Charalambos Papaxanthis

University of Burgundy | UB · Laboratoire de Cognition, Action et Plasticité Sensori-Motrtice (INSERM 1093)

Concentric and eccentric contractions show different patterns of neural activity at both peripheral and cortical levels, which are thought to influence the perception of action properties such as the weight of objects moved by others. The aim of this study was to investigate how the type of muscle contraction influences weight estimation during act...

As humans, our ability to move is a crucial and fundamental function that has developed over time through adaptation and evolution. Since gravity is always present, our central nervous system (CNS) has naturally learned to leverage it, optimizing its effects to minimize the energy expenditure of our movements. Among other results, the optimal integ...

Competition between motor and declarative memory systems, both involved simultaneously in motor learning, has been shown to reduce motor consolidation. Here, we investigated this conflict during the learning of a sequential finger-tapping task (SFTT) scheduled for either the morning or the afternoon. Sixty participants, divided into four groups, tr...

As the global population ages, it is crucial to understand sensorimotor compensation mechanisms. These mechanisms are thought to enable older adults to remain in good physical health, but despite important research efforts, they remain essentially chimeras. A major problem with their identification is the ambiguous interpretation of age-related alt...

Arm movements in our daily lives have to be adjusted for several factors in response to the demands of the environment, for example, speed, direction or distance. Previous research has shown that arm movement kinematics is optimally tuned to take advantage of gravity effects and minimize muscle effort in various pointing directions and gravity cont...

The Central Nervous System (CNS) is thought to select movement trajectories that optimize certain criteria within the environment. For example, previous work revealed that young adults' arm movements are tuned to harvest gravity effects and reduce muscle effort, as supported by kinematic and electromyographic (EMG) parameters (Gaveau et al., 2016,...

As the global population ages, it is crucial to understand sensorimotor compensation mechanisms that allow older adults to remain in good physical health, i.e. underlying successful aging. Although age-related compensation has long been conceptualized and despite important research effort in varied gerontological subfields, behavioral compensatory...

The central nervous system (CNS) is thought to use motor strategies that minimize several criteria, such as end-point variability or effort, to plan optimal motor patterns. In the case of vertical arm movements, a large body of literature demonstrated that the brain uses a motor strategy that takes advantage of the mechanical effects of gravity to...

Individuals with aphantasia report having difficulties or an inability to generate visual images of objects or events. So far, there is no evidence showing that this condition also impacts the motor system and the generation of motor simulations. We probed the neuro-physiological marker of aphantasia during explicit and implicit forms of motor simu...

Introduction Spasticity is a frequent disabling consequence following a stroke. Local muscle vibrations (LMVs) have been proposed as a treatment to address this problem. However, little is known about their clinical and neurophysiological impacts when used repeatedly during the subacute phase post-stroke. This project aims to evaluate the effects o...

Old pre-print of the now peer reviewed new version "Comparing arm to whole-body motor control disambiguates age-related deterioration from compensation". Please see the new version. As the global population ages, it is crucial to understand sensorimotor compensation mechanisms that allow older adults to remain in good physical health. Although age...

Local vibration (LV) applied over the muscle tendon constitutes a powerful stimulus to activate the muscle spindle primary (Ia) afferents which project to the spinal level and are conveyed to the cortical level. This study aimed to identify the neuromuscular changes induced by a 30-minute LV-inducing illusions of hand extension on the vibrated flex...

Action reading is thought to engage motor simulations, such as those involved during the generation of mental motor images. These simulations would yield modulations in activity of motor-related cortical regions and contribute to action language comprehension. To test these ideas, we measured corticospinal excitability during action reading, and re...

Cadre théorique Dans la littérature, un véritable consensus ressort quant à la présence de processus cognitif implicite ou explicite d’élaboration, d’exploration ou de manipulation d’images au cœur de notre esprit [1]. Dans le domaine des neurosciences du mouvement, une attention toute particulière a été portée à la simulation motrice qui consiste...

We investigated the influence of the time-of-day and sleep on skill acquisition (i.e., skill improvement immediately after a training-session) and consolidation (i.e., skill retention after a time interval including sleep). Three groups were trained at 10 a.m. (G10 am ), 3 p.m. (G3 pm ), or 8 p.m. (G8 pm ) on a finger-tapping task. We recorded the...

