Last updated on September 25, This conference program is tentative and subject to change Technical Program for Wednesday August 17, This conference program is tentative and subject to change. We preliminarily evaluated the performance consistency of an electromyography EMG -driven controller based on a two degree-of-freedom musculoskeletal hand model, whose simplified structure is more practical for real-time prosthesis control than existing, complex models.
The subject attempted to trace a series of paths of different complexity straight and curved with the fingertip of a virtual hand displayed on a computer screen; the straight-path tracing tasks were repeated on a second test day to evaluate performance consistency over time.
Additionally, task duration, straightness, and smoothness did not significantly differ between the two straight-path test days. The subject also coordinated movements of the wrist and MCP joints simultaneously during the task, much like with healthy, intact limb movement.
Our promising results suggest that a musculoskeletal model-based controller may provide consistent and effective performance across a range of operating conditions, making it potentially practical for prosthesis control.
Further research is needed to determine whether musculoskeletal model-based control 1 is effective for executing real-world tasks, and 2 can be extended to populations with neuromuscular impairment e. Keywords: Motor learning, neural control, and neuromuscular systems , Brain physiology and modeling - Sensory-motor , Human performance - Sensory-motor Abstract: Consistent repetitions of an action lead to plastic change in the motor cortex and cause shift in the direction of future movements.
This process is known as use-dependent plasticity UDP , one of the basic forms of the motor memory. We have recently demonstrated in a physiological study that success-related reinforcement signals could modulate the strength of UDP.
We tested this idea by developing a computational approach that modeled the shift in the direction of future action as a change in preferred direction of population activity of neurons in the primary motor cortex. The rate of the change follows a modified temporal difference reinforcement learning algorithm, in which the learning policy is based on comparison between what reward the population experiences on a particular trial, and what it had expected on the basis of its previous learning.
By using this model, we were able to characterize the nature of learning and retention of UDP.
Exploring the relationship between reinforcement and UDP constitutes a crucial step toward understanding the basic blocks involved in the formation of motor memories. Keywords: Motor learning, neural control, and neuromuscular systems , Neuromuscular systems - Computational modeling , Neuromuscular systems - Postural and balance Abstract: In everyday life the brain must adapt to variable situations that may require a mixture of approaches including anticipatory synergy formation, through an internal body schema, and different control strategies.
Unstable tasks are particularly challenging because deteriorate the predictive power of internal models and further enhance the instability potential of delayed sensory feedback.
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We explore this issue by means of three simulation studies: A The hybrid control of a double inverted pendulum model, B The bimanual stabilization of a saddle-like instability, C Whole-body focal-postural dynamics. The simulation results support the idea that the brain can mix different control strategies in a task-oriented and multi-referential manner. Keywords: Human performance - Sensory-motor , Neuromuscular systems - Peripheral mechanisms Abstract: Smooth physical interaction with our environment, such as when working with tools, requires adaptability to unpredictable perturbations that can be achieved through impedance control of multi-joint limbs.
Modulation of arm stiffness can be achieved either increasing co-contraction of antagonistic muscles or by increasing the gain of spinal reflex loops.
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According to the "automatic gain scaling" principle, the spinal reflex gain, as measured via the H-reflex, scales with muscle activation. A previous experiment from our labs suggested, however, that reflex gains might instead be scaled to the force exerted by the limb, perhaps as a means to counteract destabilizing external forces. The goal of our experiment was to test whether force output, rather than the muscular activity per se, could be the critical factor determining reflex gain.
Five subjects generated different levels of force at the wrist with or without assistance to dissociate applied force from agonist muscular activity. We recorded contact force, EMG and H-reflex response from a wrist flexor.
We did not find a strict relationship between reflex gain and contact force but nor did we observe consistent modulation of reflex gain simply as a function of agonist muscle activity.
These results are discussed in relation to the stability of the task constraints. Keywords: Motor learning, neural control, and neuromuscular systems , Neuromuscular systems - Computational modeling , Neuromuscular systems - Learning and adaption Abstract: Multivariable intermittent control MIC combines stability with flexibility in the control of unstable systems.
Using an underlying continuous-time optimal control design, MIC uses models of the physical system to generate multivariate open-loop control signals between samples of the observed state. Using accurate model values of physical system parameters, stability of the closed loop system is not dependent upon sample interval.
Here we consider the sensitivity of MIC to inaccurate model values of system parameters. Is this sensitivity a problem or an asset?
Prediction error between open loop and observed states provides the basis for triggering a sampling event but is also sensitive to inaccurate model values. Investigation of the mapping between prediction error and model values of physical parameters illustrates the value of prediction error to identify combinations of parameters giving stable closed loop control with low state error, similar to that provided by accurate values.
