11, 11 July 2017 | Journal of Neurophysiology, Vol. To control for these problems we also quantified the firing rates of identified single motor units within as many of the records as possible. TABLE 2. 4.Confusion matrices show that EMG patterns could be used to correctly identify the object grasped (left) or the letter spelled (right) on about half of the trials (subject 1). We tested this hypothesis by asking subjects to shape the right hand to grasp and use a set of familiar objects and then measuring the resulting configuration of the hand. Although subjects adopted distinct hand shapes for the various objects, the joint angles of the digits did not vary independently. The amount of information continued to increase monotonically up to at least the fifth or the sixth PC, even though these higher-order principal components contributed little to the variance (Table 2). Again the subjects were instructed that all of the force produced by hand muscles should go into holding the hand in specific static postures. FIG. (The fifth subject’s results also conformed after rotation of the PC axes.) Top middle and left: all of the matches in this trial and an average that could be used to update the template. As shown in Figs. 118, No. 2003a). In my PT education, I remember learning about synergies as a strategy the brain uses to decrease the degrees of freedom after a stroke/brain injury. The amplitude of each of the coefficients has been normalized relative to the maximum (or minimum values) of the first PC. 4 shows that the “actual letter” C (x axis) was classified 11 times as C (y axis) and 3 times as O (arrow). 3, Journal of Cognitive Neuroscience, Vol. To allow comparison between our results and previous work, we chose mostly objects that had also been used by other authors to formulate taxonomies of hand postures (Kamakura et al., 1980; Klatzky et al., 1987; Cutkosky and Howe, 1990). The results of the analysis presented in Figures 3 and 4 indicated that not all of the joint angles of the hand are controlled independently of each other in shaping the hand to grasp different objects. It makes sense to think of postural developmental reflexes as being included under the NM synergies umbrella, contributing to the functions of tonal distribution as well as very early stability patterns. Thus, the increase in the information transmitted by higher-order PCs does not come about because they effect large changes in select joint angles for select objects. For the testing of children, consent from a parent or legal guardian also was obtained. Figure 8, top, displays the multiunit EMG levels for subject 2’s first dorsal interosseus muscle (FDIif). Early TA activation may reflect biomechanical constraints of the stepping task, producing forward displacement of the center of mass over the changing base of support. , Hallett M, Simon SR. Aruin 7). Currently he is Assistant Professor at the University of Bologna. 215, No. 7.New hand-shape components that correspond to muscle synergies. This subject’s FDIif multiunit EMG showed peaks corresponding to the letters where the index finger was abducted away from the middle finger. The weight of the object was either supported by the table or by the subject’s other hand. The top panels show results for all of the subjects. 3, Journal of Cognitive Neuroscience, Vol. The most commonly observed synergy, involving early activation of left TA (and probably the right TA as well, as indicated by pilot testing) followed by activation of left GM, may be understood in terms of biomechanical constraints on the degrees of freedom. Figure 4 features two confusion matrices for one subject: grasping results (left) and spelling results (right). 5–7). 5, light shading) and flexion at the pip joints (Fig. Nashner FIG. This is also consistent with Figure 3, in which the range of motion among the four thumb angles is clearly different. At the other extreme, they are flexed at the mcp joint and adducted (PC1 max). FIG. Note the general similarity in the pattern for all subjects. 2). FB These were characterized by low intertrial variability in the joint angles (Fig. 96, No. 107, No. Knowing the extent to which postural muscles are recruited consistently in advance of these activities may be important for rehabilitation. The present study sought to align muscle synergies with these main postural synergies and to describe the form of membership of motor units in these postural/muscle synergies. Percent variance accounted for by each principal component. From September to March 2010 she was a visiting scholar in the Control Engineering Group at the University of Twente (Netherlands) under the supervision of Prof. Stefano Stramigioli. Instead, it was imperative that all of the force produced by their hand muscles went into holding the hand in a specific static posture. II. 3, 1 July 2007 | Journal of Neurophysiology, Vol. There was an 8- to 10-second delay between trials for repositioning of the subject and storage of data files. LM Then sequential activation of these dynamic postural synergies drive the system to produce gait motions. In this case, the instruction was to avoid producing forces against other digits while holding the more closed letter shapes (e.g., E, M, N, S, T, X). See Fig. BL They decrease the degrees of freedom during very early movements and I believe they contribute to both a perceptual and physical sense of midline as they create rudimentary central stability. Because pilot testing of 4 subjects indicated that the right TA was activated nearly synchronously with the left TA, only the left TA was monitored. 