait parameters associated with muscular strength and coordination of limb movements. Our data highlights a strong correlation between gait variability and SAH-associated gene expression. p-SP1453 expression could act as a biomarker to monitor SAH pathological development and a therapeutic target for SAH.

Abstract P796: Integrated Analysis of Gait Parameters and Gene Expression Profiles in a Murine Model of Subarachnoid Hemorrhage

Objective: Gait variability analysis has been adopted in clinical settings to characterize the presentation of various neurological diseases. However, literature and practice lack a comprehensive murine model assessment of the gait deficits that result from subarachnoid hemorrhage (SAH). Further, correlations between gait parameters and the gene expression profiles associated with SAH have yet to be identified. The present study quantitatively assesses gait deficits through a clinically relevant murine model of SAH to determine associations between gait deficits and SAH-related gene expressions. Methods: A total of 159 dynamic and static gait parameters from the endovascular perforation murine model for simulating clinical human SAH were measured using the CatWalk system. Pearson’s correlation analysis was applied, and 88 genes associated with SAH were identified from the Ingenuity Pathway Analysis database to aid the investigation of the relationship between gait variability and gene expression profiles. Results: Eighty gait parameters and the mRNA expression levels of 35 of the 88 SAH-associated genes exhibited significant change in the SAH models (p &lt; 0.05). Totals of 42 and 38 gait parameters correlated with the 35 SAH-associated genes positively and negatively with Pearson’s correlation coefficients of &gt; 0.7 and &lt; -0.7, respectively. p-SP1 453 expression in the motor cortex in SAH animal models displays a significant correlation with a subset of gait parameters associated with muscular strength and coordination of limb movements. Conclusion: This examination of gait variability and its strong correlation to gene expression profiles provides a quantitative and reliable assessment of the SAH model’s motor performance. This research provides valuable insights into the study of disease progression and offers novel therapeutic interventions in the murine modeling of SAH. p-SP1 453 expression could act as a biomarker to monitor SAH pathological development and a therapeutic target for SAH.

Innovative Long-Dose Neurorehabilitation for Balance and Mobility in Chronic Stroke: A Preliminary Case Series.

(1) Objective: The objective was two-fold: (a) test a protocol of combined interventions; (b) administer this combined protocol within the framework of a six-month, intensive, long-duration program. The array of interventions was designed to target the treatment-resistant impairments underlying persistent mobility dysfunction: weakness, balance deficit, limb movement dyscoordination, and gait dyscoordination. (2) Methods: A convenience sample of eight chronic stroke survivors (>4 months post stroke) was enrolled. Treatment was 5 days/week, 1–2.5 h/day for 6 months, as follows: strengthening exercise, balance training, limb/gait coordination training, and aerobic exercise. Outcome measures: Berg Balance Scale (BBS), Fugl-Meyer Lower Limb Coordination (FM), gait speed, 6 Minute Walk Test (6MWT), Timed up and Go (TUG), Functional Independence Measure (FIM), Craig Handicap Assessment Rating Tool (CHART), and personal milestones. Pre-/post-treatment comparisons were conducted using the Permutation Test, suitable for ordinal measures and small sample size. (3) Results: For the group, there was a statistically (p ≤ 0.04) significant improvement in balance, limb movement coordination (FM), gait speed, functional mobility (TUG), and functional activities (FIM). There were measurable differences (minimum detectible change: MDC) in BBS, FM, gait speed, 6MWT, and TUG. There were clinically significant milestones achieved for selected subjects according to clinical benchmarks for the BBS, 6MWT, gait speed, and TUG, as well as achievement of personal milestones of life role participation. Effect sizes (Cohen’s D) ranged from 0.5 to 1.0 (with the exception of the (6MWT)). After six months of treatment, the above array of gains were beyond that reported by other published studies of chronic stroke survivor interventions. Personal milestones included: walking to mailbox, gardening/yardwork, walking a distance to neighbors, return to driving, membership at a fitness center, vacation trip to the beach, swimming at local pool, returning to work, housework, cooking meals. (4) Conclusions: Stroke survivors with mobility dysfunction were able to participate in the long-duration, intensive program, with the intervention array targeted to address impairments underlying mobility dysfunction. There were either clinically or statistically significant improvements in an array of measures of impairment, functional mobility, and personal milestone achievements.

