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Lookup NU author(s): Professor Kianoush Nazarpour, Amy Barnard, Professor Andrew Jackson
Correlation structure in the activity of muscles across movements is often interpreted as evidence for low-level, hardwired constraints on upper-limb function. However, muscle synergies may also emerge from optimal strategies to achieve high-level task goals within a redundant control space. To distinguish these contrasting interpretations, we examined the structure of muscle variability during operation of a myoelectric interface in which task constraints were dissociated from natural limb biomechanics. We found that, with practice, human subjects learned to shape patterns of covariation between arbitrary pairs of hand and forearm muscles appropriately for elliptical targets whose orientation varied on a trial-by-trial basis. Thus, despite arriving at the same average location in the effector space, performance was improved by buffering variability into those dimensions that least impacted task success. Task modulation of beta-frequency intermuscular coherence indicated that differential recruitment of divergent corticospinal pathways contributed to positive correlations among muscles. However, this feedforward mechanism could not account for negative correlations observed in the presence of visual feedback. A second experiment revealed the development of fast, target-dependent visual responses consistent with “minimum intervention” control correcting predominantly task-relevant errors. Together, these mechanisms contribute to the dynamic emergence of task-specific muscle synergies appropriate for a wide range of abstract task goals.
Author(s): Nazarpour K, Barnard A, Jackson A
Publication type: Article
Publication status: Published
Journal: Journal of Neuroscience
Year: 2012
Volume: 32
Issue: 36
Pages: 12349-12360
Print publication date: 05/09/2012
Date deposited: 08/11/2012
ISSN (print): 0270-6474
ISSN (electronic): 1529-2401
Publisher: Society for Neuroscience
URL: http://dx.doi.org/10.1523/JNEUROSCI.5481-11.2012
DOI: 10.1523/JNEUROSCI.5481-11.2012
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