First Trial Postural Reactions to Unexpected Balance Disturbances: A Comparison With the Acoustic Startle Reaction

2010 ◽  
Vol 104 (5) ◽  
pp. 2704-2712 ◽  
Author(s):  
Lars B. Oude Nijhuis ◽  
John H. J. Allum ◽  
Josep Valls-Solé ◽  
Sebastiaan Overeem ◽  
Bastiaan R. Bloem
Keyword(s):  
Muscle Activation ◽  
Acoustic Startle ◽  
Muscle Synergy ◽  
Trunk Muscles ◽  
Common Element ◽  
Startle Reaction ◽  
Support Surface ◽  
Postural Reactions ◽  
Acoustic Stimuli ◽  
Postural Responses

Unexpected support-surface movements delivered during stance elicit “first trial” postural reactions, which are larger and cause greater instability compared with habituated responses. The nature of this first trial reaction remains unknown. We hypothesized that first trial postural reactions consist of a generalized startle reaction, with a similar muscle synergy as the acoustic startle response, combined with an automatic postural reaction. Therefore we compared acoustic startle responses to first trial postural reactions. Eight healthy subjects stood on a support surface that unexpectedly rotated backwards 10 times, followed by 10 startling acoustic stimuli, or vice versa. Outcome measures included full body kinematics and surface EMG from muscles involved in startle reactions or postural control. Postural perturbations and startling acoustic stimuli both elicited a clear first trial reaction, as reflected by larger kinematic and EMG responses. The ensuing habituation rate to repeated identical stimuli was comparable for neck and trunk muscles in both conditions. Onset latencies in neck muscles occurred significantly later for first trial perturbations compared with startle responses, but earlier in trunk muscles. Our results show that platform tilting initially induces reactions larger than needed to maintain equilibrium. For neck and trunk muscles, these first trial postural reactions resembled acoustic startle reflexes. First trial postural reactions may be triggered by interaction of afferent volleys formed by somatosensory and vestibular inputs. Acoustic startle reactions may also be partially triggered by vestibular inputs. Similar muscle activation driven by vestibular inputs may be the common element of first trial postural responses and acoustic startle reactions.

Muscle Synergy Organization Is Robust Across a Variety of Postural Perturbations

2006 ◽  
Vol 96 (3) ◽  
pp. 1530-1546 ◽  
Author(s):  
Gelsy Torres-Oviedo ◽  
Jane M. Macpherson ◽  
Lena H. Ting
Keyword(s):  
Muscle Activation ◽  
Balance Control ◽  
Muscle Synergy ◽  
Muscle Synergies ◽  
Support Surface ◽  
Experimental Conditions ◽  
Activation Patterns ◽  
Muscle Activation Patterns ◽  
Postural Responses ◽  
Force Vectors

We recently showed that four muscle synergies can reproduce multiple muscle activation patterns in cats during postural responses to support surface translations. We now test the robustness of functional muscle synergies, which specify muscle groupings and the active force vectors produced during postural responses under several biomechanically distinct conditions. We aimed to determine whether such synergies represent a generalized control strategy for postural control or if they are merely specific to each postural task. Postural responses to multidirectional translations at different fore-hind paw distances and to multidirectional rotations at the preferred stance distance were analyzed. Five synergies were required to adequately reconstruct responses to translation at the preferred stance distance—four were similar to our previous analysis of translation, whereas the fifth accounted for the newly added background activity during quiet stance. These five control synergies could account for >80% total variability or r2 > 0.6 of the electromyographic and force tuning curves for all other experimental conditions. Forces were successfully reconstructed but only when they were referenced to a coordinate system that rotated with the limb axis as stance distance changed. Finally, most of the functional muscle synergies were similar across all of the six cats in terms of muscle synergy number, synergy activation patterns, and synergy force vectors. The robustness of synergy organization across perturbation types, postures, and animals suggests that muscle synergies controlling task-variables are a general construct used by the CNS for balance control.