Small-Sized Reconfigurable Quadruped Robot With Multiple Sensory Feedback for Studying Adaptive and Versatile Behaviors.

Self-organization of locomotion characterizes the feature of automatically spontaneous gait generation without preprogrammed limb movement coordination. To study this feature in quadruped locomotion, we propose here a new open-source, small-sized reconfigurable quadruped robot, called Lilibot, with multiple sensory feedback and its physical simulation. Lilibot was designed as a friendly quadrupedal platform with unique characteristics, including light weight, easy handling, modular components, and multiple real-time sensory feedback. Its modular components can be flexibly reconfigured to obtain features, such as different leg orientations for testing the effectiveness and generalization of self-organized locomotion control. Its multiple sensory feedback (i.e., joint angles, joint velocities, joint currents, joint voltages, and body inclination) can support vestibular reflexes and compliant control mechanisms for body posture stabilization and compliant behavior, respectively. To evaluate the performance of Lilibot, we implemented our developed adaptive neural controller on it. The experimental results demonstrated that Lilibot can autonomously and rapidly exhibit adaptive and versatile behaviors, including spontaneous self-organized locomotion (i.e., adaptive locomotion) under different leg orientations, body posture stabilization on a tiltable plane, and leg compliance for unexpected external load compensation. To this end, we successfully developed an open-source, friendly, small-sized, and lightweight quadruped robot with reconfigurable legs and multiple sensory feedback that can serve as a generic quadrupedal platform for research and education in the fields of locomotion, vestibular reflex-based, and compliant control.

Study on preventive and therapeutic effects of Erzhi Pills on mice with Parkinson's disease induced by MPTP

The aim of this study was to investigate the preventive and therapeutic effects of Erzhi Pills on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine( MPTP)-induced Parkinson's disease( PD) in mice,and explore its possible mechanism of action. Mice were intraperitoneally injected with MPTP( 30 mg·kg-1,0. 01 m L·g-1) once daily to induce PD for 8 days. In the treatment group,Erzhi Pills were given by intragastric administration( 2. 5 g·kg-1,once daily for 30 days). The normal group received an equal volume of normalsaline. In terms of behavior,the limb movement coordination ability of the mice was detected by climbing,hanging and swimming experiments. The spatial learning and memory ability of the mice was detected by Morris water maze test. The content of MDA,as well as the activity of GSH-PX and SOD were determined in mice serum. Western blot was used to detect the protein expression levels of TH,MAOB and apoptosis-related factors CHOP and caspase-12 in brain tissues. Immunohistochemistry was used to detect the expression of TH in section of brain tissues in mice. The results showed that in behavioral aspects,as compared with the model group,the scores of limb movement ability as well as scores of spatial learning and memory ability were significantly improved in the treatment groups( P<0. 05). In terms of serological indicators,as compared with the model group,the activities of SOD and GSH-PX were significantly increased in the serum of treatment groups,and the content of MDA was significantly decreased( P<0. 05). The results of Western blot showed that as compared with the model group,the protein levels of TH in the brain tissues of the mice in treatment group were significantly up-regulated,while the protein levels of MAOB and apoptosis-related factors CHOP and caspase-12 were significantly down-regulated( P<0. 05). The results of immunohistochemistry showed that the number of TH positive cells in the brain tissues of the mice in the treatment group was significantly increased as compared with the model group( P<0. 05). In summary,Erzhi Pills have a certain preventive and therapeutic effect on MPTP-induced PD mice,which can significantly improve the limb motor coordination ability and spatial learning and memory ability of PD mice. Its mechanism may be related to down-regulating the expression of apoptosis-related factors CHOP and caspase-12,reducing the dopaminergic neuron damage and inhibiting dopaminergic neuronal apoptosis.

