Influence of central set on human postural responses

1. The effect of central set on automatic postural responses was studied in humans exposed to horizontal support-surface perturbations causing forward sway. Central set was varied by providing subjects with prior experience of postural stimulus velocities or amplitudes under 1) serial and random conditions, 2) expected and unexpected conditions, and 3) practiced and unpracticed conditions. In particular, the influence of central-set conditions was examined on the pattern and magnitude of six leg and trunk electromyograph (EMG) activations and associated ankle torque responses to postural perturbations with identical stimulus parameters. 2. The scaling of initial agonist integrated EMG (IEMG) and torque responses to postural perturbation amplitude disappeared when perturbation amplitudes were randomized. This finding suggests that the initial magnitude of postural responses were centrally set to anticipated postural perturbation amplitudes based on sequential experience with the stimulus. 3. Expectation of postural stimulus amplitude had a significant effect on initial torque responses; subjects overresponded when a larger perturbation was expected and underresponded when a smaller perturbation was expected. Expectation of postural stimulus velocity had a smaller effect on initial torque responses, and subjects consistently overresponded when the velocity of the perturbation was unexpected. This difference in amplitude and velocity expectation may be because of the capacity to encode stimulus velocity, but not amplitude information, into the earliest postural responses of the current trial. The relative strength of amplitude and velocity central-set effects varied widely with individual subjects. 4. Central-set conditions did not affect initial EMG response latencies (100 +/- 20 ms, mean +/- SD) or the relative onset of proximal and distal agonists and antagonists. Unexpected or unpracticed stimulus amplitudes, however, were associated with significant late activation of ankle antagonist, tibialis. Thus errors in initial response magnitude because of central-set effects appear to be partially corrected by reciprocal antagonist activity. Agonist IEMG, however, did not always reflect significant changes in torque responses with central-set conditions. 5. Expectation of postural stimulus amplitude and velocity had two different types of effects on the magnitudes of postural responses: 1) a directionally specific, central-set effect consisting of either increased or decreased responses, depending on expectation of stimulus amplitude; and 2) a nonspecific enhanced response to novel stimulus velocities with a gradual reduction when a velocity was presented repeatedly. Two different neural mechanisms are proposed for these two adaptive effects. 6. Reduction of postural response magnitude and antagonist activity during practice may be partially explained by adaptive mechanisms based on expectation because of prior experience with stimulus velocity and amp

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Cerebellar control of postural scaling and central set in stance

Journal of Neurophysiology ◽

10.1152/jn.1994.72.2.479 ◽

1994 ◽

Vol 72 (2) ◽

pp. 479-493 ◽

Cited By ~ 240

Author(s):

F. B. Horak ◽

H. C. Diener

Keyword(s):

