Biology subjects

Legrand, T.

Publications and source records attributed to Legrand, T..

9 recordsLinked to original sources

bioRxiv2026

Temporal structure of postural sway reveals altered cortical postural coupling in aging and stroke: insights from nonlinear dynamics and state-space analysis

BackgroundBalance maintenance in humans is not only a mechanical process, but it also relies on continuous interactions between cortical activity and body dynamics. Alterations in postural sway are commonly observed in aging and stroke and are frequently used to assess balance impairment. However, similar balance deficits do not necessarily reflect similar underlying sensorimotor control mechanisms. Therefore, investigating brain-body interactions and their relationship to characteristics of postural behavior may provide deeper insights into the neural processes underlying balance dysfunction in these populations. ObjectiveTo determine whether brain-body coupling is associated with characteristics of postural behavior captured by the temporal organization of postural fluctuations beyond conventional magnitude-based measures of postural sway, and whether these relationships differ between stroke survivors, healthy older adults, and young adults. MethodsEEG and center-of-pressure (CoP) signals were recorded simultaneously in stroke survivors (n = 12), healthy older adults (n = 18), and young controls (n = 17) during quiet standing under 4 different manipulated sensory conditions. Sway-based corticokinematic coherence (CKC) as well as linear and nonlinear features (sample entropy, SE; fractal dimension, FD) of CoP were extracted. Linear mixed-effects model assessed associations between features and CKC, and model performance was compared using Akaike Information Criterion. Multidimensional state vectors were constructed from CKC, linear and nonlinear CoP features, and Euclidean distances between consecutive states in the standardized feature space were computed to quantify condition-dependent transitions in brain-body control organization. ResultsNonlinear features showed significant, group- and feature-dependent associations with CKC in the mediolateral direction, driven by significant SE and FD effects in the stroke group and an SE effect in the older group, while no significant associations were observed in the young group. Including nonlinear features in baseline models containing only linear CoP features significantly improved model fit. CKC alone showed low classification performance (AUC 50 to 65), whereas combining CKC with linear and nonlinear features improved group discrimination (AUC up to 0.86). State-space transition analysis revealed larger condition-dependent transitions in stroke participants compared with healthy older adults, particularly going from eyes open to eyes closed when standing on foam. ConclusionBrain-body coupling during standing may be understood more comprehensively by factoring in the temporal structure of fluctuations rather than their amplitude alone. These findings support the use of nonlinear dynamical features, combined with CKC, as potential markers of balance impairment.

neuroscience↗

bioRxiv2026

Cortical involvement in stroke survivors for balance maintenance

Stroke survivors often experience balance impairments which may result in increased risk of falling. However, it is unclear whether and how a stroke changes cortical involvement for postural control. To clarify this issue, we assessed the effect of stroke on sway-based corticokinematic coherence (CKC), which is a measure of the coupling between cortical electrophysiological signals and postural sways. To that end, we recorded the center-of-pressure fluctuations and electroencephalographic cortical activity of 34 stroke survivors and 34 healthy participants performing balance tasks during which sensory information was manipulated, by either removal or alteration. We found significantly increased CKC derived from medio-lateral sway in stroke participants when standing on foam compared to healthy controls, suggesting an increase in cortical involvement to compensate for the decreased function of the hemiparetic side, even in highly functional stroke survivors. Moreover, a relationship was found between CKC and clinical scores (Berg Balance Scale and Fugl-Meyer). This suggests that CKC could be used as a biomarker to track progress beyond traditional functional recovery as measured by clinical scores.

neuroscience↗

bioRxiv2025

Separating faces in ARMS metabarcoding improves marine biodiversity monitoring: a comparison across protocols, experimental designs, and photographic surveys

Monitoring marine biodiversity requires approaches that capture its full complexity through space and time. DNA metabarcoding coupled with Autonomous Reef Monitoring Structures (ARMS) is increasingly used for this purpose, yet most applications still pool all sessile fractions and rarely benchmark molecular ouputs against photographic observations. Here, we combined photographic analysis with cytochrome c oxidase I (COI) metabarcoding across ten north-western Mediterranean sites to test, compare, and refine ARMS-based monitoring protocols. We first optimized laboratory procedures (DNA extraction and polymerase choice) and applied the control-driven, replicate-aware VTAM pipeline to minimize false positives and ensure full traceability. We then conducted the first face-by-face comparison of - and {beta}-diversity between imaging and eDNA in which each individual ARMS face was metabarcoded separately rather than pooled. Metabarcoding detected [~]15x higher site-level richness and revealed stronger correlations with geographic distance and environmental gradients, whereas photography provided complementary information on macro-taxa and surface cover. For metabarcoding, processing each face separately yielded much higher richness and markedly stronger {beta}-diversity-distance correlations than with the NOAA pooling protocol, demonstrating that pooling inflates sampling variance resulting in a loss of the ecological signal. Grouping faces into five structural categories offered a more operational alternative while further increasing -diversity and strengthening {beta}-diversity correlations. Overall, our results show that retaining ARMS microhabitat structure is critical for maximizing metabarcoding performance. Using five structural sessile fractions per ARMS combined with a control-driven bioinformatic workflow provides a reproducible, scalable framework for long-term eDNA monitoring and early detection of biodiversity change.

