H. Tsao

Publications (5)9.46 Total impact

• Article: Reorganization of the motor cortex is associated with postural control deficits in recurrent low back pain.

  H Tsao, M P Galea, P W Hodges
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  ABSTRACT: Many people with recurrent low back pain (LBP) have deficits in postural control of the trunk muscles and this may contribute to the recurrence of pain episodes. However, the neural changes that underlie these motor deficits remain unclear. As the motor cortex contributes to control of postural adjustments, the current study investigated the excitability and organization of the motor cortical inputs to the trunk muscles in 11 individuals with and without recurrent LBP. EMG activity of the deep abdominal muscle, transversus abdominis (TrA), was recorded bilaterally using intramuscular fine-wire electrodes. Postural control was assessed as onset of TrA EMG during single rapid arm flexion and extension tasks. Motor thresholds (MTs) for transcranial magnetic stimulation (TMS) were determined for responses contralateral and ipsilateral to the stimulated cortex. In addition, responses of TrA to TMS over the contralateral cortex were mapped during voluntary contractions at 10% of maximum. MTs and map parameters [centre of gravity (CoG) and volume] were compared between healthy and LBP groups. The CoG of the motor cortical map of TrA in the healthy group was approximately 2 cm anterior and lateral to the vertex, but was more posterior and lateral in the LBP group. The location of the CoG and the map volume were correlated with onset of TrA EMG during rapid arm movements. Furthermore, the MT needed to evoke ipsilateral responses was lower in the LBP group, but only on the less excitable hemisphere. These findings provide preliminary evidence of reorganization of trunk muscle representation at the motor cortex in individuals with recurrent LBP, and suggest this reorganization is associated with deficits in postural control.
  Brain 09/2008; 131(Pt 8):2161-71. · 9.46 Impact Factor
• Article: How fast are feedforward postural adjustments of the abdominal muscles?

  H. Tsao, M. P. Galea, Paul Hodges
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  ABSTRACT: Abdominal muscles can be activated during rapid but complex motor responses known as feedforward postural adjustments. Exactly how the latency of feedforward adjustments compares with other responses of varying levels of voluntary input and motoneurone excitability remains unclear. Surface electrodes were placed bilaterally over abdominal muscles and over right anterior deltoid (AD) and orbicularis oculi (OO) muscles in eight healthy volunteers. Latencies were obtained during feedforward postural adjustment, acoustic startle reflex, and voluntary activation (respiratory and nonrespiratory) to soft and startling acoustic stimuli. Results showed voluntary activation was fastest for respiratory tasks during mid- or end-expiration. Voluntary activation was also faster when triggered by startling stimuli compared with soft stimuli. These responses were slower than feedforward postural adjustments in all subjects. Feedforward adjustments were slower than acoustic startle reflexes but were somewhat flexible as their amplitude depended on amplitude of AD activation and therefore matched parameters of the movement task. The latency for feedforward postural adjustments of abdominal muscles suggests organization at a low level of the nervous system with limited central processing to match postural responses to movement demands. Copyright (c) 2009 APA, all rights reserved. PMID: 19485575 [PubMed - indexed for MEDLINE]
• Article: Reorganization of the motor cortex is associated with postural control deficits in recurrent low back pain

