In biological systems, obviously dissipative, some injection of muscle force is required in order... more In biological systems, obviously dissipative, some injection of muscle force is required in order to sustain rhythmic movement. As the movement frequency increases, the way the muscle-force-to-movement relationship evolves (in timing and amplitude) can be used to characterize some fundamental control properties, including whether the observed system is autonomous or forced. In the case of a simple rhythmic, biological movement (single-joint horizontal forearm movement), this question can be addressed by assuming that the processed electromyographic activity (EMG) is related to the muscle torques. In this case, 2 interesting phenomena can be observed as the frequency increases. The first is that the phase lag between the force and movement remains constant (40 degrees), and the second is that the co-contraction of the agonist and antagonist muscle groups increases with the square of the frequency. These results showed that the contribution of muscle forces to movement organization cannot be regarded in terms of an escapement in an autonomous system, nor in terms of a forcing function in a forced system.
After limb amputation, patients often wake up with a vivid perception of the presence of the miss... more After limb amputation, patients often wake up with a vivid perception of the presence of the missing limb, called "phantom limb". Phantom limbs have mostly been studied with respect to pain sensation. But patients can experience many other phantom sensations, including voluntary movements. The goal of the present study was to quantify phantom movement kinematics and relate these to intact limb kinematics and to the time elapsed since amputation. Six upper arm and two forearm amputees with various delays since amputation (6months to 32years) performed phantom finger, hand and wrist movements at self-chosen comfortable velocities. The kinematics of the phantom movements was indirectly obtained via the intact limb that synchronously mimicked the phantom limb movements, using a Cyberglove® for measuring finger movements and an inertial measurement unit for wrist movements. Results show that the execution of phantom movements is perceived as "natural" but effortful. T...
Ceramics are quintessential indicators of human culture and its evolution across generations of s... more Ceramics are quintessential indicators of human culture and its evolution across generations of social learners. Cultural transmission and evolution theory frequently emphasizes apprentices’ need for accurate imitation (high-fidelity copying) of their mentors’ actions. However, the ensuing prediction of standardized fashioning patterns within communities of practice has not been directly addressed in handicraft traditions such as pottery throwing. To fill this gap, we analysed variation in vessel morphogenesis amongst and within traditional potters from culturally different workshops producing for the same market. We demonstrate that, for each vessel type studied, individual potters reliably followed distinctive routes through morphological space towards a much-less-variable common final shape. Our results indicate that mastering the pottery handicraft does not result from accurately reproducing a particular model behaviour specific to the community’s cultural tradition. We provide evidence that, at the level of the elementary clay-deforming gestures, individual learning rather than simple imitation is required for the acquisition of a complex motor skill such as throwing pottery.
While craft apprenticeship can be understood as socially mediated individual learning, the ensuin... more While craft apprenticeship can be understood as socially mediated individual learning, the ensuing prediction of individual and cultural object traits within craft communities has not been investigated. Here we provide an assessment of vessel shape variations occurring through cultural transmission and their visual perception by the craftsmen. To this end, 26 Hebron potters distributed through nine familial transmission units were asked to produce vessels of three different pottery types, then 21 of the participants were invited to visually identify their proper vessels and those of five other potters. We used the Elliptical Fourier method to analyze vessel shape variation among the productions. Our findings demonstrated that the learning process modified the ceramic shape, the cultural morphological traits being combined with new individual traits. Moreover, the individual morphological traits overtook the cultural ones, which is supposed to lead to divergence of vessel shapes within the transmission chain. If certain cultural morphological traits perpetuate through generations, this certainly does not result from fidelity copying occurring through learning but from stabilizing mechanisms such as consumer demand. Our results showed that potters do perceive the subtle same-type vessel shape variations and thereby could select the individual variant they prefer to produce.
Arthroplasty is a surgical procedure to restore the function of the joint of patient suffering fr... more Arthroplasty is a surgical procedure to restore the function of the joint of patient suffering from knee osteoarthritis. However, postoperative functional deficits are reported even after a rehabilitation program. In order to determine the origin of functional deficits of patient suffering from knee osteoarthritis and total knee arthroplasty, we developed a rodent model including a chemically-induced-osteoarthritis and designed a knee prosthesis (Ti6Al4V/PEEK) biomechanically and anatomically adapted to rat knee joint. Dynamic Weight-Bearing, gait kinematics, H-reflex from vastus medialis muscle and activities from metabosensitive III and IV afferent fibers in femoral nerve were assessed at 1 and 3 months post-surgery. Results indicate that knee osteoarthritis altered considerably the responses of afferent fibers to their known activators (i.e., lactic acid and potassium chloride) and consequently their ability to modulate the spinal sensorimotor loop, although, paradoxically, motor...
