Добірка наукової літератури з теми "Premovement"

We continuously adapt our movements in daily life, forming new internal models whenever necessary and updating existing ones. Recent work has suggested that this flexibility is enabled via sensorimotor cues, serving to access the correct internal model whenever necessary and keeping new models apart from previous ones. While research to date has mainly focused on identifying the nature of such cue representations, here we investigated whether and how these cue representations generalize, interfere, and transfer within and across effector systems. Subjects were trained to make two-stage reaching movements: a premovement that served as a cue, followed by a targeted movement that was perturbed by one of two opposite curl force fields. The direction of the premovement was uniquely coupled to the direction of the ensuing force field, enabling simultaneous learning of the two respective internal models. After training, generalization of the two premovement cues' representations was tested at untrained premovement directions, within both the trained and untrained hand. We show that the individual premovement representations generalize in a Gaussian-like pattern around the trained premovement direction. When the force fields are of unequal strengths, the cue-dependent generalization skews toward the strongest field. Furthermore, generalization patterns transfer to the nontrained hand, in an extrinsic reference frame. We conclude that contextual cues do not serve as discrete switches between multiple internal models. Instead, their generalization suggests a weighted contribution of the associated internal models based on the angular separation from the trained cues to the net motor output.

Disrupted triphasic electromyography (EMG) patterns of agonist and antagonist muscle pairs during fast goal-directed movements have been found in patients with hypermetria. Since peripheral electrical stimulation (ES) and motor training may modulate motor cortical excitability through plasticity mechanisms, we aimed to investigate whether temporal ES-assisted movement training could influence premovement cortical excitability and alleviate hypermetria in patients with spinal cerebellar ataxia (SCA). The EMG of the agonist extensor carpi radialis muscle and antagonist flexor carpi radialis muscle, premovement motor evoked potentials (MEPs) of the flexor carpi radialis muscle, and the constant and variable errors of movements were assessed before and after 4 weeks of ES-assisted fast goal-directed wrist extension training in the training group and of general health education in the control group. After training, the premovement MEPs of the antagonist muscle were facilitated at 50 ms before the onset of movement. In addition, the EMG onset latency of the antagonist muscle shifted earlier and the constant error decreased significantly. In summary, temporal ES-assisted training alleviated hypermetria by restoring antagonist premovement and temporal triphasic EMG patterns in SCA patients. This technique may be applied to treat hypermetria in cerebellar disorders. (This trial is registered withNCT01983670.)

Even the simplest movements are generated by a remarkably complex pattern of muscle activity. Fast, accurate movements at a single joint are produced by a stereotyped pattern that includes a decrease in any preexisting activity in antagonist muscles. This premovement suppression is necessary to prevent the antagonist muscle from opposing movement generated by the agonist muscle. Here, we provide evidence that the primary motor cortex (M1) sends a command signal that generates this premovement suppression. Thus, output neurons in M1 sculpt complex spatiotemporal patterns of motor output not only by actively turning on muscles but also by actively turning them off.

1. Primary somatosensory cortical (SI) neurons exhibit characteristic activity before the initiation of movements. This premovement activity (PMA) may result from centrally generated as well as from peripheral inputs. We examined PMA for 55 SI neurons (10, 13, 28, and 4 in areas 3a, 3b, 1, and 2, respectively) with activity that was entrained to vibrotactile stimulation (i.e., was temporally correlated with the stimulus). We sought to determine whether the temporal characteristics of vibration-entrained discharges would change throughout the reaction time period, and, if they did, whether these changes might be accounted for by central inputs. 2. Monkeys made wrist flexions and extensions in response to sinusoidal vibration (27, 57, or 127 Hz) of their palms. Vibration remained on until the animal moved at least 5 degrees from the initial hold position. Mean firing rate (MFR), a measure of the level of activity, was derived from the number of spikes per vibratory cycle. The correlation between the vibration and the neuronal firing was described by the mean phase (MP) of the vibratory cycle at which spikes occurred. The degree of entrainment was quantified as synchronicity (Synch), a statistical parameter that could change from 0 for no entrainment to 1 for responses at a constant phase. 3. Premovement MFR increases (activation) and decreases (suppression) were observed. Moreover, two changes in MFR often were observed for the same neuron (2-event PMA). Many MFR shifts, especially the first in the two-event PMA, preceded electromyographic (EMG) onset. The pre-EMG MFR shifts more often had the same sign both for flexion and extension movements rather than having opposite signs. However, with equal frequency, post-EMG PMA events had the same or opposite sign for different movement directions. We suggest that the pre-EMG PMA has an origin different from movement-related peripheral reafference. 4. Premovement activation was accompanied by shifts of MP corresponding to earlier responses to the ongoing vibratory stimulus and by decreases of response Synch. Premovement suppression was not associated with consistent shifts of MP and Synch. We suggest that during premovement activation, asynchronous (uncorrelated with vibration) signals are integrated with the vibratory input. These asynchronous signals may make neurons more likely to discharge and to do so earlier with respect to the vibratory stimulus. The asynchronous component may also disrupt the vibration-entrained activity pattern.(ABSTRACT TRUNCATED AT 400 WORDS)

