Leah Bent - Academia.edu (original) (raw)

Papers by Leah Bent

Frontiers in Human Neuroscience, 2020

Reflex responses generated by cutaneous mechanoreceptors of the plantar foot are important for th... more Reflex responses generated by cutaneous mechanoreceptors of the plantar foot are important for the maintenance of balance during postural tasks and gait. With aging, reflex generation, particularly from fast adapting type I receptors, is reduced, which likely contributes to impaired postural stability in this population. Therefore, improving reflex generation from these receptors may serve as a tool to improve balance performance. A mechanism to enhance reflexes may lie in the phenomenon of stochastic resonance, whereby the addition of certain intensities and frequencies of noise stimuli improves the performance of a system. This study was conducted to determine whether tactile noise stimuli could improve cutaneous reflex generation. In 12 healthy young adults, we evoked cutaneous reflex responses using a 0-50 Hz Gaussian noise vibration applied to the plantar heel. Concurrently, we applied one of six subthreshold intensities of electrical tactile noise to the plantar heel [0%, 20%, 40%, 60%, 80% or 100% (threshold)] and were able to analyze data from 0%, 20% and 40% trials. Across participants, it was found that the addition of a 20% perceptual threshold (PT) noise resulted in enhanced reflex responses when analyzed in both the time and frequency domains. These data provide evidence that cutaneous reflex generation can be enhanced via a stochastic resonance effect and that 20% PT is the optimal intensity of noise to do so. Therefore, the addition of noise stimuli may be a valuable clinical intervention to improve reflex responses associated with postural balance in populations with impairments.

Frontiers in Bioengineering and Biotechnology, 2022

Understanding the processing of tactile information is crucial for the development of biofeedback... more Understanding the processing of tactile information is crucial for the development of biofeedback interventions that target cutaneous mechanoreceptors. Mechanics of the skin have been shown to influence cutaneous tactile sensitivity. It has been established that foot skin mechanics are altered due to foot posture, but whether these changes affect cutaneous sensitivity are unknown. The purpose of this study was to investigate the potential effect of posture-mediated skin deformation about the ankle joint on perceptual measures of foot skin sensitivity. Participants (N = 20) underwent perceptual skin sensitivity testing on either the foot sole (N = 10) or dorsum (N = 10) with the foot positioned in maximal dorsiflexion/toe extension, maximal plantarflexion/toe flexion, and a neutral foot posture. Perceptual tests included touch sensitivity, stretch sensitivity, and spatial acuity. Regional differences in touch sensitivity were found across the foot sole (p < 0.001) and dorsum (p &l...

Somatosensory & Motor Research, 2019

Purpose: Skin contributes to joint position sense (JPS) at multiple joints. Altered cutaneous inp... more Purpose: Skin contributes to joint position sense (JPS) at multiple joints. Altered cutaneous input at the foot can modulate gait and balance and kinesiology tape can enhance proprioception at the knee, but its effect may be dependent on existing capacity. The effect of texture at the knee, particularly in those with poor proprioception, is unknown. The aim of this study was to determine the effect of textured panels on JPS about the knee. Materials and methods: Eighteen healthy females were seated in an adjustable chair. Their left leg (target limb) moved passively from 65 to a target of flexion (115 or 90) or extension (40). Their right leg (matching limb) was passively moved towards this target angle and participants indicated when their limbs felt aligned. We tested three textured panels over the knee of the matching limb and two control conditions. The target limb maintained a control panel. Directional error, absolute error and variable error in matching between limbs were calculated. Results: On average textured panels over the knee increased JPS error compared to control pants for participants with poor JPS. These participants undershot the target at 90 of flexion significantly more with textured panels (À11 ± 3) versus control (À7 ± 3 , p ¼ 0.04). Conclusions: For participants with poor JPS accuracy, increased JPS error at 90 with a textured panel suggests these individuals utilised altered cutaneous information to adjust joint position. We propose increased error results from enhanced skin input at the knee leading to the perception of increased flexion.