A synergistic inclination of the whole body towards the supporting leg is required when producing... more A synergistic inclination of the whole body towards the supporting leg is required when producing a stepping movement. It serves to shift the centre of mass towards the stance foot. While the importance of sensory information in the setting of this postural adjustment is undisputed, it is currently unknown the extent to which pro- prioceptive aVerences (Ia) give rise to
ABSTRACT Durant la planification du pas, nous avons observé un phénomène de facilitation proprioc... more ABSTRACT Durant la planification du pas, nous avons observé un phénomène de facilitation proprioceptive corticale (Saradjian 2013). Ce phénomène, absent en microgravité permettrait de calibrer les ajustements posturaux anticipés à venir et s’expliquerait par la non-pertinence des afférences proprioceptives lorsque les contraintes d’équilibre sont supprimées. Une autre possibilité serait une altération du cadre de référence sensoriel de l’ensemble du corps en l’absence d’informations vestibulaires et cutanées générées par la gravité, permettant aux informations proprioceptives de s’exprimer. Le but de cette étude est de tester si le rétablissement d’un référentiel stimulant ces récepteurs déprimés en microgravité restaurerait une facilitation de la proprioception.
We recently found that the cortical response to proprioceptive stimulation was greater when parti... more We recently found that the cortical response to proprioceptive stimulation was greater when participants were planning a step than when they stood still, and that this sensory facilitation was suppressed in microgravity. The aim of the present study was to test whether the absence of gravity-related sensory afferents during movement planning in microgravity prevented the proprioceptive cortical processing to be enhanced. We reestablished a reference frame in microgravity by providing and translating a horizontal support on which the participants were standing and verified whether this procedure restored the proprioceptive facilitation. The slight translation of the base of support (lateral direction), which occurred prior to step initiation, stimulated at least cutaneous and vestibular receptors. The sensitivity to proprioceptive stimulation was assessed by measuring the amplitude of the cortical somatosensory-evoked potential (SEP, over the Cz electrode) following the vibration of ...
In biological systems, obviously dissipative, some injection of muscle force is required in order... more In biological systems, obviously dissipative, some injection of muscle force is required in order to sustain rhythmic movement. As the movement frequency increases, the way the muscle-force-to-movement relationship evolves (in timing and amplitude) can be used to characterize some fundamental control properties, including whether the observed system is autonomous or forced. In the case of a simple rhythmic, biological movement (single-joint horizontal forearm movement), this question can be addressed by assuming that the processed electromyographic activity (EMG) is related to the muscle torques. In this case, 2 interesting phenomena can be observed as the frequency increases. The first is that the phase lag between the force and movement remains constant (40 degrees), and the second is that the co-contraction of the agonist and antagonist muscle groups increases with the square of the frequency. These results showed that the contribution of muscle forces to movement organization cannot be regarded in terms of an escapement in an autonomous system, nor in terms of a forcing function in a forced system.
After limb amputation, patients often wake up with a vivid perception of the presence of the miss... more After limb amputation, patients often wake up with a vivid perception of the presence of the missing limb, called "phantom limb". Phantom limbs have mostly been studied with respect to pain sensation. But patients can experience many other phantom sensations, including voluntary movements. The goal of the present study was to quantify phantom movement kinematics and relate these to intact limb kinematics and to the time elapsed since amputation. Six upper arm and two forearm amputees with various delays since amputation (6months to 32years) performed phantom finger, hand and wrist movements at self-chosen comfortable velocities. The kinematics of the phantom movements was indirectly obtained via the intact limb that synchronously mimicked the phantom limb movements, using a Cyberglove® for measuring finger movements and an inertial measurement unit for wrist movements. Results show that the execution of phantom movements is perceived as "natural" but effortful. T...
Ceramics are quintessential indicators of human culture and its evolution across generations of s... more Ceramics are quintessential indicators of human culture and its evolution across generations of social learners. Cultural transmission and evolution theory frequently emphasizes apprentices’ need for accurate imitation (high-fidelity copying) of their mentors’ actions. However, the ensuing prediction of standardized fashioning patterns within communities of practice has not been directly addressed in handicraft traditions such as pottery throwing. To fill this gap, we analysed variation in vessel morphogenesis amongst and within traditional potters from culturally different workshops producing for the same market. We demonstrate that, for each vessel type studied, individual potters reliably followed distinctive routes through morphological space towards a much-less-variable common final shape. Our results indicate that mastering the pottery handicraft does not result from accurately reproducing a particular model behaviour specific to the community’s cultural tradition. We provide evidence that, at the level of the elementary clay-deforming gestures, individual learning rather than simple imitation is required for the acquisition of a complex motor skill such as throwing pottery.
