Biology subjects

Armand, S.

Publications and source records attributed to Armand, S..

4 recordsLinked to original sources

bioRxiv2025

Within- and Between-Assessor Reliability of Lower-Limb Inter-Joint Coordination During Gait in Individuals With and Without Cerebral Palsy

BackgroundInter-joint coordination plays a key role in walking, particularly in people with cerebral palsy (CP), who experience altered movement patterns. The Continuous Relative Phase (CRP) method quantifies lower-limb coordination by assessing the phase relationships between joints. However, the reliability of CRP measurements during walking in individuals with CP remains unexplored, and may be affected by measurement variability due to marker placement errors, soft tissue artifacts, and natural movement fluctuations. Quantifying this reliability is important for appropriate clinical comparisons. This study aimed to quantify within- and between-assessor reliability of lower-limb CRP measurements in individuals with CP and their non-impaired (NI) peers. MethodsCP (n=19, age=18.4{+/-}7.3 years, GMFCS I-III) and NI (n=19, age=18.3{+/-}11.2 years) individuals completed two gait assessment sessions, each including 3D motion capture of at least 10 walking trials. Two trained assessors independently placed reflective markers and conducted gait analyses. Standard error of measurement (SEM) and minimal detectable change (MDC) were computed for knee-hip and ankle-knee coordination across gait subphases. FindingsThe SEM and MDC were lower for knee-hip than ankle-knee coordination, suggesting higher measurement reliability for proximal joint coupling. For knee-hip coordination, MDC reached 15.1{+/-}0.7{degrees}(CP) and 9.3{+/-}0.6{degrees}(NI) between assessors, and 23.8{+/-}3.0{degrees}(CP) and 9.1{+/-}1.6{degrees}(NI) within assessors. For ankle-knee coordination, MDC reached 29.0{+/-}2.6{degrees}(CP) and 25.0{+/-}3.5{degrees}(NI) between assessors, peaking at 47.3{+/-}10.9{degrees}(CP) and 28.6{+/-}1.5{degrees}(NI) in mid-swing within assessors. InterpretationThis study provides the first metrological reference for reliability of CRP-based inter-joint coordination during gait in CP. Results showed poor reliability, emphazing that such measurements must be interpreted with caution. Highlights- Knee-hip showed greater reliability than ankle-knee coordination across gait phases - Cerebral palsy individuals showed higher variability than non-impaired peers The beginning and the end of gait cycle showed the poorest reliability Pre-post comparisons should account for MDC thresholds to avoid misinterpretation

bioengineering↗

bioRxiv2023

Investigating the roles of reflexes and central pattern generators in the control and modulation of human locomotion using a physiologically plausible neuromechanical model

Studying the neural components regulating movement in human locomotion is obstructed by the inability to perform invasive experimental recording. Neuromechanical simulations can provide insights by modeling the locomotor circuits. Past neuromechanical models proposed control of locomotion either driven by central pattern generators (CPGs) with simple sensory commands or by a purely reflex-based network regulated by state-machine mechanisms. However, the physiological interpretation of these state-machines remains unclear. Here, we present a physiologically plausible model to investigate spinal control and modulation of human locomotion. We propose a bio-inspired controller composed of two coupled central pattern generators (CPGs) that produce the rhythm and pattern and a reflex-based network simulating low-level reflex pathways and Renshaw cells. This reflex network is based on leaky-integration neurons, and the whole system does not rely on changing reflex gains according to the gait cycle state. The only component of the controller that maintains a state-machine mechanism is the balance controller of the trunk. The musculoskeletal model is composed of a skeletal structure and 9 muscles per leg generating movement in sagittal plane. After optimizing the open parameters, human locomotion replicating kinematics and muscle activation naturally emerged. Furthermore, when CPGs were not activated, no stable and physiologically plausible gaits could be achieved through optimization, suggesting the necessity of this component to generate rhythmic behavior without a state machine mechanism regulating reflex activation. The controller could reproduce a wide range of speeds from 0.3 to 1.9 m/s. The results also showed that the net influence of feedback on motoneurons during perturbed locomotion is predominantly inhibitory and that the CPG network provides the timing of motoneurons activation by exciting or inhibiting muscles in specific gait phases. The proposed bio-inspired controller could contribute to our understanding of locomotor circuits of the intact spinal cord and could be used to study neuromotor disorders.

neuroscience↗

bioRxiv2021

Psilocybin-induced changes in brain network integrity and segregation correlate with plasma psilocin level and psychedelic experience

The emerging novel therapeutic psilocybin produces psychedelic effects via engagement of cerebral serotonergic targets by psilocin (active metabolite). The serotonin 2A receptor critically mediates these effects by altering distributed neural processes that manifest as increased entropy, reduced functional connectivity (FC) within discrete brain networks (i.e., reduced integrity) and increased FC between networks (i.e., reduced segregation). Reduced integrity of the default mode network (DMN) is proposed to play a particularly prominent role in psychedelic phenomenology, including perceived ego-dissolution. Here, we investigate the effects of a psychoactive oral dose of psilocybin (0.2-0.3 mg/kg) on plasma psilocin level (PPL), subjective drug intensity (SDI) and their association in fifteen healthy individuals. We further evaluate associations between these measures and resting-state FC, measured with functional magnetic resonance imaging, acquired over the course of five hours after psilocybin administration. We show that PPL and SDI correlate negatively with measures of network integrity (including DMN) and segregation, both spatially constrained and unconstrained. We also find that the executive control network and dorsal attention network desegregate, increasing connectivity with other networks and throughout the brain as a function of PPL and SDI. These findings provide direct evidence that psilocin critically shapes the time course and magnitude of changes in the cerebral functional architecture and subjective experience following psilocybin administration. Our findings provide novel insight into the neurobiological mechanisms underlying profound perceptual experiences evoked by this emerging transnosological therapeutic and implicate the expression of network integrity and segregation in the psychedelic experience and consciousness.

neuroscience↗

bioRxiv2020

Sensory modulation of gait characteristics in human locomotion: a neuromusculoskeletal modeling study

The central nervous system of humans and animals is able to modulate the activity in the spinal cord to achieve several locomotion behaviors. Previous neuromechanical models investigated the modulation of human gait changing selected parameters belonging to the CPGs (Central Pattern Generators) feedforward oscillatory structures or to the feedback reflex circuits. CPG-based models could replicate slow and fast walking by changing only the oscillations properties. On the other hand, reflex-based models could achieve different behaviors mainly through optimizations of a large dimensional parameter space, but could not identify effectively individual key reflex parameters responsible for the modulation of gait characteristics. This study, investigates which reflex parameters modulate the gait characteristics through neuromechanical simulations. A recently developed reflex-based model is used to perform optimizations with different target behaviors on speed, step length and step duration in order to analyse the correlation between reflex parameters and their influence on these gait characteristics. We identified 9 key parameters that influence the target speed ranging from slow to fast walking (0.48 and 1.71 m/s) as well as a large range of step lengths (0.43 and 0.88 m) and step duration (0.51, 0.98 s). The findings show that specific reflexes during stance have a major effect on step length regulation mainly given by the contribution of positive force feedback on the ankle plantarflexors group. On the other hand, stretch reflexes active during swing of iliopsoas and gluteus maximus regulate all the gait characteristics under analysis. Additionally, the results show that the stretch reflex of the hamstrings group during landing phase is responsible for modulating the step length and step duration. Additional validation studies in simulations demonstrated that the identified reflexes are sufficient to modulate gait in human locomotion. Thus, this study provides an overview of the possible reflexes to control the gait characteristics. Author summary

neuroscience↗