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: 2.89). 09/2010; 104(3):1401-8. DOI: 10.1152/jn.00114.2010
Source: PubMed


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.

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    • "However, in accord with the approach of the present study, this is compatible with the fact that the hypergravity has a limited effect on state estimation and internal prediction (Lackner and DiZio 2009; Nowak et al. 2001). Indeed, the correlation between the grip and load force increments were as good in hypergravity as in normal gravity, although the amplitude of the load variation was possibly overestimated (Crevecoeur et al. 2010). It suggests that hyperand microgravity environments fundamentally differ by the difference of uncertainty related to the internal prediction to which subjects are exposed. "
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