scholarly journals Contribution of Sensorimotor Integration to Spinal Stabilization in Humans

2009 ◽  
Vol 102 (1) ◽  
pp. 496-512 ◽  
Author(s):  
Adam D. Goodworth ◽  
Robert J. Peterka
Keyword(s):  
Visual Information ◽  
Time Course ◽  
Visual Orientation ◽  
Model Parameters ◽  
Proprioceptive Information ◽  
Time Lags ◽  
Impulse Response Functions ◽  
Response Functions ◽  
Stimulus Amplitude ◽  
Eyes Closed

The control of upper body (UB) orientation relative to the pelvis in the frontal plane was characterized by analyzing responses to external perturbations consisting of continuous pelvis tilts (eyes open [EO] and eyes closed [EC]) and visual surround tilts (EO) at various amplitudes. Lateral sway of the lower body was prevented on all tests. UB sway was analyzed by calculating impulse–response functions (IRFs) and frequency–response functions (FRFs) from 0.023 to 10.3 Hz for pelvis tilt tests and FRFs from 0.041 to 1.5 Hz for visual tests. For pelvis tilt tests, differences between FRFs were limited to frequencies <3 Hz and were dependent on stimulus amplitude. IRFs were nearly identical across all pelvis tilt tests for the first 0.2 s, but showed amplitude-dependent changes in their time course at longer time lags. The availability of visual orientation cues (EO vs. EC) had only a small effect on the UB sway during pelvis tilt tests. This small effect of vision was consistent with the small UB sway evoked on visual tilt tests. Experimental results were interpreted using a feedback model of UB orientation control that included time-delayed sensory integration, short-latency reflexive mechanisms, and intrinsic biomechanical properties of the UB. Variation in model parameters indicated that subjects shifted toward reliance on vestibular information and away from proprioceptive information as pelvis tilt amplitudes increased. For visual tilt stimuli, model parameters indicated that subjects shifted toward reliance on vestibular and proprioceptive information and away from visual information as the stimulus amplitude increased.

A Comparison of Approaches to Select the Informativeness of Priors in BVARs

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Jan Prüser ◽  
Christoph Hanck
Keyword(s):  
Impulse Response ◽  
Prior Information ◽  
Hierarchical Modeling ◽  
Small Samples ◽  
Model Parameters ◽  
Impulse Response Functions ◽  
Response Functions ◽  
Vector Autoregressions ◽  
The Rich ◽  
Bayesian Vars

Abstract Vector autoregressions (VARs) are richly parameterized time series models that can capture complex dynamic interrelationships among macroeconomic variables. However, in small samples the rich parametrization of VAR models may come at the cost of overfitting the data, possibly leading to imprecise inference for key quantities of interest such as impulse response functions (IRFs). Bayesian VARs (BVARs) can use prior information to shrink the model parameters, potentially avoiding such overfitting. We provide a simulation study to compare, in terms of the frequentist properties of the estimates of the IRFs, useful strategies to select the informativeness of the prior. The study reveals that prior information may help to obtain more precise estimates of impulse response functions than classical OLS-estimated VARs and more accurate coverage rates of error bands in small samples. Strategies based on selecting the prior hyperparameters of the BVAR building on empirical or hierarchical modeling perform particularly well.

scholarly journals Sensorimotor integration for multisegmental frontal plane balance control in humans

2012 ◽  
Vol 107 (1) ◽  
pp. 12-28 ◽  
Author(s):  
Adam D. Goodworth ◽  
Robert J. Peterka
Keyword(s):  
Time Delay ◽  
Sensory Feedback ◽  
Sensorimotor Integration ◽  
Balance Control ◽  
Frontal Plane ◽  
Impulse Response Functions ◽  
Response Functions ◽  
Stimulus Amplitude ◽  
Sensory Reweighting ◽  
Eyes Open

