Practice modifies the developing automatic postural response

1997 ◽  
Vol 114 (1) ◽  
pp. 33-43 ◽  
Author(s):  
H. Sveistrup ◽  
Marjorie H. Woollacott
Keyword(s):  
Postural Response ◽  
Automatic Postural Response

Influence of instruction, prediction, and afferent sensory information on the postural organization of step initiation

1996 ◽  
Vol 75 (4) ◽  
pp. 1619-1628 ◽  
Author(s):  
A. Burleigh ◽  
F. Horak
Keyword(s):  
Anticipatory Postural Adjustments ◽  
Postural Response ◽  
Postural Adjustments ◽  
Automatic Postural Response ◽  
Step Initiation ◽  
Postural Responses ◽  
Automatic Response ◽  
Perturbation Velocity ◽  
Velocity Information ◽  
Automatic Postural Responses

1. Our previous study showed that two distinct postural modifications occurred when subjects were instructed to step, rather than maintain stance, in response to a backward surface translation: 1) the automatic postural responses to the surfaces perturbation were reduced in magnitude and 2) the anticipatory postural adjustments promoting foot-off were shortened in duration. This study investigates the extent to which task instruction, prediction of perturbation velocity, and afferent sensory information related to perturbation velocity are responsible for these postural modification. 2. Eleven human subjects were instructed in advance, to either maintain stance or step forward in response to a backward surface translation. Four different velocities of translation were used to perturb equilibrium. To assess the influence of predicted versus actual velocity information, the surface translations were presented in both a blocked order of increasing perturbation velocity (predictable) and a random order (unpredictable). Lower-extremity electromyographs (EMGs), ground reaction forces, and movement kinematics were quantified for both the automatic postural responses to perturbation and the anticipatory postural adjustments for step initiation. 3. The instruction to step was not solely responsible for the suppression of the automatic postural response. Prediction of perturbation velocity was required for significant suppression of the early automatic postural response when subjects stepped in response to the perturbation. When compared with the stance condition, the magnitude of the initial 50 ms of the automatic response in bilateral soleus and the left limb gastrocnemius (initial stance limb) was significantly reduced only when the perturbation velocities were presented in a blocked order. The magnitude of the automatic response was not reduced in the gastrocnemius of the right limb, which was always the initial swing limb and recruited for heel-off in the step conditions. This asymmetrical reduction of the gastrocnemius suggests that modification of the response was specific to the instruction, rather than a general decrease in the extensor muscle excitability. 4. The suppression of the early automatic postural response involved a change in the bias of the response. Despite the reduced magnitude during the predictable velocity step condition, the slope (i.e., gain) of the response with increasing velocities was not different from that of the stance condition. Thus the excitability of the automatic response was reduced by a relatively constant amount for each velocity when the perturbation velocity was predictable. 5. In contrast to the importance of velocity prediction for modification of the automatic postural response, actual velocity information was used for modification of the anticipatory postural adjustments when step was initiated in response to the surface perturbation. Regardless of whether the perturbation velocities were presented in a blocked or random order, the anticipatory postural adjustments were rapidly initiated and the duration of the postural adjustments for step initiation was shortened as the velocity of perturbation increased. 6. We conclude that the CNS uses prediction of perturbation velocity to modify the excitability of early automatic postural responses when the postural goal changes. In contrast, actual afferent velocity information can be used to modify the duration of the anticipatory postural adjustments for a voluntary step in response to perturbation. Thus the CNS utilizes feed-forward prediction to modify peripherally triggered postural responses, and utilizes immediate afferent information to modify the centrally initiated postural adjustments associated with voluntary movement.

scholarly journals Dissociation of muscle and cortical response scaling to balance perturbation acceleration

