Biology subjects

Jeka, J. J.

Publications and source records attributed to Jeka, J. J..

7 recordsLinked to original sources

bioRxiv2025

The Relationship Between Visual Motion Detection Thresholds and Visual Sensitivity to Medial/Lateral Balance Control

The ability to differentiate between self-motion and motion in the environment is an important factor for maintaining upright balance control. Visual motion can elicit the sensation of a fall by cueing a false position sense. While there is evidence supporting the role of central vision and fall risk, including measures of contrast sensitivity, depth perception, and size of the visual field, the relationship between motion detection thresholds and balance control remains unknown. The aim of this study is to explore the relationship between thresholds for visual motion detection (VMDTs) of the environment and measures of visual sensitivity to balance disturbances in the environment while walking. Thirty young adults (18-35 years) and thirty older adults (55-79 years) participated in a counter-balanced study where they 1) walked on a self-paced treadmill within a virtual environment that delivered frontal plane multi-sine visual disturbances at three amplitudes (6{degrees}, 10{degrees}, and 15{degrees}), and 2) performed 100 trials of a two-alternative forced choice (2AFC) task in which they discriminated between a counterclockwise ("left") and clockwise ("right") rotation of a visual scene under three conditions (standing, standing with optic flow, and walking). Visual sensitivity was measured using frequency response functions of the center of mass displacement relative to the screen tilt (cm/deg) while VMDTs were measured by fitting a psychometric curve to the responses of the 2AFC task. We found significant positive correlations between measures of visual sensitivity and VMDTs for 7 out of the 9 conditions in young adults, and nonsignificant positive correlations between the two measures in older adults. VMDTs were overall higher in older adults, although not significantly in the standing condition, indicating more motion in the environment is required for older adults to consciously perceive it. VMDTs also tended to increase from standing, standing with optic flow, and walking, although not significantly between the standing and standing with optic flow conditions for both populations. We interpret the positive correlations between the two measures as an indication that individuals with lower motion detection thresholds can more accurately differentiate between self-motion and motion in the environment, resulting in lower responses from visual disturbances in the environment.

neuroscience↗

bioRxiv2024

SENSITIVITY OF MEDIAL/LATERAL BALANCE CONTROL TO VISUAL DISTURBANCES WHILE WALKING IN YOUNG AND OLDER ADULTS

Humans integrate multiple sources of sensory information to estimate body orientation in space. Balance control experiments while standing provide evidence that the contributions of these sensory channels change under different conditions in a process called sensory reweighting. This study aims to address whether there is evidence for sensory reweighting while walking and explores age-related differences in medial/lateral balance control under visually perturbing walking conditions. Thirty young adults (18-35 years) and thirty older adults (55-79 years) walked on a self-paced treadmill within a virtual environment that delivered frontal plane multi-sine visual disturbances at three amplitudes (6{degrees}, 10{degrees}, and 15{degrees}). Frequency response functions were used to quantify visual sensitivity to balance disturbances, while spatiotemporal gait parameters (e.g., step width, step-width variability) were measured to assess balance control. Visual sensitivity decreased in both populations with increasing stimulus amplitude, analogous to the sensory reweighting hypothesis in balance control while standing. Despite the decrease in visual sensitivity, the compensatory upweighting of other sensory systems was not observed through measurements of remnant sway. Older adults exhibited higher visual sensitivity at all amplitudes compared to young adults, indicating a more sensitive response to visual disturbances to balance control. Both groups showed increases in step width and step width variability with higher visual amplitudes, with older adults demonstrating more pronounced effects. Weak correlations existed between changes in visual sensitivity and changes in step width and step width variability suggesting a limited interaction between sensory reweighting and gait stability.

neuroscience↗

bioRxiv2023

Visual Motion Detection Thresholds Can Be Reliably Measured During Walking and Standing