Sensitivity of prediction error to model inaccuracy is potentially an asset facilitating adaptation and supporting the rationale for MIC to combine control with flexibility. Keywords: Neuromuscular systems - Learning and adaption , Neuromuscular systems - Locomotion Abstract: In this study, we used a model-based approach to explore the potential contributions of central pattern generating circuits CPGs during adaptation to external perturbations during locomotion.
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We constructed a neuromechanical modeled of locomotion using a reduced-phase CPG controller and an inverted pendulum mechanical model. Two different forms of locomotor adaptation were examined in this study: split-belt treadmill adaptation and adaptation to a unilateral, elastic force field.
After evaluating the effect of phase resetting on the adaptation of step length symmetry, we examined the extent to which the results from these simple models could explain previous experimental observations. We found that adaptation of step length symmetry during split-belt treadmill walking could be reproduced using our model, but this model failed to replicate patterns of adaptation observed in response to force field perturbations.
Given that spinal animal models can adapt to both of these types of perturbations, our findings suggest that there may be distinct features of pattern generating circuits that mediate each form of adaptation.
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Without rapid transmission and accurate perception of somatosensory inputs, the automatic postural responses required during standing may be delayed or absent after TBI which can lead to instability. Further, the sensitivity level to which environmental perturbations can be detected is also vital, as the central nervous system will only employ balance control strategies when it perceives a change in equilibrium. Such undetectable perturbations, however small they may be, can result in fatal falls, especially after TBI.
In this investigation we used a novel computerized biofeedback based CBB intervention aimed at improving perception of external perturbations, and static and dynamic balance in a single male participant with severe TBI. We used an adaptive single interval adjustment matrix SIAM protocol to determine the perception of perturbation threshold PPT at baseline 1 day pre-intervention and follow up 1 day post-intervention.
External perturbations were provided through sinusoidal translations of 0. PPT assessment post intervention showed a decrease in PPT, suggesting an improvement in the ability gain of 0. There was a significant increase in BBS 6 points at follow up. The participant demonstrated increased muscle activation for the right gastrocnemius, left soleus, right bicep femoris and left vastus lateralis muscles at follow up. This investigation demonstrate the potential use of the CBB intervention for improving interpretation and organization of multisensory information in a task specific environment to improve balance dysfunction post TBI.
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Despite its significant impact on the deterioration in quality of life in PD patients, mechanistic causes of the instability have not been clarified. Joint inflexibility at ankle and hip joints might be such a major cause, leading to small variability in the center of pressure CoP during quiet stance. However, this conjecture is still controversial.
Thus, quantitative characterization of CoP patterns during quiet stance in PD patients remains a matter of research. Specifically, major factors responsible for the discrimination were all associated with increase in the power at a high-frequency band near and over 1 Hz along with reduction at the low-frequency regime lower than about 0.
Then, the power-ratio, defined as the relative spectral power in a band around 1 Hz, was examined, since the power in this band reflects postural sway with anti-phase coordinated motions of the ankle and hip joints.
We showed that the power-ratio values were significantly smaller in the PD patients than those in the healthy subjects.
This difference as well as the results of the linear discriminant analysis suggest joint inflexibility in PD patients, particularly at hip joint, which diminished anti-phase coordination between trunk and lower extremity, leading to postural instability in PD patients.
Keywords: Neuromuscular systems - Postural and balance , Neurorehabilitation , Motor learning, neural control, and neuromuscular systems Abstract: Falls are a leading cause of injury and mortality among adults over the age of 65 years.
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Given the strong relation between fear of falling and fall risk, identification of the mechanisms that underlie anxiety-related changes in postural control may pave the way to the development of novel therapeutic strategies aimed at reducing fall risk in older adults. First, we review potential mechanisms underlying anxiety-mediated changes in postural control in older adults with and without neurological conditions.
We then present a system that allows for the simultaneous recording of neural, physiological, and behavioral data in an immersive virtual reality VR environment while implementing sensory and mechanical perturbations to evaluate alterations in sensorimotor integration under conditions with high postural threat.
We also discuss applications of VR in minimizing falls in older adults and potential future studies. Keywords: Neuromuscular systems - Postural and balance , Neurological disorders - Mechanisms , Neurological disorders - Diagnostic and evaluation techniques Abstract: Intermittent feedback control for stabilizing human upright stance is a promising strategy, alternative to the standard time-continuous stiffness control.