To quantify the contribution of sensory information to multisegmental frontal plane balance control in humans, we developed a feedback control model to account for experimental data. Subjects stood with feet close together on a surface that rotated according to a pseudorandom waveform at three different amplitudes. Experimental frequency-response functions and impulse-response functions were measured to characterize lower body (LB) and upper body (UB) motion evoked during surface rotations while subjects stood with eyes open or closed. The model assumed that corrective torques in LB and UB segments were generated with no time delay from intrinsic musculoskeletal mechanisms and with time delay from sensory feedback mechanisms. It was found that subjects' LB control was primarily based on sensory feedback. Changes in the LB control mechanisms across stimulus amplitude were consistent with the hypothesis that sensory reweighting contributed to amplitude-dependent changes in balance responses whereby subjects decreased reliance on proprioceptive cues that oriented the LB toward the surface and increased reliance on vestibular/visual cues that oriented the LB upright toward earth vertical as stimulus amplitude increased in both eyes open and closed conditions. Sensory reweighting in the LB control system also accounted for most of the amplitude-dependent changes observed in UB responses. In contrast to the LB system, sensory reweighting was not a dominant mechanism of UB control, and UB control was more influenced by intrinsic musculoskeletal mechanisms. The proposed model refines our understanding of sensorimotor integration during balance control by including multisegmental motion and explaining how intersegmental interactions influence frontal plane balance responses.

scholarly journals POSTURAL SWAY IN LOWER EXTREMITY AMPUTEES AND OLDER ADULTS MAY SUGGEST INCREASED FALL RISK IN AMPUTEES

2020 ◽  
Vol 3 (2) ◽  
Author(s):  
Hamid Bateni
Keyword(s):  
Older Adults ◽  
Young Adults ◽  
Lower Extremity ◽  
Frequency Domain ◽  
Visual Information ◽  
Fall Risk ◽  
Postural Sway ◽  
Proprioceptive Information ◽  
Eyes Closed ◽  
Eyes Open

BACKGROUND: Falls can be detrimental to overall health and quality of life for lower extremity amputees. Most previous studies of postural steadiness focus on quantification of time series variables extracted from postural sway signals. While it has been suggested that frequency domain variables can provide more valuable information, few current studies have evaluated postural sway in amputees using frequency domain variables. OBJECTIVE: To determine time and frequency domain variables of postural sway among lower extremity amputees vs. healthy young and older adult controls. METHODOLOGY: Participants were assigned to 3 groups:  lower extremity amputation (n=6), healthy young adults (n=10), and healthy older adults (n=10). Standing barefoot on a force platform, each individual completed 3 trials of each of 3 standing conditions: eyes open, eyes closed, and standing on a foam balance pad. Time and frequency domain variables of postural sway were computed and analyzed. RESULTS: Comparison of older adults, younger adults, and amputees on the three conditions of standing eyes open, eyes closed, and on foam revealed significant differences between groups. Mean mediolateral (ML) sway distance from the center of pressure (COP), total excursions and sway velocity was significantly higher for amputees and older adults when compared to young adults (p<0.05). Furthermore, power of sway signal was substantially lower for both amputees and older adults. When compared to that of older adults, postural steadiness of amputees was more affected by the eyes closed condition, whereas older adults’ was more affected when sensory and proprioceptive information was perturbed by standing on foam.  CONCLUSION: Our findings showed that fall risk is greater in amputees than in young adults without amputation. Additionally, amputees may rely more heavily on visual information than proprioceptive information for balance, in contrast to older and young adults without amputation.  Layman's Abstract Falls can be detrimental to overall health and quality of life for lower extremity amputees. We evaluated postural sway and concluded that amputees have an increased fall risk and may rely more heavily on visual information for balance than do individuals without amputation. Article PDF Link:https://jps.library.utoronto.ca/index.php/cpoj/article/view/33804/26600 How To Cite: Bateni H. Postural sway in lower extremity amputees and older adults may suggest increased fall risk in amputees. Canadian Prosthetics & Orthotics Journal. 2020;Volume 3, Issue 2, No.4. https://doi.org/10.33137/cpoj.v3i2.33804 Corresponding Author: Hamid Bateni, PhD Physical Therapy Program, School of Allied Health and Communicative Disorders, Northern Illinois University, DeKalb, Illinois, USA.E-mail: [email protected]: https://orcid.org/0000-0001-9083-1817

Sensory reweighting of proprioceptive information of the left and right leg during human balance control

2012 ◽  
Vol 108 (4) ◽  
pp. 1138-1148 ◽  
Author(s):  
J. H. Pasma ◽  
T. A. Boonstra ◽  
S. F. Campfens ◽  
A. C. Schouten ◽  
H. Van der Kooij
Keyword(s):  
Visual Information ◽  
Balance Control ◽  
The Other ◽  
Reliable Information ◽  
Proprioceptive Information ◽  
Sensory Reweighting ◽  
Perturbation Amplitude ◽  
Eyes Closed ◽  
Platform Translation ◽  
Support Surfaces