Improvement of cerebellar ataxic gait by injecting Cbln1 into the cerebellum of cbln1-null mice

Patients and rodents with cerebellar damage display ataxic gaits characterized by impaired coordination of limb movements. Here, gait ataxia in mice with a null mutation of the gene for the cerebellin 1 precursor protein (cbln1-null mice) was investigated by kinematic analysis of hindlimb movements during locomotion. The Cbln1 protein is predominately produced and secreted from cerebellar granule cells. The cerebellum of cbln1-null mice is characterized by an 80% reduction in the number of parallel fiber-Purkinje cell synapses compared with wild-type mice. Our analyses identified prominent differences in the temporal parameters of locomotion between cbln1-null and wild-type mice. The cbln1-null mice displayed abnormal hindlimb movements that were characterized by excessive toe elevation during the swing phase, and by severe hyperflexion of the ankles and knees. When recombinant Cbln1 protein was injected into the cerebellum of cbln1-null mice, the step cycle and stance phase durations increased toward those of wild-type mice, and the angular excursions of the knee during a cycle period showed a much closer agreement with those of wild-type mice. These findings suggest that dysfunction of the parallel fiber-Purkinje cell synapses might underlie the impairment of hindlimb movements during locomotion in cbln1-null mice.

Gait ataxia in humans: vestibular and cerebellar control of dynamic stability.

During human locomotion, vestibular feedback control is fundamental for maintaining dynamic stability and adapting the gait pattern to external circumstances. Within the supraspinal locomotor network, the cerebellum represents the key site for the integration of vestibular feedback information. The cerebellum is further important for the fine-tuning and coordination of limb movements during walking. The aim of this review article is to highlight the shared structural and functional sensorimotor principles in vestibular and cerebellar locomotion control. Vestibular feedback for the maintenance of dynamic stability is integrated into the locomotor pattern via midline, caudal cerebellar structures (vermis, flocculonodular lobe). Hemispheric regions of the cerebellum facilitate feed-forward control of multi-joint coordination and higher locomotor functions. Characteristic features of the gait disorder in patients with vestibular deficits or cerebellar ataxia are increased levels of spatiotemporal gait variability in the fore-aft and the medio-lateral gait dimension. In the fore-aft dimension, pathologic increases of gait fluctuations critically depend on the locomotion speed and predominantly manifest during slow walking velocities. This feature is associated with an increased risk of falls in both patients with vestibular hypofunction as well as patients with cerebellar ataxia. Pharmacological approaches for the treatment of vestibular or cerebellar gait ataxia are currently not available. However, new promising options are currently tested in randomized, controlled trials (fampridine/FACEG; acetyl-DL-leucine/ALCAT).

Walking while Performing Working Memory Tasks Changes the Prefrontal Cortex Hemodynamic Activations and Gait Kinematics.

Background: Increasing evidence suggests that walking while performing a concurrent task negatively influences gait performance. However, it remains unclear how higher-level cognitive processes and coordination of limb movements are altered in challenging walking environments. This study investigated the influence of cognitive task complexity and walking road condition on the neutral correlates of executive function and postural control in dual-task walking.Methods: Twenty-four healthy young adults completed a series of overground walks with three walking road conditions (wide, narrow, with obstacles) with and without the concurrent n-back working memory tasks of two complexity levels (1-back and 3-back). Prefrontal brain activation was assessed by functional near-infrared spectroscopy. A three-dimensional motion analysis system was used simultaneously to measure gait performance and lower-extremity kinematics. Repeated measures analysis of variance were performed to examine the differences between the conditions.Results: In comparison with standing still, participants showed lower n-back task accuracy while walking, with the worst performance from the road with obstacles. Spatiotemporal gait parameters, lower-extremity joint movements, and the relative changes in oxygenated hemoglobin (HbO) concentration levels were all significantly different across the task complexity and walking path conditions. While dual-tasking participants were found to flex their hips and knees less, leading to a slower gait speed, longer stride time, shorter step length, and greater gait variability than during normal walking. For narrow-road walking, smaller ankle dorsiflexion and larger hip flexion were observed, along with a reduced gait speed. Obstacle negotiation was mainly characterized by increased gait variability than other conditions. HbO levels appeared to be lower during dual-task walking than normal walking. Compared to wide and obstacle conditions, walking on the narrow road was found to elicit a smaller decrement in HbO levels.Conclusion: The current study provided direct evidence that, in young adults, neural correlates of executive function and dynamic postural control tend to be altered in response to the cognitive load imposed by the walking environment and the concurrent task during ambulation. A shift of brain activation patterns between functionally connected networks may occur when facing challenging cognitive–motor interaction.