1. Single-cell activity was recorded from three different motor areas in the cerebral cortex: the primary motor cortex (MI), supplementary motor area (SMA), and premotor cortex (PM). 2. Three monkeys (Macaca fuscata) were trained to perform a sequential motor task in two different conditions. In one condition (visually triggered task, VT), they reached to and touched three pads placed in a front panel by following lights illuminated individually from behind the pads. In the other condition (internally guided task, IT), they had to remember a predetermined sequence and press the three pads without visual guidance. In a transitional phase between the two conditions, the animals learned to memorize the correct sequence. Auditory instruction signals (tones of different frequencies) told the animal which mode it was in. After the instruction signals, the animals waited for a visual signal that triggered the first movement. 3. Neuronal activity was analyzed during three defined periods: delay period, premovement period, and movement period. Statistical comparisons were made to detect differences between the two behavioral modes with respect to the activity in each period. 4. Most, if not all, of MI neurons exhibited similar activity during the delay, premovement, and movement periods, regardless of whether the sequential motor task was visually guided or internally determined. 5. More than one-half of the SMA neurons were preferentially or exclusively active in relation to IT during both the premovement (55%) and movement (65%) periods. In contrast, PM neurons were more active (55% and 64% during the premovement and movement periods) in VT. 6. During the instructed-delay period, a majority of SMA neurons exhibited preferential or exclusive relation to IT whereas the activity in PM neurons was observed equally in different modes. 7. Two types of neurons exhibiting properties of special interest were observed. Sequence-specific neurons (active in a particular sequence only) were more common in SMA, whereas transition-specific neurons (active only at the transitional phase) were more common in PM. 8. Although a strict functional dichotomy is not acceptable, these observations support a hypothesis that the SMA is more related to IT, whereas PM is more involved in VT. 9. Some indications pointing to a functional subdivision of PM are obtained.

The role of primary motor cortex (M1) in the control of hand movements is still unclear. Functional magnetic resonance imaging (fMRI) studies of unimanual performance reported a relationship between level of precision of a motor task and additional ipsilateral M1 (iM1) activation. In the present study, we determined whether the demand on accuracy of a movement influences the magnitude of the inhibitory effect between primary motor cortices (IHI). We used transcranial magnetic stimulation (TMS) to measure active IHI (aIHI) of the iM1 on the contralateral M1 (cM1) in the premovement period of a left-hand motor task. Ten healthy participants manipulated a joystick to point to targets of two different sizes. For aIHI, the conditioning stimulus (CS) was applied to iM1, and the test stimulus (TS) to cM1, with an interstimulus interval of 10 ms. The amount of the inhibitory effect of the CS on the motor-evoked potential (MEP) of the subsequent TS was expressed as percentage of the mean MEP amplitude evoked by the single TS. Across different time points of aIHI measurements in the premovement period, there was a significant effect for target size on aIHI. Preparing to point to small targets was associated with weaker aIHI compared with pointing to large targets. The present findings suggest that, during the premovement period, aIHI from iM1 on cM1 is modulated by the demand on accuracy of the motor task. This is consistent with task fMRI findings showing bilateral M1 activation during high-precision movements but only unilateral M1 activity during low-precision movements.

Ma recherche se base sur une question essentielle pour le musicien : comment construire un jeu vivant qui lui semble signifiant ? Certains artistes décrivent une expérience de l'être joué qui associe la compréhension du texte musical à son incarnation dans le jeu : les éléments musicaux sont connectés et délimités de façon sensible à travers les différentes échelles de temps par un geste qui fait sens. Premièrement, l’étude de problématiques pratiques de l’expérience pianistique amène à remettre en cause un modèle du corps objet ainsi qu’une façon d'utiliser les imaginaires pour motiver le geste qui sous-tendent l'analyse musicologique et la pédagogie traditionnelles. La segmentation du texte musical en éléments articulés dans un espace quantifié et à la succession de mouvements destinés à produire des segments sonores apparaissent insuffisants pour faire l’expérience du sens et de la continuité de l’expérience musicale. Deuxièmement, l’anthropologie théâtrale, la danse, la psychomotricité, la phénoménologie et l'expérience pratique apportent des pistes pour étudier l’émergence du sens à travers la notion de corporéité. Les notions de prémouvement et de présence ouvrent à la quête d'une qualité d'attention visant à percevoir les variations de tonicité du corps en interaction avec son environnement afin de modeler la qualité du geste. Les pratiques abordées explorent la relation à l’altérité, la construction de la spatialité et la connexion des différentes parties du corps en investissant l’imaginaire. Appliquées à l’interprétation d’une œuvre musicale, elles permettent d'articuler les éléments musicaux en s'articulant soi-même au monde et de déployer une temporalité incarnée
My research is grounded in an essential question for the musician: how do you construct a lively performance that seems meaningful to him ? Some artists describe an experience of being played that combines understanding of the musical text with its embodiment in the playing: musical elements are sensitively connected and delimited across different time scales by a gesture that makes sense. Firstly, the study of practical issues of pianistic experience brings into question a model of the body as object, and a way of using imaginaries to motivate gesture, that underlie traditional musicological analysis and pedagogy. The segmentation of musical text into articulated elements in a quantified space, and the succession of movements aimed at producing sound segments, appear insufficient for experiencing the meaning and continuity of musical experience. Secondly, theatrical anthropology, dance, psychomotricity, phenomenology and practical experience provide insights into the emergence of meaning through the notion of corporeity. The notions of premovement and presence open up the quest for a quality of attention aimed at perceiving variations in body tonicity in interaction with its environment, in order to shape the quality of gesture. These practices explore the relationship to alterity, the construction of spatiality and the connection between different parts of the body by engaging the imaginary. Applied to the performance of a musical work, they enable us to articulate musical elements in our own relation to the world, and to develop an embodied temporality