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Tugin S, Souza VH, Nazarova MA, Novikov PA, Tervo AE, Nieminen JO, Lioumis P, Ziemann U, Nikulin VV, Ilmoniemi RJ. Effect of stimulus orientation and intensity on short-interval intracortical inhibition (SICI) and facilitation (SICF): A multi-channel transcranial magnetic stimulation study. PLoS One 2021; 16:e0257554. [PMID: 34550997 PMCID: PMC8457500 DOI: 10.1371/journal.pone.0257554] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2021] [Accepted: 09/03/2021] [Indexed: 11/18/2022] Open
Abstract
Besides stimulus intensities and interstimulus intervals (ISI), the electric field (E-field) orientation is known to affect both short-interval intracortical inhibition (SICI) and facilitation (SICF) in paired-pulse transcranial magnetic stimulation (TMS). However, it has yet to be established how distinct orientations of the conditioning (CS) and test stimuli (TS) affect the SICI and SICF generation. With the use of a multi-channel TMS transducer that provides electronic control of the stimulus orientation and intensity, we aimed to investigate how changes in the CS and TS orientation affect the strength of SICI and SICF. We hypothesized that the CS orientation would play a major role for SICF than for SICI, whereas the CS intensity would be more critical for SICI than for SICF. In eight healthy subjects, we tested two ISIs (1.5 and 2.7 ms), two CS and TS orientations (anteromedial (AM) and posteromedial (PM)), and four CS intensities (50, 70, 90, and 110% of the resting motor threshold (RMT)). The TS intensity was fixed at 110% RMT. The intensities were adjusted to the corresponding RMT in the AM and PM orientations. SICI and SICF were observed in all tested CS and TS orientations. SICI depended on the CS intensity in a U-shaped manner in any combination of the CS and TS orientations. With 70% and 90% RMT CS intensities, stronger PM-oriented CS induced stronger inhibition than weaker AM-oriented CS. Similar SICF was observed for any CS orientation. Neither SICI nor SICF depended on the TS orientation. We demonstrated that SICI and SICF could be elicited by the CS perpendicular to the TS, which indicates that these stimuli affected either overlapping or strongly connected neuronal populations. We concluded that SICI is primarily sensitive to the CS intensity and that CS intensity adjustment resulted in similar SICF for different CS orientations.
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Affiliation(s)
- Sergei Tugin
- Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, Espoo, Finland
- BioMag Laboratory, University of Helsinki and Helsinki University Hospital, HUS Medical Imaging Centre, Helsinki, Finland
- * E-mail:
| | - Victor H. Souza
- Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, Espoo, Finland
- BioMag Laboratory, University of Helsinki and Helsinki University Hospital, HUS Medical Imaging Centre, Helsinki, Finland
- School of Physiotherapy, Federal University of Juiz de Fora, Juiz de Fora, MG, Brazil
| | - Maria A. Nazarova
- Centre for Cognition and Decision Making, Institute for Cognitive Neuroscience, National Research University Higher School of Economics, Moscow, Russia
- Federal State Budgetary Institution “Federal Center of Brain Research and Neurotechnologies” of the Federal Medical Biological Agency, Moscow, Russia
| | - Pavel A. Novikov
- Centre for Cognition and Decision Making, Institute for Cognitive Neuroscience, National Research University Higher School of Economics, Moscow, Russia
| | - Aino E. Tervo
- Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, Espoo, Finland
- BioMag Laboratory, University of Helsinki and Helsinki University Hospital, HUS Medical Imaging Centre, Helsinki, Finland
| | - Jaakko O. Nieminen
- Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, Espoo, Finland
- BioMag Laboratory, University of Helsinki and Helsinki University Hospital, HUS Medical Imaging Centre, Helsinki, Finland
| | - Pantelis Lioumis
- Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, Espoo, Finland
- BioMag Laboratory, University of Helsinki and Helsinki University Hospital, HUS Medical Imaging Centre, Helsinki, Finland
| | - Ulf Ziemann
- Department of Neurology and Stroke, Eberhard Karls University, Tübingen, Germany
- Hertie Institute for Clinical Brain Research, Eberhard Karls University, Tübingen, Germany
| | - Vadim V. Nikulin
- Centre for Cognition and Decision Making, Institute for Cognitive Neuroscience, National Research University Higher School of Economics, Moscow, Russia
- Department of Neurology, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany
| | - Risto J. Ilmoniemi
- Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, Espoo, Finland
- BioMag Laboratory, University of Helsinki and Helsinki University Hospital, HUS Medical Imaging Centre, Helsinki, Finland
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Turco CV, Nelson AJ. Transcranial Magnetic Stimulation to Assess Exercise-Induced Neuroplasticity. FRONTIERS IN NEUROERGONOMICS 2021; 2:679033. [PMID: 38235229 PMCID: PMC10790852 DOI: 10.3389/fnrgo.2021.679033] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/10/2021] [Accepted: 05/06/2021] [Indexed: 01/19/2024]
Abstract
Aerobic exercise facilitates neuroplasticity and has been linked to improvements in cognitive and motor function. Transcranial magnetic stimulation (TMS) is a non-invasive technique that can be used to quantify changes in neurophysiology induced by exercise. The present review summarizes the single- and paired-pulse TMS paradigms that can be used to probe exercise-induced neuroplasticity, the optimal stimulation parameters and the current understanding of the neurophysiology underlying each paradigm. Further, this review amalgamates previous research exploring the modulation of these paradigms with exercise-induced neuroplasticity in healthy and clinical populations and highlights important considerations for future TMS-exercise research.
