ORCID Profile
0000-0002-3354-7104
Current Organisation
Neuroscience Research Australia
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Publisher: American Physiological Society
Date: 05-2021
DOI: 10.1152/JAPPLPHYSIOL.00557.2020
Abstract: Muscle activity is often normalized to maximal muscle activity however, it is difficult to obtain accurate measures of maximal muscle activity in people with impaired voluntary neural drive. We determined the relationship between voluntary muscle activation and plantarflexor muscle activity across a broad range of muscle activation values in able-bodied people. The relationship between voluntary muscle activation and muscle activity can be described with simple mathematical functions capable of estimating maximal muscle activity.
Publisher: American Physiological Society
Date: 03-2016
Abstract: The soleus (Sol) and medial gastrocnemius (mGas) muscles have different patterns of activity during standing balance and may have distinct functional roles. Using surface electromyography we previously observed larger responses to galvanic vestibular stimulation (GVS) in the mGas compared with the Sol muscle. However, it is unclear whether this difference is an artifact that reflects limitations associated with surface electromyography recordings or whether a compensatory balance response to a vestibular error signal activates the mGas to a greater extent than the Sol. In the present study, we compared the effect of GVS on the discharge behavior of 9 Sol and 21 mGas motor units from freely standing subjects. In both Sol and mGas motor units, vestibular stimulation induced biphasic responses in measures of discharge timing [11 ± 5.0 (mGas) and 5.6 ± 3.8 (Sol) counts relative to the sham (mean ± SD)], and frequency [0.86 ± 0.6 Hz (mGas), 0.34 ± 0.2 Hz (Sol) change relative to the sham]. Peak-to-trough response litudes were significantly larger in the mGas (62% in the probability-based measure and 160% in the frequency-based measure) compared with the Sol (multiple P 0.05). Our results provide direct evidence that vestibular signals have a larger influence on the discharge activity of motor units in the mGas compared with the Sol. More tentatively, these results indicate the mGas plays a greater role in vestibular-driven balance corrections during standing balance.
Publisher: Springer Science and Business Media LLC
Date: 27-05-2020
Publisher: Springer Science and Business Media LLC
Date: 09-2021
Publisher: American Physiological Society
Date: 03-2021
Publisher: Springer Science and Business Media LLC
Date: 27-03-2019
Publisher: Public Library of Science (PLoS)
Date: 26-04-2017
Publisher: Wiley
Date: 18-12-2017
DOI: 10.1113/JP274781
Publisher: Wiley
Date: 06-2023
DOI: 10.14814/PHY2.15692
Abstract: Transcutaneous spinal cord stimulation (TSS) is purported to improve motor function in people after spinal cord injury (SCI). However, several methodology aspects are yet to be explored. We investigated whether stimulation configuration affected the intensity needed to elicit spinally evoked motor responses (sEMR) in four lower limb muscles bilaterally. Also, since stimulation intensity for therapeutic TSS (i.e., trains of stimulation, typically delivered at 15–50 Hz) is sometimes based on the single‐pulse threshold intensity, we compared these two stimulation types. In non‐SCI participants ( n = 9) and participants with a SCI ( n = 9), three different electrode configurations (cathode–anode) L1‐midline (below the umbilicus), T11‐midline and L1‐ASIS (anterior superior iliac spine non‐SCI only) were compared for the sEMR threshold intensity using single pulses or trains of stimulation which were recorded in the vastus medialis, medial hamstring, tibialis anterior, medial gastrocnemius muscles. In non‐SCI participants, the L1‐midline configuration showed lower sEMR thresholds compared to T11‐midline ( p = 0.002) and L1‐ASIS ( p 0.001). There was no difference between T11‐midline and L1‐midline for participants with SCI ( p = 0.245). Spinally evoked motor response thresholds were ~13% lower during trains of stimulation compared to single pulses in non‐SCI participants ( p 0.001), but not in participants with SCI ( p = 0.101). With trains of stimulation, threshold intensities were slightly lower and the incidence of sEMR was considerably lower. Overall, stimulation threshold intensities were generally lower with the L1‐midline electrode configuration and is therefore preferred. While single‐pulse threshold intensities may overestimate threshold intensities for therapeutic TSS, tolerance to trains of stimulation will be the limiting factor in most cases.
Publisher: Wiley
Date: 17-09-2019
DOI: 10.1002/HBM.24371
Publisher: American Physiological Society
Date: 10-2020
DOI: 10.1152/JAPPLPHYSIOL.00106.2020
Abstract: The slack length of a relaxed human skeletal muscle is not fixed it can be modified by contraction and stretch. Contraction of the human vastus lateralis muscle at short lengths reduces the muscle’s slack length. Even very weak contractions are sufficient to induce this effect. The effect persists for at least 5 min but can be reduced or abolished with a large- litude passive stretch.