2019 ◽  
Vol 121 (3) ◽  
pp. 867-880 ◽  
Author(s):  
Aiden M. Payne ◽  
Greg Hajcak ◽  
Lena H. Ting
Keyword(s):  
Brain Stem ◽  
Cortical Response ◽  
Postural Response ◽  
Single Trial ◽  
Motor Responses ◽  
Initial Burst ◽  
Sensory Inputs ◽  
Automatic Postural Response ◽  
Cortical Responses ◽  
Muscle Responses

The role of cortical activity in standing balance is unclear. Here we tested whether perturbation-evoked cortical responses share sensory input with simultaneous balance-correcting muscle responses. We hypothesized that the acceleration-dependent somatosensory signals that drive the initial burst of the muscle automatic postural response also drive the simultaneous perturbation-evoked cortical N1 response. We measured in healthy young adults ( n = 16) the initial burst of the muscle automatic postural response (100–200 ms), startle-related muscle responses (100–200 ms), and the perturbation-evoked cortical N1 potential, i.e., a negative peak in cortical EEG activity (100–200 ms) over the supplementary motor area. Forward and backward translational support-surface balance perturbations were applied at four levels of acceleration and were unpredictable in timing, direction, and acceleration. Our results from averaged and single-trial analyses suggest that although cortical and muscle responses are evoked by the same perturbation stimulus, their amplitudes are independently modulated. Although both muscle and cortical responses increase with acceleration, correlations between single-trial muscle and cortical responses were very weak. Furthermore, across subjects, the scaling of muscle responses to acceleration did not correspond to scaling of cortical responses to acceleration. Moreover, we observed a reduction in cortical response amplitude across trials that was related to a reduction in startle-related—but not balance-correcting—muscle activity. Therefore, cortical response attenuation may be related to a reduction in perceived threat rather than motor adaptation or changes in sensory inflow. We conclude that the cortical N1 reflects integrated sensory inputs simultaneously related to brain stem-mediated balance-correcting muscle responses and startle reflexes. NEW & NOTEWORTHY Reactive balance recovery requires sensory inputs to be transformed into appropriate balance-correcting motor responses via brain stem circuits; these are accompanied by simultaneous and poorly understood cortical responses. We used single-trial analyses to dissociate muscle and cortical response modulation with perturbation acceleration. Although muscle and cortical responses share sensory inputs, they have independent scaling mechanisms. Attenuation of cortical responses with experience reflected attenuation of brain stem-mediated startle responses rather than the amplitude of balance-correcting motor responses.

scholarly journals Effects of Vestibular Training on Postural Control of Healthy Adults

CommonHealth ◽  
2020 ◽  
Vol 1 (1) ◽  
pp. 31-36
Author(s):  
Kwadwo Osei Appiah-Kubi ◽  
Anne Galgon ◽  
Ryan Tierney ◽  
Richard Lauer ◽  
W. Geoffrey Wright
Keyword(s):  
Postural Control ◽  
Postural Stability ◽  
Medial Gastrocnemius ◽  
Postural Response ◽  
Sensory Reweighting ◽  
Vestibular Loss ◽  
Motor Responses ◽  
Automatic Postural Response ◽  
Weight Shift ◽  
Sensory Weighting