Footwear Science, 2021

Nester (2021): No change in foot soft tissue morphology and skin sensitivity after three months o... more Nester (2021): No change in foot soft tissue morphology and skin sensitivity after three months of using foot orthoses that alter plantar pressure, Footwear Science,

Skin on the foot sole plays an important role in postural control. Cooling the skin 23 of the foo... more Skin on the foot sole plays an important role in postural control. Cooling the skin 23 of the foot is often used to induce anaesthesia to determine the role of skin in motor and 24 balance control. The effect of cooling on the four classes of mechanoreceptor in the skin is 25 largely unknown and thus the aim of the current study was to characterize the effects of 26 cooling on individual skin receptors in the foot sole. Such insight will better isolate 27 individual receptor contributions to balance control. Using microneurography, we recorded 28 39 single nerve afferents innervating mechanoreceptors in the skin of the foot sole in 29 humans. Afferents were identified as fastor slowly-adapting type I or II (FA I n=16, FA II 30 n=7, SA I n=6, SA II n=11). Receptor response to vibration was compared before and after 31 cooling the receptive field (2–20 min). Overall, firing response was abolished in 30% of all 32 receptors and this was equally distributed across receptor type (p=0.69)...

PeerJ, 2018

Background Following active muscle lengthening, there is an increase in steady-state isometric fo... more Background Following active muscle lengthening, there is an increase in steady-state isometric force as compared with a purely isometric contraction at the same muscle length and level of activation. This fundamental property of skeletal muscle is known as residual force enhancement (RFE). While the basic mechanisms contributing to this increase in steady-state isometric force have been well documented, changes in central nervous system (CNS) excitability for submaximal contractions during RFE are unclear. The purpose of this study was to investigate spinal and supraspinal excitability in the RFE isometric steady-state following active lengthening of the ankle dorsiflexor muscles. Methods A total of 11 male participants (20–28 years) performed dorsiflexions at a constant level of electromyographic activity (40% of maximum). Half of the contractions were purely isometric (8 s at an ankle angle of 130°), and the other half were during the RFE isometric steady-state following active le...

Journal of Histology and Histopathology, 2020

Background: Mechanoreceptors at the terminal ends of afferent nerves in the foot sole are critica... more Background: Mechanoreceptors at the terminal ends of afferent nerves in the foot sole are critical for gait and balance. While previous studies have mapped afferent receptive fields and innervation densities across the foot sole using microneurography, the location and distribution of mechanoreceptors in the foot sole skin is unknown. In humans, histological investigations are limited to specimens obtained during amputation or embalmed tissues. These can be difficult to obtain and the latter poorly preserved at the extremity of the foot sole. Mice serve as an appropriate animal model to study mechanoreceptors whose function is conserved across mammalian species, however serial sectioning of intact mouse hind paws is challenging due to the dense bones and variety of soft tissues present. Consequently, digits and footpads are typically isolated for analysis and inferences made regarding mechanoreceptor density across the whole hind paw. There are no published protocols for serial histological sectioning of mouse hind paws and attempts at serially sectioning intact rat hind paws have been unsuccessful. Methods: We conducted eight experiments optimizing tissue preparation, chemical processing and sectioning techniques to achieve serial sectioning and staining of intact mouse hind paws. Two additional approaches (isolated hind paw skin and footpad biopsies) were compared to the intact hind paw approach to determine the optimal method for mechanoreceptor visualization and localization. Results: The optimized protocol for serial sectioning of intact hind paws included five days of fixation in 4% paraformaldehyde, ten days of decalcification in Cal-Ex™️ II, a 9-hour automated tissue processing protocol, embedding in a special formulated paraffin, and sectioning with specific techniques. Of the three approaches, intact hind paws provided the most context to structures visualized in the hind paw skin and thus, was the recommended protocol for future studies. Meissner-like corpuscles were located in the footpads and most abundantly in the footpads adjacent to digits II to V of the hind paw. Conclusion: The method for serial sectioning of the intact hind paws outlined in this study will allow future analysis of mechanoreceptor distribution and density in transgenic or disease mouse models.

Prosthetics & Orthotics International, 2019

Background: External devices are used to manage musculoskeletal pathologies by altering loading o... more Background: External devices are used to manage musculoskeletal pathologies by altering loading of the foot, which could result in altered muscle activity that could have therapeutic benefits. Objectives: To establish if evidence exists that footwear, foot orthoses and taping alter lower limb muscle activity during walking and running. Study design: Systematic literature review. Methods: CINAHL, MEDLINE, ScienceDirect, SPORTDiscus and Web of Science databases were searched. Quality assessment was performed using guidelines for assessing healthcare interventions and electromyography methodology. Results: Thirty-one studies were included: 22 related to footwear, eight foot orthoses and one taping. In walking, (1) rocker footwear apparently decreases tibialis anterior activity and increases triceps surae activity, (2) orthoses could decrease activity of tibialis posterior and increase activity of peroneus longus and (3) other footwear and taping effects are unclear. Conclusion: Modific...

