TY - JOUR T1 - Spatiotemporal organization of whole-body muscle activity during upright reaching movements in various directions: modularity or not modularity? JF - bioRxiv DO - 10.1101/155085 SP - 155085 AU - Pauline M. Hilt AU - Ioannis Delis AU - Thierry Pozzo AU - Bastien Berret Y1 - 2017/01/01 UR - http://biorxiv.org/content/early/2017/06/24/155085.abstract N2 - The modular control hypothesis suggests that motor commands are built from pre-coded modules whose specific combined recruitment can allow the performance of virtually any motor task. Despite considerable experimental support, this hypothesis remains tentative as classical findings of reduced dimensionality in muscle activity may also result from other constraints (biomechanical couplings, data averaging or low dimensionality of motor tasks). Here we assessed the effectiveness of modularity in describing muscle activity by tackling typical limitations in the experimental and computational design, and testing two essential predictions: (i) muscle patterns must be decomposable onto invariant modules and (ii) module recruitment must determine the task at hand. We designed a comprehensive experiment comprising 72 distinct point-to-point whole-body movements for which the activity of 30 muscles was recorded. To identify invariant modules, we used a space-by-time decomposition of single-trial muscle activity that has been shown to encompass classic modularity models. To critically test the decompositions, we examined not only the amount of variance they explained but also whether the direction of the movement performed on each trial could be inferred by the single-trial module activations. Overall, the modular decomposition was more effective than non-modular alternatives in terms of data approximation, direction discrimination and dimensionality reduction. These findings show that few spatial and temporal modules give a compact approximate representation of muscle patterns carrying nearly all task-relevant information of a variety of whole-body reaching movements. ER -