ecology↗

bioRxiv2024

Coastal oceanographic connectivity estimates at the global scale

MotivationOceanographic connectivity driven by ocean currents is critical in determining the distribution of marine biodiversity. It mediates the genetic and individual exchange between populations, from structuring dispersal barriers that promote long-term isolation to enabling long-distance dispersal that underpins species expansion and resilience against climate change. Despite its significance, comprehensive estimates of oceanographic connectivity on a global scale remain unavailable, while traditional approaches, often simplistic, fail to capture the complexity of oceanographic factors contributing to population connectivity. This gap hinders a deeper understating of species dispersal ecology, survival, and evolution, ultimately precluding the development of effective conservation strategies aimed at preserving marine biodiversity. To address this challenge, we present a comprehensive dataset of connectivity estimates along the worlds coastlines, known for their rich marine biodiversity. These estimates are derived from a biophysical modelling framework that combines high-resolution ocean current data with graph theory to predict multi-generational stepping-stone connectivity. Alongside, we provide coastalNet, an R package designed to streamline access, analysis, and visualization of connectivity estimates. This tool enhances the utility and application of the data, adhering to the FAIR principles of Findability, Accessibility, Interoperability, and Reusability. The dataset and package set a new benchmark for research in oceanographic connectivity, allowing a better exploration of the complex dynamics of coastal marine ecosystems. Main types of variables containedPairwise connectivity estimates (probability and time) between coastal sites. Spatial location and grainGlobal, equal-area hexagons with 8.45 km edge length. Time period and grainDaily, from 2000 to 2020. Major taxa and level of measurementCoastal marine biodiversity. Software formatA package of functions developed for R software.

ecology↗

bioRxiv2023

Cortical tracking of postural sways during standing balance.

Maintaining an upright stance requires the integration of sensory inputs from the visual, vestibular and somatosensory-proprioceptive systems by the central nervous system to develop a corrective postural strategy. However, it is unclear whether and how the cerebral cortex monitors and controls postural sways. Here, we asked whether postural sways are encoded in ongoing cortical oscillations, giving rise to a form of corticokinematic coherence (CKC) in the context of standing balance. Center-of-pressure (CoP) fluctuations and electroencephalographic cortical activity were recorded as young healthy participants performed balance tasks during which sensory information was manipulated, by either removal or alteration. We found that postural sways are represented in ongoing cortical activity during challenging balance conditions, in the form of CKC at 1-6 Hz. Time delays between cortical activity and CoP features indicated that both afferent and efferent pathways contribute to CKC, wherein the brain would monitor the CoP velocity and control its position. Importantly, CKC was behaviorally relevant, as it predicted the increase in instability brought by alteration of sensory information. Our results suggest that human sensorimotor cortical areas take part in the closed-loop control of standing balance in challenging conditions. Importantly, CKC could serve as a neurophysiological marker of cortical involvement in maintaining balance.

neuroscience↗

bioRxiv2023

An Open-Access Database of Video Stimuli for Action Observation Research in Neuroimaging Settings: Psychometric Evaluation and Motion Characterization

Video presentation has become ubiquitous in paradigms investigating the neural and behavioral responses to observed actions. In spite of the great interest in uncovering the processing of observed bodily movements and actions in neuroscience and cognitive science, at present, no standardized set of video stimuli for action observation research in neuroimaging settings exists. To facilitate future action observation research, we developed an open-access database of 135 high-definition videos of a male actor performing object-oriented actions. Actions from 3 categories: kinematically natural and goal-intact (Normal), kinematically unnatural and goal-intact (How), or kinematically natural and goal-violating (What), directed towards 15 different objects were filmed from 3 angles. Psychometric evaluation of the database revealed high video recognition accuracy (Mean accuracy = 88.61 %) and substantial inter-rater agreement (Fleiss Kappa = 0.702), establishing excellent validity and reliability. Videos exact timing of motion onset was identified using a custom motion detection frame-differencing procedure. Based on its outcome, the videos were edited to assure that motion begins at the second frame of each video. The videos timing of category recognition was also identified using a novel behavioral up-down staircase procedure. The identified timings can be incorporated in future experimental designs to counteract jittered stimulus onsets, thus vastly improving the sensitivity of neuroimaging experiments. All videos, their psychometric evaluations, and the timing of their frame of category recognition, as well as our custom programs for performing these evaluations on our, or on other similar video databases, are available at the Open Science Framework (https://osf.io/zexc4/).

