Biology subjects

White, O.

Publications and source records attributed to White, O..

4 recordsLinked to original sources

bioRxiv2018

The Effects of Varying Gravito-inertial Stressors on Grip Strength and Hemodynamic Responses Across Gender

The body behaves as a global system with many interconnected subsystems. While the effects of a gravitational change on body responses have been extensively studied in isolation, we are not aware of any study that examined two types of body responses concurrently. Here, we examined how the neurocognitive and cardiovascular systems interact in this singular context and whether these combined responses are influenced by gender. Ten women and nine men underwent three 5-minute centrifugation sessions (2.4g at the feet, 1.5g at the heart) in which participants rhythmically moved a hand-held object for 20 seconds. Grip force and hemodynamic responses were continuously measured during centrifugation and rest periods. Our results show that men optimize the modulation between grip force and the destabilizing load force, but not women. Exposure to artificial gravity induced higher heart rate and mean arterial pressure in both genders compared to baseline. However, during exposure, only women decreased heart rate across sessions. Interestingly, we found that Finishers (N=13, mostly men) and Non-Finishers (N=6, mostly women) exhibited divergent patterns of hemodynamic responses. We also suggest that the lack of grip force adaptation reported in women can be linked to challenged hemodynamic responses in that population. Finally, by deriving a simple model to predict failure to complete the experiment, we found that mean arterial pressure was the most relevant dimension, and not gender. As artificial gravity is being proposed as a countermeasure in long-term manned missions, our results are particularly important but also deserve follow-up studies.

physiology↗

bioRxiv2017

Does force-field adaptation induce after-effects on space representation?

Prism adaptation is a well-known model to study sensorimotor adaptive processes. It has been shown that following prism exposure, after-effects are not only restricted to the sensorimotor level but extend as well into spatial cognition. The main purpose of the present study was to investigate in healthy individuals whether expansion to spatial cognition is restricted to adaptive processes peculiar to prism adaptation or whether it occurs as well following other forms of adaptive process such as adaptation to a novel dynamic environment during pointing movements. Representational after-effects were assessed by the perceptual line bisection task before and after adaptation to a leftward or a rightward force field. The main results showed that adaptation developed at sensorimotor level but did not produce after-effects in space representation. However appropriate analysis showed that the slower a participant de-adapt to a rightward dynamic perturbation, the stronger the influence on the perceptual midline judgment during the late phase of the bisection task. The discussion highlights the commonalities between prism and dynamic adaptation on the effects on space representation.

neuroscience↗

bioRxiv2017

Smart switching in feedforward control of grip force during manipulation of elastic objects

Switching systems are common in artificial control systems. Here, we suggest that the brain adopts a switched feedforward control of grip forces during manipulation of objects. We measured how participants modulated grip force when interacting with soft and rigid virtual springs when stiffness varied nearly continuously between trials. We identified a sudden phase transition between two forms of feedforward control that differed in the timing of the synchronization between the anticipated load force and the applied grip force. The switch occurred several trials after a threshold stiffness level. These results suggest that in the control of grip force, the brain acts as a switching control system. This opens new research questions as to the nature of the discrete state variables that drive the switching.

neuroscience↗

bioRxiv2017

Grip force adjustments reflect prediction of dynamic consequences in varying gravitoinertial fields

One remarkable capacity when we grasp and manipulate tools relies on the ability to predict the grip force required to handle them in relation to their mechanical properties and the surrounding environment. However, rapid changes in the dynamical context may constitute a substantial challenge. Here, we test how participants can switch between different and never experienced dynamical environments induced by centrifugation of the body. Seven subjects lifted an object four times in a row successively in 1, 1.5, 2, 2.5, 2, 1.5 and 1g. We continuously measured grip force, load force and the gravitoinertial acceleration that was aligned with body axis (perceived gravity). Participants adopted stereotyped grasping movements immediately upon entry in a new environment and needed only one trial to adapt grip forces to a stable performance in each new gravity environment. While participants predictively applied larger grip forces when they expected increasing gravity steps, they did not decrease grip force proportionally when they expected decreasing gravity steps, indicating imperfect anticipation in that condition. The subjects performance could rather be explained by a combination of successful scaling of grip force according to gravity changes and a separate safety factor. The data suggest that in highly unfamiliar dynamic environments, grip force regulation is characterized by a combination of a successful anticipation of the experienced environmental condition, a safety factor reflecting strategic response to uncertainties about the environment and rapid feedback mechanisms to optimize performance under constant conditions.

neuroscience↗