The contribution of postural control and bilateral coordination to the impact of dual tasking on gait

The simultaneous performance of a cognitive task while walking typically alters the gait pattern. In some populations, these alterations have been associated with an increased risk of falls, motivating study of this response from the clinical perspective. The mechanisms responsible for these effects are not fully understood. The concurrent requirement to control upright posture and stepping, a bilaterally coordinated rhythmic task, may be the cause of this so-called dual-tasking effect. To evaluate this possibility, the present study was designed to isolate the individual contribution of these two demands by assessing the effects of cognitive loading on standing (i.e., postural control without bilateral coordination of stepping), cycling (i.e., bilateral coordination similar to stepping, but with minimal postural demands), and walking. We also investigated the effects of aging and parkinsonism on the performance of these three tasks in response to cognitive loading, also referred to as a dual task. Twenty-one healthy young adults, 15 healthy older adults, and 18 patients with Parkinson's disease were assessed while walking, standing, and cycling, with and without an additional cognitive load. In the young adults, the performance on the two motor tasks that involved bilateral coordination deteriorated significantly in response to the dual task, while standing was not impacted. Similar results, although less robust, were observed among the healthy older adults. In contrast, among the patients with Parkinson's disease, the dual-task costs, i.e., the impact of the simultaneously performed cognitive task on the gait pattern, were high in all motor tasks. These findings suggest that walking is especially vulnerable to cognitive loading, in part, because of the unique sensitivity of bilateral coordination of limb movements to the effects of dual tasking.

Effect of haptic feedback from self-touch on limb movement coordination.

Touching one's own body provides haptic feedback about the spatial configuration and movement of body parts. However, the influence of self-touch on movement performance has not been investigated so far. The authors evaluated the contribution of self-touch by asking participants to perform cyclic movement sequences with their feet while touching them with their hands, or vice versa. Hands and feet were either crossed or uncrossed (parallel), manipulating anatomical congruency of haptic feedback. The effects of self-touch (vs. object-touch), active limb (feet vs. hands) and sequence complexity were assessed in three separate experiments. Task performance was strongly and specifically disrupted in one of the anatomically incongruent conditions (hands-parallel/feet-crossed). This disruption occurred only with self-touch (Experiment 1), with the feet active (Experiment 2), and was more pronounced for the more complex movement sequence (Experiment 3). Thus, incongruent self-touch can strongly interfere with motor performance, showing that haptic information is automatically integrated in the online control of movement. The observed asymmetry between hands and feet indicates limb-specific differences regarding the use of spatial frames of reference and/or regarding the weighting of sensory information. The results emphasize the intimate connection between programming of action sequences and the anticipation of somatic feedback from self-touch.

Supplemental Material for Effect of Haptic Feedback From Self-Touch on Limb Movement Coordination

Supplemental Material for Effect of Haptic Feedback From Self-Touch on Limb Movement Coordination

Understanding the mechanisms underlying phase-locking behavior in the crayfish swimmeret system

