Papers by Charalambos Papaxanthis
Cerebral Cortex
Pain influences both motor behavior and neuroplastic adaptations induced by physical training. Mo... more Pain influences 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 influence of pain on the MI processes is not well established. This study investigated whether acute experimental pain could modulate corticospinal excitability assessed at rest and during MI (Exp. 1) and limit the use-dependent plasticity induced by MI practice (Exp. 2). Participants imagined thumb movements without pain or with painful electrical stimulations applied either on digit V or over the knee. We used transcranial magnetic stimulation to measure corticospinal excitability at rest and during MI (Exp. 1) and to evoke involuntary thumb movements before and after MI practice (Exp. 2). Regardless of its location, pain prevented the increase of corticospinal excitability that is classically observed during MI. In addition, p...
bioRxiv, 2021
Physical practice (PP) and motor imagery practice (MP) lead to the execution of fast and accurate... more 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 pointing task with constrained precision before and after PP (n= 15), MP (n= 15), or no practice (n= 15). We analyzed gains between Pre- and Post-Test for five performance parameters: movement duration, mean and maximal velocities, total displacements, and the number of velocity peaks characterizing movement smoothness. The results showed an improvement of performance after PP and MP for all parameters, except for total displacements. The gains for movement duration, and mean and maximal velocities were statistically higher after PP and MP than after no practice, and comparable between practices. However, motor gains for the number of velocity ...
Submitted to journal of Neurophysiology 1 2 3 Dominant versus nondominant arm advantage in mental... more Submitted to journal of Neurophysiology 1 2 3 Dominant versus nondominant arm advantage in mentally simulated actions in 4 right handers 5 6 Philippe Gandrey Christos Paizis Vassilis Karathanasis Nicolas Gueugneau 7 Charalambos Papaxanthis 8 9 1. Université de Bourgogne, UFR STAPS, Campus Universitaire, Dijon, France. 10 2. INSERM U1093, Cognition, Action et Plasticité sensorimotrice, Université de Bourgogne, 11 Campus Universitaire, Dijon, France. 12 3. Centre d’Expertise de la Performance, UFR STAPS, Université de Bourgogne, Dijon, 13 France. 14 15 16 Shortened Title: Right arm advantage in mental actions 17 18 19 () Professor Charalambos Papaxanthis 20 INSERM U 1093, Université de Bourgogne, UFR STAPS, Campus Universitaire, BP 27877, 21 Dijon 21078, France, Tel.: +33 3 80396748, Fax: +33 3 80396702 22 e-mail: [email protected] 23 24 Articles in PresS. J Neurophysiol (October 2, 2013). doi:10.1152/jn.00123.2013
The central nervous system (CNS) is thought to develop motor strategies that minimize various hid... more 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 recent results suggesting that the brain plans arm movements that takes advantage of gravity effects to minimize muscle effort, the present study tests the hypothesized superiority of the dominant arm motor system for effort minimization. Thirty participants (22.5 ± 2.1 years old; all right-handed) performed vertical arm movements between two targets (40° amplitude), in two directions (upwards and downwards) with their two arms (dominant and non-dominant). We recorded the arm kinematics and the electromyographic activity of the anterior and posterior deltoid to compare two motor signatures of the gravity-related optimization process; i.e., ...
Frontiers in Neural Circuits
Our sensorimotor control is well adapted to normogravity environment encountered on Earth and any... more 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 successful movements during microgravity and hypergravity conditions. To mitigate the effects of changing gravitational levels, such as the changed movement duration and decreased accuracy, we explored the possible beneficial effects of gravity compensation on movement. Local gravity compensation was achieved using a motorized robotic device capable of applying precise forces to the subject’s wrist that generated a normogravity equivalent torque at the shoulder joint during periods of microgravity and hypergravity. The efficiency of the local gravity compensation was assessed with an experiment in which participants performed a series of p...
