Motor unit number estimation--a Bayesian approach

All muscle contractions are dependent on the functioning of motor units. In diseases such as amyotrophic lateral sclerosis (ALS), progressive loss of motor units leads to gradual paralysis. A major difficulty in the search for a treatment for these diseases has been the lack of a reliable measure of disease progression. One possible measure would be an estimate of the number of surviving motor units. Despite over 30 years of motor unit number estimation (MUNE), all proposed methods have been met with practical and theoretical objections. Our aim is to develop a method of MUNE that overcomes these objections. We record the compound muscle action potential (CMAP) from a selected muscle in response to a graded electrical stimulation applied to the nerve. As the stimulus increases, the threshold of each motor unit is exceeded, and the size of the CMAP increases until a maximum response is obtained. However, the threshold potential required to excite an axon is not a precise value but fluctuates over a small range leading to probabilistic activation of motor units in response to a given stimulus. When the threshold ranges of motor units overlap, there may be alternation where the number of motor units that fire in response to the stimulus is variable. This means that increments in the value of the CMAP correspond to the firing of different combinations of motor units. At a fixed stimulus, variability in the CMAP, measured as variance, can be used to conduct MUNE using the "statistical" or the "Poisson" method. However, this method relies on the assumptions that the numbers of motor units that are firing probabilistically have the Poisson distribution and that all single motor unit action potentials (MUAP) have a fixed and identical size. These assumptions are not necessarily correct. We propose to develop a Bayesian statistical methodology to analyze electrophysiological data to provide an estimate of motor unit numbers. Our method of MUNE incorporates the variability of the threshold, the variability between and within single MUAPs, and baseline variability. Our model not only gives the most probable number of motor units but also provides information about both the population of units and individual units. We use Markov chain Monte Carlo to obtain information about the characteristics of individual motor units and about the population of motor units and the Bayesian information criterion for MUNE. We test our method of MUNE on three subjects. Our method provides a reproducible estimate for a patient with stable but severe ALS. In a serial study, we demonstrate a decline in the number of motor unit numbers with a patient with rapidly advancing disease. Finally, with our last patient, we show that our method has the capacity to estimate a larger number of motor units.     

A Neural Network-Based Optimal Spatial Filter Design Method for Motor Imagery Classification

In this study, a novel spatial filter design method is introduced. Spatial filtering is an important processing step for feature extraction in motor imagery-based brain-computer interfaces. This paper introduces a new motor imagery signal classification method combined with spatial filter optimization. We simultaneously train the spatial filter and the classifier using a neural network approach. The proposed spatial filter network (SFN) is composed of two layers: a spatial filtering layer and a classifier layer. These two layers are linked to each other with non-linear mapping functions. The proposed method addresses two shortcomings of the common spatial patterns (CSP) algorithm. First, CSP aims to maximize the between-classes variance while ignoring the minimization of within-classes variances. Consequently, the features obtained using the CSP method may have large within-classes variances. Second, the maximizing optimization function of CSP increases the classification accuracy indirectly because an independent classifier is used after the CSP method. With SFN, we aimed to maximize the between-classes variance while minimizing within-classes variances and simultaneously optimizing the spatial filter and the classifier. To classify motor imagery EEG signals, we modified the well-known feed-forward structure and derived forward and backward equations that correspond to the proposed structure. We tested our algorithm on simple toy data. Then, we compared the SFN with conventional CSP and its multi-class version, called one-versus-rest CSP, on two data sets from BCI competition III. The evaluation results demonstrate that SFN is a good alternative for classifying motor imagery EEG signals with increased classification accuracy.     