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Affiliation(s)
| | - Aimee J. Nelson
- Department of Kinesiology, McMaster University, Hamilton, ON, Canada
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Fisher KM, Baker SN. A Re-evaluation of Whether Non-monosynaptic Homonymous H Reflex Facilitation Tests Propriospinal Circuits. Front Syst Neurosci 2021; 15:641816. [PMID: 33833670 PMCID: PMC8021928 DOI: 10.3389/fnsys.2021.641816] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2020] [Accepted: 03/02/2021] [Indexed: 11/13/2022] Open
Abstract
The C3-C4 propriospinal system is an important pathway mediating movement in cats; it contributes to movements in primates (including humans), and may have a role in recovery after lesion. Validated clinical tests of this system would find many applications, therefore we sought to test whether non-monosynaptic homonymous facilitation of the forearm flexor H reflex is mediated solely via a C3-C4 propriospinal pathway. In one anesthetized macaque monkey, median nerve stimulation elicited an H reflex in the flexor carpi radialis (FCR). Median nerve conditioning stimuli at sub-threshold intensities facilitated the H reflex, for inter-stimulus intervals up to 30 ms. Successive spinal surgical hemisections were then made. C2 lesion left the homonymous facilitation intact, suggesting mediation by spinal, not supraspinal pathways. Facilitation also remained after a second lesion at C5, indicating a major role for segmental (C7-C8) rather than propriospinal (C3-C4) interneurons. In separate experiments in five healthy human subjects, a threshold tracking approach assessed changes in peripheral axon excitability after conditioning stimulation. This was found to be enhanced up to 20 ms after the conditioning stimulus, and could partly, although not completely, underlie the H reflex facilitation seen. We conclude that homonymous facilitation of the H reflex in FCR can be produced by segmental spinal mechanisms, as well as by a supranormal period of nerve excitability. Unfortunately, this straightforward test cannot therefore be used for selective assessment of propriospinal circuits.
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Affiliation(s)
- Karen M Fisher
- Henry Wellcome Building, Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Stuart N Baker
- Henry Wellcome Building, Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
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Howells J, Sangari S, Matamala JM, Kiernan MC, Marchand-Pauvert V, Burke D. Interrogating interneurone function using threshold tracking of the H reflex in healthy subjects and patients with motor neurone disease. Clin Neurophysiol 2020; 131:1986-1996. [PMID: 32336595 DOI: 10.1016/j.clinph.2020.03.028] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2020] [Revised: 02/21/2020] [Accepted: 03/15/2020] [Indexed: 11/18/2022]
Abstract
OBJECTIVE The excitability of the lower motoneurone pool is traditionally tested using the H reflex and a constant-stimulus paradigm, which measures changes in the amplitude of the reflex response. This technique has limitations because reflex responses of different size must involve the recruitment or inhibition of different motoneurones. The threshold-tracking technique ensures that the changes in excitability occur for an identical population of motoneurones. We aimed to assess this technique and then apply it in patients with motor neurone disease (MND). METHODS The threshold-tracking approach was assessed in 17 healthy subjects and 11 patients with MND. The soleus H reflex was conditioned by deep peroneal nerve stimulation producing reciprocal Ia and so-called D1 and D2 inhibitions, which are believed to reflect presynaptic inhibition of soleus Ia afferents. RESULTS Threshold tracking was quicker than the constant-stimulus technique and reliable, properties that may be advantageous for clinical studies. D1 inhibition was significantly reduced in patients with MND. CONCLUSIONS Threshold tracking is useful and may be preferable under some conditions for studying the excitability of the motoneurone pool. The decreased D1 inhibition in the patients suggests that presynaptic inhibition may be reduced in MND. SIGNIFICANCE Reduced presynaptic inhibition could be evidence of an interneuronopathy in MND. It is possible that the hyperreflexia is a spinal pre-motoneuronal disorder, and not definitive evidence of corticospinal involvement in MND.
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Affiliation(s)
- James Howells
- Brain & Mind Centre, The University of Sydney, N.S.W. 2006, Australia
| | - Sina Sangari
- Sorbonne Université, INSERM, CNRS, Laboratoire d'Imagerie Biomédicale, LIB, F-75006 Paris, France
| | - José Manuel Matamala
- Department of Neurological Science and Biomedical Neuroscience Institute, Faculty of Medicine, University of Chile, Santiago, Chile
| | - Matthew C Kiernan
- Brain & Mind Centre, The University of Sydney, N.S.W. 2006, Australia; Department of Neurology, Royal Prince Alfred Hospital and The University of Sydney, N.S.W. 2006, Australia
| | | | - David Burke
- Department of Neurology, Royal Prince Alfred Hospital and The University of Sydney, N.S.W. 2006, Australia.