02, 19 May 2014 | Frontiers in Neurology, Vol. Pondering Postural Control: Neuromuscular Synergies - HeartSpace Physical TherapyHeartSpace Physical Therapy. (1998) rotated the PCs of one subject into alignment with the others, and Jerde et al. 9). 1, 1 October 2005 | Journal of Neurophysiology, Vol. Not surprisingly, the unit with the largest amplitude waveform (unit 3) exhibited a tuning curve that closely resembled the parent muscle. Y The correlation was weaker in five cases (** = P < 0. 2, 1 January 2008 | The Journal of Comparative Neurology, Vol. A minimal number of muscle groups, identified as being important in postural preparations for stepping tasks by previous researchers21,22,24,27,28 or on the basis of pilot work, were included in the search for clearly defined synergies. 11 echoed the results of the EMG PC analysis presented in Fig. Opposition space as a structuring concept for the analysis of skilled hand movements. , Sahrmann SA, Abrams RA, et al. The slopes of the two lines, however, were significantly different from zero (p < 0.05) for all three subjects. The SME (the percent of the information possible) is plotted against the number of PCs used to reconstruct hand postures for each of the subjects. As might be expected, the exact waveforms corresponding to EMGpc1 to -3 differed across subjects and even across the two recording sessions (grasping and spelling) for a given subject. Muscle activity was amplified, band-pass filtered (60–500 Hz) and digitized at 1,000 samples/s. For example, if the muscle activations characterized by EMGpc1 produced the postures defined by HSpc2, then the b2 weighting coefficient would be close to one and the other weighting coefficients would be close to zero. When we talk about hip and ankle strategies as part of balance control, we are talking about synergies. We made tracings of both of the subjects' feet to ensure consistent foot position during testing. The postural synergies implied by the first two principal components are depicted in Figure 6. The average hand postures produced by one subject for the six named objects have been rendered as three-dimensional images. NOTE: We request your email address only to inform the recipient that it was you who recommended this article, and that it is not junk mail. Release of pressure on the switch resulted in opening of the circuit at the start of the movement, and contact of the foot with the step closed the circuit at the end of the movement. P “As a biological phenomenon, a commonly accepted general definition of muscle synergy is simply a stable spatiotemporal pattern of activity across muscles simultaneously involved in the performance of a movement.” (McMorland AJ). Movement times were slower for “place” than for “step.” One of the more robust findings in the literature on postural adjustments is that the timing and sequencing of postural muscle activity are more variable for slower or less forceful movements.12,19,22,47 Another possibility is that the equilibrium requirements for “place” at the time of right foot contact with the step, involving complete deceleration of the right lower extremity and stabilization of the COM position over a new base of support, produced more complex postural muscle activity. A two-dimensional coordinate system for hand shape. ), whereas “fishing rod” and “rope” were located at the other extreme. , Latash ML. Hand and brain. For example the first three grasping and spelling PCs for subject 1 are shown on the right side of Fig. Of course we initially sought to relate the activity of each muscle to the angular excursion of individual joints (using individual linear regressions), but we found that the activity of each of the seven muscles was correlated (P < 0.001, n = 416) with the trial-to-trial values of ≥7 of the 17 joint angles. This result can be taken to suggest that the control of hand posture involves principally two synergies, manifested either singly or in combination. On average, the first three PCs accounted for ∼90% of the variance, with the first two PCs accounting for ∼84% (Table2), suggesting a substantial reduction in the number of degrees of freedom, from 15 to 2 or 3 degrees of freedom. A pair of bipolar surface electrodes was attached to the skin over each of 5 muscles, and 2 pairs were placed over the first dorsal interosseous (FDI). Effects of practice on modes and synergies To our knowledge, the current study in the first to address effects of practice on muscle synergies at two levels of a hypothetical hierarchy. An object was named at the beginning of each trial. However, we found that rotating the PC axes (Flanders and Herrmann, 1992) for this subject greatly improved the correlation with the PCs from the other subjects, as can be seen by comparing the open symbols in Figure 5(top panel) with the data for the other four subjects.