Sensory Information ◽

Normal Subjects ◽

Anterior Lobe ◽

Rate Of Change ◽

Response Magnitude ◽

Body Sway ◽

Magnitude Scaling ◽

Postural Responses ◽

Surface Displacements ◽

Central Set

1. The effects of cerebellar deficits in humans on scaling the magnitude of automatic postural responses based on sensory feedback and on predictive central set was investigated. Electromyographic (EMG) and surface reactive torques were compared in patients with anterior lobe cerebellar disorders and in normal healthy adults exposed to blocks of four velocities and five amplitudes of surface translations during stance. Correlations between the earliest postural responses (integrated EMG and initial rate of change of torque) and translation velocity provided a measure of postural magnitude scaling using sensory information from the current displacement. Correlations of responses with translation amplitude provided a measure of scaling dependent on predictive central set based on sequential experience with previous like displacements because the earliest postural responses occurred before completion of the displacements and because scaling to displacement amplitude disappeared when amplitudes were randomized in normal subjects. 2. Responses of cerebellar patients to forward body sway induced by backward surface displacements were hypermetric, that is, surface-reactive torque responses were two to three times larger than normal with longer muscle bursts resulting in overshooting of initial posture. Despite this postural hypermetria, the absolute and relative latencies of agonist muscle bursts at the ankle, knee, and hip were normal in cerebellar patients. 3. Although they were hypermetric, the earliest postural responses of cerebellar patients were scaled normally to platform displacement velocities using somatosensory feedback. Cerebellar patients, however, were unable to scale initial postural response magnitude to expected displacement amplitudes based on prior experience using central set. Randomization of displacement amplitudes eliminated the set effect of amplitude on initial responses in normal subjects, but responses to randomized and blocked trials were not different in cerebellar patients. 4. Cerebellar patients compensated for hypermetric responses and lack of anticipatory scaling of earliest gastrocnemius activity by scaling large, reciprocally activated tibialis and quadriceps antagonist activity with the displacement velocity and amplitude. Correlations between these antagonist EMG integrals and displacement amplitudes were preserved when amplitudes were randomized, suggesting that feedback-dependent and not set-dependent mechanisms were responsible for scaling of antagonists by cerebellar patients. Antagonist compensation for initial hypermetric responses also could be induced in normals when they overresponded to unexpectedly small amplitudes of surface displacements. 5. The major effects of anterior lobe cerebellar damage on human postural responses involves impairment of response magnitude based on predictive central set and not on use of velocity feedback or on the temporal synergic organization of multijoint postural coordination.(ABSTRACT TRUNCATED AT 400 WORDS)

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Influence of stimulus parameters on human postural responses

Journal of Neurophysiology ◽

10.1152/jn.1988.59.6.1888 ◽

1988 ◽

Vol 59 (6) ◽

pp. 1888-1905 ◽

Cited By ~ 250

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.

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Postural responses exhibit multisensory dependencies with discordant visual and support surface motion

Journal of Vestibular Research ◽

10.3233/ves-2004-14401 ◽

2004 ◽

Vol 14 (4) ◽

pp. 307-319 ◽

Cited By ~ 1

Author(s):

Emily A. Keshner ◽

Robert V. Kenyon ◽

Jessica Langston

Keyword(s):

Support Surface ◽

Wide Field ◽

Stimulus Amplitude ◽

Visual Inputs ◽

Postural Responses ◽

Wide Field Of View ◽

Postural System ◽

Surface Translation ◽

Anterior Posterior

The purpose of this study was to identify how the postural system weights coincident yet discordant disturbances of the visual and proprioceptive/vestibular systems. Eleven healthy subjects (25–38 yrs) received either fore-aft translations of an immersive, wide field-of-view visual environment (0.1 Hz, ± 3.7 m/sec), or anterior-posterior translations of the support surface (0.25 Hz, ± 15 cm/sec), or both concurrently. Kinematics of the head, trunk, and shank were collected with an Optotrak system and angular motion of each segment plotted across time. With only support surface translation, segmental responses were small (1°–2°) and mostly opposed the direction of sled translation. When only the visual scene was moving, segmental responses increased as the trial progressed. When the inputs were presented coincidentally, response amplitudes were large even at the onset of the trial. Mean RMS values across subjects were significantly greater with combined stimuli than for either stimulus presented alone and areas under the power curve across subjects were significantly increased at the frequency of the visual input when both inputs were presented. Thus, intra-modality dependencies were observed, such that responses to the visual inputs significantly increased and responses to the somatosensory signals reflected the stimulus amplitude only when the two inputs were combined. We believe it unlikely that the role of any single pathway contributing to postural control can be accurately characterized in a static environment if the function of that pathway is context dependent.

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Head sway response to optic flow: Effect of age is more important than the presence of unilateral vestibular hypofunction

Journal of Vestibular Research ◽

10.3233/ves-2006-16306 ◽

2006 ◽

Vol 16 (3) ◽

pp. 137-145

Author(s):

Patrick J. Sparto ◽

Joseph M. Furman ◽

Mark S. Redfern

Keyword(s):

