Publications
788 results found
Niazi IK, Jiang N, Jochumsen M, et al., 2013, Detection of movement-related cortical potentials based on subject-independent training., Med Biol Eng Comput, Vol: 51, Pages: 507-512
To allow a routinely use of brain-computer interfaces (BCI), there is a need to reduce or completely eliminate the time-consuming part of the individualized training of the user. In this study, we investigate the possibility of avoiding the individual training phase in the detection of movement intention in asynchronous BCIs based on movement-related cortical potential (MRCP). EEG signals were recorded during ballistic ankle dorsiflexions executed (ME) or imagined (MI) by 20 healthy subjects, and attempted by five stroke subjects. These recordings were used to identify a template (as average over all subjects) for the initial negative phase of the MRCPs, after the application of an optimized spatial filtering used for pre-processing. Using this template, the detection accuracy (mean ± SD) calculated as true positive rate (estimated with leave-one-out procedure) for ME was 69 ± 21 and 58 ± 11 % on single trial basis for healthy and stroke subjects, respectively. This performance was similar to that obtained using an individual template for each subject, which led to accuracies of 71 ± 6 and 55 ± 12 % for healthy and stroke subjects, respectively. The detection accuracy for the MI data was 65 ± 22 % with the average template and 60 ± 13 % with the individual template. These results indicate the possibility of detecting movement intention without an individual training phase and without a significant loss in performance.
Gervasio S, Farina D, Sinkjær T, et al., 2013, Crossed reflex reversal during human locomotion., J Neurophysiol, Vol: 109, Pages: 2335-2344
During human walking, precise coordination between the two legs is required in order to react promptly to any sudden hazard that could threaten stability. The networks involved in this coordination are not yet completely known, but a direct spinal connection between soleus (SOL) muscles has recently been revealed. For this response to be functional, as previously suggested, we hypothesize that it will be accompanied by a reaction in synergistic muscles, such as gastrocnemius lateralis (GL), and that a reversal of the response would occur when an opposite reaction is required. In the present study, surface EMGs of contralateral SOL and GL were analyzed after tibial nerve (TN), sural nerve (SuN), and medial plantar nerve (MpN) stimulation during two tasks in which opposite reactions are functionally expected: normal walking (NW), just before ipsilateral heel strike, and hybrid walking (HW) (legs walking in opposite directions), at ipsilateral push off and contralateral touchdown. Early crossed facilitations were observed in the contralateral GL after TN stimulation during NW, and a reversal of such responses occurred during HW. These results underline the functional significance of short-latency crossed responses and represent the first evidence for short-latency reflex reversal in the contralateral limb for humans. Muscle afferents seem to mediate the response during NW, while during HW cutaneous afferents are likely involved. It is thus possible that different afferents mediate the crossed response during different tasks.
Krigslund R, Dosen S, Popovski P, et al., 2013, A novel technology for motion capture using passive UHF RFID tags., IEEE Trans Biomed Eng, Vol: 60, Pages: 1453-1457
Although there are several existing methods for human motion capture, they all have important limitations and hence there is the need to explore fundamentally new approaches. Here, we present a method based on a radio frequency identification (RFID) system with passive ultra high frequency (UHF) tags placed on the body segments whose kinematics is to be captured. Dual polarized antennas are used to estimate the inclination of each tag based on the polarization of the tag responses. The method has been validated experimentally for the shank and thigh in the sagittal plane during treadmill walking. The reference segment angles for the validation were obtained by an optoelectronic system. Although the method is in its initial phase of development, the results of the validation are promising and show that the movement information can be extracted from the RFID response signals.
Conradsen I, Moldovan M, Jennum P, et al., 2013, Dynamics of muscle activation during tonic-clonic seizures., Epilepsy Res, Vol: 104, Pages: 84-93
The purpose of our study was to elucidate the dynamics of muscle activation during generalised tonic-clonic seizures (GTCS). We recorded surface electromyography (EMG) from the deltoid muscle during 26 GTCS from 13 patients and compared it with GTCS-like events acted by 10 control subjects. GTCS consisted of a sequence of phases best described quantitatively by dynamics of the low frequency (LF) wavelet component (2-8Hz). Contrary to the traditional view, the tonic phase started with a gradual increase in muscle activity. A longer clonic phase was associated with a shorter onset of the tonic phase and a higher seizure occurrence. Increase in LF occurred during the onset phase and during the transition from the tonic to the clonic phase, corresponding to the vibratory movements. The clonic phase consisted of EMG discharges of remarkably constant duration (0.2s) separated by silent periods (SP) of exponentially increasing duration - features that could not be reproduced voluntarily. The last SP was longer in seizures with higher EMG peak frequency whereas the energy of the last clonus was higher in seizures with a short clonic phase. We found specific features of muscle activation dynamics during GTCS. Our findings suggest that the same inhibitory mechanisms that contribute to GTCS termination counteract seizure initiation, accounting for the gradual onset. Both active inhibition and mechanisms related to metabolic depletion act synergistically to stop the seizure. Analysis of the ictal EMG dynamics is a valuable tool for monitoring the balance between pro-convulsive and anti-convulsive factors.