Neuroscience
Motor imagery (MI) is the mental simulation of an action without any apparent muscular contractio... more 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 prevent overt motor output. The current study investigated the extent of SICI modulation during MI through a methodological and a conceptual reconsideration of i) the importance of parameters to assess SICI (Exp.1) and ii) the inhibitory process within the primary motor cortex as an inherent feature of MI (Exp.2). Participants performed two tasks: 1) rest and 2) imagery of isometric abduction of the right index finger. Using transcranial magnetic stimulation, motor evoked potentials were elicited in the right first dorsal interosseous muscle. An adaptive threshold-hunting paradigm was used, where the stimulus intensity required to maintain a fixed motor evoked potential amplitude was quantified. To test SICI, we conditioned the test stimulus with a conditioning stimulus (CS) of different intensities. Results revealed an Intensity by Task interaction showing that SICI decreased during MI as compared to rest only for the higher CS intensity (Exp.1). At the lowest CS intensities, a Task main effect revealed that SICI increased during MI (Exp.2). SICI modulation during MI depends critically on the CS intensity. By optimising CS intensity, we have shown that SICI circuits may increase during MI, revealing a potential mechanism to prevent the production of a movement while the motor system is activated.
Frontiers in Aging Neuroscience
Several sensorimotor modifications are known to occur with aging, possibly leading to adverse out... more 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 the body-limbs and thus to genuinely produce movements that minimize muscle effort. This is supported, amongst other results, by directiondependent kinematics where relative durations to peak accelerations and peak velocity are shorter for upward than for downward movements. The present study compares the motor planning of fast and slow vertical arm reaching movements between 18 young (24 ± 3 years old) and 17 older adults (70 ± 5 years old). We found that older participants still exhibit strong directional asymmetries (i.e., differences between upward and downward movements), indicating that optimization processes during motor planning persist with healthy aging. However, the size of these differences was increased in older participants, indicating that gravity-related motor planning changes with age. We discuss this increase as the possible result of an overestimation of gravity torque or increased weight of the effort cost in the optimization process. Overall, these results support the hypothesis that feedforward processes and, more precisely, optimal motor planning, remain active with healthy aging.
Medicine & Science in Sports & Exercise
ABSTRACT Purpose It is not known yet whether the neurophysiological specificity of eccentric, con... more ABSTRACT 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 could have additional effects. Methods Twelve young participants imagined contractions of the wrist flexors, firstly with the arm motionless (static mode) and second, with a congruent passive movement (wrist extension during eccentric MI and wrist flexion during concentric MI). Motor-evoked potentials (MEP) and H-reflexes were elicited in flexor carpi radialis (FCR) at rest and during the three types of MI. As a secondary outcome, the MEP of one antagonist (extensor carpi radialis), elicited concomitantly with FCR MEP recording, were also analyzed. Results In static mode, FCR MEP were facilitated during isometric (P = 0.046) and concentric (P = 0.039) MI, but not during eccentric MI (P = 0.902). With passive congruent movements, FCR MEP were enhanced during all imagined contraction types, including eccentric (P = 0.047). FCR H-reflexes increased only during eccentric MI accompanied with wrist extension (P = 0.003). Extensor carpi radialis MEP were modulated only when a passive congruent movement was provided (P = 0.040). Conclusions Like actual contractions, eccentric MI exhibits specific neural correlates, compared with isometric and concentric MI, which should be considered when using this modality for training. The present results showed that adding passive movements congruent to the eccentric MI task would enhance its impact over corticospinal structures.
Use-dependent plasticity, a mechanism underlying motor learning, can be induced by physical pract... more Use-dependent plasticity, a mechanism underlying motor learning, can be induced by physical practice or action observation. In the current study, we tested whether motor imagery, defined as the mental representation of the action without sensory inputs, could induce use-dependent plasticity as well. By means of transcranial magnetic stimulation (TMS) over the left primary motor cortex, we evoked isolated thumb movements in the right hand and assessed corticospinal excitability in the flexor and extensor pollicis brevis muscles. We measured the mean TMS-induced movement direction before and after an acute session of motor imagery practice in two experiments. In a first experiment, participants in the imagery group were instructed to repeatedly imagine their thumb moving in a direction deviated by 90° from the pre-test movement. The imagery group, but not the control group, deviated the post-training TMS-induced movements towards the training target direction (+34° ±55° and -13° ±53°,...
