An examination of the effects of equilibrium on the control of goal-directed reaching in humans

• Main Author: Hua, Silvia
• Other Authors: Paul Stapley (Supervisor)
• Format: Others
• Language: en
• Published: McGill University 2012
• Subjects: Biology - Neuroscience
• Online Access: http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=106579

Goal-directed reaching movements executed from seated positions exhibit rapid, automatic corrections in response to a change in target position. In the standing posture, corrections in arm trajectory during reaching movements are accompanied by feedforward corrections in postural activity which create the dynamical conditions necessary for successful task execution. However, it is unknown how equilibrium constraints associated with standing as opposed to sitting, which has little or no equilibrium constraints, influence the neural processes underlying online corrections of goal-directed movements. This thesis aimed to address this question. Eight healthy adult subjects (3 males, 5 females) performed regular reach-to-point movements and an online arm correction task when seated and when standing. It was hypothesized that the increased equilibrium constraints during stance would influence the online control of goal-directed reaching, resulting in differences in focal movement endpoint kinematics. The focal reaching movement was described using spatiotemporal kinematics of the reaching hand. Whole-body kinematic analyses were also performed to compare the movement strategies utilized in each postural configuration. It was found that the postural configuration (seated vs. standing) in which the movements were executed generally did not affect focal movement parameters (velocity profile, movement time, time to correction, and peak velocity), despite resulting in different whole-body kinematic strategies (i.e. extent of elbow flexion-extension, shoulder adduction-abduction, trunk rotation, pelvis rotation, pelvis obliquity, and pelvis translation). These results highlight the efficacy of the neural processes underlying the end goal of arm reaching movements and their online control. The processes of control do not appear to be affected by the higher demands placed on the CNS required for the maintenance of postural equilibrium during stance. === En position assise, les mouvements de pointage sur une cible visuelle démontrent des corrections rapides et automatiques lors d'une perturbation spatiale de la cible. En position debout, des corrections posturales anticipent les corrections de la trajectoire de la main et créent les conditions dynamiques requises pour le déroulement du mouvement. Cependant, nous ne savons pas comment la position debout, qui pose plus de contraintes d'équilibre sur le mouvement que la position assise, affecte les processus neuraux à la base des corrections en ligne des mouvements de pointage. Le but de cette étude est d'aborder cette question. Les sujets (3 hommes, 5 femmes) ont pointé une cible visuelle en étant assis et en étant debout. Pour 33% des essais, la cible a été déplacée vers la droite sans prévenir le sujet, exigeant une correction en ligne du mouvement. La configuration posturale (assise/debout) n'a influencé ni la trajectoire de la main ni la correction en ligne du mouvement de la main, bien que les stratégies cinématiques du corps entier décrivant ces deux conditions posturales soient différentes. Ces résultats soulignent l'efficacité des processus neuraux à la base de mouvements de pointage et de contrôle en ligne; il semble que ces processus ne soient pas influencés par la demande neurale augmentée requise pour garder l'équilibre en restant debout.