Applied Ergonomics, 2019

Prolonged sitting, common in many workplaces, reduces blood flow to the lower limb and has negati... more Prolonged sitting, common in many workplaces, reduces blood flow to the lower limb and has negative health outcomes. CoreChair is an active-sitting chair that encourages increased movement to help mitigate these outcomes. Physiological and cognitive measures were recorded in ten participants over four hours of sitting in both the CoreChair and a traditional office chair. Sitting in both chairs led to increases in calf circumference (p<0.0001), reduced tactile sensitivity (p=0.02), and a cognitive decline in attention (p=0.035) over time. However, the increase in calf circumference was smaller in the CoreChair at the second (p= 0.017) and third hour (p= 0.012) compared to the traditional chair. Additionally, for the attention task, the traditional chair generated more attention-task errors (p=0.005), while no changes were observed with the CoreChair (p=0.13). These findings suggest that during prolonged sitting CoreChair may have modest physiological and cognitive benefits compared to a traditional chair.

Journal of Biomechanics, 2019

Motor Control, 2013

The integration of vestibular and somatosensory information for the control of lower limb muscula... more The integration of vestibular and somatosensory information for the control of lower limb musculature remains elusive. To determine whether a subthreshold vestibular input influences the cutaneous evoked response, the isometric EMG activity in the posturally inactive soleus muscles of 13 healthy, seated subjects was collected. Vestibular afferents were activated using galvanic vestibular stimulation (GVS; 1.8–2.5mA, 500ms), while percutaneous electrical stimulation was delivered to the distal tibial nerve (11ms train of 3 × 1.0 ms pulses, 200Hz) to activate foot sole skin afferents. GVS elicited responses in soleus both independently and when combined with cutaneous stimulation. The responses to the combined sensory input showed an interaction between the two sensory modalities to influence muscle activation. Of note is the presence of significant muscle modulation in the combined condition, where subthreshold vestibular inputs altered the outcome of the cutaneous reflex response. T...

Brain and Behavior, 2017

This is an open access article under the terms of the Creative Commons Attribution License, which... more This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Physiological Reports, 2017

The reduction in steady-state isometric torque following a shortening muscle action when compared... more The reduction in steady-state isometric torque following a shortening muscle action when compared to a purely isometric contraction at the same muscle length and level of activation is termed torque depression (TD). The purpose of this study was to investigate spinal and supraspinal neural responses during the TD state of a maximal voluntary activation of the ankle dorsiflexors. Thirteen subjects (10 male) were recruited for the study. To explore alterations in corticospinal excitability during voluntary muscle activation in the TD state, motor evoked potentials (MEPs), cervicomedullary motor evoked potentials (CMEPs), and maximal compound muscle action potentials (Mmax) were elicited during the isometric steady-state following active shortening (i.e., TD) and the purely isometric condition. A 15% reduction in steady-state isometric torque (P < 0.05) was observed following isokinetic shortening at 40°/sec. Although mean evoked responses (MEP and CMEP) were not different in the TD state as compared with purely isometric state, the changes in evoked responses were inversely related to one another depending on the level of TD. These findings indicate that supraspinal and spinal responses are interrelated in the TD state. Furthermore, antagonist muscle coactivation during the isometric reference contraction was positively related to TD. These findings suggest the possibility of a relationship between the central nervous system and TD in humans. Further work should be performed to definitively link TD to specific spinal interneurons.

