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Complex Upper-Limb Movements Are Generated by Combining Motor Primitives that Scale with the Movement Size

2018; Nature Portfolio; Volume: 8; Issue: 1 Linguagem: Inglês

10.1038/s41598-018-29470-y

2045-2322

José García Vivas Miranda, Jean‐François Daneault, Gloria Vergara‐Diaz, Ângelo Frederico Souza de Oliveira e Torres, Ana Paula Quixadá, Marcus de Lemos Fonseca, João Paulo Bomfim Cruz Vieira, Vitor Sotero dos Santos, Thiago C. Figueiredo, Elen Beatriz Pinto, Norberto Peña, Paolo Bonato,

Action Observation and Synchronization

The hand trajectory of motion during the performance of one-dimensional point-to-point movements has been shown to be marked by motor primitives with a bell-shaped velocity profile. Researchers have investigated if motor primitives with the same shape mark also complex upper-limb movements. They have done so by analyzing the magnitude of the hand trajectory velocity vector. This approach has failed to identify motor primitives with a bell-shaped velocity profile as the basic elements underlying the generation of complex upper-limb movements. In this study, we examined upper-limb movements by analyzing instead the movement components defined according to a Cartesian coordinate system with axes oriented in the medio-lateral, antero-posterior, and vertical directions. To our surprise, we found out that a broad set of complex upper-limb movements can be modeled as a combination of motor primitives with a bell-shaped velocity profile defined according to the axes of the above-defined coordinate system. Most notably, we discovered that these motor primitives scale with the size of movement according to a power law. These results provide a novel key to the interpretation of brain and muscle synergy studies suggesting that human subjects use a scale-invariant encoding of movement patterns when performing upper-limb movements.