Jiang N, Muceli S, Graimann B, et al., 2013, Effect of arm position on the prediction of kinematics from EMG in amputees, Medical and Biological Engineering and Computing, Vol: 51, Pages: 143-151, ISSN: 0140-0118
Myoelectric control has been extensively applied in multi-function hand/wrist prostheses. The performance of this type of control is however, influenced by several practical factors that still limit its clinical applicability. One of these factors is the change in arm posture during the daily use of prostheses. In this study, we investigate the effect of arm position on the performance of a simultaneous and proportional myoelectric control algorithm, both on trans-radial amputees and able-bodied subjects. The results showed that changing arm position adversely influences the performance of the algorithm for both subject groups, but that this influence is less pronounced in amputee subjects with respect to able-bodied subjects. Thus, the impact of arm posture on myoelectric control cannot be inferred from results on able-bodied subjects and should be directly investigated in amputee subjects.
Oliveira AS, Silva PB, Lund ME, et al., 2013, Fast changes in direction during human locomotion are executed by impulsive activation of motor modules., Neuroscience, Vol: 228, Pages: 283-293
This study investigated the modular control of complex locomotor tasks that require fast changes in direction, i.e., cutting manoeuvres. It was hypothesized that such tasks are accomplished by an impulsive (burst-like) activation of a few motor modules, as observed during walking and running. It was further hypothesized that the performance in cutting manoeuvres would be associated to the relative timing of the activation impulses. Twenty-two healthy men performed 90° side-step cutting manoeuvres while electromyography (EMG) activity from 16 muscles of the supporting limb and trunk, kinematics, and ground reaction forces were recorded. Motor modules and their respective temporal activations were extracted from the EMG signals by non-negative matrix factorization. The kinematic analysis provided the velocity of the centre of mass and the external work absorbed during the load acceptance (negative work, external work during absorption (W-Abs)) and propulsion phases (positive work, external work during propulsion (W-Prp)) of the cutting manoeuvres. Five motor modules explained the EMG activity of all muscles and were driven in an impulsive way, with timing related to the initial contact (M2), load acceptance (M3), and propulsion (M4). The variability in timing between impulses across subjects was greater for cutting manoeuvres than for running. The timing difference between M2 and M3 in the cutting manoeuvres was significantly associated to W-Abs (r(2)=0.45) whereas the timing between M3 and M4 was associated to W-Prp (r(2)=0.43). These results suggest that complex locomotor tasks can be achieved by impulsive activation of muscle groups, and that performance is associated to the specific timing of the activation impulses.
Istenič R, Negro F, Holobar A, et al., 2013, Surface EMG pre-processing techniques for the detection of common input to motor neuron populations, Pages: 256-259
In this paper we compared four surface EMG preprocessing techniques to improve the detection of common input to two motor neuron populations. We proposed multichannel approach named Activity index and its improvement higherorder Activity index. Both methods were compared to raw and rectified EMG. Techniques were evaluated on simulated EMG signals of two motor neuron populations and EMG-EMG coherence was used as a measure. Higher-order Activity index performed better than original Activity index, coherence values were in the range of rectified EMG. © 2013 IEEE.
Kristensen SR, Niazi IK, Jochumsen M, et al., 2013, Changes in corticospinal excitability following the use of a BCI based protocol combined with sham visual feedback, Biosystems and Biorobotics, Pages: 599-602
Visual feedback may be beneficial when a brain computer interface (BCI) system is used in a rehabilitation setting. Here we investigate if sham visual feedback at two levels (60% and 85% correct) on generated Contingent negative variation (CNVs) can affect induced plasticity following an already established intervention. This was compared to no visual feedback. Subjects were asked to imagine 50 dorsiflexion movements while a peripheral electrical stimulation (to the deep branch of the common peroneal nerve (CPN)) was timed to arrive during the most negative phase of the CNV. Changes were quantified using transcranial magnetic stimulation (TMS) to the area of the brain representing the tibialis anterior muscle (TA). The results indicate that visual sham feedback lead to significant increases in the cortical projections to the TA compared to no sham visual feedback (p <0.001). This can have implications for designing of BCI systems used in a future rehabilitation setting.