Older Adults ◽

Optic Flow ◽

Stimulus Frequency ◽

Support Surface ◽

Stimulus Amplitude ◽

Full Field ◽

Vestibular Hypofunction ◽

Postural Responses ◽

Effect Of Age ◽

Anterior Posterior

Background: The purpose of this study was to examine how older adults with vestibular impairment use sensory feedback for postural control. Methods: Nine older adult subjects with unilateral vestibular hypofunction (UVH, mean age 69 y) and 14 older (mean age 70 y) and 8 young adult controls (CON, mean age 28 y) viewed full-field optic flow scenes while standing on a fixed or sway-referenced support surface. The subjects with UVH had 100% caloric asymmetry. Optic flow consisted of sinusoidal anterior-posterior movement of the visual surround at three frequencies and three amplitudes of stimulation. The anterior-posterior head sway was measured. The number of head sway responses that were coupled to the optic flow and magnitude of head sway during optic flow relative to during quiet stance on fixed floor was quantified. Results: The number of trials in which the head sway response was significantly coupled to the optic flow was significantly greater in the Older UVH and Older CON subjects compared with the Young CON subjects. Furthermore, the magnitude of head sway was two to three times greater in Older UVH and CON compared with Young CON subjects. There was no difference in coupling or magnitude of head sway between Older UVH and Older CON subjects. The amplitude of sway was also dependent on the amount of surface support, stimulus frequency, and stimulus amplitude. Conclusions: Older adults with unilateral vestibular hypofunction who are able to effectively compensate show no difference in postural responses elicited by optic flow compared with age-matched controls.

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Do Aging and Tactile Noise Stimulation Affect Responses to Support Surface Translations in Healthy Adults?

Current Gerontology and Geriatrics Research ◽

10.1155/2016/2941964 ◽

2016 ◽

Vol 2016 ◽

pp. 1-9 ◽

Cited By ~ 3

Author(s):

Marius Dettmer ◽

Amir Pourmoghaddam ◽

Beom-Chan Lee ◽

Charles S. Layne

Keyword(s):

Older Adults ◽

Healthy Aging ◽

Mixed Model ◽

Center Of Pressure ◽

Support Surface ◽

Older Individuals ◽

Postural Response ◽

Postural Perturbation ◽

Low Level ◽

Postural Responses

Appropriate neuromuscular responses to support surface perturbations are crucial to prevent falls, but aging-related anatomical and physiological changes affect the appropriateness and efficiency of such responses. Low-level noise application to sensory receptors has shown to be effective for postural improvement in a variety of different balance tasks, but it is unknown whether this intervention may have value for improvement of corrective postural responses. Ten healthy younger and ten healthy older adults were exposed to sudden backward translations of the support surface. Low-level noise (mechanical vibration) to the foot soles was added during random trials and temporal (response latency) and spatial characteristics (maximum center-of-pressure excursion and anterior-posterior path length) of postural responses were assessed. Mixed-model ANOVA was applied for analysis of postural response differences based on age and vibration condition. Age affected postural response characteristics, but older adults were well able to maintain balance when exposed to a postural perturbation. Low-level noise application did not affect any postural outcomes. Healthy aging affects some specific measures of postural stability, and in high-functioning older individuals, a low-level noise intervention may not be valuable. More research is needed to investigate if recurring fallers and neuropathy patients could benefit from the intervention in postural perturbation tasks.

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

Journal of Neurophysiology ◽

10.1152/jn.00766.2012 ◽

2013 ◽

Vol 110 (9) ◽

pp. 2236-2245 ◽

Cited By ~ 33

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.

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Organization of postural responses following a rotational support surface perturbation, after TKA: Sagittal plane rotations

Gait & Posture ◽

10.1016/j.gaitpost.2006.02.003 ◽

2007 ◽

Vol 25 (1) ◽

pp. 112-120 ◽

Cited By ~ 23

Author(s):

William H. Gage ◽

James S. Frank ◽

Stephen D. Prentice ◽

Peter Stevenson

Keyword(s):

Sagittal Plane ◽

Support Surface ◽

Surface Perturbation ◽

Postural Responses

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Activity of neuromuscular compartments in lateral gastrocnemius evoked by postural corrections during stance

Journal of Neurophysiology ◽

10.1152/jn.1993.70.6.2337 ◽

1993 ◽

Vol 70 (6) ◽

pp. 2337-2349 ◽

Cited By ~ 6

Author(s):

