Andrea d'Avella: “Muscle synergies for motor control”
12:00 〜 13:00
CiNet 1F Conference Room
Department of Biomedical and Dental Sciences and Morphofunctional Imaging
University of Messina, Italy
Laboratory of Neuromotor Physiology
Santa Lucia Foundation, Rome, Italy
Host PI : Eiichi Naito
Friday Lunch Seminar is held from 12:15 to 13:00 but this one will start at 12:00.
A fundamental challenge in neuroscience is understanding how the central nervous system (CNS) succeeds in controlling motor skills that require the coordination of many degrees-of-freedom. A long-standing hypothesis is that the CNS relies on muscle synergies, coordinated activations of groups of muscles, to simplify motor control. Evidence that the combinations of a small number of muscle synergies underlies the generation of muscle activation patterns has come from several studies performed in the last two decades with different species and experimental tasks. Muscle synergies, extracted from multi-muscle EMG recordings using multidimensional decomposition algorithms such as non-negative matrix factorization, capture regularities in the spatial, temporal, and spatiotemporal organization of the muscle patterns. The CNS might then simplify control by using muscle synergies as a set of modules that provide a low-dimensional yet adequate representation of the motor commands. However, whether muscle synergies are only a parsimonious description of the regularities of the motor commands rather than a key feature of their neural organization is still debated.
Stronger evidence for a neural organization of muscle synergies would come from testing muscle synergies as a causal model and from identifying their neural substrates. According to the first approach, if muscle synergies are organized by the CNS they must affect the difficulty in learning or adapting motor skills. An experiment with human subjects using myoelectric control to move a mass in a virtual environment has tested the prediction that it must be harder to adapt to perturbations that require new or modified synergies than to adapt to perturbations that can be compensated by recombining existing synergies.
Novel perturbations were generated by altering the mapping between recorded EMG and simulated force applied on the mass, as in a complex surgical rearrangement of the tendons. After identifying muscle synergies, two types of virtual surgeries were performed. After compatible virtual surgeries, a full range of movements could still be achieved recombining the synergies, whereas after incompatible virtual surgeries new or modified synergies were required. In contrast, both types of surgeries could be compensated with similar changes in the recruitment of individual muscles. As predicted, adaptation after compatible surgeries was faster than after incompatible ones. According to the second approach, to identify neural substrates of muscle synergies, hand movements were evoked by electrical stimulation of motor cortical areas of non-human primates. Across stimulation sites, the evoked muscle activation patterns could be accurately reconstructed by the combinations of a few muscle synergy highly similar to the muscle synergies extracted during voluntary reach, grasp, and transport movements. Moreover, the activity recorded from a population of cortical units showed a spatiotemporal organization that resembled that of the forelimb muscles involved in the movements. Decomposition of both muscle and neural activity patterns into spatiotemporal synergies revealed similar dimensionality, timing, and amplitude modulation. In sum, both experimental approaches suggest that muscle synergies are key elements organized by the CNS for controlling a complex musculoskeletal system by directly mapping task goals into a small number of synergy combination parameters.
The Friday Lunch Seminar is CiNet's main regular meeting series, held every week at 12:15 in the beautiful main lecture theatre on the ground floor at CiNet. The talks are typically 40mins long and orientated towards an inter-disciplinary audience. They are informal, social, and most people bring their own lunch to eat during the talk. They are open to anyone who is feeling curious and wants to come, regardless of where you work.