  H Tsao, MP Galea, PW Hodges
  [show abstract] [hide abstract]
  ABSTRACT: Many people with recurrent low back pain (LBP) have deficits in postural control of the trunk muscles and this may contribute to the recurrence of pain episodes. However, the neural changes that underlie these motor deficits remain unclear. As the motor cortex contributes to control of postural adjustments, the current study investigated the excitability and organization of the motor cortical inputs to the trunk muscles in 11 individuals with and without recurrent LBP. EMG activity of the deep abdominal muscle, transversus abdominis (TrA), was recorded bilaterally using intramuscular fine-wire electrodes. Postural control was assessed as onset of TrA EMG during single rapid arm flexion and extension tasks. Motor thresholds (MTs) for transcranial magnetic stimulation (TMS) were determined for responses contralateral and ipsilateral to the stimulated cortex. In addition, responses of TrA to TMS over the contralateral cortex were mapped during voluntary contractions at 10% of maximum. MTs and map parameters [centre of gravity (CoG) and volume] were compared between healthy and LBP groups. The CoG of the motor cortical map of TrA in the healthy group was ~2 cm anterior and lateral to the vertex, but was more posterior and lateral in the LBP group. The location of the CoG and the map volume were correlated with onset of TrA EMG during rapid arm movements. Furthermore, the MT needed to evoke ipsilateral responses was lower in the LBP group, but only on the less excitable hemisphere. These findings provide preliminary evidence of reorganization of trunk muscle representation at the motor cortex in individuals with recurrent LBP, and suggest this reorganization is associated with deficits in postural control.
• Article: Reorganisation of the motor cortex is associated with postural control deficits in recurrent low back pain

  H. Tsao, M. P. Galea, P. W. Hodges
  [show abstract] [hide abstract]
  ABSTRACT: Many people with recurrent low back pain (LBP) have deficits in postural control of the trunk muscles and this may contribute to the recurrence of pain episodes. However, the neural changes that underlie these motor deficits remain unclear. As the motor cortex contributes to control of postural adjustments, the current study investigated the excitability and organization of the motor cortical inputs to the trunk muscles in 11 individuals with and without recurrent LBP. EMG activity of the deep abdominal muscle, transversus abdominis (TrA), was recorded bilaterally using intramuscular fine-wire electrodes. Postural control was assessed as onset of TrA EMG during single rapid arm flexion and extension tasks. Motor thresholds (MTs) for transcranial magnetic stimulation (TMS) were determined for responses contralateral and ipsilateral to the stimulated cortex. In addition, responses of TrAtoTMS over the contralateral cortex were mapped during voluntary contractions at 10% ofmaximum.MTs andmap parameters [centre of gravity (CoG) and volume] were compared between healthy and LBP groups.The CoG of themotor corticalmap of TrA in the healthy group was »2 cmanterior and lateral to the vertex, but wasmore posterior and lateral in the LBP group.The location of the CoG and themap volume were correlated with onset of TrA EMG during rapid armmovements. Furthermore, the MT needed to evoke ipsilateral responses was lower in the LBP group, but only on the less excitable hemisphere.These findings provide preliminary evidence of reorganization of trunk muscle representation at the motor cortex in individuals with recurrent LBP, and suggest this reorganization is associated with deficits in postural control.
• Article: Bilateral activation of the abdominal muscles induces longer reaction time

  H. Tsao, M. Overs, J. Wu, M. P. Galea, P. W. Hodges
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  ABSTRACT: Objective: Bilateral deficit is the increase in reaction time during bilateral activation compared to unilateral activation. This has been reported extensively for the limb muscles and is argued to be due to concurrent inhibition through transcallosal pathways. Unlike the limb muscles, the axial muscles are commonly activated bilaterally during functional tasks and have bilateral projections to their motoneurones. Thus it is reasonable to hypothesise that there will be no bilateral deficit for these muscles. Methods: Recordings of electromyographic (EMG) activity were made using surface electrodes placed bilaterally over the abdominal muscles in eight healthy right-handed subjects. Subjects performed either right or left pelvic elevation (unilateral abdominal activation), or posterior pelvic tilt (bilateral abdominal activation) “as fast as possible” in response to an auditory tone. Movements were performed as either a simple or choice reaction time task. Results: Bilateral activation induced significantly longer reaction time than unilateral activation, and was observed during both simple and choice reaction time tasks. Conclusions: The results demonstrate that reaction time is delayed during bilateral activation of the abdominal muscles. Significance: These findings suggest that bilateral deficit is present for the axial muscles. This could be mediated through inhibition at various levels of the nervous system or variations in postural demand.