In humans, moving efficiently along the gravity axis requires shifts in muscular contraction modes. Rising the arm up involves shortening contractions of arm flexors, while the reverse movement can rely on lengthening contractions with the help of gravity. Although this control mode is universal, the neuromuscular mechanisms that drive gravity-orie...

Time-of-day is rarely considered during experimental protocols investigating motor behavior and neural activity. The goal of this work was to investigate differences in functional cortical connectivity at rest linked to the time of the day using functional Near-Infrared Spectroscopy (fNIRS). Since resting-state brain is shown to be a succession of...

Schizophrenia patients often present with neurological signs such as left/right confusion, impaired coordination of movements, and motor abnormalities may occur secondary to antipsychotic medications. Neuropsychological tests identify various dysfunctions, such as difficulty in focusing attention, difficulty in abstract thinking or difficulty in ch...

Action reading is thought to engage motor simulations, yielding modulations in activity of motor-related cortical regions, and contributing to action language comprehension. To test these ideas, we measured 1) corticospinal excitability during action reading, and 2) reading comprehension ability, in individuals with normal and impaired imagery (i.e...

Arm movements in our daily lives have to be adjusted for several factors in response to the demands of the environment, for example, speed, direction or distance. Previously, we had shown that arm movement kinematics is optimally tuned to take advantage of gravity effects and minimize muscle effort in various pointing directions and gravity context...

Several sensorimotor control studies have provided evidence supporting that the central nervous system optimizes gravity effects to minimize muscle effort. Recently, this hypothesis has been supported by the consistent observation of direction-specific negative epochs in the phasic electromyographic signal of antigravity muscles during vertical arm...

The mirror neurons network in the human brain is activated both during the observation of action and the execution of the same action, facilitating thus the transformation of visual information into motor representations, to understand the actions and intentions of others. How this transformation takes place, however, is still under debate. One pre...

While action language and motor imagery both engage the motor system, determining whether these two processes indeed share the same motor representations would contribute to better understanding their underlying mechanisms. We conducted two experiments probing the mutual influence of these two processes. In Exp.1, hand-action verbs were presented s...

Studies of regularities in human movement control have led to the idea that our brains incorporate generic motor laws that guide our behaviors and thus these regularities. Among these, it has been argued that a generic internal model of gravity minimizes the body's energy expenditure during actions performed in the vertical plane. According to this...

This study investigates the effects of error-based and reinforcement training on the acquisition and long-term retention of free throw accuracy in basketball. Sixty participants were divided into four groups (n = 15 per group): (i) the error-based group (sensory feedback), (ii) the reinforcement group (binary feedback including success or failure),...

Individuals with aphantasia report having difficulties or an inability to generate visual images of objects or events. So far, there is no evidence showing that this condition also impacts the motor system and the generation of motor simulations. We probed the neurophysiological marker of aphantasia during explicit and implicit forms of motor simul...

The passage of time impacts motor memory consolidation1. Recently, we have shown that this effect depends on the time-of-day, notably with a deterioration of skill 24 hours after a morning training2. Here, we tried to understand the underlying mechanisms of this deterioration. Twenty-four healthy adults were trained on a finger tapping task (speed...

The optimization of mental practice (MP) protocols matters for sport and motor rehabilitation. In this study, we were interested in the benefits of aerobic exercise in MP, given its positive effects on the acquisition and consolidation of motor skills induced by physical practice (PP). Four experimental groups were tested: i) physical practice with...

The reading of action verbs has been shown to activate motor areas, whereby sentence context may serve to either globally strengthen this activation or to selectively sharpen it. To investigate this issue, we manipulated the presence of manual actions and sentence context, assessing the level of corticospinal excitability by means of transcranial m...

Controversy persists regarding the representation of negated actions, specifically concerning activation and inhibitory mechanisms in the motor system, and whether this occurs in one or two steps. We conducted two experiments probing corticospinal excitability (CSE) and short-interval intracortical inhibition (SICI) in the primary motor cortex at d...

While the time-of-day significantly impacts motor performance, its effect on motor learning has not yet been elucidated. Here, we investigated the influence of the time-of-day on skill acquisition (i.e., skill improvement immediately after a training-session) and consolidation (i.e., skill retention after a time interval). Three groups were trained...

INTRODUCTION: The application of tendon vibration (TV) stimulates the primary and secondary endings of the muscle spindles [1]. The integration of sensory information by the brain can produce illusions of movement in the opposite direction to the vibrated tendon. Prolonged application (several minutes) can induce cortical and spinal changes in the...