A Direct Brain-to-Brain Interface in Humans

We describe the first direct brain-to-brain interface in humans and present results from experiments involving six different subjects. Our non-invasive interface, demonstrated originally in August 2013, combines electroencephalography (EEG) for recording brain signals with transcranial magnetic stimulation (TMS) for delivering information to the brain. We illustrate our method using a visuomotor task in which two humans must cooperate through direct brain-to-brain communication to achieve a desired goal in a computer game. The brain-to-brain interface detects motor imagery in EEG signals recorded from one subject (the “sender”) and transmits this information over the internet to the motor cortex region of a second subject (the “receiver”). This allows the sender to cause a desired motor response in the receiver (a press on a touchpad) via TMS. We quantify the performance of the brain-to-brain interface in terms of the amount of information transmitted as well as the accuracies attained in (1) decoding the sender’s signals, (2) generating a motor response from the receiver upon stimulation, and (3) achieving the overall goal in the cooperative visuomotor task. Our results provide evidence for a rudimentary form of direct information transmission from one human brain to another using non-invasive means.     

Pre-processing and transfer entropy measures in motor neurons controlling limb movements

Directed information transfer measures are increasingly being employed in modeling neural system behavior due to their model-free approach, applicability to nonlinear and stochastic signals, and the potential to integrate repetitions of an experiment. Intracellular physiological recordings of graded synaptic potentials provide a number of additional challenges compared to spike signals due to non-stationary behaviour generated through extrinsic processes. We therefore propose a method to overcome this difficulty by using a preprocessing step based on Singular Spectrum Analysis (SSA) to remove nonlinear trends and discontinuities. We apply the method to intracellular recordings of synaptic responses of identified motor neurons evoked by stimulation of a proprioceptor that monitors limb position in leg of the desert locust. We then apply normalized delayed transfer entropy measures to neural responses evoked by displacements of the proprioceptor, the femoral chordotonal organ, that contains sensory neurones that monitor movements about the femoral-tibial joint. We then determine the consistency of responses within an individual recording of an identified motor neuron in a single animal, between repetitions of the same experiment in an identified motor neurons in the same animal and in repetitions of the same experiment from the same identified motor neuron in different animals. We found that delayed transfer entropy measures were consistent for a given identified neuron within and between animals and that they predict neural connectivity for the fast extensor tibiae motor neuron.     

Normalized Index of Synergy for Evaluating the Coordination of Motor Commands

Humans perform various motor tasks by coordinating the redundant motor elements in their bodies. The coordination of motor outputs is produced by motor commands, as well properties of the musculoskeletal system. The aim of this study was to dissociate the coordination of motor commands from motor outputs. First, we conducted simulation experiments where the total elbow torque was generated by a model of a simple human right and left elbow with redundant muscles. The results demonstrated that muscle tension with signal-dependent noise formed a coordinated structure of trial-to-trial variability of muscle tension. Therefore, the removal of signal-dependent noise effects was required to evaluate the coordination of motor commands. We proposed a method to evaluate the coordination of motor commands, which removed signal-dependent noise from the measured variability of muscle tension. We used uncontrolled manifold analysis to calculate a normalized index of synergy. Simulation experiments confirmed that the proposed method could appropriately represent the coordinated structure of the variability of motor commands. We also conducted experiments in which subjects performed the same task as in the simulation experiments. The normalized index of synergy revealed that the subjects coordinated their motor commands to achieve the task. Finally, the normalized index of synergy was applied to a motor learning task to determine the utility of the proposed method. We hypothesized that a large part of the change in the coordination of motor outputs through learning was because of changes in motor commands. In a motor learning task, subjects tracked a target trajectory of the total torque. The change in the coordination of muscle tension through learning was dominated by that of motor commands, which supported the hypothesis. We conclude that the normalized index of synergy can be used to evaluate the coordination of motor commands independently from the properties of the musculoskeletal system.     

