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Full-Text Articles in Medicine and Health Sciences
The Pontomedullary Reticular Formation Contributes To The Compensatory Postural Responses Observed Following Removal Of The Support Surface In The Standing Cat, Paul Stapley, Trevor Drew
The Pontomedullary Reticular Formation Contributes To The Compensatory Postural Responses Observed Following Removal Of The Support Surface In The Standing Cat, Paul Stapley, Trevor Drew
Dr Paul J Stapley
This study was designed to determine the contribution of reticular neurons in the pontomedullary reticular formation (PMRF) to the postural responses produced to compensate for an unexpected perturbation. We recorded the activity of 48 neurons in the PMRF, including 41 reticulospinal neurons, to removal of the support surface under each of the four limbs in four cats. The perturbations produced robust postural responses that were divided into three periods: an initial postural response (P1) that displaced the center of vertical pressure over the two diagonal supporting limbs; a secondary response (P2) during which the cat restored a tripedal support pattern; …
Feedback Regulation Of Temporal Muscle Activation Patterns For Postural Control Before And After Peripheral Neuropathy, L Ting, D Lockhart, P Stapley, J Macpherson
Feedback Regulation Of Temporal Muscle Activation Patterns For Postural Control Before And After Peripheral Neuropathy, L Ting, D Lockhart, P Stapley, J Macpherson
Dr Paul J Stapley
Introduction: Neural mechanislllS determining temporal pattcl1ls of muscle activity during poshlral responses are not understood. Fulluwing pyridoxine inuuced somatosensory loss in cats, unset latencies of automatic poshu-al responses are delayed, and balance is impaired. We introduce a new method for correlating temporal patterns of muscle activation with task-level variahles in the context of postural responses to perturbation. Methods: We measured postmal responses to support smface tronslations before and after loss of group I afferents indnced by pyridoxine intoxication. We reconstructed temporal EMG patterns llsing a feedback loop with delays, on CoM acceleration. velocity, and displacement. Resnlts: Prior to lesion, temporal …
Muscle Synergies Of Feed-Forward Postural Adjustments During Reaching To Multi-Directional Targets In Standing, J Leonard, S Chvatal, L Ting, P Stapley
Muscle Synergies Of Feed-Forward Postural Adjustments During Reaching To Multi-Directional Targets In Standing, J Leonard, S Chvatal, L Ting, P Stapley
Dr Paul J Stapley
Standing balance can be controlled using feedback (FB) or feedforward (FF) mechanisms, depending on the nature of a postural disturbance. Unexpected disturbances of balance elicit automatic postural responses (APR) to restore body position (Horak and Macpherson 1996). Studies of APR have shown that the CNS recruits a small number of muscle synergies to simplify complex task-level goals (e.g. CoM stabilization) to produce the appropriate muscle activation patterns (Ting & McKay, 2007). Successful execution of goal-directed voluntary movements while standing requires FF programming of postural adjustments that serve to initiate movement of the body towards the target (preparatory postural adjustment, pPA) …
Human Whole-Body Reaching In Normal Gravity And Microgravity Reveals A Strong Temporal Coordination Between Postural And Focal Task Components, Jerome Patron, Paul Stapley, Thierry Pozzo
Human Whole-Body Reaching In Normal Gravity And Microgravity Reveals A Strong Temporal Coordination Between Postural And Focal Task Components, Jerome Patron, Paul Stapley, Thierry Pozzo
Dr Paul J Stapley
Previous experiments by our group in normal gravity (1 G) have revealed spatial relationships between postural and focal components of whole-body reaching and pointing movements. We suggested that these relationships could be explained partly through the use of gravity to displace the CoM and attain the object or target position. In this study we compared human whole-body reaching in 1 G and microgravity (0 G) in order to more fully investigate how gravity contributes to strategies adopted for task execution and to determine possible invariant temporal relationships between multiple segments. Whole-body reaching movements made from the standing position in two …
Decoupling Of Stretch Reflex And Background Muscle Activity During Anticipatory Postural Adjustments In Humans, Siddharth Vedula, Robert Kearney, Ross Wagner, Paul Stapley
Decoupling Of Stretch Reflex And Background Muscle Activity During Anticipatory Postural Adjustments In Humans, Siddharth Vedula, Robert Kearney, Ross Wagner, Paul Stapley
Dr Paul J Stapley
We studied the evolution of stretch reXexes in relation to background electromyographic (EMG) activity in the soleus muscle preceding the onset of voluntary arm raise movements. Our objective was to investigate if changes in reXex EMG and muscle activity occur simultaneously and are similarly scaled in amplitude. Ten human subjects stood with each foot on pedals able to exert short dorsiXexor pulses during stance. Subjects were asked to product consistent voluntary arm raise movements to a target upon a visual cue. In ¼ of trials, no pulse perturbations were given, but in the remaining ¾’s of all trials pulses were …
Postural Responses To Multidirectional Perturbations To The Hand During Stance, Ali Forghani, Sheida Rabipour, Theodore E. Milner, Paul J. Stapley
Postural Responses To Multidirectional Perturbations To The Hand During Stance, Ali Forghani, Sheida Rabipour, Theodore E. Milner, Paul J. Stapley
Dr Paul J Stapley
Humans are easily able to maintain their balance while applying force with their hands to move or stabilize objects. Based on Newton's laws, the applied force must be counteracted by ground reaction force (GRF) to maintain balance. However, because the GRF is partitioned between the two legs there is no unique solution. Furthermore, central nervous system (CNS) can employ an infinite number of muscle activation patterns to achieve ground reaction force (GRF) vectors needed to satisfy both the task-level goal and balance. This study examines the postural response when hand position must remain stable as an external force is applied …