Bržan PP, Gallego JÁ, Farina D, et al., 2013, On repeatability of motor unit characterization in pathological tremor, Biosystems and Biorobotics, Pages: 553-556
The study compares the discharge characteristics of individual motor units, identified noninvasively from flexor carpi radialis and extensor carpi ulnaris muscles of nine essential and four Parkinsonian patients during three repetitions of rest, postural and kinetic conditions. The number of identified motor units and their discharge characteristics demonstrated relatively high consistency across the task repetitions and indicated potential differences in motor unit discharge properties between essential and Parkisonian tremor.
Kamavuako EN, Rosenvang JC, Bog MF, et al., 2013, Influence of the feature space on the estimation of hand grasping force from intramuscular EMG, Biomedical Signal Processing and Control, Vol: 8, Pages: 1-5, ISSN: 1746-8094
The study compares the performance of different combinations of nine features extracted from intramuscular electromyogram (EMG) recordings for the estimation of grasping force within the range 0-100% maximum voluntary contraction (MVC). Single-channel intramuscular EMG was recorded from the flexor digitorum profundus (FDP) muscle from 11 subjects who exerted three force profiles during power grasping. The ability of the features to estimate force with a 1st order polynomial (poly1) and an artificial neural network (ANN) model was assessed using the adjusted coefficient of determination (R2). Willison amplitude (WAMP) and root mean square (RMS) showed the highest R 2 (∼0.88) values for poly1. The performance of all the features to predict force significantly increased (P < 0.01) when an ANN was applied. In this case, the Modified Mean Absolute Value (MMAV) demonstrated the best performance (∼0.91). The results showed that a single channel intramuscular EMG recording represents the entire grasping force range (0-100% MVC) measured from the FDP muscle. The association between EMG and force depends on the features extracted and on the model. © 2012 Elsevier Ltd.
Sartori M, Gizzi L, Farina D, 2013, Musculoskeletal modeling of human locomotion based on low-dimensional impulsive activation signals: Perspectives for neurotechnologies, Biosystems and Biorobotics, Pages: 1239-1242
Human locomotion can be expressed as the action of impulsive activation signals over muscle groups. This view has been used in this study for generating a musculoskeletal model for the prediction of muscle forces and joint moments. A set of activation signals of impulsive nature has been extracted from experimental electromyographic (EMG) recordings in several locomotor tasks. These activations signals were used as input to the musculoskeletal model whose unknown parameters were obtained by calibration. Once calibrated, the model could work in open-loop, estimating joint moments over multiple degrees of freedom using only the recorded kinematics (and the internal impulsive controller). It is shown that the accuracy in estimation of the joint moments was comparable when using the low-dimensional activations signals, as proposed in this study, with respect to using the experimental EMG signals, as in more common EMG-driven musculoskeletal models. These results have implications, which are discussed in this contribution, in the design of control systems in human-machine interfacing for neurorehabilitation, such as active orthoses or prostheses.
Dosen S, Dideriksen JL, Rocon E, et al., 2013, Tremor suppression using electromyography and surface sensory electrical stimulation, Biosystems and Biorobotics, Pages: 539-543
Functional electrical stimulation has been tested previously for the suppression of pathological tremor. Typically, the tremor is detected using motion sensors, and the stimulation is delivered supra motor threshold activating muscles to oppose the tremulous oscillations. Here we present a novel system that estimates tremor from the recorded electromyography signals and delivers stimulation below the motor threshold, activating sensory nerve fibers. The hypothesis (backed up by the previous studies) is that the generated sensory inflow will modulate the sensory feedback loops and/or project to the supraspinal centers acting on the true tremor sources/generators. The system was tested in two patients suffering from Parkinson disease and one Essential tremor patient, and the results were promising, i.e., tremor was significantly attenuated.