To keep balance, information from different sensory systems is integrated to generate corrective torques. Current literature suggests that this information is combined according to the sensory reweighting hypothesis, i.e., more reliable information is weighted more strongly than less reliable information. In this approach, no distinction has been made between the contributions of both legs. In this study, we investigated how proprioceptive information from both legs is combined to maintain upright stance. Healthy subjects maintained balance with eyes closed while proprioceptive information of each leg was perturbed independently by continuous rotations of the support surfaces (SS) and the human body by platform translation. Two conditions were tested: perturbation amplitude of one SS was increased over trials while the other SS 1) did not move or 2) was perturbed with constant amplitude. With the use of system identification techniques, the response of the ankle torques to the perturbation amplitudes (i.e., the torque sensitivity functions) was determined and how much each leg contributed to stabilize stance (i.e., stabilizing mechanisms) was estimated. Increased amplitude of one SS resulted in a decreased torque sensitivity. The torque sensitivity to the constant perturbed SS showed no significant differences. The properties of the stabilizing mechanisms remained constant during perturbations of each SS. This study demonstrates that proprioceptive information from each leg is weighted independently and that the weight decreases with perturbation amplitude. Weighting of proprioceptive information of one leg has no influence on the weight of the proprioceptive information of the other leg. According to the sensory reweighting hypothesis, vestibular information must be up-weighted, because closing the eyes eliminates visual information.

scholarly journals Influence of Bilateral Vestibular Loss on Spinal Stabilization in Humans

2010 ◽  
Vol 103 (4) ◽  
pp. 1978-1987 ◽  
Author(s):  
Adam D. Goodworth ◽  
Robert J. Peterka
Keyword(s):  
Stimulus Frequency ◽  
Body Motion ◽  
Upper Body ◽  
Visual Orientation ◽  
Proprioceptive Information ◽  
Lower Body ◽  
Vestibular Loss ◽  
Bilateral Vestibular Loss ◽  
Eyes Closed ◽  
Proprioceptive Signal

The control of upper body (UB) orientation relative to the pelvis in the frontal plane was characterized in bilateral vestibular loss subjects (BVLs) and compared with healthy control subjects (Cs). UB responses to external perturbations were evoked using continuous pelvis tilts (eyes open and eyes closed) at various amplitudes. Lateral sway of the lower body was prevented on all tests. UB sway was summarized using root-mean-square measures and dynamic behavior was characterized using frequency response functions (FRFs) from 0.023 to 10.3 Hz. Both subject groups had similar FRF variations as a function of stimulus frequency and were relatively unaffected by visual availability, indicating that visual orientation cues contributed very little to UB control. BVLs had larger UB sway at frequencies below ∼1 Hz compared with Cs. A feedback model of UB orientation control was used to identify sensory contributions to spinal stability and differences between subject groups. The model-based interpretation of experimental results indicated that a phasic proprioceptive signal encoding the angular velocity of UB relative to lower body motion was a major contributor to overall system damping. Parametric system identification showed that BVLs used proprioceptive information that oriented the UB toward the pelvis to a greater extent compared with Cs. Both subject groups used sensory information that oriented the UB vertical in space to a greater extent as pelvis tilt amplitudes increased. In BVLs, proprioceptive information signaling the UB orientation relative to the fixed lower body provided the vertical reference, whereas in Cs, vestibular information also contributed to the vertical reference.

Impulse-response functions and anthropogenic CO2

1995 ◽  
Vol 22 (4) ◽  
pp. 413-416 ◽  
Author(s):  
Francesco N. Tubiello ◽  
Michael Oppenheimer
Keyword(s):  
Impulse Response ◽  
Impulse Response Functions ◽  
Response Functions ◽  
Anthropogenic Co2

scholarly journals Mirror neurons are modulated by grip force and reward expectation in the sensorimotor cortices (S1, M1, PMd, PMv)

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Md Moin Uddin Atique ◽  
Joseph Thachil Francis
Keyword(s):  
Neural Activity ◽  
Visual Information ◽  
Mirror Neurons ◽  
Grip Force ◽  
Neural Representation ◽  
Virtual Object ◽  
Time Lags ◽  
Subjective Value ◽  
Machine Interface ◽  
Definition Of