Postural Responses To Unexpected Perturbations Of Balance During Reaching, Hari Trivedi, Julia Leonard, Lena Ting, Paul Stapley
Postural Responses To Unexpected Perturbations Of Balance During Reaching, Hari Trivedi, Julia Leonard, Lena Ting, Paul Stapley
Dr Paul J Stapley
To study the interaction between feedforward and feedback modes of postural control, we investigated postural responses during unexpected perturbations of the support surface that occurred during forward reaching in a standing position. We examined postural responses in lower limb muscles of nine human subjects. Baseline measures were obtained when subjects executed reaching movements to a target placed in front of them (R condition) and during postural responses to forward and backward support-surface perturbations (no reaching, P condition) during quiet stance. Perturbations were also given at different delays after the onset of reaching movements (RP conditions) as well as with the …
Neck Muscle Fatigue And Postural Control In Patients With Whiplash Injury, Paul Stapley, Maria Beretta, Elena Toffola, Marco Schieppati
Neck Muscle Fatigue And Postural Control In Patients With Whiplash Injury, Paul Stapley, Maria Beretta, Elena Toffola, Marco Schieppati
Dr Paul J Stapley
Objectives: To examine if patients with whiplash injury show identifiable increases in neck muscle fatigability and associated increase in postural body sway after contractions of dorsal neck muscles, and if physiotherapy treatment reduces these effects. Methods: Sway was measured during stance in 13 patients before and after 5 min of isometric dorsal neck muscle contractions and after recovery, pre- and post-physiotherapy, using a force platform. Amplitude and median frequency of neck muscle EMG were calculated during the contracting period. After each stance trial, patients gave a subjective score of sway. Results: Pre-treatment, seven patients showed EMG signs of fatigue (increases …
A Common Neural Substrate For The Control Of Anticipatory And Compensatory Postural Responses, Paul Stapley, Benedicte Schepens, Trevor Drew
A Common Neural Substrate For The Control Of Anticipatory And Compensatory Postural Responses, Paul Stapley, Benedicte Schepens, Trevor Drew
Dr Paul J Stapley
We have shown previously that reticulospinal neurones (RSNs) in the brainstem pontomedullary reticular formation (PMRF) contribute to the production of the anticipatory postural adjustments (APAs) that precede reaching movements executed in a standing pOSition (Schepens and Drew, 2004, 2006; Schepens, Stapley and Drew, 2008). More recently (Stapley and Drew, 2009), we have also shown that cells in the PMRF contribute to the production of the compensatory responses that are produced by unexpected perturbations (drops) of the support surface from under one paw during quiet stance. In this poster we address the question of whether the same cells in the PMRF …
Reaching To Multiple Targets When Standing: The Spatial Organization Of Feedforward Postural Adjustments, Julia Leonard, Ryan Brown, Paul Stapley
Reaching To Multiple Targets When Standing: The Spatial Organization Of Feedforward Postural Adjustments, Julia Leonard, Ryan Brown, Paul Stapley
Dr Paul J Stapley
We examined the spatial organization of feedforward postural adjustments produced prior to and during voluntary arm reaching movements executed while standing. We sought to investigate whether the activity of postural muscles before and during reaching was directionally tuned and whether a strategy of horizontal force constraint could be observed. To this end, eight human subjects executed self-paced reach-to-point movements on the random illumination of one of 13 light targets placed within a 180° array centered along the midline of the body. Analysis was divided into two periods: a first corresponding to the 250 ms preceding the onset of the reaching …
Postural Adjustments For Online Corrections Of Arm Movements In Standing Humans, Julia Leonard, Valeriya Gritsenko, Ryan Ouckama, Paul Stapley
Postural Adjustments For Online Corrections Of Arm Movements In Standing Humans, Julia Leonard, Valeriya Gritsenko, Ryan Ouckama, Paul Stapley
Dr Paul J Stapley
The aim of this study was to investigate how humans correct ongoing arm movements while standing. Specifically, we sought to understand whether the postural adjustments in the legs required for online corrections of arm movements are predictive or rely on feedback from the moving limb. To answer this question we measured online corrections in arm and leg muscles during pointing movements while standing. Nine health right-handed subjects reached with their dominant arm to a visual target in front of them and aligned with their midline. In some trials, the position of the target would switch from the central target to …
Reflex Changes Associated With Anticipatory Postural Adjustments Preceding Voluntary Arm Movements In Standing Humans, Siddharth Vedula, Paul J. Stapley, Robert E. Kearney
Reflex Changes Associated With Anticipatory Postural Adjustments Preceding Voluntary Arm Movements In Standing Humans, Siddharth Vedula, Paul J. Stapley, Robert E. Kearney
Dr Paul J Stapley
Dynamic changes in human stability, such as those induced by upper body movements, are preceded by anticipatory postural adjustments (APAs) in the rest of the body. We measured the excitability of the stretch reflex of the triceps-surae muscle group during APAs associated with unilateral right arm raises in standing humans. Our results demonstrate that reflex excitability and underlying muscle activity are linked during the APA period, but that they differ in their relative timing. This supports the idea that reflexes are controlled independently of muscle activation.