Farina D, Jiang N, Rehbaum H, et al., 2013, Simultaneous and proportional myocontrol of multiple degrees of freedom, Biosystems and Biorobotics, Pages: 1225-1228
Myoelectric control is known since decades. Academic methods are usually based on the supervised classification of electromyographic (EMG) signals into a set of pre-defined functions. Therefore, such methods are sequential and non-proportional. In this talk, novel approaches based on the simultaneous and proportional control of multiple degrees of freedom using EMG will be presented. These methods can be either based on supervised regression (e.g., artificial neural networks) or on EMG signal factorization. The latter method is particularly promising because it does not require training. Results of the application of the new control schemes for both able-bodied and amputee subjects will be presented.
Markovic M, Dosen S, Farina D, 2013, Switching between the modes of control: Implications for the closed loop control of prostheses, Biosystems and Biorobotics, Pages: 277-281
From the point of view of a theory of human operator, closed loop control of an upper limb prosthesis is an interesting and challenging control task. Namely, the user has to switch between the two different controlled systems, i.e., the opening and closing of the hand is controlled via an integrator (first order system), while the force control is proportional (zero order system). Our goal was to investigate how the switching between different control modes affects the overall control performance. To test this experimentally, we have used a visuomanual tracking task. The preliminary results (collected from 3 subjects) show that both control modes can be learned quite easily. However, during switching, there is a significant performance drop, especially when changing from the first order to zero order system. This research can provide insights into the mechanisms relevant for the closed loop control of prosthesis and user training.
D’Alonzo M, Dosen S, Cipriani C, et al., 2013, The HyVE: Hybrid vibro-electrotactile stimulation for sensory feedback in upper limb prostheses, Biosystems and Biorobotics, Pages: 385-389
This work presents preliminary experiments using a new hybrid vibro-electrotactile interface named HyVE. It integrates vibrotactile with electrotactile stimulation over the same physical location, and it is thus able to provide a dual-modality sensory feedback on the body site where it is applied. Since HyVE was envisioned as a feedback system for prosthetic limbs, as a first step, we investigated the capability of human subjects to discriminate the properties of the two stimulation types when they are delivered simultaneously. Preliminary results are very promising: nine subjects were able to discriminate 9 stimuli (combinations of 3 electro- and 3 vibro-tactile stimuli) with a mean success rate of 70 %. These results suggest that a hybrid interface can be used to implement two parallel information channels in a compact way. This could be exploited for the closed loop control of an upper limb prosthesis.
Minetto MA, Holobar A, Botter A, et al., 2013, Origin and development of muscle cramps., Exerc Sport Sci Rev, Vol: 41, Pages: 3-10
Cramps are sudden, involuntary, painful muscle contractions. Their pathophysiology remains poorly understood. One hypothesis is that cramps result from changes in motor neuron excitability (central origin). Another hypothesis is that they result from spontaneous discharges of the motor nerves (peripheral origin). The central origin hypothesis has been supported by recent experimental findings, whose implications for understanding cramp contractions are discussed.
Oliveira AS, Silva PB, Lund ME, et al., 2013, Effects of perturbations to balance on neuromechanics of fast changes in direction during locomotion., PLoS One, Vol: 8
This study investigated whether the modular control of changes in direction while running is influenced by perturbations to balance. Twenty-two healthy men performed 90° side-step unperturbed cutting manoeuvres while running (UPT) as well as manoeuvres perturbed at initial contact (PTB, 10 cm translation of a moveable force platform). Surface EMG activity from 16 muscles of the supporting limb and trunk, kinematics, and ground reaction forces were recorded. Motor modules composed by muscle weightings and their respective activation signals were extracted from the EMG signals by non-negative matrix factorization. Knee joint moments, co-contraction ratios and co-contraction indexes (hamstrings/quadriceps) and motor modules were compared between UPT and PTB. Five motor modules were enough to reconstruct UPT and PTB EMG activity (variance accounted for UPT = 92 ± 5%, PTB = 90 ± 6%). Moreover, higher similarities between muscle weightings from UPT and PTB (similarity = 0.83 ± 0.08) were observed in comparison to the similarities between the activation signals that drive the temporal properties of the motor modules (similarity = 0.71 ± 0.18). In addition, the reconstruction of PTB EMG from fixed muscle weightings from UPT resulted in higher reconstruction quality (82 ± 6%) when compared to reconstruction of PTB EMG from fixed activation signals from UPT (59 ± 11%). Perturbations at initial contact reduced knee abduction moments (7%), as well as co-contraction ratio (11%) and co-contraction index (12%) shortly after the perturbation onset. These changes in co-contraction ratio and co-contraction index were caused by a reduced activation of hamstrings that was also verified in the activation signals of the specific motor module related to initial contact. Our results suggested that perturbations to balance influence modular control of cutting manoeuvres, especially the temporal properties of muscle recruitment, due to altered a