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Latella C, van der Groen O, Ruas CV, Taylor JL. Effect of fatigue-related group III/IV afferent firing on intracortical inhibition and facilitation in hand muscles. J Appl Physiol (1985) 2019; 128:149-158. [PMID: 31725359 DOI: 10.1152/japplphysiol.00595.2019] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Fatiguing exercise causes a reduction in motor drive to the muscle. Group III/IV muscle afferent firing is thought to contribute to this process; however, the effect on corticospinal and intracortical networks is poorly understood. In two experiments, participants performed sustained maximal isometric finger abductions of the first dorsal interosseous (FDI) muscle, with postexercise blood flow occlusion (OCC) to maintain the firing of group III/IV afferents or without occlusion (control; CON). Before and after exercise, single- and paired-pulse transcranial magnetic stimulation (TMS) tested motor evoked potentials (MEPs), intracortical facilitation [ICF (12 ms)], and short-interval intracortical inhibition [SICI2 (2 ms), SICI3 (3 ms)]. Ulnar nerve stimulation elicited maximal M waves (MMAX). For experiment 1 (n = 16 participants), TMS intensities were 70% and 120% of resting motor threshold (RMT) for the conditioning and MEP stimuli, respectively. For experiment 2 (n = 16 participants), the MEP was maintained at 1 mV before and after exercise and the conditioning stimulus individualized. In experiment 1, MEP/MMAX was reduced after exercise (~48%, P = 0.007) but was not different between conditions. No changes occurred in ICF or SICI. In experiment 2, MEP/MMAX increased (~27%, P = 0.027) and less inhibition (SICI2: ~21%, P = 0.021) occurred after exercise for both conditions, whereas ICF decreased for CON only (~28%, P = 0.006). MEPs and SICI2 were modulated by fatiguing contractions but not by group III/IV afferent firing, whereas sustained afferent firing appeared to counteract postexercise reductions in ICF in FDI. The findings do not support the idea that actions of group III/IV afferents on motor cortical networks contribute to the reduction in voluntary activation observed in other studies.NEW & NOTEWORTHY This is the first study to investigate, in human hand muscles, the action of fatigue-related group III/IV muscle afferent firing on intracortical facilitation and inhibition. In fatigued and nonexercised hand muscles, intracortical inhibition is reduced after exercise but is not modulated differently by the firing of group III/IV afferents. However, facilitation is maintained for the fatigued muscle when group III/IV afferents fire, but these results are unlikely to explain the reduction in voluntary activation observed in other studies.
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Affiliation(s)
- Christopher Latella
- Centre for Exercise and Sports Science Research, School of Medical and Health Sciences, Edith Cowan University, Joondalup, Perth, Western Australia, Australia.,Neurophysiology Research Laboratory, Edith Cowan University, Joondalup, Perth, Western Australia, Australia
| | - Onno van der Groen
- Centre for Exercise and Sports Science Research, School of Medical and Health Sciences, Edith Cowan University, Joondalup, Perth, Western Australia, Australia.,Neurorehabilitation and Robotics Laboratory, Edith Cowan University, Joondalup, Perth, Western Australia, Australia
| | - Cassio V Ruas
- Centre for Exercise and Sports Science Research, School of Medical and Health Sciences, Edith Cowan University, Joondalup, Perth, Western Australia, Australia
| | - Janet L Taylor
- Centre for Exercise and Sports Science Research, School of Medical and Health Sciences, Edith Cowan University, Joondalup, Perth, Western Australia, Australia.,Neurophysiology Research Laboratory, Edith Cowan University, Joondalup, Perth, Western Australia, Australia.,Neuroscience Research Australia, Randwick, New South Wales, Australia
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Contribution of corticospinal drive to ankle plantar flexor muscle activation during gait in adults with cerebral palsy. Exp Brain Res 2019; 237:1457-1467. [PMID: 30900000 DOI: 10.1007/s00221-019-05520-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2018] [Accepted: 03/13/2019] [Indexed: 01/02/2023]
Abstract
Impaired plantar flexor muscle activation during push-off in late stance contributes importantly to reduced gait ability in adults with cerebral palsy (CP). Here we used low-intensity transcranial magnetic stimulation (TMS) to suppress soleus EMG activity during push-off as an estimate of corticospinal drive in CP adults and neurologically intact (NI) adults. Ten CP adults (age 34 years, SD 14.6, GMFCS I-II) and ten NI adults (age 33 years, SD 9.8) walked on a treadmill at their preferred walking speed. TMS of the leg motor cortex was elicited just prior to push-off during gait at intensities below threshold for motor-evoked potentials. Soleus EMG from steps with and without TMS were averaged and compared. Control experiments were performed while standing and in NI adults during gait at slow speed. TMS induced a suppression at a latency of about 40 ms. This suppression was similar in the two populations when differences in control EMG and gait speed were taken into account (CP 18%, NI 16%). The threshold of the suppression was higher in CP adults. The findings suggest that corticospinal drive to ankle plantar flexors at push-off is comparable in CP and NI adults. The higher threshold of the suppression in CP adults may reflect downregulation of cortical inhibition to facilitate corticospinal drive. Interventions aiming to facilitate excitability in cortical networks may contribute to maintain or even improve efficient gait in CP adults.
