Tool Embodiment Is Reflected in Movement Multifractal Nonlinearity

Recent advances in neuroscience have linked dynamical systems theory to cognition. The main contention is that extended cognition relies on a unitary brain-body-tool system showing the expected signatures of interaction-dominance reflected in a multifractal behavior. This might be particularly relevant when it comes to understanding how the brain is able to embody a tool to perform a task. Here we applied the multifractal formalism to the dynamics of hand movement while one was performing a computer task (the herding task) using a mouse or its own hand as a tool to move an object on the screen. We applied a focus-based multifractal detrended fluctuation analysis to acceleration time series. Then, multifractal nonlinearity was assessed by comparing original series to a finite set of surrogates obtained after Iterated Amplitude Adjusted Fourier transformation, a method that removes nonlinear multiscale dependencies while preserving the linear structure of the time series. Both hand and mouse task execution demonstrated multifractal nonlinearity, a typical form of across-scales interactivity in cognitive control. In addition, a wider multifractal spectrum was observed in mouse condition, which might highlight a richer set of interactions when the cognitive system is extended to the embodied mouse. We conclude that the emergence of multifractal nonlinearity from a brain-body-tool system pleads for recent theories of radical tool embodiment. Multifractal nonlinearity may be a promising metric to appreciate how physical objects—but also virtual tools and potentially prosthetics—are efficiently embodied by the brain

Corrigendum: Frequency-Specific Fractal Analysis of Postural Control Accounts for Control Strategies

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Studying the influence of a solid shell on lava dome growth and evolution using the level set method

A finite element formulation of the level set method, a technique to trace flow fronts and interfaces without element distortion, is presented to model the evolution of the free surface of a spreading flow for a highly viscous medium on a horizontal surface. As an example for this class of problem we consider the evolution of an axisymmetric lava dome. Equilibrium configurations of lava domes have been modelled analytically as brittle shells enclosing pressurized magma. The existence of the brittle shell may be viewed as a direct consequence of the strong temperature dependence of the viscosity. The temperature dependence leads to the formation of a thin predominantly elastic-plastic boundary layer along the free surface and acts as a constraint for the shape and flow of the lava dome. In our model, we adopt Iverson's assumption that the thin boundary layer behaves like an ideal plastic membrane shell enclosing the ductile interior of the lava dome. The effect of the membrane shell is then formally identical to a surface tension-like boundary condition for the normal stress at the free surface. The interior of the dome is modelled as a Newtonian fluid and the axisymmetry equations of motion are formulated in a Eulerian framework. We show that the level set is an effective tool to trace and model deforming interfaces for the example of the free surface of a lava dome. We demonstrate that Iverson's equilibrium dome shapes are indeed steady states of a transient model. We also show how interface conditions in the form of surface tension involving higher order spatial derivative (curvature) can be considered within a standard finite element framework

Multifractality in the Movement System When Adapting to Arm Cranking in Wheelchair Athletes, Able-Bodied Athletes, and Untrained People

Complexity science has helped neuroscientists shed new light on brain-body coordination during movement performance and motor learning in humans. A critical intuition based on monofractal approaches has been a fractal-like coordination in the movement system, more marked in motor-skilled people. Here we aimed to show that heterogeneity in scaling exponents of movements series, literally multifractality, may reflect a special kind of interactions spanning multiple temporal scales at once, which can be grasped by a focus-based multifractal detrended fluctuation analysis. We analyzed multifractality in the variability structure of a 10-min arm cranking movement series repeated as 3 sets a day for 3 days, comparatively with their linearized (phase-randomized) surrogate series in sedentary (SED) untrained people, wheelchair athletes (WATH), and able-bodied athletes (ATH). Arm cranking exercise was chosen to minimize external variations, which tend to interfere with internal origin of variability. Participants were asked to maintain a regular effort and torque output served as the performance variable. Our first hypothesis suggests greater multiscale interactions in trained (WATH, ATH) versus untrained (SED) people, reflected in a wider range of scaling exponents characterizing movement series, providing the system with significant robustness. As a second hypothesis, we addressed a possible advantage in WATH over ATH due to greater motor skills in upper-limbs. Multifractal metrics in original and surrogate series showed ubiquitous, but different, multifractal behaviors in expert (ATH and WATH indistinctively) versus novice (SED) people. Experts exhibited high multifractality during the first execution of the task; then multifractality dropped in following repetitions. We suggest an exacerbated robustness of the movement system coordination in experts when discovering the task. Once task novelty has worn off, poor external sources of variability and limited risks of task failure have been identified, which is reflected in the narrower range of scale interactions, possibly as an energy cost effective adaptation. Multifractal corollaries of movement adaptation may be helpful in sport training and motor rehabilitation programs