Influence of Postural Anxiety on Postural Reactions to Multi-Directional Surface Rotations

2004 ◽  
Vol 92 (6) ◽  
pp. 3255-3265 ◽  
Author(s):  
M. G. Carpenter ◽  
J. S. Frank ◽  
A. L. Adkin ◽  
A. Paton ◽  
J.H.J. Allum
Keyword(s):  
Angular Displacement ◽  
Center Of Mass ◽  
Trunk Muscles ◽  
Support Surface ◽  
Control Mechanisms ◽  
Postural Reactions ◽  
Postural Threat ◽  
Postural Responses ◽  
Total Body ◽  
Ground Condition

Previous studies have shown significant effects of increased postural anxiety in healthy young individuals when standing quietly or performing voluntary postural tasks. However, little is known about the influence of anxiety on reactive postural control. The present study examined how increased postural anxiety influenced postural reactions to unexpected surface rotations in multiple directions. Ten healthy young adults (mean age: 25.5 yr, range: 22–27 yr) were required to recover from unexpected rotations of the support surface (7.5° amplitude, 50°/s velocity) delivered in six different directions while standing in a low postural threat (surface height: 60 cm above ground) or high postural threat (surface height: 160 cm above ground) condition. Electromyographic data from 12 different postural leg, hip, and trunk muscles was collected simultaneously. Full body kinematic data were also used to determine total body center of mass (COM) and segment displacements. Four distinct changes were observed with increased postural anxiety: increased amplitude in balance-correcting responses (120–220 ms) in all leg, trunk, and arm muscles; decreased onset latency of deltoid responses; reduced magnitude of COM displacement; and reduced angular displacement of leg, pelvis, and trunk. These observations suggest that changes in dynamic postural responses with increased anxiety are mediated by alterations in neuro-muscular control mechanisms and thus may contribute significantly to the pathophysiology of balance deficits associated with aging or neurological disease.

First trial and StartReact effects induced by balance perturbations to upright stance

2013 ◽  
Vol 110 (9) ◽  
pp. 2236-2245 ◽  
Author(s):  
A. D. Campbell ◽  
J. W. Squair ◽  
R. Chua ◽  
J. T. Inglis ◽  
M. G. Carpenter
Keyword(s):  
Startle Response ◽  
Support Surface ◽  
Wrist Movement ◽  
Repeated Presentation ◽  
Trial Effect ◽  
Acoustic Stimuli ◽  
Postural Responses ◽  
Startreact Effect ◽  
Startling Stimulus ◽  
Repeated Test

Postural responses (PR) to a balance perturbation differ between the first and subsequent perturbations. One explanation for this first trial effect is that perturbations act as startling stimuli that initiate a generalized startle response (GSR) as well as the PR. Startling stimuli, such as startling acoustic stimuli (SAS), are known to elicit GSRs, as well as a StartReact effect, in which prepared movements are initiated earlier by a startling stimulus. In this study, a StartReact effect paradigm was used to determine if balance perturbations can also act as startle stimuli. Subjects completed two blocks of simple reaction time trials involving wrist extension to a visual imperative stimulus (IS). Each block included 15 CONTROL trials that involved a warning cue and subsequent IS, followed by 10 repeated TEST trials, where either a SAS (TESTSAS) or a toes-up support-surface rotation (TESTPERT) was presented coincident with the IS. StartReact effects were observed during the first trial in both TESTSAS and TESTPERT conditions as evidenced by significantly earlier wrist movement and muscle onsets compared with CONTROL. Likewise, StartReact effects were observed in all repeated TESTSAS and TESTPERT trials. In contrast, GSRs in sternocleidomastoid and PRs were large in the first trial, but significantly attenuated over repeated presentation of the TESTPERT trials. Results suggest that balance perturbations can act as startling stimuli. Thus first trial effects are likely PRs which are superimposed with a GSR that is initially large, but habituates over time with repeated exposure to the startling influence of the balance perturbation.

scholarly journals Subject-Specific Muscle Synergies in Human Balance Control Are Consistent Across Different Biomechanical Contexts

2010 ◽  
Vol 103 (6) ◽  
pp. 3084-3098 ◽  
Author(s):  
Gelsy Torres-Oviedo ◽  
Lena H. Ting
Keyword(s):  
Muscle Activation ◽  
Balance Control ◽  
Nonnegative Matrix ◽  
The Body ◽  
Muscle Synergy ◽  
Muscle Synergies ◽  
Support Surface ◽  
Activation Patterns ◽  
Muscle Activation Patterns ◽  
Specific Muscle