Publisher: Oxford University Press (OUP)
Date: 02-2022
Publisher: American Physiological Society
Date: 03-2022
DOI: 10.1152/JAPPLPHYSIOL.00809.2021
Abstract: Proprioception, which can be defined as the awareness of the mechanical and spatial state of the body and its musculoskeletal parts, is critical to motor actions and contributes to our sense of body ownership. To date, clinical proprioceptive tests have focused on a person’s ability to detect, discriminate, or match limb positions or movements, and reveal that the strength of the relationship between deficits in proprioception and physical function varies widely. Unfortunately, these tests fail to assess higher-level proprioceptive abilities. In this Perspective, we propose that to understand fully the link between proprioception and function, we need to look beyond traditional clinical tests of proprioception. Specifically, we present a novel framework for human proprioception assessment that is ided into two categories: low-level and high-level proprioceptive judgments. Low-level judgments are those made in a single frame of reference and are the types of judgments made in traditional proprioceptive tests (i.e., detect, discriminate or match). High-level proprioceptive abilities involve proprioceptive judgments made in a different frame of reference. For ex le, when a person indicates where their hand is located in space. This framework acknowledges that proprioception is complex and multifaceted and that tests of proprioception should not be viewed as interchangeable, but rather as complimentary. Crucially, it provides structure to the way researchers and clinicians can approach proprioception and its assessment. We hope this Perspective serves as the catalyst for discussion and new lines of investigation.
Publisher: American Physiological Society
Date: 09-2022
Publisher: American Physiological Society
Date: 07-2019
DOI: 10.1152/JAPPLPHYSIOL.00168.2019
Abstract: When assessing passive joint range of motion in neurological conditions, concomitant involuntary muscle activity is generally regarded small enough to ignore. This assumption is untested. If false, many clinical and laboratory studies that rely on these assessments may be in error. We determined to what extent small amounts of involuntary muscle activity limit passive range of motion in 30 able-bodied adults. Subjects were seated with the knee flexed 90° and the ankle in neutral, and predicted maximal plantarflexion torque was determined using twitch interpolation. Next, with the knee flexed 90° or fully extended, the soleus muscle was continuously electrically stimulated to generate 1, 2.5, 5, 7.5, and 10% of predicted maximal torque, in random order, while the ankle was passively dorsiflexed to a torque of 9 N·m by a blinded investigator. A trial without stimulation was also performed. Ankle dorsiflexion torque-angle curves were obtained at each percent of predicted maximal torque. On average (mean, 95% confidence interval), each 1% increase in plantarflexion torque decreases ankle range of motion by 2.4° (2.0 to 2.7° knee flexed 90°) and 2.3° (2.0 to 2.5° knee fully extended). Thus 5% of involuntary plantarflexion torque, the amount usually considered small enough to ignore, decreases dorsiflexion range of motion by ~12°. Our results indicate that even small amounts of involuntary muscle activity will bias measures of passive range and hinder the differential diagnosis and treatment of neural and nonneural mechanisms of contracture. NEW & NOTEWORTHY The soleus muscle in able-bodied adults was tetanically stimulated while the ankle was passively dorsiflexed. Each 1% increase in involuntary plantarflexion torque at the ankle decreases the range of passive movement into dorsiflexion by °. Thus the range of ankle dorsiflexion decreases by ~12° when involuntary plantarflexion torque is 5% of maximum, a torque that is usually ignored. Thus very small amounts of involuntary muscle activity substantially limit passive joint range of motion.
Publisher: BMJ
Date: 09-2022
DOI: 10.1136/BMJOPEN-2022-060976
Abstract: Research must be well designed, properly conducted and clearly and transparently reported. Our independent medical research institute wanted a simple, generic tool to assess the quality of the research conducted by its researchers, with the goal of identifying areas that could be improved through targeted educational activities. Unfortunately, none was available, thus we devised our own. Here, we report development of the Quality Output Checklist and Content Assessment (QuOCCA), and its application to publications from our institute’s scientists. Following consensus meetings and external review by statistical and methodological experts, 11 items were selected for the final version of the QuOCCA: research transparency (items 1–3), research design and analysis (items 4–6) and research reporting practices (items 7–11). Five pairs of raters assessed all 231 articles published in 2017 and 221 in 2018 by researchers at our institute. Overall, the results were similar between years and revealed limited engagement with several recommended practices highlighted in the QuOCCA. These results will be useful to guide educational initiatives and their effectiveness. The QuOCCA is brief and focuses on broadly applicable and relevant concepts to open, high-quality, reproducible and well-reported science. Thus, the QuOCCA could be used by other biomedical institutions and in idual researchers to evaluate research publications, assess changes in research practice over time and guide the discussion about high-quality, open science. Given its generic nature, the QuOCCA may also be useful in other research disciplines.