One of the fundamental challenges in neuroscience is to understand how the intrinsic properties of neurons and the properties of neural networks combine to produce behavior. Networks that produce rhythmic motor behaviors, such as locomotion, provide important model systems to address this problem. A particularly good model for this purpose is the neural circuit underlying the coordinated rhythmic limb movements in the crayfish swimmeret system. During forward swimming, rhythmic movements of swimmerets on different segments of the crayfish abdomen progress from back to front with the same period, but neighboring swimmerets are phase-lagged by 25% of the period. This coordination of limb movements is maintained over a wide range of frequency. The exact mechanisms underlying this robustly stable phase-locking are not known. Here, we use mathematical modeling and analysis in conjunction with recent experimental results to obtained insight into these mechanisms. The rhythmic behavior of each swimmeret is driven by a local pattern generating circuit consisting of a half-center oscillator (HCO). These local pattern generating circuits are connected through well-described intersegmental connections. We model the neural circuitry of the swimmeret system as a chain of HCOs. First, we examine the phase response properties of HCOs for two fundamentally different mechanisms that produce anti-phase activity in HCOs: the “escape” and “release” mechanisms. We demonstrate that the “escape” and “release” mechanisms give rise to very different phase response properties, and we use phase plane arguments to explain the different shapes of the phase response curves. We then examine a chain of four nearest-neighbor coupled HCOs. We use the coupled oscillator theory and symmetry arguments to show that the phase-locking 25% phase-locking observed in the crayfish swimmeret system arises naturally from the network connectivity, but this phase-locking is robustly stable for only some combinations of connectivity and the escape/release mechanisms.

The relationship between visual orienting and interlimb synchrony in a patient with a superior parietal infarction: A case study

Much work indicates that parietal cortex mediates the transformation of visual information into the motor commands necessary for successful performance of many unimanual tasks. Accumulating evidence suggests that parietal cortex also mediates the coordination of bimanual movements, during which the natural tendency is to couple the limbs temporally. However, the extent to which parietal oculomotor and/or visual processes contribute to temporal coupling of the limbs during bimanual task performance is unknown. In the current study, we monitored the eye movements of a patient with a left parietal infarction as she performed a series of bimanual visuomotor tasks. We demonstrate the impact of an ipsilesional (leftward) orientation bias on her ability to synchronize the onset of bimanual limb movements; the movements were performed in serial fashion, i.e., left limb before right, when the patient was permitted to freely shift saccades and the visual target cuing the left (ipsilesional) limb movement was presented at greater (leftward) eccentricities. Disruption of interlimb synchrony as such was not, however, evident when the patient was required to fixate or when visual targets were presented at lesser ipsilesional eccentricities. Additionally, despite the disruptive influence of oculomotor and visual factors on interlimb synchrony, the patient appeared capable of using visual feedback to straighten the right (contralesional) limb trajectory, thus improving the spatial component of task performance. Results suggest that parietal cortex plays an important role in the coordination of limb movements during performance of bimanual visuomotor tasks. This role appears to involve orienting gaze or attention to the goals of each limb so that the nervous system can synchronize the activity of both limbs and thereby ensure successful task completion.

Stability, limb coordination and substrate type: the ecorelevance of gait sequence pattern in primates

The coordination of limb movements during mammalian locomotion has been well documented in the literature. Most mammals use lateral sequence (LS) gaits, in which a forelimb follows an ipsilateral hind limb during the stride cycle. Primates, however, tend to utilize diagonal sequence (DS) gaits, whereby a contralateral forelimb follows a given hind limb during the stride cycle. A number of scenarios have been offered to explain why primates favor DS gaits, most of them relating to the use of the arboreal habitat and, in particular, the exploitation of a terminal branch niche. Yet to date, there is surprisingly little evidence to support the advantage of DS gaits for negotiating different aspects of the terminal branch environment. Nonetheless, it is apparent that primates possess unique morphologies and a higher than typically recognized degree of flexibility in gait sequence pattern, both of which likely offer advantages for moving upon discontinuous and unstable terminal branches. This paper reviews potential explanations for the use of DS gaits in primates and considers mechanisms by which gait sequence may be altered during different types of arboreal challenges.