The musculoskeletal redundancy of the body provides multiple solutions for performing motor tasks. We have proposed that the nervous system solves this unconstrained problem through the recruitment of motor modules or functional muscle synergies that map motor intention to action. Consistent with this hypothesis, we showed that trial-by-trial variations in muscle activation for multidirectional balance control in humans were constrained by a small set of muscle synergies. However, apparent muscle synergy structures could arise from characteristic patterns of sensory input resulting from perturbations or from low-dimensional optimal motor solutions. Here we studied electromyographic (EMG) responses for balance control across a range of biomechanical contexts, which alter not only the sensory inflow generated by postural perturbations, but also the muscle activation patterns used to restore balance. Support-surface translations in 12 directions were delivered to subjects standing in six different postural configurations: one-leg, narrow, wide, very wide, crouched, and normal stance. Muscle synergies were extracted from each condition using nonnegative matrix factorization. In addition, muscle synergies from the normal stance condition were used to reconstruct muscle activation patterns across all stance conditions. A consistent set of muscle synergies were recruited by each subject across conditions. When balance demands were extremely different from the normal stance (e.g., one-legged or crouched stance), task-specific muscle synergies were recruited in addition to the preexisting ones, rather generating de novo muscle synergies. Taken together, our results suggest that muscle synergies represent consistent motor modules that map intention to action, regardless of the biomechanical context of the task.

A Feedback Model Reproduces Muscle Activity During Human Postural Responses to Support-Surface Translations

2008 ◽  
Vol 99 (2) ◽  
pp. 1032-1038 ◽  
Author(s):  
Torrence D. J. Welch ◽  
Lena H. Ting
Keyword(s):  
Postural Control ◽  
Muscle Activity ◽  
Muscle Activation ◽  
Control Process ◽  
Temporal Patterns ◽  
Human Dimensions ◽  
Support Surface ◽  
Level Control ◽  
Muscle Activation Patterns ◽  
Postural Responses

Although feedback models have been used to simulate body motions in human postural control, it is not known whether muscle activation patterns generated by the nervous system during postural responses can also be explained by a feedback control process. We investigated whether a simple feedback law could explain temporal patterns of muscle activation in response to support-surface translations in human subjects. Previously, we used a single-link inverted-pendulum model with a delayed feedback controller to reproduce temporal patterns of muscle activity during postural responses in cats. We scaled this model to human dimensions and determined whether it could reproduce human muscle activity during forward and backward support-surface perturbations. Through optimization, we found three feedback gains (on pendulum acceleration, velocity, and displacement) and a common time delay that allowed the model to best match measured electromyographic (EMG) signals. For each muscle and each subject, the entire time courses of EMG signals during postural responses were well reconstructed in muscles throughout the lower body and resembled the solution derived from an optimal control model. In ankle muscles, >75% of the EMG variability was accounted for by model reconstructions. Surprisingly, >67% of the EMG variability was also accounted for in knee, hip, and pelvis muscles, even though motion at these joints was minimal. Although not explicitly required by our optimization, pendulum kinematics were well matched to subject center-of-mass (CoM) kinematics. Together, these results suggest that a common set of feedback signals related to task-level control of CoM motion is used in the temporal formation of muscle activity during postural control.

Central programming of postural movements: adaptation to altered support-surface configurations

1986 ◽  
Vol 55 (6) ◽  
pp. 1369-1381 ◽  
Author(s):  
F. B. Horak ◽  
L. M. Nashner
Keyword(s):  
Muscle Activation ◽  
The Body ◽  
Trunk Muscles ◽  
Support Surface ◽  
Horizontal Shear ◽  
Hip Joints ◽  
Activation Patterns ◽  
Muscle Activation Patterns ◽  
Ankle Joints ◽  
Support Surfaces