Motor lateralization refers to differences in the neural organization of cerebral hemispheres, resulting in different control specializations between the dominant and the non-dominant motor systems. Multiple studies proposed that the dominant hemisphere is specialized for open-loop optimization-like processes. Recently, comparing arm kinematics bet...

The reading of action verbs has been shown to activate motor areas, whereby sentence context may serve to either globally strengthen this activation or to selectively sharpen it. To investigate this issue, we manipulated the presence of manual actions and sentence context, assessing the level of corticospinal excitability by means of transcranial m...

While action language and motor imagery both engage the motor system, determining whether these two processes indeed share the same motor representations would contribute to better understanding their underlying mechanisms. We conducted two experiments probing the mutual influence of these two processes. In Exp.1, hand-action verbs were presented s...

Background: Whole-body tracking of visual motion cues is used in balance training to improve weight shifting ability in old age and sports. Research question: How tracking of a complex (pink noise) and a periodic visual target motion during anteroposterior weight shifting affects postural and muscle responses to unilateral hip vibration. Methods:...

Our brain has the extraordinary capacity to improve motor skills through mental practice. Conceptually, this ability is attributed to internal forward models, which are cerebellar neural networks that can predict the sensory consequences of motor commands. In our study, we employed single and dual-coil transcranial magnetic stimulations to probe th...

Time-of-day influences both physical and mental performances. Its impact on motor learning is, however, not well established yet. Here, using a finger tapping-task, we investigated the time-of-day effect on skill acquisition (i.e., immediately after a physical or mental practice session) and consolidation (i.e., 24 h later). Two groups (one physica...

The central nervous system (CNS) develops motor strategies that minimize various hidden criteria, such as end-point variance or effort. A large body of literature suggests that the dominant arm is specialized for such open-loop optimization-like processes, whilst the non-dominant arm is specialized for closed-loop postural control. Building on rece...

Background Whole-body tracking of visual motion cues is used in balance training to improve weight shifting ability in old age and sports. Research question How tracking of a complex (pink noise) and a periodic visual target motion during anteroposterior weight shifting affects postural and muscle responses to unilateral hip vibration. Methods Tw...

The human sensorimotor control has evolved in the Earth’s environment where all movement is influenced by the gravitational force. Changes in this environmental force can severely impact the performance of arm movements which can be detrimental in completing certain tasks such as piloting or controlling complex vehicles. For this reason, subjects t...

Physical practice (PP) and motor imagery practice (MP) lead to the execution of fast and accurate arm movements. However, there is currently no information about the influence of MP on movement smoothness, nor about which performance parameters best discriminate these practices. In the current study, we assessed motor performances with an arm point...

Time-of-day influences both physical and mental performance. Its impact on motor learning is, however, not well established yet. Here, using a finger tapping-task, we investigated the time-of-day effect on skill acquisition (i.e., immediately after a physical or mental practice session) and consolidation (i.e., 24 hours later). Two groups (one phys...

Our sensorimotor control is well adapted to normogravity environment encountered on Earth and any change in gravity significantly disturbs our movement. In order to produce appropriate motor commands for aimed arm movements such as pointing or reaching, environmental changes have to be taken into account. This adaptation is crucial when performing...

Physical practice (PP) and motor imagery practice (MP) lead to the execution of fast and accurate arm movements. However, there is currently no information about the influence of MP on movement smoothness, nor about which performance parameters best discriminate these practices. In the current study, we assessed motor performances with an arm point...

Specific neural mechanisms operate at corticospinal levels during eccentric and concentric contractions. Here, we investigated the difference in corticospinal excitability (CSE) when preparing these two types of contraction. In this study we enrolled 16 healthy participants. They were asked to perform an instructed-delay reaction time task involvin...

Pain inf luences both motor behavior and neuroplastic adaptations induced by physical training. Motor imagery (MI) is a promising method to recover motor functions, for instance in clinical populations with limited endurance or concomitant pain. However, the inf luence of pain on the MI processes is not well established. This study investigated whe...

The central nervous system (CNS) is thought to develop motor strategies that minimize various hidden criteria, such as end-point variance or effort. A large body of literature suggests that the dominant arm is specialized for such open-loop optimization-like processes whilst the non-dominant arm is specialized for closed-loop control. Building on r...

