Compositionality - Combinations of Muscle Synergies in the Construction of Motor Behavior Emilio...
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![Page 1: Compositionality - Combinations of Muscle Synergies in the Construction of Motor Behavior Emilio Bizzi Massachusetts Institute of Technology.](https://reader031.fdocuments.in/reader031/viewer/2022032708/56649e755503460f94b75db1/html5/thumbnails/1.jpg)
Compositionality - CombinationsCompositionality - Combinations
of Muscle Synergies in theof Muscle Synergies in the
Construction of Motor BehaviorConstruction of Motor Behavior
Emilio BizziMassachusetts Institute of Technology
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Compositionality: The genetic code and language are examplesof systems in which discreteelements can generate a large number of meaningful entitiesthat are quite distinct from thoseof their elements
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Modularity
• Does the vertebrate motor system construct movements combining discrete modular elements?
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The Structure of Skeletal Muscle
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EMG recordings from 16 leg muscles
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a
b
c
synergy
muscles
Evidence for muscle synergies ?
• If a group of muscles is controlled as a unit, i.e. as a synergy, then the level of activity of those muscles should be correlated
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Extraction algorithm
• We developed an iterative algorithm to extract a set of time-varying synergies that minimize the total reconstruction error
[d’Avella & Tresch, NIPS 14]
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Synergy identification
– EMGs were averaged every 100ms
– The number of synergies was chosen as the minimum number that could explain at least 95% of the variation in the data
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Three kicking synergies
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Synergies extracted from jumping swimming and walking
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Synergy validation
• Are the identified synergies just an arbitrary description of the constraints in the motor output?
• In support of a neural origin of synergies synergy recruitment capture well the pattern
of covariation across different episodes similar synergies are extracted across
behaviors
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______300ms
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Summary of results• The muscle patterns recorded in a variety of
natural behaviors can be reconstructed as combination of a small number of muscle synergies
• Synergies are similar across behaviors
• A few synergies are identified only in specific behaviors
• Some synergies have a single dominant muscle and they are part of the same sequence in different behaviors
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Focal microstimulation of thelumbar spinal cord hasRevealed a small number of circuits that are organizedto produce muscle synergies.
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Motor control primitives in the spinal cord
Mussa-Ivaldi, Giszter and BizziCold Spring Harbor Symposium on Quantitative Biology, vol. 55 (1990)
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Regions of the lumbar spinal cord containing the neural circuitry that
specifies the force fields
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Tonic Forces
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Costimulation of the lumbar interneurons
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Motor systems – levels of control
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Examples of Cell Activity Recorded in the Primary Motor Cortex
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Two other types of memory cells
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Collaborators
A. d’AvellaS. Giszter
F. A. Mussa-IvaldiP. Saltiel
M. TreschVincent C. K. Cheung
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The finding that combination of synergies can explain our data suggest that our synergies may correspond to building blocks of the CPGs, sometimes formulated as a mosaic of “unit burst generators” (Grillner, 1985)
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Results• The EMG patterns recorded during
natural motor behaviors can be reconstructed by combinations of a few time-varying muscle synergies
• In some behaviors, there is a systematic relationship between synergy activation coefficients and features of the movement (e.g. kick direction)
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Motor systems – levels of control
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Copyright ©2005 Society for Neuroscience
Cheung, V. C. K. et al. J. Neurosci. 2005;25:6419-6434
Figure 4. Examples of swimming synergies from analysis stage I
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Summary
The main finding is that both intact and deafferented behaviors are primarily generated by the same set of synergies.
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Modularity in the spinal cord
• ‘Half-centers’ for the control of rhythmic behaviors (e.g. locomotion) (Brown 1910, Jankowska 1967)
• Central pattern generators (CPGs) by combinations of ‘unit burst generators’ (Grillner 1981)
• Force field modules (Bizzi 1991)
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Copyright ©2005 Society for Neuroscience
Cheung, V. C. K. et al. J. Neurosci. 2005;25:6419-6434
Figure 9. Reconstructing the original EMGs with synergies and their coefficients
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Copyright ©2005 Society for Neuroscience
Cheung, V. C. K. et al. J. Neurosci. 2005;25:6419-6434
Stage I analysis of swimming EMGs before and after deafferentation