Journal of neurophysiology, Jan 5, 2017

Single unit microneurography was used to record the firing characteristics of the four classes of... more Single unit microneurography was used to record the firing characteristics of the four classes of foot sole cutaneous afferents (fast and slowly adapting type I and II; FAI, FAII, SAI, SAII) in response to sinusoidal vibratory stimuli. Frequency (3-250Hz) and amplitude (0.001-2mm) combinations were applied to afferent receptive fields through a 6mm diameter probe. The impulses per cycle, defined as the number of action potentials evoked per vibration sine wave, were measured over one second of vibration at each frequency-amplitude combination tested. Afferent entrainment threshold (lowest amplitude at which an afferent could entrain 1:1 to the vibration frequency) and afferent firing threshold (minimum amplitude for which impulses per cycle was greater than zero) were then obtained for each frequency. Increases in vibration frequency are generally associated with decreases in expected impulses per cycle (p < 0.001), but each foot sole afferent class appears uniquely tuned to vibr...

BMC veterinary research, Jan 7, 2017

The purpose of this study was to measure the muscular activation in four forelimb muscles while d... more The purpose of this study was to measure the muscular activation in four forelimb muscles while dogs performed agility tasks (i.e., jumping and A-frame) and to provide insight into potential relationships between level of muscular activation and risk of injury. Muscle activation in eight healthy, client-owned agility dogs was measured using ultrasound-guided fine-wire electromyography of four specific forelimb muscles: Biceps Brachii, Supraspinatus, Infraspinatus, and Triceps Brachii - Long Head, while dogs performed a two jump sequence and while dogs ascended and descended an A-frame obstacle at two different competition heights. The peak muscle activations during these agility tasks were between 1.7 and 10.6 fold greater than walking. Jumping required higher levels of muscle activation compared to ascending and descending an A-frame, for all muscles of interest. There was no significant difference in muscle activation between the two A-frame heights. Compared to walking, all of th...

Journal of Neurophysiology, 2017

Muscle spindles provide exquisitely sensitive proprioceptive information regarding joint position... more Muscle spindles provide exquisitely sensitive proprioceptive information regarding joint position and movement. Through passively driven length changes in the muscle-tendon unit (MTU), muscle spindles detect joint rotations because of their in-parallel mechanical linkage to muscle fascicles. In human microneurography studies, muscle fascicles are assumed to follow the MTU and, as such, fascicle length is not measured in such studies. However, under certain mechanical conditions, compliant structures can act to decouple the fascicles, and, therefore, the spindles, from the MTU. Such decoupling may reduce the fidelity by which muscle spindles encode joint position and movement. The aim of the present study was to measure, for the first time, both the changes in firing of single muscle spindle afferents and changes in muscle fascicle length in vivo from the tibialis anterior muscle (TA) during passive rotations about the ankle. Unitary recordings were made from 15 muscle spindle affere...

Experimental brain research, Feb 17, 2016

Visuo-vestibular recalibration, in which visual information is used to alter the interpretation o... more Visuo-vestibular recalibration, in which visual information is used to alter the interpretation of vestibular signals, has been shown to influence both oculomotor control and navigation. Here we investigate whether vision can recalibrate the vestibular feedback used during the re-establishment of equilibrium following a perturbation. The perturbation recovery responses of nine participants were examined following exposure to a period of 11 s of galvanic vestibular stimulation (GVS). During GVS in VISION trials, occlusion spectacles provided 4 s of visual information that enabled participants to correct for the GVS-induced tilt and associate this asymmetric vestibular signal with a visually provided 'upright'. NoVISION trials had no such visual experience. Participants used the visual information to assist in realigning their posture compared to when visual information was not provided (p < 0.01). The initial recovery response to a platform perturbation was not impacted by...

Journal of applied physiology (Bethesda, Md. : 1985), Jan 28, 2016

It has previously been shown that cutaneous sensory input from across a broad region of skin can ... more It has previously been shown that cutaneous sensory input from across a broad region of skin can influence proprioception at joints of the hand. The current experiment tested whether cutaneous input from different skin regions across the foot can influence proprioception at the ankle joint. The ability to passively match ankle joint position (17° and 7° plantarflexion and 7° dorsiflexion) was measured while cutaneous vibration was applied to the sole (heel, distal metatarsals) or dorsum of the target foot. Vibration was applied at two different frequencies to preferentially activate Meissner's corpuscles (45Hz, 80μm) or Pacinian corpuscles (255Hz, 10μm) at amplitudes ~3dB above mean perceptual thresholds. Results indicated that cutaneous input from all skin regions across the foot could influence joint matching error and variability, although the strongest effects were observed with heel vibration. Furthermore, the influence of cutaneous input from each region was modulated by j...