We studied the extent to which automatic postural actions in standing human subjects are organized by a limited repertoire of central motor programs. Subjects stood on support surfaces of various lengths, which forced them to adopt different postural movement strategies to compensate for the same external perturbations. We assessed whether a continuum or a limited set of muscle activation patterns was used to produce different movement patterns and the extent to which movement patterns were influenced by prior experience. Exposing subjects standing on a normal support surface to brief forward and backward horizontal surface perturbations elicited relatively stereotyped patterns of leg and trunk muscle activation with 73- to 110-ms latencies. Activity began in the ankle joint muscles and then radiated in sequence to thigh and then trunk muscles on the same dorsal or ventral aspect of the body. This activation pattern exerted compensatory torques about the ankle joints, which restored equilibrium by moving the body center of mass forward or backward. This pattern has been termed the ankle strategy because it restores equilibrium by moving the body primarily around the ankle joints. To successfully maintain balance while standing on a support surface short in relation to foot length, subjects activated leg and trunk muscles at similar latencies but organized the activity differently. The trunk and thigh muscles antagonistic to those used in the ankle strategy were activated in the opposite proximal-to-distal sequence, whereas the ankle muscles were generally unresponsive. This activation pattern produced a compensatory horizontal shear force against the support surface but little, if any, ankle torque. This pattern has been termed the hip strategy, because the resulting motion is focused primarily about the hip joints. Exposing subjects to horizontal surface perturbations while standing on support surfaces intermediate in length between the shortest and longest elicited more complex postural movements and associated muscle activation patterns that resembled ankle and hip strategies combined in different temporal relations. These complex postural movements were executed with combinations of torque and horizontal shear forces and motions of ankle and hip joints. During the first 5-20 practice trials immediately following changes from one support surface length to another, response latencies were unchanged. The activation patterns, however, were complex and resembled the patterns observed during well-practiced stance on surfaces of intermediate lengths.(ABSTRACT TRUNCATED AT 400 WORDS)

Startle induces early initiation of classically conditioned postural responses

2012 ◽  
Vol 108 (11) ◽  
pp. 2946-2956 ◽  
Author(s):  
A. D. Campbell ◽  
R. Chua ◽  
J. T. Inglis ◽  
M. G. Carpenter
Keyword(s):  
Center Of Pressure ◽  
Motor Preparation ◽  
Support Surface ◽  
Conditioning Paradigm ◽  
Acoustic Stimuli ◽  
Postural Responses ◽  
Hip Kinematics ◽  
Surface Translation ◽  
Classically Conditioned ◽  
Insight Into

Startling acoustic stimuli (SAS) induce the early release of prepared motor responses. The current study used SAS, in conjunction with a classical conditioning paradigm, to examine advanced motor preparation of conditioned postural responses (PRs). After generalized startle responses were induced, standing posture was perturbed in 2 blocks of 15 Conditioning trials, where in each trial the onset of a nonstartling auditory cue [i.e., a conditioned stimulus (CS)] preceded a leftward support-surface translation. Upon completion of each block, a single trial was conducted. After block 1, a CS-Only trial was used to induce conditioned PRs in the absence of balance perturbations. After block 2, a post-Conditioning Startle trial that involved a CS subsequently followed by a SAS was used to examine motor preparation of conditioned PRs. PRs were quantified in terms of center of pressure displacements, ankle and hip kinematics, as well as surface electromyography of proximal and distal bilateral muscle pairs. Results indicated that repeated experience with cued balance perturbations led to PR conditioning and, more importantly, motor preparation of PRs. Conditioning was evidenced in biomechanical and electromyographic responses observed in CS-Only trials, as well as the progressive changes to evoked response parameters during repeated Conditioning trials. SAS presented in post-Conditioning Startle trials evoked early onsets of biomechanical and electromyographic responses, while preserving relative response parameters that were each distinct from generalized startle responses. These results provide important insight into both the consequences of using cues in dynamic postural control studies and the neural mechanisms governing PRs.

A Limited Set of Muscle Synergies for Force Control During a Postural Task

2005 ◽  
Vol 93 (1) ◽  
pp. 609-613 ◽  
Author(s):  
Lena H. Ting ◽  
Jane M. Macpherson
Keyword(s):  
Degrees Of Freedom ◽  
Neural Control ◽  
Muscle Activation ◽  
Balance Control ◽  
Computational Techniques ◽  
Muscle Synergies ◽  
Support Surface ◽  
Muscle Activation Patterns ◽  
Automatic Postural Response ◽  
Postural Responses

Recently developed computational techniques have been used to reduce muscle activation patterns of high complexity to a simple synergy organization and to bring new insights to the long-standing degrees of freedom problem in motor control. We used a nonnegative factorization approach to identify muscle synergies during postural responses in the cat and to examine the functional significance of such synergies for natural behaviors. We hypothesized that the simplification of neural control afforded by muscle synergies must be matched by a similar reduction in degrees of freedom at the biomechanical level. Electromyographic data were recorded from 8–15 hindlimb muscles of cats exposed to 16 directions of support surface translation. Results showed that as few as four synergies could account for >95% of the automatic postural response across all muscles and all directions. Each synergy was activated for a specific set of perturbation directions, and moreover, each was correlated with a unique vector of endpoint force under the limb. We suggest that, within the context of active balance control, postural synergies reflect a neural command signal that specifies endpoint force of a limb.

