Sensorimotor Mapping for Anticipatory Grip Force Modulation

After an exposure to weightlessness, the central nervous system operates under new dynamic and sensory contexts. To find optimal solutions for rapid adaptation, cosmonauts have to decide whether parameters from the world or their body have changed and to estimate their properties. Here, we investigated sensorimotor adaptation after a spaceflight of 10 days. Five cosmonauts performed forward point-to-point arm movements in the sagittal plane 40 days before and 24 and 72 h after the spaceflight. We found that, whereas the shape of hand velocity profiles remained unaffected after the spaceflight, hand path curvature significantly increased 1 day after landing and returned to the preflight level on the third day. Control experiments, carried out by 10 subjects under normal gravity conditions, showed that loading the arm with varying loads (from 0.3 to 1.350 kg) did not affect path curvature. Therefore, changes in path curvature after spaceflight cannot be the outcome of a control process based on the subjective feeling that arm inertia was increased. By performing optimal control simulations, we found that arm kinematics after exposure to microgravity corresponded to a planning process that overestimated the gravity level and optimized movements in a hypergravity environment (∼1.4 g). With time and practice, the sensorimotor system was recalibrated to Earth's gravity conditions, and cosmonauts progressively generated accurate estimations of the body state, gravity level, and sensory consequences of the motor commands (72 h). These observations provide novel insights into how the central nervous system evaluates body (inertia) and environmental (gravity) states during sensorimotor adaptation of point-to-point arm movements after an exposure to weightlessness.

Section: Sensorimotor Adaptations After Spaceflightsupporting

confidence: 92%

Section: Sensorimotor Adaptations After Spaceflightmentioning

confidence: 77%

Section: Sensorimotor Adaptations After Spaceflightmentioning

confidence: 96%

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Sensorimotor adaptation of point-to-point arm movements after spaceflight: the role of internal representation of gravity force in trajectory planning

Gaveau

Païzis

Berret

et al. 2011

“…In this framework, varying the gravity induces a mismatch between the expected and actual inertial constraints, with the consequences for reaching control and object manipulation presented above. We previously suggested this mechanism to explain the increases in the gain of grip force modulation with load force experienced during vertical reaching movements (Crevecoeur et al 2010b). However, this interpretation was subject to caution because this previous study could not dissociate possible effects of mass estimation errors from a possible influence of changes in the environmental dynamics (Crevecoeur et al 2009b).…”

Section: Discussionmentioning

confidence: 99%

Gravity-dependent estimates of object mass underlie the generation of motor commands for horizontal limb movements

Crevecoeur

McIntyre

Thonnard

et al. 2014

Crevecoeur F, McIntyre J, Thonnard JL, Lefèvre P. Gravitydependent estimates of object mass underlie the generation of motor commands for horizontal limb movements. J Neurophysiol 112: 384 -392, 2014. First published April 30, 2014 doi:10.1152/jn.00061.2014.-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 load, 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 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 gravity has a direct effect on movement kinematics, with faster movements observed after transitions from normal gravity to hypergravity (1.8g), followed by significant movement slowing after the transition from hypergravity 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 hypergravity 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 attribute changes in weight to changes in mass and scale 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. reaching control; object manipulation; altered gravity; feedback control; motor adaptation; horizontal movements ANY MOVEMENT, from the mundane lift of a coffee cup to the skillful performance of elite athletes or musicians, requires accurate knowledge of both gravitational constraints pulling on our limbs and on the objects that we manipulate and inertial loads arising when we move the objects around. To achieve this, building internal models of the effect of gravito-inertial

“…Several studies have characterized the sensorimotor control of precision grip and shown that in general, the grip force exhibits a predictive compensation for the load constraints induced by the interaction with the object. Such anticipatory scaling is known to be based on internal models, prior knowledge of the object properties, and cutaneous feedback of the mechanical properties of the fingertip/object interface (André et al 2010;Augurelle et al 2003;Crevecoeur et al 2010;Danion and Sarlegna 2007;Flanagan and Wing 1993, 1995Johansson and Westling 1984;Westling and Johansson 1984;Witney et al 2004).…”

mentioning

confidence: 99%

Adaptive control of grip force to compensate for static and dynamic torques during object manipulation

Crevecoeur

Giard

Thonnard³

et al. 2011

Manipulating a cup by the handle requires compensating for the torque induced by the moment of the mass of the cup relative to the location of the handle. In the present study, we investigated the control strategy of subjects asked to perform grip-lift movements with an object with center of mass located away from the grip axis. Participants were asked to lift the manipulandum with a two-fingers precision grip and stabilize it in front of a visual target. Subjects showed a gradual and slow adaptation of the grip-force scaling across trials: the grip force tended to decrease slowly, and the temporal coordination between grip-force and load-torque rates displayed gradually, better-coordinated patterns. Importantly, this adaptation was much slower than the stabilization of the same parameters measured either when no torque came into play or after previous adaptation to the presence of a torque. In contrast, the maximum rotation induced by the torque was controlled efficiently after only few trials, and an unexpected decrease in the tangential torque produced significant overcompensation. An unexpected increase in torque produced a consistent opposite effect. This shows that the compensation for the dynamic torque was based on an anticipatory, dynamic counter-torque produced by the arm and wrist motor commands. The comparatively slow stabilization of grip-force control suggests a specific adaptation process engaged by the presence of the torque. This paradigm, including tangential torques, clearly constitutes a powerful tool to extract the adaptive component of grip control during object manipulation.