Publisher: Wiley
Date: 09-2016
DOI: 10.14814/PHY2.12947
Publisher: Springer Science and Business Media LLC
Date: 29-04-2019
DOI: 10.1007/S00221-019-05546-7
Abstract: Whether visible or not, knowing the location of our hands is fundamental to how we perceive ourselves and interact with our environment. The present study investigated perceived hand location in the absence of vision in 30 participants. Their right index finger was placed 10, 20 or 30 cm away on either side of the body midline, with and without their left index finger placed 10 cm to the left of the right index. On average, at each position, participants perceived their right hand closer to the body midline than it actually was. This underestimation increased linearly with increased distance of the hand from body midline [slope 0.77 (0.74 to 0.81), mean (95% CI)]. Participants made smaller errors in perceived hand location when the right hand was in the contralateral workspace [mean difference 2.13 cm (1.57 to 2.69)]. Presence of the left hand on the support surface had little or no effect on perceived location of the right hand [mean difference [Formula: see text] cm ([Formula: see text] to 0.02)]. Overall, participants made systematic perceptual errors immediately after hand placement. The magnitude of these errors grew linearly as the hand got further away from the body midline. Because of their magnitude, these errors may contribute to errors in motor planning when visual feedback is not available. Also, these errors are important for studies in which perceived hand location is assessed after some time, for ex le, when studying illusions of body ownership and proprioceptive drift.
Publisher: American Physiological Society
Date: 08-2018
Publisher: American Physiological Society
Date: 10-2019
Publisher: Wiley
Date: 2020
DOI: 10.1113/JP279193
Publisher: Public Library of Science (PLoS)
Date: 15-08-2018
Publisher: Wiley
Date: 04-10-2016
DOI: 10.1111/APHA.12792
Abstract: Knowledge of which body parts belong to us is referred to as the sense of body ownership. There is increasing evidence that this important aspect of human proprioception is highly malleable. Research into ownership of in idual body parts was stimulated by Botvinick and Cohen's rubber-hand illusion (Nature 391,1998, 756), which demonstrated that an artificial body part can be incorporated in one's body representation and can cause real body parts to be sensed erroneously. Here, we review key studies that have advanced our understanding of the sense of body ownership, including the important role played by multisensory integration and spatiotemporal congruence of sensory signals. We also discuss our recent discovery that body ownership can be induced in response to movement stimuli by signals from a single class of sensory receptor, namely muscle spindles.
Publisher: Wiley
Date: 08-2019
DOI: 10.1113/JP278335
Publisher: American Physiological Society
Date: 10-2018
Publisher: Wiley
Date: 28-11-2019
DOI: 10.1113/JP278630
Abstract: How we judge the location of our body parts can be affected by a range of factors that change how our brain interprets proprioceptive signals. We examined the effect of several such factors on how we perceive an object's width and the spacing between our thumb and fingers when grasping. Grasp‐related perceptions were slightly wider when using all digits, in line with our tendency to grasp larger objects with the entire hand. Surprisingly, these perceptions were not affected by the frames of reference for judgements (object width versus grasp aperture), whether the object was grasped actively or passively, or the strength of the grasp. These results show that the brain maintains a largely stable representation of the hand when grasping stationary objects. This stability may underpin our dexterity when grasping a vast array of objects. Various factors can alter how the brain interprets proprioceptive signals, leading to errors in how we perceive our body and execute motor tasks. This study determined the effect of critical factors on hand‐based perceptions. In Experiment 1, 20 participants grasped without lifting an unseen 6.5 cm‐wide object with two grasp configurations: thumb and all fingers, and thumb and index finger. Participants reported perceived grasp aperture (body reference frame) or perceived object width (external reference frame) using visual charts. In Experiment 2, 20 participants grasped the object with three grasp intensities (1, 5 and 15% maximal grasp force) actively or passively and reported perceived grasp aperture. A follow‐up experiment addressed whether results from Experiment 2 were influenced by the external force applied during passive grasp. Overall, there was a mean difference of 0.38 cm (95% confidence interval (CI), 0.12 to 0.63) between the two grasp configurations (all digits compared to thumb and index finger). Perceived object width compared to perceived grasp aperture differed by only −0.04 cm (95% CI, −0.30 to 0.21). There was no real effect of grasp intensity on perceived grasp aperture (−0.01 cm 95% CI, −0.03 to 0.01) or grasp type (active versus passive 0.18 cm 95% CI, −0.19 to 0.55). Overall, grasp‐related perceptions are slightly wider when using all digits, in line with our tendency to grasp larger objects with the entire hand. The other factors – frame of reference, grasp intensity and grasp type – had no meaningful effect on these perceptions. These results provide evidence that the brain maintains a largely stable representation of the hand.