Hammad SHH, Farina D, Kamavuako EN, et al., 2013, Identification of a self-paced hitting task in freely moving rats based on adaptive spike detection from multi-unit M1 cortical signals., Front Neuroeng, Vol: 6, ISSN: 1662-6443
Invasive brain-computer interfaces (BCIs) may prove to be a useful rehabilitation tool for severely disabled patients. Although some systems have shown to work well in restricted laboratory settings, their usefulness must be tested in less controlled environments. Our objective was to investigate if a specific motor task could reliably be detected from multi-unit intra-cortical signals from freely moving animals. Four rats were trained to hit a retractable paddle (defined as a "hit"). Intra-cortical signals were obtained from electrodes placed in the primary motor cortex. First, the signal-to-noise ratio was increased by wavelet denoising. Action potentials were then detected using an adaptive threshold, counted in three consecutive time intervals and were used as features to classify either a "hit" or a "no-hit" (defined as an interval between two "hits"). We found that a "hit" could be detected with an accuracy of 75 ± 6% when wavelet denoising was applied whereas the accuracy dropped to 62 ± 5% without prior denoising. We compared our approach with the common daily practice in BCI that consists of using a fixed, manually selected threshold for spike detection without denoising. The results showed the feasibility of detecting a motor task in a less restricted environment than commonly applied within invasive BCI research.
Gu Y, Farina D, Murguialday AR, et al., 2013, Comparison of movement related cortical potential in healthy people and amyotrophic lateral sclerosis patients., Front Neurosci, Vol: 7, ISSN: 1662-4548
OBJECTIVE: To understand the brain motor functions and neurophysiological changes due to motor disorder by comparing electroencephalographic data between healthy people and amyotrophic lateral sclerosis (ALS) patients. METHODS: The movement related cortical potential (MRCP) was recorded from seven healthy subjects and four ALS patients. They were asked to imagine right wrist extension at two speeds (fast and slow). The peak negativity (PN) and rebound rate (RR) were extracted from MRCP for comparison. RESULTS: The statistical analysis has showed that there was no significant difference in PN between the healthy and the ALS subjects. However, the healthy subjects presented faster RR than ALS during both fast and slow movement imagination. CONCLUSIONS: The weaker RR of ALS patients might reflect the impairment of motor output pathways or the degree of motor degeneration. SIGNIFICANCE: The comparison between healthy people and ALS patients provides a way to explain the movement disorder through brain electrical signal. In addition, the characteristics of MRCP could be used to monitor and guide brain plasticity in patients.
Hahne JM, Rehbaum H, Biessmann F, et al., 2012, Simultaneous and proportional control of 2D wrist movements with myoelectric signals, ISSN: 2161-0363
Previous approaches for extracting real-time proportional control information simultaneously for multiple degree of Freedom(DoF) from the electromyogram (EMG) often used non-linear methods such as the multilayer perceptron (MLP). In this pilot study we show that robust control is also possible with conventional linear regression if EMG power measures are available for a large number of electrodes. In particular, we show that it is possible to linearize the problem with simple nonlinear transformations of band-pass power. Because of its simplicity the method scales well to high dimensions, is easily regularized when insufficient training data is available, and is particularly well suited for real-time control as well as on-line optimization. © 2012 IEEE.
, 2012, Real time simultaneous and proportional control of multiple degrees of freedom from surface EMG: Preliminary results on subjects with limb deficiency., Pages: 1346-1349, ISSN: 1557-170X
We present the real time simultaneous and proportional control of two degrees of freedom (DoF), using surface electromyographic signals from the residual limbs of three subject with limb deficiency. Three subjects could control a virtual object in two dimensions using their residual muscle activities to achieve goal-oriented tasks. The subjects indicated that they found the control intuitive and useful. These results show that such a simultaneous and proportional control paradigm is a promising direction for multi-functional prosthetic control.