Multivariate information-theoretic measures reveal directed information structure and task relevant changes in fMRI connectivity

The human brain undertakes highly sophisticated information processing facilitated by the interaction between its sub-regions. We present a novel method for interregional connectivity analysis, using multivariate extensions to the mutual information and transfer entropy. The method allows us to identify the underlying directed information structure between brain regions, and how that structure changes according to behavioral conditions. This method is distinguished in using asymmetric, multivariate, information-theoretical analysis, which captures not only directional and non-linear relationships, but also collective interactions. Importantly, the method is able to estimate multivariate information measures with only relatively little data. We demonstrate the method to analyze functional magnetic resonance imaging time series to establish the directed information structure between brain regions involved in a visuo-motor tracking task. Importantly, this results in a tiered structure, with known movement planning regions driving visual and motor control regions. Also, we examine the changes in this structure as the difficulty of the tracking task is increased. We find that task difficulty modulates the coupling strength between regions of a cortical network involved in movement planning and between motor cortex and the cerebellum which is involved in the fine-tuning of motor control. It is likely these methods will find utility in identifying interregional structure (and experimentally induced changes in this structure) in other cognitive tasks and data modalities.     

Motor neurons loss in Parkinson Disease: An electrophysiological study (MUNE)

The aim of this study was to evaluate the involvement of a peripheral motor neuron in Parkinson Disease (PD) using the motor unit number estimation (MUNE) method, which reflects motor unit loss in motor neuron diseases. Multipoint incremental MUNE method was calculated in abductor pollicis brevis (APB) and abductor digiti minimi (ADM) in forty one (41) patients with PD and forty five (45) healthy volunteers. From the analysis, the MUNE of APB was lower in PD than in the control group, especially in the sub-group aged 60 years or older. MUNE was negatively correlated with the age of patients for APB, but not with the duration of the disease and advancement of PD. The loss of motor units in sporadic Parkinson's disease revealed by multipoint incremental MUNE method is considered a sign of lower motor neuron involvement, however, loss of motor neurons is slight and does not manifest equally in all muscles . Thus, the results from this experiment should be treated with concern, as it could be a landmark for further experiments.     

基于EMD的左右手运动想象脑电信号分析研究

基于经验模态分解（EMD）理论,提出一种左右手运动想象脑电信号分析方法。首先利用时间窗对脑电信号数据进行划分,对每段数据通过经验模态分解法将其分解为一组固有模态函数IMF,提取主要信号所在的IMF层去除信号中的噪声。对含有主要信号的几层IMF进行Hilbert变换,得到瞬时频率与对应的瞬时幅值。再提取左右手想象的特定频段mu节律和beta节律的能量信号作为特征,分别利用支持向量机（SVM）和Fisher进行了分类比较。对EMD和小波包在去噪和特征提取进行了比较。结果表明,EMD是一种很有效的去噪方法,经过EMD分解后提取的能量信号在区分左右手想象上更具有优势,识别率高。     

Protein kinase C and rho activated coiled coil protein kinase 2 (ROCK2) modulate Alzheimer's APP metabolism and phosphorylation of the Vps10-domain protein, SorL1

Background

Cultured spinal motor neurons are a valuable tool to study basic mechanisms of development, axon growth and pathfinding, and, importantly, to analyze the pathomechanisms underlying motor neuron diseases. However, the application of this cell culture model is limited by the lack of efficient gene transfer techniques which are available for other neurons. To address this problem, we have established magnetofection as a novel method for the simple and efficient transfection of mouse embryonic motor neurons. This technique allows for the study of the effects of gene expression and silencing on the development and survival of motor neurons.

Results

We found that magnetofection, a novel transfection technology based on the delivery of DNA-coated magnetic nanobeads, can be used to transfect primary motor neurons. Therefore, in order to use this method as a new tool for studying the localization and transport of axonal proteins, we optimized conditions and determined parameters for efficient transfection rates of >45% while minimizing toxic effects on survival and morphology. To demonstrate the potential of this method, we have used transfection with plasmids encoding fluorescent fusion-proteins to show for the first time that the spinal muscular atrophy-disease protein Smn is actively transported along axons of live primary motor neurons, supporting an axon-specific role for Smn that is different from its canonical function in mRNA splicing. We were also able to show the suitability of magnetofection for gene knockdown with shRNA-based constructs by significantly reducing Smn levels in both cell bodies and axons, opening new opportunities for the study of the function of axonal proteins in motor neurons.