In upright standing and walking, the motion of the body relative to the environment is estimated from a combination of visual, vestibular and somatosensory cues. Associations between vestibular or somatosensory impairments and balance problems are well established, but less is known about how the ability of the visual system to detect motion affects balance control. Here we asked whether motion detection thresholds can be reliably measured during walking and standing. Typically, motion threshold values have been obtained while sitting, with the head fixated to eliminate self-motion. In this study we 1) tested whether a visual motion detection threshold can be reliably measured during standing and walking in the presence of natural self-motion; and 2) investigated whether visual motion detection thresholds differ during standing and walking. MethodsTwenty-nine subjects stood on and walked along a self-paced, instrumented treadmill inside a virtual environment displayed on a large dome. Participants performed a 2-alternative forced choice experiment in which they discriminated between a counterclockwise ("left") and clockwise ("right") rotation of a visual scene projected on a large dome. A 6-down 1-up adaptive staircase algorithm was implemented to change the amplitude of the rotation. A psychometric fit to the participants binary responses provided an estimate for the detection threshold ResultsWe found strong correlations between the repeated measurements in both the walking (R = 0.84, p < 0.001) and the standing condition (R = 0.73, p < 0.001) as well as good agreement between the repeated measures with Bland-Altman plots. Average thresholds during walking (mean = 1.04 degrees, SD = 0.43 degrees) were significantly higher than during standing (mean = 0.73 degrees, SD = 0.47 degrees). ConclusionVisual motion detection thresholds can be reliably measured during both walking and standing, and thresholds are higher during walking.

neuroscience↗

bioRxiv2023

Reinforcement-Based Processes Actively Regulate MotorExploration Along Redundant Solution Manifolds

From a babys babbling to a songbird practicing a new tune, exploration is critical to motor learning. A hallmark of exploration is the emergence of random walk behaviour along solution manifolds, where successive motor actions are not independent but rather become serially dependent. Such exploratory random walk behaviour is ubiquitous across species, neural firing, gait patterns, and reaching behaviour. Past work has suggested that exploratory random walk behaviour arises from an accumulation of movement variability and a lack of error-based corrections. Here we test a fundamentally different idea--that reinforcement-based processes regulate random walk behaviour to promote continual motor exploration to maximize success. Across three human reaching experiments we manipulated the size of both the visually displayed target and an unseen reward zone, as well as the probability of reinforcement feedback. Our empirical and modelling results parsimoniously support the notion that exploratory random walk behaviour emerges by utilizing knowledge of movement variability to update intended reach aim towards recently reinforced motor actions. This mechanism leads to active and continuous exploration of the solution manifold, currently thought by prominent theories to arise passively. The ability to continually explore muscle, joint, and task redundant solution manifolds is beneficial while acting in uncertain environments, during motor development, or when recovering from a neurological disorder to discover and learn new motor actions.

neuroscience↗

bioRxiv2021

A Neuromuscular Model of Human Locomotion Combines Spinal Reflex Circuits with Voluntary Movements

Existing models of human walking use low-level reflexes or neural oscillators to generate movement. While appropriate to generate the stable, rhythmic movement patterns of steady-state walking, these models lack the ability to change their movement patterns or spontaneously generate new movements in the specific, goal-directed way characteristic of voluntary movements. Here we present a neuromuscular model of human locomotion that bridges this gap and combines the ability to execute goal directed movements with the generation of stable, rhythmic movement patterns that are required for robust locomotion. The model represents goals for voluntary movements of the swing leg on the task level of swing leg joint kinematics. Smooth movements plans towards the goal configuration are generated on the task level and transformed into descending motor commands that execute the planned movements, using internal models. The movement goals and plans are updated in real time based on sensory feedback and task constraints. On the spinal level, the descending commands during the swing phase are integrated with a generic stretch reflex for each muscle. Stance leg control solely relies on dedicated spinal reflex pathways. Spinal reflexes stimulate Hill-type muscles that actuate a biomechanical model with eight internal joints and six free-body degrees of freedom. The model is able to generate voluntary, goal-directed reaching movements with the swing leg and combine multiple movements in a rhythmic sequence. During walking, the swing leg is moved in a goal-directed manner to a target that is updated in real-time based on sensory feedback to maintain upright balance, while the stance leg is stabilized by low-level reflexes and a behavioral organization switching between swing and stance control for each leg. With this combination of reflex-based stance leg and voluntary, goal-directed control of the swing leg, the model controller generates rhythmic, stable walking patterns in which the swing leg movement can be flexibly updated in real-time to step over or around obstacles.