neuroscience↗

bioRxiv2023

Afferents to Action: Cortical proprioceptive processing assessed with corticokinematic coherence specifically predicts gross motor skills

Voluntary motor control is thought to be predicated on the ability to efficiently integrate and process somatosensory afferent information. However, current approaches in the field of motor control have not factored in objective markers of how the brain actually tracks incoming somatosensory information. Here, we asked whether motor performance relates with such markers obtained with an analysis of the coupling between peripheral kinematics and cortical oscillations during continuous movements, best known as corticokinematic coherence (CKC). Motor performance was evaluated by measuring both gross and fine motor skills using the Box and Blocks Test (BBT) and the Purdue Pegboard Test (PPT), respectively, and with a biomechanics measure of coordination. Sixty-one participants completed the BBT, while equipped with electroencephalography and electromyography, and the PPT. We evaluated CKC, from the signals collected during the BBT, as the coherence between movement rhythmicity and brain activity, and coordination as the cross-correlation between muscle activity. CKC at movements first harmonic was positively associated with BBT scores, and showed a relationship with PPT scores, but only in synergy with BBT scores, where participants with lower PPT score had higher CKC than expected based on their BBT score. Coordination was not associated with motor performance and at most, weakly related to CKC. These findings demonstrate that cortical somatosensory processing in the form of strengthened brain-peripheral coupling is specifically associated with better gross motor skills. CKC might be considered as a valuable addition to classical tests of proprioceptive acuity, with important perspectives for future clinical studies and practice. Significance StatementWhether standing upright, jogging, or in Olympic competition, our nervous system not only sends out motor commands prompting muscles to contract, but also receives incoming information to fine-tune motor actions. Though the machinery involved in sensing mechanical changes is well-described, the neural processing of this information is not, making its relevance to motor function unresolved. We found that the coupling strength between peripheral kinematics and cortical activity was related to motor function and at most, only weakly related to conventional muscle-only assessments. We present novel behavioral relevance of this coupling and its specific relationship to gross motor skill. Our study paves the way for including novel brain-centered approaches to complement classical assessment sensorimotor functions in health and disease.

neuroscience↗

bioRxiv2023

Unravelling the role of oceanographic connectivity in intra-specific diversity of marine forests at global scale

AimIntra-specific diversity results from complex interactions of intermingled eco-evolutionary processes along species history, but their relative contribution has not been addressed at the global scale. Here, we unravel the role of present-day oceanographic connectivity in explaining the genetic differentiation of marine forests across the ocean. LocationGlobal. Time periodContemporary. Major taxa studiedMarine forests of brown macroalgae (order Fucales, Ishigeales, Laminariales, Tilopteridale). MethodsThrough systematic literature revision, we compiled a comprehensive dataset of genetic differentiation, encompassing 662 populations of 34 species. A biophysical model coupled with network analyses estimated multigenerational oceanographic connectivity and centrality across the marine forest global distribution. This approach integrated species dispersive capacity and long-distance dispersal events. Linear mixed models tested the relative contribution of site-specific processes, connectivity, and centrality in explaining genetic differentiation. ResultsWe show that spatiality dependent eco-evolutionary processes, as described by our models, are prominent drivers of genetic differentiation in marine forests (significant models in 92.6 % of the cases with an average R2 of 0.49 {+/-} 0.07). Specifically, we reveal that 19.6 % of variance is explicitly induced by contemporary connectivity and centrality. Moreover, we demonstrate that LDD is key in connecting populations of species distributed across large water masses and continents. Main conclusionsWe deciphered the role of present-day connectivity in observed patterns of genetic differentiation of marine forests. Our findings significantly contribute to the understanding of the drivers of intra-specific diversity on a global scale, with implications for biogeography and evolution. These results can guide well-informed conservation efforts, including the designation of marine protected areas, as well as spatial planning for genetic diversity in aquaculture, which is particularly relevant for sessile ecosystems structuring species such as brown macroalgae.

ecology↗

bioRxiv2021

Temporally stable beta sensorimotor oscillations and cortico-muscular coupling underlie force steadiness

As humans, we seamlessly hold objects in our hands, and may even lose consciousness of these objects. This phenomenon raises the unsettled question of the involvement of the cerebral cortex, the core area for voluntary motor control, in dynamically maintaining steady muscle force. To address this issue, we measured magnetoencephalographic brain activity from healthy adults who maintained a steady pinch grip. Using a novel analysis approach, we uncovered fine-grained temporal modulations in the [~]20-Hz sensorimotor brain rhythm and its coupling with muscle activity, with respect to several aspects of muscle force (rate of increase/decrease or plateauing high/low). These modulations preceded changes in force features by [~]40 ms and possessed behavioral relevance, as less salient or absent modulation predicted a more stable force output. These findings have consequences for the existing theories regarding the functional role of cortico-muscular coupling, and suggest that steady muscle contractions are characterized by a stable rather than fluttering involvement of the sensorimotor cortex.

neuroscience↗