Although it is premature to advance any concrete hypothesis on the origin of these three patterns of muscle synergy, we believe a description of these patterns is nonetheless important because the patterns provide physiological markers that can be used for shedding light on the complex processes that follow accidents involving the cortical motor system. The first synergy is dominated by flexors muscles of the elbow and by the Tr. Therefore muscle tuning curves have more varied and complex shapes than synergy tuning curves. doi:10.3389/fnhum.2016.00620, Levin, M. F., Desrosiers, J., Beauchemin, D., Bergeron, N., and Rochette, A. J. Neurosci. Child Neurol. Overall, such neurons do not appear to be as well tuned to instantaneous motor parameters as they are to the final multijoint posture terminating a movement (Aflalo and Graziano, 2006) or to temporally extended trajectories (Hatsopoulos et al., 2007; Saleh et al., 2012). Evidence for altered upper extremity muscle synergies in chronic stroke survivors with mild and moderate impairment. The answer is implicitly that, so far, no precise answer can be given due to the lack of data and knowledge about patients’ status. For the reasons explained, synergies could be integrated in a multifactorial assessment to better estimate the residual potential of the patient and consequently suggest the best rehabilitation path available. Two basic synergies are extracted on healthy people free movements. The same synergy vectors were found over repeated optimizations with random initial conditions. The muscle synergies analysis was designed to investigate how muscles coactivate and how their eliciting commands change in time during movement production. Units are grouped by area (PMd, PMv, MI). doi:10.1109/JBHI.2014.2326660, Puig, J., Pedraza, S., Blasco, G., Daunis-I-Estadella, J., Prados, F., Remollo, S., et al. As described previously (Overduin et al., 2008), 40 trials in each condition were selected, time aligned to the moment of object removal from the first well, cropped to a 100-bin period around this time (G1: [−0.35:+0.55] s, G2: [−0.5:+0.6] s), averaged over trials, and concatenated over conditions to give the muscle data matrix Dm (“m” indicating “muscle” data). 192, No. Here, we investigated whether populations of motor cortical neurons reflect recruitment of motor primitives in the form of spatiotemporal synergies. D, The most prominent covariation involving synergy coefficients was that between the second synergy's amplitude, c2n, and object mass. Alterations in upper limb muscle synergy structure in chronic stroke survivors. 11, No. doi: 10.1080/00222895.1984.10735316, Lee, D. D., and Seung, H. S. (1999). Although beyond the scope of this report, other methods for comparing bases extracted from spatiotemporal data from different sources, such as bidirectional independent component averaged representation (Brown et al., 2012, 2013), could potentially be adapted for the muscular and neural time series data considered here. Exp. Peak activation for W2 occurred at 247, 270, and 337°; peak activation for W3 occurred at 90, 90, and 135°. Our recent study (Imagawa et al., 2013) revealed that several muscles that have different action directions (ADs), which are the mechanical characteristics of each muscle that represents endpoint force vectors (Kutch et al., 2010; Hagio and Kouzaki, 2015b), are co-activated in the multi-directional and intentional movement of the COP. 362, 1772–1783. doi: 10.1152/jn.00956.2009, Lee, W. A. Muscle synergies and complexity of neuromuscular control during gait in cerebral palsy. J. Neurophysiol. We then fit the synergies to both the EMG and unit firing data from the 247 (G1) or 56 (G2) trials spanned by these subensembles after first reducing the neural synergies to the six of 54 (G1) or six of 17 (G2) channels spanned by the subensemble's units. 97, 3024–3035. 4A). The higher the Silhouette, the better elements fit to their cluster. As shown in Figure 7A, even similar muscle synergies among subjects indicated different ADs among subjects. The mean Normalized Jerk within the cluster is quite low, indicating a quite smooth movement execution. 20, No. Our computational procedure identified synergies A2 and A3 to be fractionations of synergy U1 for the unaffected arm, and A4–A6 as fractionations of synergy U3. Front. Several approaches and algorithms have been proposed for synergies extraction (Tresch et al., 2006). Keywords: center of pressure, electromyogram-weighted averaging method, motor control, muscle synergy, non-negative matrix factorization, Citation: Kubo A, Hagio S, Kibushi B, Moritani T and Kouzaki M (2017) Action Direction of Muscle Synergies in Voluntary Multi-Directional Postural Control. 1, Journal of Motor Behavior, Vol. They were normalized by the maximum activation. doi: 10.1152/jn.00810.2005, Torres-Oviedo, G., and Ting, L. H. (2007). Muscle synergies in postural control have also been discussed in numerous studies (Krishnamoorthy et al., 2003; Torres-Oviedo and Ting, 2007; Chvatal et al., 2011). The costs of publication of this article were defrayed in part by the payment of page charges. Hum. The goal of this study was to show the coordinative structure of muscles that contribute to voluntary postural control. To authors’ opinion, while still being improvable, this procedure allows a coherent method for the profiling of the clinical status of patients in the framework of muscle synergies. The task for healthy, young subjects was to shift and align their center of pressure (COP) to targets dispersed in 12 different directions in the horizontal plane by leaning their bodies for 10 s. Electromyograms (EMGs) of 18 muscles and COPs were recorded in the experiment. 4, 1 February 2009 | Journal of Neurophysiology, Vol. A sufficient rest period was allowed between blocks to prevent fatigue. Each element of Wirepresents a muscle whose relative contribution to the muscle synergy is time invariant and takes a value between 0 and 1. Such spatial synergies could provide the animal with a mechanism to control its muscles continuously (if not as efficiently as in the case of spatiotemporal synergies) by specifying a time course of task-specific amplitude coefficients for each of the synergies (cf. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.