Alvaro Gallego J, Ibanez J, Dideriksen JL, et al., 2012, A Multimodal Human-Robot Interface to Drive a Neuroprosthesis for Tremor Management, IEEE TRANSACTIONS ON SYSTEMS MAN AND CYBERNETICS PART C-APPLICATIONS AND REVIEWS, Vol: 42, Pages: 1159-1168, ISSN: 1094-6977
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- Citations: 31
Farina D, Cianca E, Marchetti N, et al., 2012, Special issue: wearable computing and communication for e-Health., Med Biol Eng Comput, Vol: 50, Pages: 1117-1118
Kilen A, Gizzi L, Jensen BR, et al., 2012, Changes in human muscle oxygen saturation and mean fiber conduction velocity during intense dynamic exercise--effect of muscular training status., Muscle Nerve, Vol: 46, Pages: 746-754
INTRODUCTION: In this study we investigated whether an association exists between muscle fiber conduction velocity (MFCV) and local muscle oxygen saturation (StO(2)) in the superficial part of the latissimus dorsi muscle of runners and swimmers during exhaustive dynamic exercise. METHODS: Participants performed arm cranking with increasing intensity until exhaustion. RESULTS: Runners' MFCV was unchanged with increasing arm-cranking exercise intensity, but was higher (P < 0.05) than swimmers' MFCV at the same workload. Swimmers' MFCV increased (P < 0.05) with increasing exercise intensity and reached values at exhaustion similar to those of the runners. StO(2) was similar in swimmers and runners at rest and decreased with increasing exercise intensity. StO(2) was higher (P < 0.05) at the same workload in swimmers compared with runners. StO(2) and MFCV were significantly but very weakly correlated in both swimmers and runners. CONCLUSION: No association exists between surface MFCV and StO(2) in either trained or untrained human skeletal muscle during exhaustive intense dynamic exercise.
Carotti ESG, Jensen W, De Martin JC, et al., 2012, MDL-based joint denoising and compression of intracortical signals, Pages: 657-660, ISSN: 1520-6149
Intra-cortical signals are usually affected by high levels of noise (0 dB SNR is not uncommon) either due to the recording equipment or to magnetical and electrical couplings between surrounding sources and the recording system. Besides from hindering effective exploitation of the information content in the signals, noise also influences the bandwidth needed to transmit them, which is a problem especially when a large number of channels are to be recorded. In this paper we propose a novel technique for joint denoising and compression of intra-cortical signals based on the Minimum Description Length principle (MDL). This method was tested on simulated signals and the results showed that the proposed technique achieves improvements in SNR (up to.6 dB over MNML for very noisy signals) and compression ratios greater than alternative denoising/compression methods. © 2012 IEEE.
Gizzi L, Nielsen JF, Felici F, et al., 2012, Motor modules in robot-aided walking., J Neuroeng Rehabil, Vol: 9
BACKGROUND: It is hypothesized that locomotion is achieved by means of rhythm generating networks (central pattern generators) and muscle activation generating networks. This modular organization can be partly identified from the analysis of the muscular activity by means of factorization algorithms. The activity of rhythm generating networks is described by activation signals whilst the muscle intervention generating network is represented by motor modules (muscle synergies). In this study, we extend the analysis of modular organization of walking to the case of robot-aided locomotion, at varying speed and body weight support level. METHODS: Non Negative Matrix Factorization was applied on surface electromyographic signals of 8 lower limb muscles of healthy subjects walking in gait robotic trainer at different walking velocities (1 to 3 km/h) and levels of body weight support (0 to 30%). RESULTS: The muscular activity of volunteers could be described by low dimensionality (4 modules), as for overground walking. Moreover, the activation signals during robot-aided walking were bursts of activation timed at specific phases of the gait cycle, underlying an impulsive controller, as also observed in overground walking. This modular organization was consistent across the investigated speeds, body weight support level, and subjects. CONCLUSIONS: These results indicate that walking in a Lokomat robotic trainer is achieved by similar motor modules and activation signals as overground walking and thus supports the use of robotic training for re-establishing natural walking patterns.