Modulation of soleus H-reflex during dorsal and plantar flexions in the human ankle joint

Recording of the H-reflex was used to study the changes in the reflex excitability of soleus motoneurons during dorsal and plantar flexions of the ipsilateral and contralateral feet performed with different strengths by 15 healthy subjects. The dorsiflexion of the ipsilateral foot was accompanied by the “classic” reciprocal inhibition of the soleus motoneurons, the degree of the inhibition being directly proportional to the strength of the contraction of pretibial muscles and depending on the presence of foot support. The plantar flexion of the ipsilateral foot was accompanied by changes in reflex excitability, which were inversely proportional to the strength of the flexion. This was apparently related to the activation of a mechanism protecting the muscle against excessive contraction. The dorsal and plantar flexions of the contralateral foot were accompanied by similar changes in the reflex excitability of soleus motoneurons, namely, an increase in the case of weak contraction and a decrease in the case of strong contraction. However, the increase in reflex excitability during contralateral dorsiflexion was smaller and its decrease began at a weaker contraction than in the case of contralateral plantar flexion. The changes in the reflex excitability of soleus motoneurons during movements of the contralateral foot, which were also strength-dependent, confirmed the presence of cross-projections that are likely to be part of the generator of the central pattern of lower limb movement coordination.

Bilateral actions of the reticulospinal tract on arm and shoulder muscles in the monkey: stimulus triggered averaging

The motor output of the pontomedullary reticular formation (PMRF) was investigated to determine the reticulospinal system's capacity for bilateral control of the upper limbs. Stimulus triggered electromyographic averages (StimulusTA) were constructed from muscles of both upper limbs while two awake monkeys (Macaca fascicularis) performed a reaching task using either arm. Extensor and flexor muscles were studied at the wrist, elbow, and shoulder; muscles acting on the scapula were also studied. Post-stimulus effects (PStEs) resulted from 435 (81%) of 535 sites tested. Of 1611 PStEs analyzed, 58% were post-stimulus suppression (PStS), and 42% were post-stimulus facilitation (PStF). Onset latency was earlier for PStF than PStS, duration was longer for PStS, and amplitude was larger for PStF. Ipsilateral and contralateral PStEs were equally prevalent; bilateral responses were typical. In the ipsilateral forelimb and shoulder, the prevalent pattern was flexor PStF and extensor PStS; the opposite pattern was prevalent contralaterally. Sites producing strong ipsilateral upper trapezius PStF were concentrated in a region caudal and ventral to abducens. The majority of muscles studied had no clear somatotopic organization. Overall, the results indicate the monkey PMRF has the capacity to support bilateral coordination of limb movements using reciprocal actions within a limb and between sides.

The Beat Goes On, and Up and Down.Focus on “Bursts of Information: Coordinating Interneurons Encode Multiple Parameters of a Periodic Motor Pattern”

The effective production of many motor behaviors requires the strict coordination of discrete motor pattern generating circuits ([Hill et al. 2003][1]). Locomotor behaviors usually require this coordination at several levels of the nervous system, within single limbs (interjoint coordination),

The Netrin 1 ReceptorsUnc5h3andDccAre Necessary at Multiple Choice Points for the Guidance of Corticospinal Tract Axons

Migrating axons require the correct presentation of guidance molecules, often at multiple choice points, to find their target. Netrin 1, a bifunctional cue involved in both attracting and repelling axons, is involved in many cell migration and axon pathfinding processes in the CNS. The netrin 1 receptor DCC and its Caenorhabditis elegans homolog UNC-40 have been implicated in directing the guidance of axons toward netrin sources, whereas the C. elegans UNC-6 receptor, UNC-5 is necessary for migrations away from UNC-6. However, a role of vertebrate UNC-5 homologs in axonal migration has not been demonstrated. We demonstrate that the Unc5h3 gene product, shown previously to regulate cerebellar granule cell migrations, also controls the guidance of the corticospinal tract, the major tract responsible for coordination of limb movements. Furthermore, we show that corticospinal tract fibers respond differently to loss of UNC5H3. In addition, we observe corticospinal tract defects in mice homozygous for a spontaneous mutation that truncates the Dcc transcript. Postnatal day 0 netrin 1 mutant mice also demonstrate corticospinal tract abnormalities. Last, interactions between the Dcc and Unc5h3 mutations were observed in gene dosage experiments. This is the first evidence of an involvement in axon guidance for any member of the vertebrate unc-5 family and confirms that both the cellular and axonal guidance functions of C. elegans unc-5 have been conserved in vertebrates.