neuroscience↗

bioRxiv2019

The onset time of balance control during walking is phase-independent, but the magnitude of the response is not

The human body is mechanically unstable during walking. Maintaining upright stability requires constant regulation of muscle force by the central nervous system to push against the ground and move the body mass in the desired way. Activation of muscles in the lower body in response to sensory or mechanical perturbations during walking is usually highly phase-dependent, because the effect any specific muscle force has on the body movement depends upon the body configuration. Yet the resulting movement patterns of the upper body after the same perturbations are largely phase-independent. This is puzzling, because any change of upper-body movement must be generated by parts of the lower body pushing against the ground. How do phase-dependent muscle activation patterns along the lower body generate phase-independent movement patterns of the upper body? We hypothesize that in response to a perceived threat to balance, the nervous system generates a functional response by pushing against the ground in any way possible with the current body configuration. This predicts that the changes in the ground reaction force patterns following a balance perturbation should be phase-independent. Here we test this hypothesis by disturbing upright balance using Galvanic vestibular stimulation at three different points in the gait cycle. We measure the resulting changes in whole-body center of mass movement and the location of the center of pressure of the ground reaction force. We find that the whole-body balance response is not phase-independent as expected: balance responses are initiated faster and are smaller following a disturbance late in the gait cycle. Somewhat paradoxically, the initial center of pressure changes are larger for perturbations late in the gait cycle. The onset of the center of pressure changes however, does not depend on the phase of the perturbation. The results partially support our hypothesis of a phase-independent functional balance response underlying the phase-dependent recruitment of different balance mechanisms at different points of the gait cycle. We conclude that the central nervous system recruits any available mechanism to push against the ground to maintain balance as fast as possible in response to a perturbation, but the different mechanisms do not have equal strength.

neuroscience↗

bioRxiv2019

Repetitive subconcussive head impacts and changes in sensory processing for balance control

BackgroundRepetitive subconcussive head impacts (RHI) may be associated with current and future detrimental neurological effects. However, the effects of RHI on sensory processing for balance control is unknown and may have significant clinical implications if athletes are still participating in sport despite impairments.\n\nResearch QuestionAre there changes in sensory processing for balance control during standing and walking following RHI?\n\nMethodsThirty healthy, adult, amateur soccer players (15 males, 15 females, 21.8{+/-}2.8 years, 69.9{+/-}11.5 kg, 171.4{+/-}8.2 cm) volunteered for the standing balance assessment (i.e., experiment 1). A distinct cohort of twenty healthy, adult, amateur soccer players (10 males, 10 females, 22.3{+/-}4.5 years, 70.0{+/-}10.5 kg, 170.5{+/-}9.8 cm) volunteered for the walking balance assessment (i.e., experiment 2). We used a repeated measures design across three time points (pre-heading, 0-hours post-heading, 24-hours post-heading). Participants were randomly assigned to an experimental (i.e., performed 10 soccer headers in 10 minutes) or a control group (i.e., did not perform any soccer heading between sessions). In experiment 1, participants stood in a virtual reality cave while experiencing simultaneous perturbations to their visual, vestibular, and proprioceptive systems. In experiment 2, participants walked blindfolded along a foam walkway and experienced a vestibular perturbation on the second heel strike of the right foot. Changes in sensory processing were assessed using repeated measures ANOVAs.\n\nResultsThere were no changes in sensory reweighting during experiment 1 and no changes in balance responses to the vestibular stimulus in experiment 2.\n\nSignificanceAlthough the cumulative effects of RHI may result in later-life cognitive, behavioral, and mood impairments, a single episode of repeated soccer headers does not appear to be associated with acute impairments in sensory processing for balance control.

neuroscience↗