Oliveira ASC, Gizzi L, Kersting UG, et al., 2012, Modular organization of balance control following perturbations during walking., J Neurophysiol, Vol: 108, Pages: 1895-1906
Balance recovery during walking requires complex sensory-motor integration. Mechanisms to avoid falls are active concomitantly with human locomotion motor patterns. It has been suggested that gait can be described by a set of motor modules (synergies), but little is known on the modularity of gait during recovery of balance due to unexpected slips. Our hypothesis was that muscular activation during reactive recovery of balance during gait has a modular organization. The aim of the study was to verify this hypothesis when perturbations were delivered in different directions. Eight healthy men walked on a 7-m walkway, which had a moveable force platform embedded in the middle. Subjects experienced unperturbed walking as well as perturbations delivered in the sagittal (forward and backward) and frontal (leftward and rightward) planes. Bilateral full-body kinematics and surface electromyography (EMG) from lower limbs, trunk, and neck were recorded during walking. Synergies and activation signals were extracted from surface EMG signals. Four modules were sufficient to explain the unperturbed gait and the gait perturbed in any of the perturbation directions. Moreover, three of four modules extracted from the unperturbed gait were the same for gait perturbed forward, leftward, and rightward (similarity in synergies = 0.94 ± 0.03). On the other hand, the activation signals were different between unperturbed and perturbed gait (average correlation coefficient = 0.55 ± 0.16). These strategies to recover balance were robust across subjects. In conclusion, changes in lower limb and trunk kinematics provoked by perturbations were reflected in minimal adjustments in the muscular modular organization of walking, with three of four modules preserved from normal walking. Conversely, the activation signals were all substantially influenced by the perturbations, being the result of integration of afferent information and supraspinal control.
Holobar A, Glaser V, Gallego JA, et al., 2012, Non-invasive characterization of motor unit behaviour in pathological tremor, JOURNAL OF NEURAL ENGINEERING, Vol: 9, ISSN: 1741-2560
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Shalchyan V, Jensen W, Farina D, 2012, Spike detection and clustering with unsupervised wavelet optimization in extracellular neural recordings., IEEE Trans Biomed Eng, Vol: 59, Pages: 2576-2585
Automatic and accurate detection of action potentials of unknown waveforms in noisy extracellular neural recordings is an important requirement for developing brain-computer interfaces. This study introduces a new, wavelet-based manifestation variable that combines the wavelet shrinkage denoising with multiscale edge detection for robustly detecting and finding the occurrence time of action potentials in noisy signals. To further improve the detection performance by eliminating the dependence of the method to the choice of the mother wavelet, we propose an unsupervised optimization for best basis selection. Moreover, another unsupervised criterion based on a correlation similarity measure was defined to update the wavelet selection during the clustering to improve the spike sorting performance. The proposed method was compared to several previously proposed methods by using a wide range of realistic simulated data as well as selected experimental recordings of intracortical signals from freely moving rats. The detection performance of the proposed method substantially surpassed previous methods for all signals tested. Moreover, updating the wavelet selection for the clustering task was shown to improve the classification performance with respect to maintaining the same wavelet as for the detection stage.
Falla D, O'Leary S, Farina D, et al., 2012, The change in deep cervical flexor activity after training is associated with the degree of pain reduction in patients with chronic neck pain., Clin J Pain, Vol: 28, Pages: 628-634
OBJECTIVES: Altered activation of the deep cervical flexors (longus colli and longus capitis) has been found in individuals with neck pain disorders but the response to training has been variable. Therefore, this study investigated the relationship between change in deep cervical flexor muscle activity and symptoms in response to specific training. METHODS: Fourteen women with chronic neck pain undertook a 6-week program of specific training that consisted of a craniocervical flexion exercise performed twice per day (10 to 20 min) for the duration of the trial. The exercise targets the deep flexor muscles of the upper cervical region. At baseline and follow-up, measures were taken of neck pain intensity (visual analogue scale, 0 to 10), perceived disability (Neck Disability Index, 0 to 50) and electromyography (EMG) of the deep cervical flexors (by a nasopharyngeal electrode suctioned over the posterior oropharyngeal wall) during performance of craniocervical flexion. RESULTS: After training, the activation of the deep cervical flexors increased (P<0.0001) with the greatest change occurring in patients with the lowest values of deep cervical flexor EMG amplitude at baseline (R(2)=0.68; P<0.001). There was a significant relationship between initial pain intensity, change in pain level with training, and change in EMG amplitude for the deep cervical flexors during craniocervical flexion (R(2)=0.34; P<0.05). DISCUSSION: Specific training of the deep cervical flexor muscles in women with chronic neck pain reduces pain and improves the activation of these muscles, especially in those with the least activation of their deep cervical flexors before training. This finding suggests that the selection of exercise based on a precise assessment of the patients' neuromuscular control and targeted exercise interventions based on this assessment are likely to be the most beneficial to patients with neck pain.
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