Abstracts

Joseph McIntyre, Tecnalia, Spain

Perspectives on the role of gravity for eye-hand coordination.

In many aspects, the weightless conditions of orbital spaceflight have provided us with unique opportunities to test key hypotheses with respect to human neurophysiology and cognition. Moving the limbs and maintaining an upright posture implicitly require that the forces of gravity be taken into account when generating motor commands. This invites the questions: Are gravity-related components of muscle activations generated through reflexive reactions to forces sensed in the limb during the motion? Is the static pull of gravity on the body resisted through the intervention of specialized graviceptor inputs on the motor system’s final pathway? Or do the brain’s cognitive capabilities enable predictive actions based on multisensory cues? In this talk I will present a number of examples of how experiments performed in weightlessness have provided insights into the reference frames, internal models and neural circuits underpinning sensorimotor behaviour in humans.

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Lionel Bringoux, Aix-Marseille Université, France

How do different gravity-related force fields influence motor control and adaptation during whole-body reaching?

This presentation explores how gravity-related force fields affect motor control and adaptation during whole-body reaching. Experiments conducted in microgravity (0g) and hypergravity (1.8g) revealed fast reorganization of arm and postural control in 0g, but persistent impairments in 1.8g. Participants maintained accuracy and online correction ability in 0g, suggesting flexible internal models. However, adaptation failed under hypergravity, likely due to residual Earth-based motor organization. Overall, initial state estimates and internal models play a key role in adjusting motor behavior to novel gravitational contexts.

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Pierre Denise, Université de Caen, France

Effect of gravity level on perception of whole-body movements.

Although many perceptual consequences of microgravity can lead to mission-threatening errors, errors associated with misinterpretation of self-motion and time are perhaps among the most critical. Some observations suggest that weightlessness alters the perception of movements and time, but most of these observations are indirect or anecdotal. Understanding how gravity affects the perception of self-motion and time is therefore critical to the development of effective operational microgravity environments and the training of astronauts. To answer this question, we conducted several parabolic flight experiments to assess the effect of gravity on the perception of the amplitude and duration of passive rotations and translations during whole-body movements.

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Simon Vandergooten, UCLouvain

From Earth to Orbit : influence of graviceptive inputs on reach and grip behavior.

Gravity has long been proposed to play a unique role in sensorimotor coordination, either as a driving force considered by the motor system to minimize energy expenditure, or as an unmistakable external cue for spatial orientation. Investigating the impact of gravity on daily-life activities such as object manipulation tasks, an essential skill for the success of future space missions, has so far been limited to short-term and transient exposures to weightlessness during parabolic flights. It therefore remained unknown whether or how the brain adapts to long-term and stable exposure to weightlessness as experienced by astronauts on the ISS. In this thesis, we study the kinematics of arm movements and the dynamics of finger forces in human participants exposed to weightless environments or to tilted postures while manipulating objects. We first explore the sensorimotor coordination of astronauts before, during, and after their mission onboard the ISS. It appears that gravitational and visual cues play a critical role in sensorimotor integration and eye-hand coordination. We then study how, on Earth, body tilt with respect to gravity influences sensorimotor coordination and test if the upright posture, by virtue of being at a biomechanical singularity induced by the force of gravity, represents a unique condition in which sensorimotor coordination is the most stable. Finally, we investigate the contributions of gravitational and biomechanical effects to kinematics features of reaching arm movements along the vertical and horizontal axes both on the ground and in space. We show with numerical simulations based on optimal control model considering the nonlinear arm dynamics that the formation of arm movement trajectories in the motor system is shaped by both effects and is quickly adapted to changes in the environment dynamics. These studies contribute to a better understanding of the role played by graviceptive inputs in object manipulation.

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Organizers / contact

• Philippe Lefèvre