D. C. Dunbar ◽

J. M. Macpherson

Keyword(s):

Three Dimensional ◽

Area Under The Curve ◽

Gluteus Medius ◽

Emg Activity ◽

Support Surface ◽

Lateral Gastrocnemius ◽

Tuning Curves ◽

Postural Responses ◽

Upward Displacement ◽

Neuromuscular Compartments

1. The electromyographic (EMG) activity of the four neuromuscular compartments in lateral gastrocnemius (LG) of cats was investigated to determine whether these intramuscular subdivisions could be activated differentially during automatic postural corrections. EMG electrodes were surgically implanted into each of the four compartments of left LG-LG1, LG2, LG3, and LGm--in two cats. Electrodes were also implanted into soleus and gluteus medius for comparative purposes. 2. Quiet quadrupedal stance was disturbed first by linearly translating the cats on a movable platform in each of 16 different horizontal directions. Mechanical events during corrections were characterized in terms of the three-dimensional forces exerted by each paw on the platform. EMG and force traces were quantified (area under the curve) and normalized, and tuning curves were constructed that relate muscle response and force change to direction of platform movement. 3. In a second series of trials, translations were presented along one direction only over a series of six velocities ranging from 5 to 16 cm/s. The third series of perturbations, termed the pop-up, consisted of a rapid upward displacement of the support under the left hindlimb only over a series of six amplitudes ranging from 1 to 10 mm. Evoked EMG activity and average change in force were normalized and regressions were computed onto velocity and amplitude, respectively. The slopes of the regressions were compared. 4. EMG tuning curves associated with the multidirectional horizontal translations revealed no differential activity across LG compartments. Similarly, there was no statistical difference among the slopes of the regressions within LG. In contrast, soleus exhibited significantly different slopes from LG for the regressions. Thus it is concluded that LG compartments are not differentially activated during automatic postural responses to perturbations of the support surface.

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Incorporating Voluntary Knee Flexion Into Nonanticipatory Balance Corrections

Journal of Neurophysiology ◽

10.1152/jn.01303.2006 ◽

2007 ◽

Vol 98 (5) ◽

pp. 3047-3059 ◽

Cited By ~ 12

Author(s):

Lars B. Oude Nijhuis ◽

Bastiaan R. Bloem ◽

Mark G. Carpenter ◽

John H. J. Allum

Keyword(s):

Knee Flexion ◽

Balance Control ◽

Critical Role ◽

Support Surface ◽

Trunk Flexion ◽

Postural Perturbation ◽

Automatic Balance ◽

Human Balance ◽

Balance Deficits ◽

Balance Corrections

Knee movements play a critical role in most balance corrections. Loss of knee flexibility may cause postural instability. Conversely, trained voluntary knee flexions executed during balance corrections might help to overcome balance deficits. We examined whether bilateral knee flexion could be added to automatic balance corrections generated by sudden balance perturbations. We investigated how this could be achieved and whether it improved or worsened balance control. Twenty-four healthy subjects participated in three different test conditions, in which they had to flex their knees following an auditory cue (VOLUNTARY condition), had to restore their balance in response to multidirectional rotations of a support surface (REACTIVE condition), or the combination of these two (COMBINED condition). A new variable set (PREDICTED), calculated as the mathematical sum of VOLUNTARY and REACTIVE, was compared with the COMBINED variable set. COMBINED responses following forward rotations were close to PREDICTED, or greater, suggesting adequate integration of knee flexion into the automatic balance reactions. For backward rotations, the COMBINED condition resulted in several near-falls, and this was generally associated with smaller knee flexion and smaller EMG responses. Subjects compensated by using greater trunk flexion and arm movements. Activity in several muscles displayed earlier onsets for the COMBINED condition following backward rotations. We conclude that healthy adults can incorporate voluntary knee flexion into their automatic balance corrections and that this depends on the direction of the postural perturbation. These findings highlight the flexibility of the human balance repertoire and underscore both the advantages and limitations of using trained voluntary movements to aid balance corrections in man.

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