Here we show that such an intermittent controller can be established naturally through reinforcement learning. To this end, we used a single inverted pendulum model of the upright posture and a very simple reward function that gives a certain amount of punishments when the inverted pendulum falls or changes its position in the state space.
We found that the acquired feedback controller exhibits hallmarks of the intermittent feedback control strategy, namely the action of the feedback controller is switched-off intermittently when the state of the pendulum is located near the stable manifold of the unstable saddle-type upright equilibrium of the inverted pendulum with no active control: this action provides an opportunity to exploit transiently converging dynamics toward the unstable upright position with no help of the active feedback control.
We then speculate about a possible physiological mechanism of such reinforcement learning, and suggest that it may be related to the neural activity in the pedunculopontine tegmental nucleus PPN of the brainstem.
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Keywords: Neuromuscular systems - Postural and balance , Neurological disorders - Traumatic brain injury , Human performance - Cognition Abstract: Assessment, treatment, and management of sport-related concussions are a widely recognized public health issue. Although several neuropsychological and motor assessment tools have been developed and implemented for sports teams at various levels and ages, the sensitivity of these tests has yet to be validated with more objective measures to make return-to-play RTP decisions more confidently.
The present study sought to analyze the residual effect of concussions on a sample of adolescent athletes who sustained one or more previous concussions compared to those who had no concussion history. For this purpose, a wide variety of assessment tools containing both neurocognitive and electroencephalogram EEG elements were used.
All clinical testing and EEG were repeated at 8 months, 10 months, and 12 months post-injury for both healthy and concussed athletes. The concussed athletes performed poorer than healthy athletes on processing speed and impulse control subtest of neurocognitive test on month 8, but no alterations were marked in terms of visual and postural stability.
EEG analysis revealed significant differences in brain activities of concussed athletes through all three intervals. These long-term neurocognitive and EEG deficits found from this ongoing sport-related concussion study suggest that the post-concussion physiological deficits may last longer than the observed clinical recovery. Keywords: Neuromuscular systems - Postural and balance Abstract: Postural instability affects a large number of people and can compromise even simple activities of the daily routine.
Therapies for balance training can strongly benefit from auxiliary devices specially designed for this purpose. In this paper, we present a system for balance training that uses the metaphor of a game, what contributes to the motivation and engagement of the patients during a treatment. Such approach is usually named exergame, in which input devices for posturographic assessment and a visual output perform the interaction with the subject.
The proposed system uses two force platforms, one positioned under the feet and the other under the hip of the subject.
The force platforms employ regular load cells and a microcontroller-based signal acquisition module to capture and transmit the samples to a computer. Moreover, a computer vision module performs body key-point detection, based on real time segmentation of markers attached to the subject. For the validation of the system, we conducted experiments with 20 neurologically intact volunteers during two tests: comparison of the stabilometric parameters obtained from the system with those obtained from a commercial baropodometer and the practice of several exergames.
Results show that the proposed system is completely functional and can be used as a versatile tool for balance training. Keywords: Connectivity measurements , Data mining and processing - Pattern recognition , Physiological systems modeling - Signals and systems Abstract: The brain is inherently multiscalar in both space and time. We argue that this multiscalar nature is reflected in the blood oxygenation level dependent BOLD fluctuations used to map functional connectivity.
We present evidence that global fluctuations in activity, quasiperiodic spatiotemporal patterns, and aperiodic time-varying activity coexist within the BOLD signal. These processes can be separated using careful analysis and appear to reflect electrical activity on similar scales, suggesting that the BOLD signal fluctuations can provide novel insight into the functional architecture of the brain.
Keywords: Connectivity measurements , Independent component analysis Abstract: Functional magnetic resonance imaging fMRI studies utilizing measures of hemodynamic signal, such as the blood-oxygenation-level dependent BOLD signal, have discovered that resting-state brain activities are organized into multiple large-scale functional networks, coined as resting state networks RSNs. However, an important limitation of the available fMRI studies is that hemodynamic signals only provide an indirect measure of neuronal activity and that the neurobiological basis of the fMRI RSNs is not clear.
Several approaches have been developed to search and identify the electrophysiological correlates of spontaneous fMRI fluctuations. The current study reviewed and compared two recently developed approaches based on the time courses and the spatial patterns of simultaneously acquired EEG and fMRI data.
Keywords: Connectivity measurements Abstract:. Keywords: Nonlinear dynamic analysis - Phase locking estimation , Connectivity measurements Abstract: To investigate the reorganization of functional brain network following amputation, twenty-two right-hand amputees and twenty-four age- and education-matched controls participated in a resting-state EEG study. EEG networks in alpha and beta bands were constructed using phase synchronization.