Frontiers in neurorobotics, 2018
Switched systems are common in artificial control systems. Here, we suggest that the brain adopts... more Switched 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 objects when stiffness varied 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 in the range 100-200 N/m. 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.
European journal of sport science, 2018
The neural mechanisms explaining strength increase following mental training by motor imagery (MI... more The neural mechanisms explaining strength increase following mental training by motor imagery (MI) are not clearly understood. While gains are mostly attributed to cortical reorganization, the sub-cortical adaptations have never been investigated. The present study investigated the effects of MI training on muscle force capacity and the related spinal and supraspinal mechanisms. Eighteen young healthy participants (mean age: 22.5 ± 2.6) took part in the experiment. They were distributed into two groups: a control group (n = 9) and an MI training group (n = 9). The MI group performed seven consecutive sessions (one per day) of imagined maximal isometric plantar flexion (4 blocks of 25 trials per session). The control group did not engage in any physical or mental training. Both groups were tested for the isometric maximal plantar flexion torque (MVC) and the rate of torque development (RTD) before and after the training session. In addition, soleus and medial gastrocnemius spinal and...
Neuroscience
Goal-oriented arm movements are characterized by a balance between speed and accuracy. The relati... more Goal-oriented arm movements are characterized by a balance between speed and accuracy. The relation between speed and accuracy has been formalized by Fitts' law and predicts a linear increase in movement duration with task constraints. Up to now this relation has been investigated on a short-time scale only, that is during a single experimental session, although chronobiological studies report that the motor system is shaped by circadian rhythms. Here, we examine whether the speed-accuracy trade-off could vary during the day. Healthy adults carried out arm-pointing movements as accurately and fast as possible toward targets of different sizes at various hours of the day, and variations in Fitts' law parameters were scrutinized. To investigate whether the potential modulation of the speed-accuracy trade-off has peripheral and/or central origins, a motor imagery paradigm was used as well. Results indicated a daily (circadian-like) variation for the durations of both executed and mentally simulated movements, in strictly controlled accuracy conditions. While Fitts' law was held for the whole sessions of the day, the slope of the relation between movement duration and task difficulty expressed a clear modulation, with the lowest values in the afternoon. This variation of the speed-accuracy trade-off in executed and mental movements suggests that, beyond execution parameters, motor planning mechanisms are modulated during the day. Daily update of forward models is discussed as a potential mechanism.
Behavioural Brain Research
The efficacy of motor imagery (MI) practice to facilitate muscle stretching remains controversial... more The efficacy of motor imagery (MI) practice to facilitate muscle stretching remains controversial and the underlying neurophysiological mechanisms unexplored. We evaluated the effects of MI practice during a sit-and-reach task. Healthy participants were randomly assigned to a MI practice (n=15) or Control (n=15) group and completed 2 blocks of 5 sit-and-reach trials. During the first block (B1), participants performed 5 maximal stretching trials of 10s. During the second block (B2), trials were divided into two consecutive parts: i) reproducing the maximum performance of B1 (10s, B2 part 1), and ii) attempting to outperform the maximum performance of B1 (10s, B2 part 2). Participants performed kinesthetic MI of hamstring stretching during B2 trials in the MI practice group. We recorded electromyography from the hamstring and rectus femoris of the dominant leg. We also processed skin conductance as an index of sympathetic activity. We measured greater performance improvements from B1 to B2 part 2 in the MI practice group compared to Control (p<0.05). Participants in the MI practice group exhibited reduced hamstring activation during both B2 part 1 (p<0.001) and B2 part 2 (p<0.001) compared to Control. Skin conductance revealed higher sympathetic activation during B2 part 2 compared to both B1 and B2 part 1 in the two groups. Thus, performing MI during actual movement is likely to improve stretching performance through reduced muscle activation. Such improvement may be grounded in a cortical gain over spinal reflexes.
eLife
The brain has evolved an internal model of gravity to cope with life in the Earth's gravitati... more The brain has evolved an internal model of gravity to cope with life in the Earth's gravitational environment. How this internal model benefits the implementation of skilled movement has remained unsolved. One prevailing theory has assumed that this internal model is used to compensate for gravity's mechanical effects on the body, such as to maintain invariant motor trajectories. Alternatively, gravity force could be used purposely and efficiently for the planning and execution of voluntary movements, thereby resulting in direction-depending kinematics. Here we experimentally interrogate these two hypotheses by measuring arm kinematics while varying movement direction in normal and zero-G gravity conditions. By comparing experimental results with model predictions, we show that the brain uses the internal model to implement control policies that take advantage of gravity to minimize movement effort.