AbstractMirror Neurons (MNs) respond similarly when primates make or observe grasping movements. Recent work indicates that reward expectation influences rostral M1 (rM1) during manual, observational, and Brain Machine Interface (BMI) reaching movements. Previous work showed MNs are modulated by subjective value. Here we expand on the above work utilizing two non-human primates (NHPs), one male Macaca Radiata (NHP S) and one female Macaca Mulatta (NHP P), that were trained to perform a cued reward level isometric grip-force task, where the NHPs had to apply visually cued grip-force to move and transport a virtual object. We found a population of (S1 area 1–2, rM1, PMd, PMv) units that significantly represented grip-force during manual and observational trials. We found the neural representation of visually cued force was similar during observational trials and manual trials for the same units; however, the representation was weaker during observational trials. Comparing changes in neural time lags between manual and observational tasks indicated that a subpopulation fit the standard MN definition of observational neural activity lagging the visual information. Neural activity in (S1 areas 1–2, rM1, PMd, PMv) significantly represented force and reward expectation. In summary, we present results indicating that sensorimotor cortices have MNs for visually cued force and value.

scholarly journals Conscious perception and perceptual echoes: a binocular rivalry study

2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
Canhuang Luo ◽  
Rufin VanRullen ◽  
Andrea Alamia
Keyword(s):  
Binocular Rivalry ◽  
Visual Information ◽  
Visual Stimulation ◽  
Brain Regions ◽  
Travelling Wave ◽  
Alpha Power ◽  
Conscious Perception ◽  
Impulse Response Functions ◽  
Band Frequency ◽  
Underlying Mechanisms

Abstract Alpha rhythms (∼10Hz) in the human brain are classically associated with idling activities, being predominantly observed during quiet restfulness with closed eyes. However, recent studies demonstrated that alpha (∼10Hz) rhythms can directly relate to visual stimulation, resulting in oscillations, which can last for as long as one second. This alpha reverberation, dubbed perceptual echoes (PE), suggests that the visual system actively samples and processes visual information within the alpha-band frequency. Although PE have been linked to various visual functions, their underlying mechanisms and functional role are not completely understood. In this study, we investigated the relationship between conscious perception and the generation and the amplitude of PE. Specifically, we displayed two coloured Gabor patches with different orientations on opposite sides of the screen, and using a set of dichoptic mirrors, we induced a binocular rivalry between the two stimuli. We asked participants to continuously report which one of two Gabor patches they consciously perceived, while recording their EEG signals. Importantly, the luminance of each patch fluctuated randomly over time, generating random sequences from which we estimated two impulse-response functions (IRFs) reflecting the PE generated by the perceived (dominant) and non-perceived (suppressed) stimulus, respectively. We found that the alpha power of the PE generated by the consciously perceived stimulus was comparable with that of the PE generated during monocular vision (control condition) and higher than the PE induced by the suppressed stimulus. Moreover, confirming previous findings, we found that all PEs propagated as a travelling wave from posterior to frontal brain regions, irrespective of conscious perception. All in all our results demonstrate a correlation between conscious perception and PE, suggesting that the synchronization of neural activity plays an important role in visual sampling and conscious perception.

Use of ionic currents to identify and estimate parameters in models of channel blockade

1990 ◽  
Vol 259 (2) ◽  
pp. H626-H634
Author(s):  
C. F. Starmer ◽  
V. V. Nesterenko ◽  
F. R. Gilliam ◽  
A. O. Grant
Keyword(s):  
Time Course ◽  
Experimental Studies ◽  
Ionic Currents ◽  
Blocking Agent ◽  
Model Parameters ◽  
Protein Conformations ◽  
Channel Blockade ◽  
Channel Blocking ◽  
Individual Contributions ◽  
Modulated Receptor

Models of ion channel blockade are frequently validated with observations of ionic currents resulting from electrical or chemical stimulation. Model parameters for some models (modulated receptor hypothesis) cannot be uniquely determined from ionic currents. The time course of ionic currents reflects the activation (fraction of available channels that conduct in the presence of excitation) and availability of channels (the ability of the protein to make a transition to a conducting conformation and where this conformation is not complexed with a drug). In the presence of a channel blocking agent, the voltage dependence of availability appears modified and has been interpreted as evidence that drug-complexed channels exhibit modified transition rates between channel protein conformations. Because blockade and availability both modify ionic currents, their individual contributions to macroscopic conductance cannot be resolved from ionic currents except when constant affinity binding to a bindable site is assumed. Experimental studies of nimodipine block of calcium channels and lidocaine block of sodium channels illustrate these concepts.

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