Conclusions

In this study we have established an optimized magnetofection protocol as a novel transfection method for primary motor neurons that is simple, efficient and non-toxic. We anticipate that this novel approach will have a broad applicability in the study of motor neuron development, axonal trafficking, and molecular mechanisms of motor neuron diseases.     

Axon typing of rat muscle nerves using a double staining procedure for cholinesterase and carbonic anhydrase.

We developed a method for detecting activity of axonal cholinesterase (CE) and carbonic anhydrase (CA)--markers for motor and sensory nerve fibers (NFs)--in the same histological section. To reach this goal, cross-sections of muscle nerves were sequentially incubated with the standard protocols for CE and CA histochemistry. A modified incubation medium was used for CA in which Co++ is replaced by Ni++. This avoids interference of the two histochemical reactions because Co++ binds unspecifically to the brown copper-ferroferricyanide complex representing CE activity, whereas Ni++ does not. Cross-sections of the trapezius muscle nerve containing efferent and afferent NFs in segregated fascicles showed that CE activity was confined to motor NFs. Axonal CA was detected solely in sensory NFs. The number of labeled motor and sensory NFs determined in serial cross-sections stained with either the new or the conventional technique was not significantly different. Morphometric analysis revealed that small unreactive NFs (diameter less than 5 microns) are afferent, medium-sized ones (5 microns less than d less than 7 microns) are unclassifiable, and large ones (d greater than 7 microns) are efferent. The heterogenous CE activity of thick (alpha) motor NFs is linked to the type of their motor units. "Fast" motor units contain CE reactive NFs; "slow" ones have CE negative neurites.     

Isolation of mature spinal motor neurons and single-cell analysis using the comet assay of early low-level DNA damage induced in vitro and in vivo.

We developed an isolation technique for motor neurons from adult rat spinal cord. Spinal cord enlargements were discretely microdissected into ventral horn tissue columns that were trypsin-digested and subjected to differential low-speed centrifugation to fractionate ventral horn cell types. A fraction enriched in alpha-motor neurons was isolated. Motor neuron enrichment was verified by immunofluorescence for choline acetyltransferase and prelabeling axon projections to skeletal muscle. Adult motor neurons were isolated from na?ve rats and were exposed to oxidative agents or were isolated from rats with sciatic nerve lesions (avulsions). We tested the hypothesis, using single-cell gel electrophoresis (comet assay), that hydrogen peroxide, nitric oxide, and peroxynitrite exposure in vitro and axotomy in vivo induce DNA damage in adult motor neurons early during their degeneration. This study contributes three important developments in the study of motor neurons. It demonstrates that mature spinal motor neurons can be isolated and used for in vitro models of motor neuron degeneration. It shows that adult motor neurons can be isolated from in vivo models of motor neuron degeneration and evaluated on a single-cell basis. This study also demonstrates that the comet assay is a feasible method for measuring DNA damage in individual motor neurons. Using these methods, we conclude that motor neurons undergoing oxidative stress from reactive oxygen species and axotomy accumulate DNA damage early in their degeneration.     

The human chromokinesin Kid is a plus end-directed microtubule-based motor

Kid is a kinesin-like DNA-binding protein known to be involved in chromosome movement during mitosis, although its actual motor function has not been demonstrated. Here, we describe the initial characterization of Kid as a microtubule-based motor using optical trapping microscopy. A bacterially expressed fusion protein consisting of a truncated Kid fragment (amino acids 1-388 or 1-439) is indeed an active microtubule motor with an average speed of approximately 160 nm/s, and the polarity of movement is plus end directed. We could not detect processive movement of either monomeric Kid or dimerizing chimeric Kid; however, low levels of processivity (a few steps) cannot be detected with our method. These results are consistent with Kid having a role in chromosome congression in vivo, where it would be responsible for the polar ejection forces acting on the chromosome arms.     

