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The Journal of Neuroscience, January 7, 2009, 29(1):191-205; doi:10.1523/JNEUROSCI.3426-08.2009

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Behavioral/Systems/Cognitive
Modular Control of Pointing beyond Arm's Length

Bastien Berret,^1,2 François Bonnetblanc,^1,2 Charalambos Papaxanthis,^1,2 and Thierry Pozzo^1,2,3

¹Université de Bourgogne, Dijon, Campus Universitaire, Unité de Formation et de Recherche en Sciences et Techniques des Activités Physiques et Sportives, and ²Institut National de la Santé et de la Recherche Médicale, Unité 887, Motricité-Plasticité, F-21078 Dijon, France, and ³Italian Institute of Technology, 16163 Genoa, Italy

Correspondence should be addressed to Thierry Pozzo, Institut National de la Santé et de la Recherche Médicale, Unité 887, Campus Universitaire, Motricité-Plasticité, F-21078 Dijon, France. Email: thierry.pozzo{at}u-bourgogne.fr

Hand reaching and bipedal equilibrium are two important functions of the human motor behavior. However, how the brain plans goal-oriented actions combining target reaching with equilibrium regulation is not yet clearly understood. An important question is whether postural control and reaching are integrated in one single module or controlled separately. Here, we show that postural control and reaching motor commands are processed by means of a modular and flexible organization. Principal component and correlation analyses between pairs of angles were used to extract global and local coupling during a whole-body pointing beyond arm's length. A low-dimensional organization of the redundant kinematic chain allowing simultaneous target reaching and regulation of the center of mass (CoM) displacement in extrinsic space emerged from the first analysis. In follow-up experiments, both the CoM and finger trajectories were constrained by asking participants to reach from a reduced base of support with or without knee flexion, or by moving the endpoint along a predefined trajectory (straight or semicircular trajectories). Whereas joint covaried during free conditions and under equilibrium restrictions, it was decomposed in two task-dependent and task-independent modules, corresponding to a dissociation of arm versus legs, trunk, and head coordination, respectively, under imposed finger path conditions. A numerical simulation supported the idea that both postural and focal subtasks are basically integrated into the same motor command and that the CNS is able to combine or to separate the movement into autonomous functional synergies according to the task requirements.

Key words: whole-body pointing; equilibrium; center of mass; finger trajectory; joint coupling; modular control

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Received July 22, 2008; revised Nov. 24, 2008; accepted Nov. 26, 2008.

Correspondence should be addressed to Thierry Pozzo, Institut National de la Santé et de la Recherche Médicale, Unité 887, Campus Universitaire, Motricité-Plasticité, F-21078 Dijon, France. Email: thierry.pozzo{at}u-bourgogne.fr

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