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Vucic S, van den Bos M, Menon P, Howells J, Dharmadasa T, Kiernan MC. Utility of threshold tracking transcranial magnetic stimulation in ALS. Clin Neurophysiol Pract 2018; 3:164-172. [PMID: 30560220 PMCID: PMC6275211 DOI: 10.1016/j.cnp.2018.10.002] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2018] [Revised: 10/17/2018] [Accepted: 10/29/2018] [Indexed: 12/21/2022] Open
Abstract
Upper motor neuron [UMN] and lower motor neuron [LMN] dysfunction, in the absence of sensory features, is a pathognomonic feature of amyotrophic lateral sclerosis [ALS]. Although the precise mechanisms have yet to be elucidated, one leading hypothesis is that UMN precede LMN dysfunction, which is induced by anterograde glutamatergic excitotoxicity. Transcranial magnetic stimulation (TMS) is a neurophysiological tool that provides a non-invasive and painless assessment of cortical function. Threshold tracking methodologies have been recently adopted for TMS, whereby changes in threshold rather than motor evoked potential (MEP) amplitude serve as outcome measures. This technique is reliable and provides a rapid assessment of cortical function in ALS. Utilisng the threshold tracking TMS technique, cortical hyperexcitability was demonstrated as an early feature in sporadic ALS preceding the onset of LMN dysfunction and possibly contributing to disease spread. Separately, cortical hyperexcitability was reported to precede the clinical onset of familial ALS. Of further relevance, the threshold tracking TMS technique was proven to reliably distinguish ALS from mimicking disorders, even in the presence of a comparable degree of LMN dysfunction, suggesting a diagnostic utility of TMS. Taken in total, threshold tracking TMS has provided support for a cortical involvement at the earliest detectable stages of ALS, underscoring the utility of the technique for probing the underlying pathophysiology. The present review will discuss the physiological processes underlying TMS parameters, while further evaluating the pathophysiological and diagnostic utility of threshold tracking TMS in ALS.
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Affiliation(s)
- Steve Vucic
- Western Clinical School, University of Sydney, Sydney, Australia
| | | | - Parvathi Menon
- Western Clinical School, University of Sydney, Sydney, Australia
| | - James Howells
- Brain and Mind Centre, University of Sydney and Institute of Clinical Neurosciences, Royal Prince Alfred Hospital, Sydney, Australia
| | - Thanuja Dharmadasa
- Brain and Mind Centre, University of Sydney and Institute of Clinical Neurosciences, Royal Prince Alfred Hospital, Sydney, Australia
| | - Matthew C Kiernan
- Brain and Mind Centre, University of Sydney and Institute of Clinical Neurosciences, Royal Prince Alfred Hospital, Sydney, Australia
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I-wave origin and modulation. Brain Stimul 2012; 5:512-25. [DOI: 10.1016/j.brs.2011.07.008] [Citation(s) in RCA: 219] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2011] [Revised: 07/15/2011] [Accepted: 07/21/2011] [Indexed: 12/16/2022] Open
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Long-term effects of repetitive transcranial magnetic stimulation on markers for neuroplasticity: differential outcomes in anesthetized and awake animals. J Neurosci 2011; 31:7521-6. [PMID: 21593336 DOI: 10.1523/jneurosci.6751-10.2011] [Citation(s) in RCA: 196] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Long-term effects of repetitive transcranial magnetic stimulation (rTMS) have been associated with neuroplasticity, but most physiological studies have evaluated only the immediate effects of the stimulation on neurochemical markers. Furthermore, although it is known that baseline excitability state plays a major role in rTMS outcomes, the role of spontaneous neural activity in metaplasticity has not been investigated. The first aim of this study was to evaluate and compare the long-term effects of high- and low-frequency rTMS on the markers of neuroplasticity such as BDNF and GluR1 subunit of AMPA receptor. The second aim was to assess whether these effects depend on spontaneous neural activity, by comparing the neurochemical alterations induced by rTMS in anesthetized and awake rats. Ten daily sessions of high- or low-frequency rTMS were applied over the rat brain, and 3 d later, levels of BDNF, GluR1, and phosphorylated GluR1 were assessed in the hippocampus, prelimbic cortex, and striatum. We found that high-frequency stimulation induced a profound effect on neuroplasticity markers; increasing them in awake animals while decreasing them in anesthetized animals. In contrast, low-frequency stimulation did not induce significant long-term effects on these markers in either state. This study highlights the importance of spontaneous neural activity during rTMS and demonstrates that high-frequency rTMS can induce long-lasting effects on BDNF and GluR1 which may underlie the clinical benefits of this treatment in neuroplasticity-related disorders.
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Pell GS, Roth Y, Zangen A. Modulation of cortical excitability induced by repetitive transcranial magnetic stimulation: Influence of timing and geometrical parameters and underlying mechanisms. Prog Neurobiol 2011; 93:59-98. [DOI: 10.1016/j.pneurobio.2010.10.003] [Citation(s) in RCA: 223] [Impact Index Per Article: 17.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2010] [Revised: 10/14/2010] [Accepted: 10/20/2010] [Indexed: 01/10/2023]
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Caveats when studying motor cortex excitability and the cortical control of movement using transcranial magnetic stimulation. Clin Neurophysiol 2010; 121:121-3. [DOI: 10.1016/j.clinph.2009.10.009] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2009] [Revised: 10/13/2009] [Accepted: 10/14/2009] [Indexed: 11/22/2022]
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McNulty PA, Jankelowitz SK, Wiendels TM, Burke D. Postactivation Depression of the Soleus H Reflex Measured Using Threshold Tracking. J Neurophysiol 2008; 100:3275-84. [PMID: 18922951 DOI: 10.1152/jn.90435.2008] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The interpretation of changes in the soleus H reflex is problematic in the face of reflex gain changes, a nonlinear input/output relationship for the motoneuron pool, and a nonhomogeneous response of different motoneurons to afferent inputs. By altering the stimulus intensity to maintain a constant reflex output, threshold tracking allows a relatively constant population of α-motoneurons to be studied. This approach was used to examine postactivation (“homosynaptic”) depression of the H reflex (HD) in 23 neurologically healthy subjects. The H reflex was elicited by tibial nerve stimulation at 0.05, 0.1, 0.3, 1, and 2 Hz at rest and during voluntary plantar flexion at 2.5, 5, and 10% of maximum. A computerized threshold tracking procedure was used to set the current needed to generate a target H reflex 10% of Mmax. The current needed to produce the target reflex increased with stimulus rate but not significantly beyond 1 Hz. In three subjects, the current needed to produce H reflexes of 5, 10, 15, and 20% Mmax at 0.3, 1, and 2 Hz increased with rate and with the size of the test H reflex. HD was significantly reduced during voluntary contractions. Using threshold tracking, HD was maximal at lower frequencies than previously emphasized, probably because HD is greater the larger the test H reflex. This would reinforce the greater sensitivity of small motoneurons to reflex inputs.