Coordinate-Based Lead Location Does Not Predict Parkinson's Disease Deep Brain Stimulation Outcome

Background

Effective target regions for deep brain stimulation (DBS) in Parkinson''s disease (PD) have been well characterized. We sought to study whether the measured Cartesian coordinates of an implanted DBS lead are predictive of motor outcome(s). We tested the hypothesis that the position and trajectory of the DBS lead relative to the mid-commissural point (MCP) are significant predictors of clinical outcomes. We expected that due to neuroanatomical variation among individuals, a simple measure of the position of the DBS lead relative to MCP (commonly used in clinical practice) may not be a reliable predictor of clinical outcomes when utilized alone.

Methods

55 PD subjects implanted with subthalamic nucleus (STN) DBS and 41 subjects implanted with globus pallidus internus (GPi) DBS were included. Lead locations in AC-PC space (x, y, z coordinates of the active contact and sagittal and coronal entry angles) measured on high-resolution CT-MRI fused images, and motor outcomes (Unified Parkinson''s Disease Rating Scale) were analyzed to confirm or refute a correlation between coordinate-based lead locations and DBS motor outcomes.

Results

Coordinate-based lead locations were not a significant predictor of change in UPDRS III motor scores when comparing pre- versus post-operative values. The only potentially significant individual predictor of change in UPDRS motor scores was the antero-posterior coordinate of the GPi lead (more anterior lead locations resulted in a worse outcome), but this was only a statistical trend (p<.082).

Conclusion

The results of the study showed that a simple measure of the position of the DBS lead relative to the MCP is not significantly correlated with PD motor outcomes, presumably because this method fails to account for individual neuroanatomical variability. However, there is broad agreement that motor outcomes depend strongly on lead location. The results suggest the need for more detailed identification of stimulation location relative to anatomical targets.     

Mechanisms of spinal cord electrical stimulation action on autonomic functions

The method of transcutaneous electrical stimulation of the spinal cord (ESSC) has recently begun to be actively used for both experimental studies of human motor functions and the rehabilitation of motor function in patients with spinal cord pathology. The spinal cord is the most important center of the regulation of vital functions, and ESSC affects as spinal locomotor networks as the visceral system too, which should be taken into account for the development of an improved method of rehabilitation and its use in experiments on healthy volunteers. We present a review of studies on the possible mechanisms of ESSC effects on the peripheral and cerebral circulation, cardiovascular, respiratory, excretory, and digestive systems of mammals.     

Arm-plane representation of shoulder compensation during pointing movements in patients with stroke

Improvements in functional motor activities are often accompanied by motor compensations to overcome persistent motor impairment in the upper limb. Kinematic analysis is used to objectively quantify movement patterns including common motor compensations such as excessive trunk displacement during reaching. However, a common motor compensation to assist reaching, shoulder abduction, is not adequately characterized by current motion analysis approaches. We apply the arm-plane representation that accounts for the co-variation between movements of the whole arm, and investigate its ability to identify and quantify compensatory arm movements in stroke subjects when making forward arm reaches. This method has not been previously applied to the analysis of motion deficits. Sixteen adults with right post-stroke hemiparesis and eight healthy age-matched controls reached in three target directions (14 trials/target; sampling rate: 100 Hz). Arm-plane movement was validated against endpoint, joint, and trunk kinematics and compared between groups. In stroke subjects, arm-plane measures were correlated with arm impairment (Fugl-Meyer Assessment) and ability (Box and Blocks) scores and were more sensitive than clinical measures to detect mild motor impairment. Arm-plane motion analysis provides new information about motor compensations involving the co-variation of shoulder and elbow movements that may help to understand the underlying motor deficits in patients with stroke.     