Behavioural brain research, Jan 23, 2016
An acute bout of aerobic exercise induces neuroplasticity in the motor cortex. Moreover, paired a... more An acute bout of aerobic exercise induces neuroplasticity in the motor cortex. Moreover, paired associative stimulation (PAS) is known to induce neuroplasticity in M1. However, the possible influence of the type of exercise on the neuroplastic changes remains unknown. The present study investigated the effects of two different modes of muscle contraction produced during locomotor exercise on changes in corticospinal (CS) excitability. Subjects performed two 30-min treadmill exercises at an intensity corresponding to 60% of their maximal heart rate with either a +10% (uphill) or -10% (downhill) slope. These exercises were followed or not by paired associative stimulation method (PAS25) which consisted of 200 paired stimuli (0.25Hz, 15min) of median nerve electrical stimulation followed by transcranial magnetic stimulation of the hand M1 area (ISI 25ms). Motor evoked potentials (MEP), assessed through abductor pollicis brevis (APB) activity were obtained before exercise, at 5min, 15mi...
Scientific Reports, 2016
Actual and imagined movement speed increases from early morning until mid-afternoon. Here, we inv... more Actual and imagined movement speed increases from early morning until mid-afternoon. Here, we investigated the neural correlates of these daily changes. Fifteen subjects performed actual and imagined right finger opposition movement sequences at 8 am and 2 pm. Both actual and imagined movements were significantly faster at 2 pm than 8 am. In the morning, actual movements significantly activated the left primary somatosensory and motor areas, and bilaterally the cerebellum; in the afternoon activations were similar but reduced. Contrast analysis revealed greater activity in the cerebellum, the left primary sensorimotor cortex and parietal lobe in the morning than in the afternoon. Imagined movements in the morning significantly activated the parietal association cortices bilaterally, the left supplementary and premotor areas, and the right orbitofrontal cortex and cerebellum. In the afternoon, the frontal lobe was significantly activated with the right cerebellum. Contrast analysis revealed increased activity in the left parietal lobe in the morning than in the afternoon. For both tasks, speed in the morning was significantly related to the BOLD signal in the brain areas resulted more active. These findings suggest that motor performance is continuously updated on a daily basis with a predominant role of the frontoparietal cortex and cerebellum. An intriguing feature of our motor behavior is the daily modulation of motor performance. Indeed, several motor parameters, such as force 1-3 , speed 4 , reaction time 5,6 , and manual dexterity 7,8 progressively improve from early morning until mid-afternoon. Interestingly, it has also been shown that mental movement time, that is the time of an imagined movement, also exhibits daily variations 4,9,10. So far, it has been suggested that the daily modulation of physical and mental motor performance follows circadian rhythms, similarly to what occurs for biological mechanisms, such as hormonal secretion, body temperature, and the sleep/awake cycle 11. Recent findings propose that daily active movements, which also follow the daily rhythm imposed by natural (alternation of dark and light) and social (professional, educational) rules, may be, in addition to other basic circadian factors, a potential factor that regulates the fluctuation of motor performance 12. The underlying mechanism for the observed daily modulation of physical and mental motor performance would be the continuous update of motor prediction via active movements. Motor prediction is generated by forward models, which are neural processes that mimic the causal flow of the physical process by predicting the future sensorimotor state (e.g., position, velocity) given the efferent copy of the motor command and the current state 13,14. Better performance in the afternoon with respect to the morning, as that observed in the time of mental arm movements 4 , may be due to the continuous update of internal predictive models by means of self-supervised learning 15 , a process that minimizes prediction errors, namely the errors between the output from the forward model and the sensory outcome of the motor command.
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Papers by Charalambos Papaxanthis