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Berardelli A, Abbruzzese G, Chen R, Orth M, Ridding MC, Stinear C, Suppa A, Trompetto C, Thompson PD. Consensus paper on short-interval intracortical inhibition and other transcranial magnetic stimulation intracortical paradigms in movement disorders. Brain Stimul 2008; 1:183-91. [DOI: 10.1016/j.brs.2008.06.005] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2008] [Accepted: 06/09/2008] [Indexed: 10/21/2022] Open
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Schmied A, Attarian S. Enhancement of single motor unit inhibitory responses to transcranial magnetic stimulation in amyotrophic lateral sclerosis. Exp Brain Res 2008; 189:229-42. [PMID: 18496679 DOI: 10.1007/s00221-008-1420-y] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2007] [Accepted: 05/02/2008] [Indexed: 12/11/2022]
Abstract
In healthy human subjects, transcranial magnetic stimulation (TMS) applied to the motor cortex induces concurrent inhibitory and excitatory effects on motoneurone activity. In amyotrophic lateral sclerosis (ALS), a neurodegenerative disease affecting both cortical and spinal motor neurons, paired-pulse studies based on electromyographic (EMG) recording have revealed a decrease in TMS-induced inhibition. This suggested that inhibition loss may promote excito-toxicity in this disease. Against this hypothesis, an abnormally high incidence of inhibitory responses to TMS has been observed in the peristimulus time histograms (PSTHs) in ALS single motor unit studies. The disappearance of cortico-motoneuronal excitatory inputs might, however, have facilitated the detection of single motor unit inhibitory responses in the PSTHs. This question was addressed here using a new approach, where the strength of the excitatory and inhibitory effects of TMS on motoneurone activity was assessed from the duration of inter-spike intervals (ISIs). This analysis was conducted on single motor unit (MU), tested on healthy subjects and patients with ALS or Kennedy's disease (KD), a motor neuron disease which unlike ALS, spares the cortico-spinal pathway. MUs tested on KD patients behaved like those of healthy subjects unlike those tested on ALS patients. The present data reveal that in ALS, the TMS-induced inhibitory effects are truly enhanced during voluntary contractions and not reduced, as observed in paired-pulse TMS studies under resting conditions. The possible contribution of inhibitory loss to the physiopathology of ALS therefore needs to be reconsidered. The present data do not support the idea that inhibition loss may underlie excito-toxicity in ALS.
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Affiliation(s)
- Annie Schmied
- Plasticity and Physiopathology of Movement, P3M, UMR 6196, CNRS, University Aix-Marseilles II, 31 Chemin Joseph Aiguier, 13402 Marseilles Cedex 20, France.
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Chen R, Cros D, Curra A, Di Lazzaro V, Lefaucheur JP, Magistris MR, Mills K, Rösler KM, Triggs WJ, Ugawa Y, Ziemann U. The clinical diagnostic utility of transcranial magnetic stimulation: Report of an IFCN committee. Clin Neurophysiol 2008; 119:504-532. [DOI: 10.1016/j.clinph.2007.10.014] [Citation(s) in RCA: 348] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2007] [Revised: 10/12/2007] [Accepted: 10/18/2007] [Indexed: 12/11/2022]
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Bastiaanse CM, Degen S, Baken BCM, Dietz V, Duysens J. Suppression of cutaneous reflexes by a conditioning pulse during human walking. Exp Brain Res 2006; 172:67-76. [PMID: 16429270 DOI: 10.1007/s00221-005-0305-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2005] [Accepted: 11/09/2005] [Indexed: 10/25/2022]
Abstract
There are two ways in which responses to successive unexpected stimuli are attenuated, namely through habituation and conditioning. For the latter, it suffices that the unexpected stimulus is preceded by another just perceivable stimulus. In spinal cord reflexes this is termed conditioning, while in brainstem reflexes this is usually referred to as prepulse inhibition. Cutaneous reflexes in Tibialis Anterior (TA) are particularly strong during gait and they are thought to involve a transcortical loop. Can these reflexes be suppressed by giving a brief pulse prior to a reflex-evoking pulse given to the same nerve? To examine this question, electromyographic signals were recorded in healthy humans during walking. Sural nerve stimulation (train of five pulses (1 ms duration)) at 200 Hz were applied at two times perception threshold during different phases of the step cycle. The preceding pulse (single pulse of 1 ms at same intensity) was applied to the same nerve 150 ms before the reflex-evoking pulse train. Conditioning stimulation with a single pulse lowered significantly the following reflex response in the ipsilateral TA but much less in other muscles such as biceps femoris. The preceding pulse did not disturb the phase-dependent modulation or the typical reflex reversal. The finding that TA is selectively involved indicates that the suppressing mechanism may involve the motor cortex, which is known to be involved in the control of TA. The conditioning pulse did not cause a reduction in background activity. Therefore, the suppression of the reflex responses points to a premotoneuronal source such as presynaptic inhibition.