Publisher: Wiley
Date: 17-12-2016
DOI: 10.1113/JP273200
Publisher: American Physiological Society
Date: 03-2018
DOI: 10.1152/JAPPLPHYSIOL.00889.2017
Abstract: The discharge patterns of genioglossus motor units during breathing have been well-characterized in previous studies, but their localization and territories are not known. In this study, we used two newly developed intramuscular multichannel electrodes to estimate the territories of genioglossus motor units in the anterior and posterior regions of the muscle. Seven healthy men participated. Each electrode contained fifteen bipolar channels, separated by 1 mm, and was inserted percutaneously below the chin, perpendicular to the skin, to a depth of 36 mm. Single motor unit activity was recorded with subjects awake, supine, and breathing quietly through a nasal mask for 180 s. Motor unit territories were estimated from the spike-triggered averages of the electromyographic signal from each channel. A total of 30 motor units were identified: 22 expiratory tonic, 1 expiratory phasic, 2 tonic, 3 inspiratory tonic, and 2 inspiratory phasic. Motor units appeared to be clustered based on unit type, with peak activities for expiratory units predominantly located in the anterior and superficial fibers of genioglossus and inspiratory units in the posterior region. Of these motor unit types, expiratory tonic units had the largest estimated territory, a mean 11.3 mm (SD 1.9). Estimated territories of inspiratory motor units ranged from 3 to 6 mm. In accordance with the distribution of motor unit types, the estimated territory of genioglossus motor units varied along the sagittal plane, decreasing from anterior to posterior. Our findings suggest that genioglossus motor units have large territories relative to the cross-sectional size of the muscle. NEW & NOTEWORTHY In this study, we used a new multichannel intramuscular electrode to address a fundamental property of human genioglossus motor units. We describe the territory of genioglossus motor units in the anterior and posterior regions of the muscle and show a decrease in territory size from anterior to posterior and that expiratory-related motor units have larger estimated territories than inspiratory-related motor units.
Publisher: American Physiological Society
Date: 02-2016
Abstract: Motoneurons often fire repetitively and for long periods. In sustained voluntary contractions the excitability of motoneurons declines. We provide the first detailed description of the time course of human motoneuron recovery after sustained activity at a constant discharge rate. We recorded the discharge of single motor units (MUs, n = 30) with intramuscular wire electrodes inserted in triceps brachii during weak isometric contractions. Subjects ( n = 15) discharged single MUs at a constant frequency (∼10 Hz) with visual feedback for prolonged durations (3–7 min) until rectified surface electromyogram (sEMG) of triceps brachii increased by ∼100%. After a rest of 1–2, 15, 30, 60, 120, or 240 s, subjects briefly resumed the contraction with the target MU at the same discharge rate. Each MU was tested with three to four rest periods. The magnitude of sEMG was increased when contractions were resumed, and the target motoneuron discharged at the test frequency following rest intervals of 2–60 s ( P = 0.001–0.038). The increased sEMG indicates that greater excitatory drive was needed to discharge the motoneuron at the test rate. The increase in EMG recovered exponentially with a time constant of 28 s but did not return to baseline even after a rest period of ∼240 s. Thus the decline in motoneuron excitability from a weak contraction takes several minutes to recover fully.
Publisher: Springer Science and Business Media LLC
Date: 07-12-2018
DOI: 10.1038/S41598-018-35895-2
Abstract: We have previously shown that, with the hands apart vertically, passively grasping an artificial finger induces a sense of ownership over the artificial finger and coming-together of the hands. The present study investigated this grasp illusion in the horizontal plane. Thirty healthy participants were tested in two conditions ( grasp and no grasp ) with their hands at different distances apart, either crossed or uncrossed. After 3 min, participants reported perceived spacing between index fingers, perceived index finger location, and, for the grasp condition, perceived ownership over the artificial finger. On average, there was no ownership at any of the hand configurations. With the hands uncrossed 7.5, 15 or 24 cm apart, there was no difference in perceived spacing between the grasp and no grasp conditions. With the hands crossed and 15 cm apart, perceived spacing between index fingers was 3.2 cm [0.7 to 5.7] (mean [95% CI]) smaller during the grasp condition compared to no grasp . Therefore, compared to when the hands are vertically separated, there is an almost complete lack of a g rasp illusion in the horizontal plane which indicates the brain may process sensory inputs from the hands differently based on whether the hands are horizontally or vertically apart.
Publisher: Wiley
Date: 25-04-2018
DOI: 10.1113/JP275527
Publisher: Public Library of Science (PLoS)
Date: 15-02-2019
Publisher: Wiley
Date: 09-06-2017
DOI: 10.1113/JP274579
Publisher: Wiley
Date: 31-03-2016
DOI: 10.1113/JP272017
Publisher: Ubiquity Press, Ltd.
Date: 2023
DOI: 10.5334/TOHM.731
No related grants have been discovered for Martin Héroux.