Background: Postural stability depends on the integration of multisensory inputs to drive motor outputs. When visual and somatosensory input is available and reliable, this reduces the postural control system’s reliance on the vestibular system. Despite this, vestibular loss can still cause severe postural dysfunction (1,2). Training one or more of the three sensory systems can alter sensory weighting and change postural behavior. Vestibular activation exercises, including horizontal and vertical headshaking, influence vestibular-ocular and -motor responses and have been showed to be effective in vestibular rehabilitation (3–8).   Purpose/Hypothesis: To assess sensory reweighting of postural control processing and vestibular-ocular and -motor responses after concurrent vestibular activation with postural training. It was hypothesized that the effect of this training would significantly alter the pattern of sensory weighting by changing the ratio of visual, somatosensory and vestibular dependence needed to maintain postural stability, and significantly decrease vestibular responses. Methods: Forty-two young healthy individuals (22 females; 23.0+3.9 years; 1.6+0.1 meters) were randomly assigned into four groups: 1) visual feedback weight shift training (WST) coupled with an active horizontal headshake (HHS), 2) same WST with vertical headshake (VHS), 3) WST with no headshake (NHS) and 4) no training/headshake control (CTL) groups. The headshake groups performed an intensive body WST together with horizontal or vertical rhythmic headshake at 80 to 120 beats/minute. The NHS group performed the WST with no headshake while the controls did not perform any training. Five 15-minute training sessions were performed on consecutive days for one week with the weight shift exercises involving upright limits of stability activities on a flat surface, foam or rocker board (Fig. 1). All groups performed baseline- and post-assessments including sensory organization test (SOT) and force platform ramp perturbations, coupled with electromyographic (EMG) recordings. A video head impulse test was also used to record horizontal vestibulo-ocular reflex (VOR) gain. A between- and within-group repeated measures ANOVA was used to analyze five COP sway variables, the equilibrium and composite scores and sensory ratios of the SOT as well as EMG signals and horizontal VOR gain. Similarly, COP variables, EMG, as well as vestibular reflex data (vertical VOR, vestibulo-collic reflex [VCR] and vestibulo-spinal [VSR] gains) during ramp perturbations were analyzed. Alpha level was set at p<.05. Results: The training showed a significant somatosensory downweighting (p=.050) in the headshake groups compared to the other groups. Training also showed significant decreased horizontal VOR gain (p=.040), faster automatic postural response (p=.003) (Figs. 2-4) with improved flexibility (p=.010) in the headshake groups. Muscle activation pattern in medial gastrocnemius (p=.033) was significantly decreased in the headshake. Conclusion: The concurrent vestibular activation and weight shift training modifies vestibular-dependent responses after the training intervention as evidenced in somatosensory downweighting, decreased VOR gain, better postural flexibility and faster automatic postural response. Findings suggest this is predominantly due to vestibular adaptation and habituation of VOR, VCR and VSR which induced sensory reweighting. Clinical relevance: Findings may be used to guide the development of a vestibular-postural rehabilitation intervention in impaired neurological populations, such as with vestibular disorders or sensory integration problems.

Bilateral Vestibular Loss in Cats Leads to Active Destabilization of Balance During Pitch and Roll Rotations of the Support Surface

2007 ◽  
Vol 97 (6) ◽  
pp. 4357-4367 ◽  
Author(s):  
Jane M. Macpherson ◽  
Dirk G. Everaert ◽  
Paul J. Stapley ◽  
Lena H. Ting
Keyword(s):  
Center Of Mass ◽  
The Body ◽  
Support Surface ◽  
Postural Response ◽  
Vestibular Loss ◽  
Bilateral Vestibular Loss ◽  
Automatic Postural Response ◽  
Vestibular Information ◽  
Body Center ◽  
Proprioceptive Inputs

Although the balance difficulties accompanying vestibular loss are well known, the underlying cause remains unclear. We examined the role of vestibular inputs in the automatic postural response (APR) to pitch and roll rotations of the support surface in freely standing cats before and in the first week after bilateral labyrinthectomy. Support surface rotations accelerate the body center of mass toward the downhill side. The normal APR consists of inhibition in the extensors of the uphill limbs and excitation in the downhill limbs to decelerate the body and maintain the alignment of the limbs with respect to earth-vertical. After vestibular lesion, cats were unstable during rotation perturbations and actively pushed themselves downhill rather than uphill, using a postural response that was opposite to that seen in the control trials. The extensors of the uphill rather than downhill limbs were activated, whereas those of the downhill limbs were inhibited rather than being excited. We propose that vestibular inputs provide an important reference to earth-vertical, which is critical to computing the appropriate postural response during active orientation to the vertical. In the absence of this vestibular information, subjects orient to the support surface using proprioceptive inputs, which drives the body downhill resulting in instability and falling. This is consistent with current models of sensory integration for computation of body posture and orientation.