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Affiliation(s)
- C M Bastiaanse
- Department of Rehabilitation Medicine, Radboud University Nijmegen Medical Center, P.O. Box 9101, 6500 Nijmegen, HB, The Netherlands
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Moliadze V, Giannikopoulos D, Eysel UT, Funke K. Paired-pulse transcranial magnetic stimulation protocol applied to visual cortex of anaesthetized cat: effects on visually evoked single-unit activity. J Physiol 2005; 566:955-65. [PMID: 15919717 PMCID: PMC1464771 DOI: 10.1113/jphysiol.2005.086090] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
In this study, we tested the paired-pulse transcranial magnetic stimulation (ppTMS) protocol - a conditioning stimulus (CS) given at variable intervals prior to a test stimulus (TS) - for visually evoked single-unit activity in cat primary visual cortex. We defined the TS as being supra-threshold when it caused a significant increase or decrease in the visually evoked activity. By systematically varying the interstimulus interval (ISI) between 2 and 30 ms and the strength of CS within the range 15-130% of TS, we found a clear dependence of the ppTMS effect on CS strength but little relation to ISI. The CS effect was strongest with an ISI of 3 ms and steadily declined for longer ISIs. A switch from enhancement of intracortical inhibition at short ISIs (2-5 ms, SICI) to intracortical facilitation (ICF) at longer ISIs (7-30 ms), as demonstrated for human motor cortex, was not evident. Whether the CS caused facilitation or suppression of the TS effect mainly depended on the strength of CS and the polarity of the TS effect: within a range of 60-130% a positive correlation between ppTMS and TS effect was evident, resulting in a stronger facilitation if the TS caused facilitation of visual activity, and more suppression if the TS was suppressive by itself. The correlation inverted when CS was reduced to 15-30%. The ppTMS effect was not simply the sum of the CS and TS effect, it was much smaller at weak CS strength (15-50%) but stronger than the sum of CS and TS effects at CS strength 60-100%. Differences in the physiological state between sensory and motor cortices and the interactions of paired synaptic inputs are discussed as possible reasons for the partly different effects of ppTMS in cat visual cortex and human motor cortex.
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Affiliation(s)
- Vera Moliadze
- Department of Neurophysiology, Medical Faculty, Ruhr-University Bochum, 44780 Bochum, Germany
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Bostock H, Lin CSY, Howells J, Trevillion L, Jankelowitz S, Burke D. After-effects of near-threshold stimulation in single human motor axons. J Physiol 2005; 564:931-40. [PMID: 15746167 PMCID: PMC1464467 DOI: 10.1113/jphysiol.2005.083394] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Subthreshold electrical stimuli can generate a long-lasting increase in axonal excitability, superficially resembling the phase of superexcitability that follows a conditioning nerve impulse. This phenomenon of 'subthreshold superexcitability' has been investigated in single motor axons in six healthy human subjects, by tracking the excitability changes produced by conditioning stimuli of different amplitudes and waveforms. Near-threshold 1 ms stimuli caused a mean decrease in threshold at 5 ms of 22.1 +/- 6.0% (mean +/-s.d.) if excitation occurred, or 6.9 +/- 2.6% if excitation did not occur. The subthreshold superexcitability was maximal at an interval of about 5 ms, and fell to zero at 30 ms. It appeared to be made up of two components: a passive component linearly related to conditioning stimulus amplitude, and a non-linear active component. The active component appeared when conditioning stimuli exceeded 60% of threshold, and accounted for a maximal threshold decrease of 2.6 +/- 1.3%. The passive component was directly proportional to stimulus charge, when conditioning stimulus duration was varied between 0.2 and 2 ms, and could be eliminated by using triphasic stimuli with zero net charge. This change in stimulus waveform had little effect on the active component of subthreshold superexcitability or on the 'suprathreshold superexcitability' that followed excitation. It is concluded that subthreshold superexcitability in human motor axons is mainly due to the passive electrotonic effects of the stimulating current, but this is supplemented by an active component (about 12% of suprathreshold superexcitability), due to a local response of voltage-dependent sodium channels.
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Affiliation(s)
- Hugh Bostock
- Sobell Department of Neurophysiology, Institute of Neurology, Queen Square, London WC1N 3BG, UK.
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Novak K, de Camargo AB, Neuwirth M, Kothbauer K, Amassian VE, Deletis V. The refractory period of fast conducting corticospinal tract axons in man and its implications for intraoperative monitoring of motor evoked potentials. Clin Neurophysiol 2004; 115:1931-41. [PMID: 15261873 DOI: 10.1016/j.clinph.2004.03.016] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/17/2004] [Indexed: 11/29/2022]
Abstract
OBJECTIVE To determine the absolute and relative refractory period (RRP) of fast conducting axons of the corticospinal tract in response to paired high intensity (HI or supramaximal) and moderate intensity (MI or submaximal) electrical stimuli. The importance of the refractory period of fast conducting corticospinal tract axons has to be considered if repetitive transcranial electrical stimulation (TES) is to be effective for eliciting motor evoked potentials (MEPs) intraoperatively. METHODS Direct (D) waves were recorded from the epidural space of the spinal cord in 14 patients, undergoing surgical correction of spinal deformities. To assess the absolute and RRPs of the corticospinal tract, paired transcranial electrical stimuli at interstimulus intervals (ISI) from 0.7 to 4.1 ms were applied. Recovery of conditioned D wave at short (2 ms) and long (4 ms) ISI was correlated with muscle MEP threshold. The refractory period for peripheral nerve was tested in comparison to that for the corticospinal tract. In four healthy subjects sensory nerve action potentials of the median nerve were studied after stimulation with paired stimuli. RESULTS HI TES revealed a mean duration of 0.82 ms for the absolute refractory period of the corticospinal tract, while MI stimulation resulted in a mean refractory period duration of 1.47 ms. Stimuli of HI produced faster recovery of D wave amplitude during the RRP. Furthermore, short trains of transcranial electrical stimuli did not elicit MEPs when D wave showed incomplete recovery. A similar influence of stimulus intensity on recovery time was found for the refractory period of peripheral nerve. CONCLUSIONS The recovery of D wave amplitude is dependent upon stimulus intensity. High intensity produces fast recovery. This is an important factor for the generation of MEPs. When HI TES is used to elicit MEPs, short and long ISIs are equally effective. When MI TES is used to elicit MEPs, only a long ISI of 4 ms is effective.
