Assoc Prof Janet Taylor

TEAM LEADER PROFILE

Principal Research Fellow, NHMRC Conjoint Senior Lecturer, UNSW
Honorary Senior Lecturer, USyd

+612 9399 1716


Janet Taylor (MBBS, MBiomedE, MD) received her doctorate for research in neurophysiology from the University of New South Wales in 1991 and was a postdoctoral fellow at the University of Alberta, Edmonton and at NeuRA for Neurology, Queens Square, London. She has been at NeuRA since 1993. Her interests include proprioception, which includes the sensations related to position, movement and forces produced by or imposed on the body, and the neural control of human movement, particularly during muscle fatigue. She is currently Chair of Commission I: Locomotion for the International Union of Physiological Sciences.

Projects Assoc Prof Janet Taylor is currently involved with

CURRENT PROJECTS

Investigations into the firing behaviour of human motoneurones in health and after neurological inju

This basic science project aims to examine the behaviour of human motoneurones during sustained activation to reveal their mechanisms of recovery after activation. We will take the fundamental findings from this study and compare the behaviour of motoneurones innervating muscles affected by neurological injury such as spinal cord injury and stroke.

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Investigations into the firing behaviour of human motoneurones in health and after neurological injury

Understanding the effects of sleep disruption in people with Multiple Sclerosis

Investigating the role that sleep disruption plays in people with Multiple Sclerosis

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Understanding the effects of sleep disruption in people with Multiple Sclerosis

Stimulation-induced plasticity in the motor pathway in the spinal cord

For people who do not have a complete loss of the pathway, the spinal end of the corticospinal pathway is another potential site for improvement.

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Stimulation-induced plasticity in the motor pathway in the spinal cord

Plasticity in the motor pathway in the spinal cord in muscle training

We propose that training for muscle strength by performing repeated strong voluntary contractions can increase the strength of the connections between the corticospinal cells and the motoneurones.

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Plasticity in the motor pathway in the spinal cord in muscle training

Role of the nervous system in muscle fatigue in humans

Current studies in healthy volunteers are investigating processes that affect the motoneurones in the spinal cord. These are the nerve cells that receive signals from the brain and then drive the muscles. During voluntary muscle activity, the motoneurones fire repeatedly and this firing controls the timing and strength of muscle contractions. If the firing of motoneurones is impeded then this contributes to fatigue.

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Role of the nervous system in muscle fatigue in humans

RESEARCH TEAM

David Kennedy

DAVID KENNEDY Research Assistant

Siobhan Fitzpatrick

SIOBHAN DONGÉS Postdoctoral Fellow

James Nuzzo

JIM NUZZO PhD student

Jack Brooks

JACK BROOKS PhD student

Matt Jones

MATTHEW JONES PhD student

Jessica D'Amico

DR JESSICA D’AMICO Research Officer

Harry Finn

HARRISON FINN PhD student

PUBLICATIONS

Time course of human motoneuron recovery after sustained low-level voluntary activity.

Héroux ME, Butler AA, Gandevia SC, Taylor JL, Butler JE

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.

Arm posture-dependent changes in corticospinal excitability are largely spinal in origin.

Nuzzo JL, Trajano GS, Barry BK, Gandevia SC, Taylor JL

Biceps brachii motor evoked potentials (MEPs) from cortical stimulation are influenced by arm posture. We used subcortical stimulation of corticospinal axons to determine whether this postural effect is spinal in origin. While seated at rest, 12 subjects assumed several static arm postures, which varied in upper-arm (shoulder flexed, shoulder abducted, arm hanging to side) and forearm orientation (pronated, neutral, supinated). Transcranial magnetic stimulation over the contralateral motor cortex elicited MEPs in resting biceps and triceps brachii, and electrical stimulation of corticospinal tract axons at the cervicomedullary junction elicited cervicomedullary motor evoked potentials (CMEPs). MEPs and CMEPs were normalized to the maximal compound muscle action potential (Mmax). Responses in biceps were influenced by upper-arm and forearm orientation. For upper-arm orientation, biceps CMEPs were 68% smaller (P= 0.001), and biceps MEPs 31% smaller (P= 0.012), with the arm hanging to the side compared with when the shoulder was flexed. For forearm orientation, both biceps CMEPs and MEPs were 34% smaller (bothP< 0.046) in pronation compared with supination. Responses in triceps were influenced by upper-arm, but not forearm, orientation. Triceps CMEPs were 46% smaller (P= 0.007) with the arm hanging to the side compared with when the shoulder was flexed. Triceps MEPs and biceps and triceps MEP/CMEP ratios were unaffected by arm posture. The novel finding is that arm posture-dependent changes in corticospinal excitability in humans are largely spinal in origin. An interplay of multiple reflex inputs to motoneurons likely explains the results.

Neural Contributions to Muscle Fatigue: From the Brain to the Muscle and Back Again.

Taylor JL, Amann M, Duchateau J, Meeusen R, Rice CL
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