Influence of stimulus parameters on human postural responses

1988 ◽  
Vol 59 (6) ◽  
pp. 1888-1905 ◽  
Author(s):  
H. C. Diener ◽  
F. B. Horak ◽  
L. M. Nashner
Keyword(s):  
Short Duration ◽  
Muscle Activation ◽  
Sensory Information ◽  
Temporal Organization ◽  
Emg Activity ◽  
Support Surface ◽  
Stimulus Velocity ◽  
Velocity Amplitude ◽  
Muscle Activation Patterns ◽  
Postural Responses

1. The role of sensory information in shaping muscle activation patterns to postural perturbations in humans was investigated by varying velocity, amplitude, or duration of the perturbing stimulus. Ten normal subjects were exposed to 120 backward translations of the support surface under conditions of varying velocities (10-35 cm/s, constant amplitude), varying amplitudes (1.2-12 cm, constant velocity), or varying durations (40-800 ms). The effects of perturbation parameters on movement kinematics and EMG latencies, patterns, and integrated areas in six trunk and leg muscles were examined. Integrated EMG activity was normalized across subjects and the early (first 75 ms), middle (second 75 ms), and late (last 350 ms) components were analyzed separately. 2. Ankle, knee, and hip angle trajectories and surface reactive forces suggest that a relatively consistent movement strategy was scaled to the perturbation velocities and amplitudes applied. 3. Short-duration perturbations (75 ms) evoked a single burst of muscle activity (75-100 ms duration) in gastrocnemius, hamstrings, paraspinal, and rectus abdominis muscles at latencies too long to be explained by simple stretch reflexes. EMG latencies, patterns, and integrated areas were independent of the velocity and amplitude of the short-duration perturbations, suggesting a minimal time to incorporate peripheral velocity information into the triggered response. 4. For translations lasting longer than 75 ms, the integrated areas of the early agonist EMG bursts were positively correlated with stimulus velocity. The integrated area of later, more tonic EMG components were best correlated with stimulus amplitude. These relationships were found in both distal (stretched) muscles and in proximal muscles. Absolute latencies (94-145 ms), intersegmental latencies (18-29 ms), and burst durations (75-100 ms) were not influenced by the velocity or amplitude of the stimulus. 5. These results suggest that the spatial and temporal organization of automatic postural responses may be organized independently of response intensity. Within a particular spatial-temporal pattern, the amount of muscle activation appears to be adjusted by sensory information, which specifies velocity and amplitude of the perturbation.

scholarly journals Influence of Pairing Startling Acoustic Stimuli with Postural Responses Induced by Light Touch Displacement

2020 ◽  
Vol 10 (1) ◽  
pp. 382 ◽  
Author(s):  
John E. Misiaszek ◽  
Sydney D. C. Chodan ◽  
Arden J. McMahon ◽  
Keith K. Fenrich
Keyword(s):  
Acoustic Startle ◽  
Light Touch ◽  
Acoustic Stimuli ◽  
Sensory State ◽  
Threatening Stimulus ◽  
Postural Responses ◽  
History Of ◽  
Arm Tracking ◽  
Unexpected Stimulus ◽  
Selection Of

The first exposure to an unexpected, rapid displacement of a light touch reference induces a balance reaction in naïve participants, whereas an arm-tracking behaviour emerges with subsequent exposures. The sudden behaviour change suggests the first trial balance reaction arises from the startling nature of the unexpected stimulus. We investigated how touch-induced balance reactions interact with startling acoustic stimuli. Responses to light touch displacements were tested in 48 participants across six distinct combinations of touch displacement (DISPLACEMENT), acoustic startle (STARTLE), or combined (COMBINED) stimuli. The effect of COMBINED depended, in part, on the history of the preceding stimuli. Participants who received 10 DISPLACEMENT initially, produced facilitated arm-tracking responses with subsequent COMBINED. Participants who received 10 COMBINED initially, produced facilitated balance reactions, with arm-tracking failing to emerge until the acoustic stimuli were discontinued. Participants who received five DISPLACEMENT, after initially habituating to 10 STARTLE, demonstrated re-emergence of the balance reaction with the subsequent COMBINED. Responses evoked by light touch displacements are influenced by the startling nature of the stimulus, suggesting that the selection of a balance reaction to a threatening stimulus is labile and dependent, in part, on the context and sensory state at the time of the disturbance.

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