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Affiliation(s)
- Klaus Novak
- Institute for Neurology and Neurosurgery, Beth Israel Medical Center-Singer Division, 170 East End Avenue, Room 311, New York, NY 10128, USA
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20
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Chen R. Interactions between inhibitory and excitatory circuits in the human motor cortex. Exp Brain Res 2003; 154:1-10. [PMID: 14579004 DOI: 10.1007/s00221-003-1684-1] [Citation(s) in RCA: 351] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2003] [Accepted: 07/15/2003] [Indexed: 12/13/2022]
Abstract
Cortical activity depends on the balance between excitatory and inhibitory influences. Several different excitatory and inhibitory systems in the human motor cortex can be tested by transcranial magnetic stimulation (TMS). While considerable information is known about these different inhibitory and excitatory phenomena individually, how they are related to each other and how they interact is not well understood. Several recent studies have investigated the interactions between some of these circuits by applying them together. It has been found that short-interval intracortical inhibition (SICI) and long-interval intracortical inhibition (LICI) are mediated by different circuits. LICI appears to inhibit SICI, which may occur through presynaptic GABA(B) receptors. Interhemispheric inhibition elicited by stimulation of the contralateral motor cortex also inhibits SICI and may share inhibitory mechanisms with LICI. Long-interval afferent inhibition induced by median nerve stimulation inhibits LICI but does not interact with SICI. Based on these results, a model of interactions between different inhibitory systems that can be tested and refined in the future is proposed. Further studies of the interaction between different cortical inhibitory and excitatory circuits should improve our understanding of the functional organization of the motor cortex and allow better interpretation of abnormal findings in disease states. It may also be developed into a new way of studying the pathophysiology of diseases and the effects of intervention.
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Affiliation(s)
- Robert Chen
- Division of Neurology and Krembil Neuroscience Centre, Toronto Western Research Institute, University Health Network, University of Toronto, Ontario, Canada.
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Baret M, Katz R, Lamy JC, Pénicaud A, Wargon I. Evidence for recurrent inhibition of reciprocal inhibition from soleus to tibialis anterior in man. Exp Brain Res 2003; 152:133-6. [PMID: 12898091 DOI: 10.1007/s00221-003-1547-9] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2003] [Accepted: 04/30/2003] [Indexed: 12/01/2022]
Abstract
Reciprocal inhibition between ankle flexors and extensors has been the subject of numerous studies in Man. They have demonstrated that this reciprocal inhibition is in all likelihood caused by a disynaptic pathway at least partly fed by Ia afferents. It is thus generally agreed that this reciprocally organized inhibition between ankle flexors and extensors in Man is similar to the reciprocal Ia inhibition described in the cat. This conclusion has, however, been challenged, when Jankowska and McCrea described in the cat a non-reciprocal group I inhibition involving interneurones co-excited by Ia and Ib afferents and mediating inhibition to both antagonistic and non-antagonistic motoneurones. The only way to distinguish between reciprocal Ia inhibition and non-reciprocal group I inhibition is to test if the inhibition is blocked by recurrent inhibition, since only Ia interneurones are inhibited by recurrent inhibition. In the present study, reciprocal inhibition from soleus to tibialis anterior was thus investigated following activation of soleus-coupled Renshaw cells in normal human subjects. It was found that reciprocal inhibition induced in tibialis anterior motoneurones by the activation of soleus group I afferents is deeply depressed by activation of soleus-coupled Renshaw cells. This finding provides the missing data to identify disynaptic inhibition between antagonistic ankle muscles as a reciprocal Ia inhibition.