Influence of individual energy cost on running capacity in warm, humid environments

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Analyse modulaire in vivo du contrôle du flux énergétique dans le muscle squelettique de rat par spectroscopie RMN 31P (influence de l'hypoxie et de l'activité physique)

Nous étudions les propriétés cinétiques in vivo de l énergétique dans le muscle squelettique actif. Le métabolisme énergétique est abordé comme un système de transfert d énergie via des intermédiaires métaboliques : un système à deux modules (Producteur et Consommateur) connectés par un intermédiaire énergétique commun (PCr). L analyse MoCA associée à la mesure de PCr par SRM 31P permet d obtenir in vivo les coefficients d élasticité et de contrôle pour une large gamme d activité. Notre première étude montre un déplacement du contrôle sur le flux, de la demande vers la production, à mesure que l activité contractile augmente; ce changement est principalement dû à un changement de sensibilité du Producteur vis-à-vis des intermédiaires énergétiques. L analyse top-down d élasticité est utilisée pour identifier les cibles de l hypoxie chronique (6 semaines, 10,5%O2), de l hypothyroïdisme et de l activité physique chronique, décrits comme des stress pouvant modifier des réactions du Producteur et/ou du Consommateur. Les propriétés internes du système ne sont pas affectées par les changements de masse mitochondriale et/ou du type de fibres musculaires. La détermination expérimentale des propriétés internes du système permet de quantifier l effet direct de l hypoxie aiguë. Dans nos conditions, la principale adaptation du métabolisme énergétique à l hypoxie chronique est une baisse de la sensibilité du Producteur vis-à-vis d une diminution de l O2 ambiant. La mise au point de notre approche permet d étudier de manière intégrée le métabolisme énergétique du muscle squelettique et d identifier les altérations fonctionnelles suite à des stimuli physiologiques ou pathologiques.We attempted to describe quantitatively the main kinetic properties of energy metabolism of contracting skeletal muscles of rats in vivo. For that, energy metabolism was defined as a two-module system (supply-demand) connected by energetic intermediate (PCr as representative) assessed in vivo by 31P MRS; such a simplification allowed application of top-down (modular) control analysis to obtain elasticity and control coefficients over a broad spectrum of muscle activities. The main finding of our first study was the shift of control over the contraction from demand at low workloads to supply at high workloads. This was mainly due to the change in sensitivity of supply toward energetic intermediates. Top-down elasticity analysis was used to identify the targets (supply and/or demand) of hypoxic conditioning (6 weeks at 10.5% O2), hypothyroïdism and chronic physical activity, described as stress generating muscle remodelling. No change in the elasticity of neither supply nor demand toward intermediates were observed: internal properties of the system were unaffected by reported changes in mitochondrial content and/or change in fibre type composition. Once internal properties experimentally obtained, the direct effect of acute hypoxia by measuring the contraction energy flux change was quantified. The main response of energy metabolism to chronic hypoxia was the decrease in sensitivity of supply toward acute decrease in ambient O2. As demonstrated by these applications, the design and set up of our experimental modular approach has the potential to detect a number of physiological effects on energy metabolism of skeletal muscle at a system level of integration.BORDEAUX2-SCD-Sc.Sport/Educ.phys (335222105) / SudocSudocFranceF

Multiscale Entropy of Cardiac and Postural Control Reflects a Flexible Adaptation to a Cognitive Task

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Entropy in postural and cardiac-autonomic control as a marker of adaptability to a mental task in young vs. middle-aged healthy males

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