Physiological mechanisms and movement analysis in Parkinson's disease

We present new ideas about motor control in the human central nervous system and about pathophysiological mechanisms of Parkinson's disease, and we describe the Posturo-Locomotion-Manual (PLM) method, which is a new technique utilizing optoelectronic camera recording for objective, fully quantitative, and standardized assessment of human motor performance. In the PLM test, recordings of body movements are made during a simple motor task, where the subject repeatedly moves a small object from its starting position on the floor to a shelf located at chin height a few steps forward. The duration of the postural (raising up), locomotor and the goal-directed manual phase of the forward directed body movement is automatically calculated by a small computer as well as the degree of coordination (simultaneity) of these phases. The technique has high resolution and has been used for clinical assessment of motor performance, drug testing, and so on, in neurological and geriatric practice.     

Limitations of the surface electromyography technique for estimating motor unit synchronization

Motor unit synchronization was estimated from the surface electromyograms (EMG) of the first dorsal interosseus muscle of human volunteers by a simplified surface-EMG technique (Milner-Brown et al. 1973, 1975). Single motor units were identified from intramuscular recordings and were used to obtain a spike-triggered average of the surface-EMG. The discharge rate of a reference motor unit was controlled at two levels (high and low), and the effect of motor unit activity on the surface-EMG estimate of synchronization was studied in 56 motor units. The surface-EMG estimate of motor unit synchronization was significantly higher when the reference motor unit discharged at the high rate than when it discharged at the low rate. A regression analysis indicated that the synchronization ratio calculated from the surface EMG was significantly correlated with the level of EMG activity in the muscle. Motor unit synchronization was also estimated from surface-EMG measurements that were derived by computer simulation. The simulation permitted manipulation of motor unit activity (discharge rate and recruitment) with a complete absence of synchrony among the units in the pool. The stimulated surface-EMG index was influenced by an artifact associated with signal rectification, and this effect changed non-monotonically with motor unit activity. Furthermore, the increase in the motor unit activity reduced the signal-to-noise ratio of the spike-triggered surface EMG average, and consequently decreased the sensitivity of the surface-EMG index as an estimate of motor unit synchronization. We conclude that the simplified surface-EMG method (Milner-Brown et al. 1973, 1975) does not provide a useful index of motor unit synchronization due to its inability to accurately distinguish the synchronization from methodological effects related to a rectification artifact and variation in the signal-to-noise ratio.     

Configuration of the two kinesin motor domains during ATP hydrolysis

To understand the mechanism of kinesin movement we have investigated the relative configuration of the two kinesin motor domains during ATP hydrolysis using fluorescence polarization microscopy of ensemble and single molecules. We found that: (i) in nucleotide states that induce strong microtubule binding, both motor domains are bound to the microtubule with similar orientations; (ii) this orientation is maintained during processive motion in the presence of ATP; (iii) the neck-linker region of the motor domain has distinct configurations for each nucleotide condition tested. Our results fit well with a hand-over-hand type movement mechanism and suggest how the ATPase cycle in the two motor domains is coordinated. We propose that the motor neck-linker domain configuration controls ADP release.     

A new cryo-EM single-particle ab initio reconstruction method visualizes secondary structure elements in an ATP-fueled AAA+ motor

The generation of ab initio three-dimensional (3D) models is a bottleneck in the studies of large macromolecular assemblies by single-particle cryo-electron microscopy. We describe here a novel method, in which established methods for two-dimensional image processing are combined with newly developed programs for joint rotational 3D alignment of a large number of class averages (RAD) and calculation of 3D volumes from aligned projections (VolRec). We demonstrate the power of the method by reconstructing an ∼ 660-kDa ATP-fueled AAA+ motor to 7.5 Å resolution, with secondary structure elements identified throughout the structure. We propose the method as a generally applicable automated strategy to obtain 3D reconstructions from unstained single particles imaged in vitreous ice.