While craft apprenticeship can be understood as socially mediated individual learning, the ensuin... more While craft apprenticeship can be understood as socially mediated individual learning, the ensuing prediction of individual and cultural object traits within craft communities has not been investigated. Here we provide an assessment of vessel shape variations occurring through cultural transmission and their visual perception by the craftsmen. To this end, 26 Hebron potters distributed through nine familial transmission units were asked to produce vessels of three different pottery types, then 21 of the participants were invited to visually identify their proper vessels and those of five other potters. We used the Elliptical Fourier method to analyze vessel shape variation among the productions. Our findings demonstrated that the learning process modified the ceramic shape, the cultural morphological traits being combined with new individual traits. Moreover, the individual morphological traits overtook the cultural ones, which is supposed to lead to divergence of vessel shapes within the transmission chain. If certain cultural morphological traits perpetuate through generations, this certainly does not result from fidelity copying occurring through learning but from stabilizing mechanisms such as consumer demand. Our results showed that potters do perceive the subtle same-type vessel shape variations and thereby could select the individual variant they prefer to produce.
Arthroplasty is a surgical procedure to restore the function of the joint of patient suffering fr... more Arthroplasty is a surgical procedure to restore the function of the joint of patient suffering from knee osteoarthritis. However, postoperative functional deficits are reported even after a rehabilitation program. In order to determine the origin of functional deficits of patient suffering from knee osteoarthritis and total knee arthroplasty, we developed a rodent model including a chemically-induced-osteoarthritis and designed a knee prosthesis (Ti6Al4V/PEEK) biomechanically and anatomically adapted to rat knee joint. Dynamic Weight-Bearing, gait kinematics, H-reflex from vastus medialis muscle and activities from metabosensitive III and IV afferent fibers in femoral nerve were assessed at 1 and 3 months post-surgery. Results indicate that knee osteoarthritis altered considerably the responses of afferent fibers to their known activators (i.e., lactic acid and potassium chloride) and consequently their ability to modulate the spinal sensorimotor loop, although, paradoxically, motor...
A synergistic inclination of the whole body towards the supporting leg is required when producing... more A synergistic inclination of the whole body towards the supporting leg is required when producing a stepping movement. It serves to shift the centre of mass towards the stance foot. While the importance of sensory information in the setting of this postural adjustment is undisputed, it is currently unknown the extent to which pro- prioceptive aVerences (Ia) give rise to
ABSTRACT Durant la planification du pas, nous avons observé un phénomène de facilitation proprioc... more ABSTRACT Durant la planification du pas, nous avons observé un phénomène de facilitation proprioceptive corticale (Saradjian 2013). Ce phénomène, absent en microgravité permettrait de calibrer les ajustements posturaux anticipés à venir et s’expliquerait par la non-pertinence des afférences proprioceptives lorsque les contraintes d’équilibre sont supprimées. Une autre possibilité serait une altération du cadre de référence sensoriel de l’ensemble du corps en l’absence d’informations vestibulaires et cutanées générées par la gravité, permettant aux informations proprioceptives de s’exprimer. Le but de cette étude est de tester si le rétablissement d’un référentiel stimulant ces récepteurs déprimés en microgravité restaurerait une facilitation de la proprioception.
We recently found that the cortical response to proprioceptive stimulation was greater when parti... more We recently found that the cortical response to proprioceptive stimulation was greater when participants were planning a step than when they stood still, and that this sensory facilitation was suppressed in microgravity. The aim of the present study was to test whether the absence of gravity-related sensory afferents during movement planning in microgravity prevented the proprioceptive cortical processing to be enhanced. We reestablished a reference frame in microgravity by providing and translating a horizontal support on which the participants were standing and verified whether this procedure restored the proprioceptive facilitation. The slight translation of the base of support (lateral direction), which occurred prior to step initiation, stimulated at least cutaneous and vestibular receptors. The sensitivity to proprioceptive stimulation was assessed by measuring the amplitude of the cortical somatosensory-evoked potential (SEP, over the Cz electrode) following the vibration of ...
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