Efficient control of voluntary movements along the gravity axis requires adapted shifts in muscular contraction modes. In daily life, rising the arm up involves shortening (i.e., concentric) contractions of arm flexors, while the reverse movement can rely on lengthening (i.e., eccentric) contractions of the same muscles with the help of gravity for...

Our brain has the extraordinary capacity to improve motor skills through mental practice. Conceptually, this ability is attributed to internal forward models, which are neural networks that can predict the sensory consequences of motor commands. While the cerebellum is considered as a potential locus of internal forward models, evidence for its inv...

Background: In sports, the risk of pathology or event that leads to an injury, a cessation of practice or even to an immobilization is high. The subsequent reduction of physical activity, or hypoactivity, induces neural and muscular changes that adversely affect motor skills and functional motor rehabilitation. Because the implementation of physic...

Recent kinematic results, combined with model simulations, have provided support for the hypothesis that the human brain shapes motor patterns that use gravity effects to minimize muscle effort. Because many different muscular activation patterns can give rise to the same trajectory, here, we specifically investigate gravity-related movement proper...

It well-known that mental training improves skill performance. Here, we evaluated skill acquisition and consolidation after physical or motor imagery practice, by means of an arm pointing task requiring speed-accuracy trade-off. In the main experiment, we showed a significant enhancement of skill after both practices (72 training trials), with a be...

Developmental dyslexia is associated with vision and hearing impairments. Whether these impairments are causes or comorbidities is controversial. Because both senses are heavily involved in reading, cognitive theories argue that sensory impairments are comorbidities that result from a lack of reading practice. Sensory theories instead argue that th...

Movements rely on a mixture of feedforward and feedback mechanisms. With experience, the brain builds internal representations of actions in different contexts. Many factors are taken into account in this process among which is the immutable presence of gravity. Any displacement of a massive body in the gravitational field generates forces and torq...

Developmental Dyslexia is a specific learning disorder causing reading deficits. Although it has long been considered a purely cognitive disorder, mounting evidence revealed that Developmental Dyslexia is associated with sensory impairments. Because these impairments are restrained to vision and hearing-both senses being heavily involved in reading...

Developmental dyslexia (DD), a severe and frequent disorder of reading acquisition, is characterized by a diversity of cognitive and motor deficits whose interactions still remain under debate. Although deficits in the automatization of sensorimotor control have been highlighted, internal action representation allowing prediction has never before b...

Motor imagery (MI) is the mental simulation of an action without any apparent muscular contraction. By means of transcranial magnetic stimulation, few studies revealed a decrease of short-interval intracortical inhibition (SICI) within the primary motor cortex. However, this decrease is ambiguous, as one would expect greater inhibition during MI to...

Several sensorimotor modifications are known to occur with aging, possibly leading to adverse outcomes such as falls. Recently, some of those modifications have been proposed to emerge from motor planning deteriorations. Motor planning of vertical movements is thought to engage an internal model of gravity to anticipate its mechanical effects on th...

Motor imagery, defined as the mental representation of an action without movement-related sensory inputs, is a well-known intervention to improve motor performance. In the current study, we tested whether use-dependent plasticity, a mechanism underlying motor learning, could be induced by an acute session of motor imagery. By means of transcranial...

Motor imagery (MI) is the mental simulation of an action without any apparent muscular contraction. By means of transcranial magnetic stimulation, few studies revealed a decrease of short-interval intracortical inhibition (SICI) within the primary motor cortex. However, this decrease is ambiguous, as one would expect greater inhibition during MI to...

Purpose: It is not known yet whether the neurophysiological specificity of eccentric, concentric and isometric contractions can also be observed when these are mentally simulated. Therefore our aim was to assess corticospinal excitability during motor imagery (MI) of different contraction types and to test whether a passive movement during MI coul...

Several sensorimotor modifications are known to occur with aging, possibly leading to adverse outcomes such as falls. Recently, some of those modifications have been proposed to emerge from motor planning deteriorations. Motor planning of vertical movements is thought to engage an internal model of gravity to anticipate its mechanical effects on th...

Recent kinematic results, combined with model simulations, have provided support for the hypothesis that the human brain uses an internal model of gravity to shape motor patterns that minimise muscle effort. Because many different muscular activation patterns can give rise to the same trajectory, here we analyse muscular activation patterns during...