Planning of spatially-oriented locomotion following focal brain damage in humans: A pilot study

Motor impairments in human gait following stroke or focal brain damage are well documented. Here, we investigated whether stroke and/or focal brain damage also affect the navigational component of spatially oriented locomotion. Ten healthy adult participants and ten adult brain-damaged patients had to walk towards distant targets from different starting positions (with vision or blindfolded). No instructions as to which the path to follow were provided to them. We observed very similar geometrical forms of paths across the two groups of participants and across visual conditions. This spatial stereotypy of whole-body displacements was observed following brain damage, even in the most severely impaired (hemiparetic) patients. This contrasted with much more variability at the temporal level. In particular, healthy participants and non-hemiparetic patients varied their walking speed according to curvature changes along the path. On the contrary, the walking speed profiles were not stereotypical and were not systematically constrained by path geometry in hemiparetic patients where it was associated with different stepping behaviors. These observations confirm the dissociation between cognitive and motor aspects of gait recovery post-stroke. The impact of these findings on the understanding of the functional and anatomical organization of spatially-oriented locomotion and for rehabilitation purposes is discussed and contextualized in the light of recent advances in electrophysiological studies

Contrôle et guidage de la locomotion humaine

The aim of this experimental work is to provide elements of understanding relatively to some organizing principles of human locomotion. Its originality comes from the analysis of human locomotion through its sensorimotor and cognitive components: here, locomotion is thought and analyzed as a motor activity that combines a continuous, fine coordination of the limbs and trunk across each step with the planning strategies of goal-directed movements. Thus, two levels of description of locomotion are considered, the analysis of the processes underlying the generation and control of both the locomotor pattern (across each step cycle) and the locomotor trajectory. The own and combined effects of the speed, the mode of locomotion as well as the geometrical properties of the path, on the regulation of locomotor activity are tested. This is realized mainly through kinematic recordings but also using electromyographic and videooculographic measurements. The origins of some kinematic invariants that were reported both for step and path formation are studied and the organization of head, eye and body movements for the steering of locomotion is characterized. Finally, the interests of some general approaches and principles, like the notions of segmentation and optimality, are discussed within the general framework of locomotor path planning.L'objectif de ce travail est de fournir quelques éléments de compréhension sur les règles d'organisation de l'activité locomotrice chez l'homme. Son originalité réside dans le fait d'analyser la locomotion humaine dans ses composantes (sensori)motrice et cognitive : ainsi la locomotion est considérée et analysée comme l'activité coordonnée des membres inférieurs combinée à des stratégies de planification communes à l'ensemble des mouvements orientés vers un but spatial. Deux niveaux de description de la locomotion sont pris en compte, l'analyse des processus aboutissant à la formation du pas et ceux liés à la génération de la trajectoire locomotrice. Les effets propres et conjoints du mode et de la vitesse de locomotion, ainsi que de la géométrie des trajets, sur la régulation de l'activité locomotrice, sont étudiés au moyen (principalement) de l'analyse cinématique mais également électromyographique et vidéooculographique. Les origines de certains invariants cinématiques de la locomotion humaine sont étudiées pour ces deux niveaux d'analyse et la caractérisation des mouvements du regard et du corps lors deschangements de direction de marche est réalisée. Enfin, quelques approches et principes particulièrement intéressants, comme le principe de segmentation et celui d'optimalité, sont discutés dans le cadre général de l'étude expérimentale et de la modélisation des processus de génération et de contrôle des trajectoires locomotrices

Microsaccades are modulated by both attentional demands of a visual discrimination task and background noise

Microsaccades are miniature saccades occurring once or twice per second during visual fixation. While microsaccades and saccades share similarities at the oculomotor level, the functional roles of microsaccades are still debated. In this study, we examined the hypothesis that the microsaccadic activity is affected by the type of noisy background during the execution of a particular discrimination task. Human subjects had to judge the orientation of a tilted stimulus embedded in static or dynamic backgrounds in a forced choice-task paradigm, as adapted from Rucci, Iovin, Poletti, and Santini (2007). Static backgrounds induced more microsaccades than dynamic ones only during the execution of the discrimination task. A directional bias of microsaccades, dictated by the stimulus orientation, was temporally coupled with this period of increased activity. Both microsaccade rates and orientations were comparable across background types after the response time although subjects maintained fixation until the end of the trial. This represents a background-specific modulation of the microsaccadic activity driven by attentional demands. The visual influence of microsaccades on discrimination performances was modeled at the retinal level for both types of backgrounds. A higher simulated microsaccadic activity was necessary for static backgrounds in order to achieve discrimination performance scores comparable to that of dynamic ones. Taken together, our experimental and theoretical findings further support the idea that microsaccades are under attentional control and represent an efficient sampling strategy allowing spatial information acquisition