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Affiliation(s)
- M Baret
- E03 49 INSERM, Service de Médecine Physique et Réadaptation, Hôpital La Salpêtrière, 75651 Paris cedex 13, France
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Roshan L, Paradiso GO, Chen R. Two phases of short-interval intracortical inhibition. Exp Brain Res 2003; 151:330-7. [PMID: 12802553 DOI: 10.1007/s00221-003-1502-9] [Citation(s) in RCA: 175] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2003] [Accepted: 04/16/2003] [Indexed: 10/26/2022]
Abstract
Short-interval intracortical inhibition (SICI) is a widely used method to study cortical inhibition, and abnormalities have been found in several neurological and psychiatric disorders. Previous studies suggested that SICI involves two phases and the first phase may be explained by axonal refractoriness. Our objectives are to further investigate the mechanisms of the two phases of SICI. SICI was studied in 11 normal volunteers by a paired transcranial magnetic stimulation (TMS) paradigm applied to the left motor cortex with a subthreshold conditioning stimulus (80% resting motor threshold for rest condition and 95% active motor threshold for active condition) followed by a suprathreshold test stimulus at interstimulus intervals (ISIs) of 1-4.5 ms in steps of 0.5 ms. Motor-evoked potentials (MEPs) were recorded from the right first dorsal interosseous muscle. Three different test stimulus intensities adjusted to produce 0.2, 1 and 4 mV MEPs at rest were studied with the target muscle relaxed and during 20% maximum contraction. Maximum inhibition was observed at ISIs of 1 ms and 2.5 ms for the rest condition and the difference among ISIs was reduced with voluntary contraction. SICI increased with larger test MEP amplitude and decreased with voluntary contraction. At test MEP of 0.2 mV, some subjects showed facilitation and this is likely related to short-interval intracortical facilitation. For rest SICI, the correlation between adjacent ISIs was much higher from 3 to 4.5 ms than from 1 to 2.5 ms or between 1 and 2.5 ms. There was no correlation between SICI at different test MEP amplitudes. We conclude that maximum SICI at ISIs of 1 and 2.5 ms are mediated by different mechanisms. SICI at 1 ms cannot be fully explained by axonal refractoriness and synaptic inhibition may be involved. SICI is a complex phenomenon and inhibition at different ISIs may be mediated by different inhibitory circuits.
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Affiliation(s)
- Lailoma Roshan
- Division of Neurology and Krembil Neuroscience Centre, Toronto Western Research Institute, University Health Network, University of Toronto, 5W-445, 399 Bathurst Street, Toronto, Ontario, M5T 2S8, Canada
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Di Lazzaro V, Oliviero A, Tonali PA, Mazzone P, Insola A, Pilato F, Saturno E, Dileone M, Rothwell JC. Direct demonstration of reduction of the output of the human motor cortex induced by a fatiguing muscle contraction. Exp Brain Res 2003; 149:535-8. [PMID: 12677336 DOI: 10.1007/s00221-003-1408-6] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2002] [Accepted: 02/03/2003] [Indexed: 10/20/2022]
Abstract
A brief period of strong muscle contraction suppresses the amplitude of EMG responses evoked in relaxed muscle by transcranial magnetic stimulation (TMS) of the contralateral motor cortex. Here we investigate this phenomenon in more detail by recording the descending motor volleys evoked by TMS from electrodes in the cervical epidural space of three conscious patients implanted with chronic electrical stimulators for control of pain. We confirm that fatigue suppresses I waves evoked by TMS. In addition, D waves were suppressed in two of the patients, suggesting that axonal excitability might also be compromised by a period of intense muscle contraction.
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Affiliation(s)
- V Di Lazzaro
- Institute of Neurology, Università Cattolica, L go A Gemelli 8, 00168 Rome, Italy.
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Awiszus F. Chapter 2 TMS and threshold hunting. TRANSCRANIAL MAGNETIC STIMULATION AND TRANSCRANIAL DIRECT CURRENT STIMULATION, PROCEEDINGS OF THE 2ND INTERNATIONAL TRANSCRANIAL MAGNETIC STIMULATION (TMS) AND TRANSCRANIAL DIRECT CURRENT STIMULATION (TDCS) SYMPOSIUM 2003; 56:13-23. [PMID: 14677378 DOI: 10.1016/s1567-424x(09)70205-3] [Citation(s) in RCA: 273] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Affiliation(s)
- Friedemann Awiszus
- Neuromuscular Research Group, Department of Orthopaedics, Otto-von-Guericke Universität, D-39120 Magdeburg, Germany.
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Lin CSY, Chan JHL, Pierrot-Deseilligny E, Burke D. Excitability of human muscle afferents studied using threshold tracking of the H reflex. J Physiol 2002; 545:661-9. [PMID: 12456841 PMCID: PMC2290676 DOI: 10.1113/jphysiol.2002.026526] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
In human peripheral nerves, physiological evidence has been presented for a number of biophysical differences between cutaneous afferents and alpha motor axons. The differences in strength-duration properties for cutaneous afferents and motor axons in the median nerve have been attributed to greater expression of a persistent Na(+) conductance (I(Na,P)) on cutaneous afferents. However, it is unclear whether the biophysical properties of human group Ia afferents differ from those of cutaneous afferents. The present studies were undertaken to determine whether the properties of human group Ia afferents can be studied indirectly using 'threshold tracking' to measure the excitability changes in the H reflex, and to determine whether the excitability of group Ia afferents differs from that of cutaneous afferents. The strength-duration properties of the soleus H reflex and soleus motor axons were measured at rest and during sustained voluntary contractions. Similar experiments were performed on the median nerve at the wrist to study the strength-duration properties of cutaneous afferents, alpha motor axons and H reflex of the thenar muscles. In addition, the technique of 'latent addition' was used to determine whether there was a difference in a low-threshold conductance on soleus Ia afferent and motor axons. The present findings indicate that the strength-duration time constant (tau(SD)) for the H reflex is longer than that for alpha motor axons, but similar to that for cutaneous afferents. There were no differences in tau(SD) for the soleus H reflex at rest and during contractions, suggesting that tau(SD) for the H reflex is largely unaffected by changes in synaptic or motoneurone properties. Finally, the difference in latent addition suggests that the longer tau(SD) of the soleus H reflex may indeed be due to greater activity of a persistent Na(+) conductance on Ia afferents than on soleus alpha motor axons.
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Affiliation(s)
- Cindy S-Y Lin
- Prince of Wales Medical Research Institute, University of New South Wales, and College of Health Sciences, University of Sydney, Sydney, Australia
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