Ratio of Shear to Load Ground-Reaction Force May Underlie the Directional Tuning of the Automatic Postural Response to Rotation and Translation

2004 ◽  
Vol 92 (2) ◽  
pp. 808-823 ◽  
Author(s):  
Lena H. Ting ◽  
Jane M. Macpherson
Keyword(s):  
Ground Reaction Force ◽  
Center Of Pressure ◽  
Full Range ◽  
Center Of Mass ◽  
Reaction Force ◽  
Postural Response ◽  
Directional Tuning ◽  
Automatic Postural Response ◽  
Consistent Feature ◽  
Perturbation Direction

This study sought to identify the sensory signals that encode perturbation direction rapidly enough to shape the directional tuning of the automatic postural response. We compared reactions to 16 directions of pitch and roll rotation and 16 directions of linear translation in the horizontal plane in freely standing cats. Rotations and translations that displaced the center of mass in the same direction relative to the feet evoked similar patterns of muscle activity and active ground-reaction force, suggesting the presence of a single, robust postural strategy for stabilizing the center of mass in both rotation and translation. Therefore we postulated there should be a common sensory input that encodes the direction of the perturbation and leads to the directional tuning of the early electromyographic burst in the postural response. We compared the mechanical changes induced by rotations and translations prior to the active, postural response. The only consistent feature common to the full range of rotation and translation directions was the initial change in ground-reaction force angle. Other variables including joint angles, ground-reaction force magnitudes, center of pressure, and center of mass in space showed opposite or nonsignificant changes for rotation and translation. Change in force angle at the paw reflects the ratio of loading force to slip force, analogous to slips during finger grip tasks. We propose that cutaneous sensors in the foot soles detect change in ground-reaction force angle and provide the critical input underlying the directional tuning of the automatic postural response for balance.

Bilateral labyrinthectomy in the cat: effects on the postural response to translation

1995 ◽  
Vol 73 (3) ◽  
pp. 1181-1191 ◽  
Author(s):  
J. T. Inglis ◽  
J. M. Macpherson
Keyword(s):  
Visual Information ◽  
Center Of Mass ◽  
Afferent Input ◽  
Support Surface ◽  
Postural Response ◽  
Automatic Postural Response ◽  
Somatosensory Information ◽  
Postural Responses ◽  
Before And After ◽  
Evoked Activity

1. This study examined the role of vestibular afferent information on the postural responses of four cats, evoked by movements of the support surface during stance. Animals were exposed to linear translations of the supporting surface in eight evenly spaced directions in the horizontal plane, before and after bilateral labyrinthectomy. Postural responses were quantified in terms of the ground reaction forces under each paw and the evoked activity in selected muscles. 2. The cats were able to stand on the platform within 1-3 days after labyrinthectomy and were able to maintain balance during all perturbations of stance, even when they stood in total darkness, completely deprived of visual information. After lesion, postural responses were characterized by normal latency and normal spatial and temporal patterning of electromyographic (EMG) response. The pattern of force response showed the force constraint strategy that characterizes postural responses in the intact animal. 3. The only deficit in the postural response after lesion was a hypermetria, or active over-response that caused the animals to overbalance somewhat but did not impair their ability to remain upright. Analysis of the trajectory of the animal's center of mass during the trials indicated that the hypermetria was due to an abnormally large, active response on the part of the animal and could not be attributed to changes in the passive stiffness of the musculoskeletal system. The hypermetria was transient, and response amplitude returned to control levels after the rapid compensation phase of 10-15 days. 4. It is concluded that vestibular information is not essential for triggering the rapid, automatic postural response to translations of the support surface, nor is it necessary for the selection or shaping of the evoked response. Instead, somatosensory information appears to predominate in these postural adjustments. However, vestibular afferent input does influence the scaling of the postural response.

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