Contrôle et guidage de la locomotion humaine

L objectif de ce travail est de fournir quelques éléments de compréhension sur les règles d organisation de l activité locomotrice chez l homme. Son originalité réside dans le fait d analyser la locomotion humaine dans ses composantes (sensori)motrice et cognitive : ainsi la locomotion est considérée et analysée comme l activité coordonnée des membres inférieurs combinée à des stratégies de planification communes à l ensemble des mouvements orientés vers un but spatial. Deux niveaux de description de la locomotion sont pris en compte, l analyse des processus aboutissant à la formation du pas et ceux liés à la génération de la trajectoire locomotrice. Les effets propres et conjoints du mode et de la vitesse de locomotion, ainsi que de la géométrie des trajets, sur la régulation de l activité locomotrice, sont étudiés au moyen (principalement) de l analyse cinématique mais également électromyographique et vidéooculographique. Les origines de certains invariants cinématiques de la locomotion humaine sont étudiées pour ces deux niveaux d analyse et la caractérisation des mouvements du regard et du corps lors des changements de direction de marche est réalisée. Enfin, quelques approches et principes particulièrement intéressants, comme le principe de segmentation et celui d optimalité, sont discutés dans le cadre général de l étude expérimentale et de la modélisation des processus de génération et de contrôle des trajectoires locomotrices.The aim of this experimental work is to provide elements of understanding relatively to some organizing principles of human locomotion. Its originality comes from the analysis of human locomotion through its sensorimotor and cognitive components: here, locomotion is thought and analyzed as a motor activity that combines a continuous, fine coordination of the limbs and trunk across each step with the planning strategies of goal-directed movements. Thus, two levels of description of locomotion are considered, the analysis of the processes underlying the generation and control of both the locomotor pattern (across each step cycle) and the locomotor trajectory. The own and combined effects of the speed, the mode of locomotion as well as the geometrical properties of the path, on the regulation of locomotor activity are tested. This is realized mainly through kinematic recordings but also using electromyographic and videooculographic measurements. The origins of some kinematic invariants that were reported both for step and path formation are studied and the organization of head, eye and body movements for the steering of locomotion is characterized. Finally, the interests of some general approaches and principles, like the notions of segmentation and optimality, are discussed within the general framework of locomotor path planning.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

The effect of background noise on microsaccades generation in humans

International audienc

The effects of background noise on microsaccades generation in humans

International audienc

Contribution à l'étude de la relation entre cinématique du mouvement et géométrie de la trajectoire du corps, lors de la marche le long de trajets courbés

Hicheur Halim, Vieilledent Stéphane, Richardson M.-J.-E., Berthoz A. Contribution à l'étude de la relation entre cinématique du mouvement et géométrie de la trajectoire du corps, lors de la marche le long de trajets courbés. In: Les Cahiers de l'INSEP, n°34, 2003. Expertise et sport de haut niveau. pp. 391-396

Chapitre 9. La génération de trajectoires locomotrices chez l’homme

We present in this chapter recent findings about some production, control and steering mechanisms of locomotion in human subjects. During the reproduction of curved locomotor paths drawn on the floor, we investigate the relationship between the radius of curvature of the trajectory and the tangential velocity of the walker and found co-variations of both parameters according to the prediction of the so called « power law » already used by the CNS during handwriting or visual perception of curved movements. During the reproduction of polygonal paths, we investigate the influence of learning methods of the shape of the path to be followed. We found that mental simulation, a high level cognitive activity based on mental imagery, allowed subjects to perform the task as accurately as what they did when they learned it with actual walking. Our set of results suggests the existence of simplifying rules used by the CNS during locomotion. However, we discuss them as a subtle interplay between central knowledge of the navigation space and multisensory inputs arising from peripheral organs leading to the construction of a mental model of the locomotor trajectory