Sensorimotor Mapping for Anticipatory Grip Force Modulation

Center for Systems Engineering and Applied Mechanics, Université catholique de Louvain, Louvain-la-Neuve, Belgium.
Journal of Neurophysiology (Impact Factor: 3.04). 09/2010; 104(3):1401-8. DOI: 10.1152/jn.00114.2010
Source: PubMed

ABSTRACT During object manipulation, predictive grip force modulation allows compensation for inertial forces induced by the object's acceleration. This coupling between grip force (GF) and load force (LF) during voluntary movements has demonstrated high levels of complexity, adaptability, and flexibility under many loading conditions in a broad range of experimental studies. The association between GF and LF indicates the presence of internal models underlying predictive GF control. The present experiment sought to identify the variables taken into account during GF modulation at the initiation of a movement. Twenty subjects performed discrete point-to-point movements under normal and hypergravity conditions induced by parabolic flights. Two control experiments performed under normal gravitational conditions compared the observed effect of the increase in gravity with the effects of a change in movement kinematics and a change in mass. In hypergravity, subjects responded accurately to the increase in weight during stationary holding but overestimated inertial loads. During dynamic phases, the relationship between GF and LF under hypergravity varied in a manner similar to the control test in which object mass was increased, whereas a change in movement kinematics could not reproduce this result. We suggest that the subjects' strategy for anticipatory GF modulation is based on sensorimotor mapping that combines the perception of the weight encoded during stationary holding with an internal representation of the movement kinematics. In particular, such a combination reflects a prior knowledge of the unequivocal relationship linking mass, weight, and loads under the invariant gravitational context experienced on Earth.


Available from: Jean-Louis Thonnard, May 29, 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In everyday life, we seamlessly adapt our movements and consolidate them to multiple behavioral contexts. This natural flexibility seems to be contingent on the presence of dynamic sensorimotor cues and cannot be reproduced when static visual or haptic cues are given to signify different behavioral contexts. So far dynamic sensorimotor cues have only been succesful in learning two opposing perturbations if provided before exposure to the perturbation. Here we show that vestibular cues, that are only available during the perturbation, improve the formation and recall of multiple control strategies. We exposed subjects to inertial forces, by accelerating them laterally on a vestibular platform. The coupling between reaching movement (forward-backward) and acceleration direction (leftward-rightward) switched every 160 trials, resulting in two opposite force environments. When exposed for a second time to the same environment, with the opposite environment in between, subjects showed retention resulting in a ~3x faster adaptation rate compared to the first exposure. Our results suggest that vestibular cues provide dynamic contextual information, which is used to facilitate independent learning and recall of multiple motor memories. Vestibular cues provide feedback about the underlying cause of reach errors, thereby disambiguating the various task environments and reducing interference of motor memories.
    Journal of Neurophysiology 06/2013; 110(6). DOI:10.1152/jn.00914.2012 · 3.04 Impact Factor
  • 64th IAF Congress, Beijing, China; 10/2013
  • [Show abstract] [Hide abstract]
    ABSTRACT: Moving requires handling gravitational and inertial constraints pulling on our body and on the objects that we manipulate. Although previous work emphasized that the brain uses internal models of each type of mechanical loads, little is known about their interaction during motor planning and execution. In this report, we examine visually guided reaching movements in the horizontal plane performed by naive participants exposed to changes in vertical gravity during parabolic flight. This approach allowed us to isolate the effect of gravity because the environmental dynamics along the horizontal axis remained unchanged. We show that vertical gravity has a direct effect on movement kinematics with faster movements observed following transitions from normal to hyper-gravity (1.8g), followed by significant movement slowing after the transition from hyper- to zero-gravity. We recorded finger forces applied on an object held in precision grip and found that the coupling between grip force and inertial loads displayed a similar effect, with an increase in grip force modulation gain under hyper-gravity, followed by a reduction of modulation gain after entering the zero-gravity environment. We present a computational model to illustrate that these effects are compatible with the hypothesis that participants partially attributed changes in weight to changes in mass, and scaled incorrectly their motor commands with changes in gravity. These results highlight a rather direct internal mapping between the force generated during stationary holding against gravity and the estimation of inertial loads that limb and hand motor commands must overcome.
    Journal of Neurophysiology 04/2014; 112(2). DOI:10.1152/jn.00061.2014 · 3.04 Impact Factor