Intracortical Inhibition Assessed with Paired-Pulse Transcranial Magnetic Stimulation is Modulated during Shortening and Lengthening Contractions in Young and Old Adults

Paired-pulse transcranial magnetic stimulation (ppTMS) is a noninvasive method to measure cortical inhibition in vivo. Long interpulse interval (50–500 ms) ppTMS (LI-ppTMS) provokes intracortical inhibitory circuits and can reveal pathologically impaired cortical inhibition in disorders such as epilepsy. Adaptation of ppTMS protocols to rodent disease models is highly desirable to facilitate basic and translational research. We previously adapted single-pulse TMS (spTMS) methods to rats, but ppTMS has yet to be applied. Specifically, whether ppTMS elicits an inhibitory response in rodents is unknown. ppTMS in rats also requires anesthesia, a setting under which the preservation of these measures is undetermined. We therefore tested, in anesthetized rats, whether anesthetic choice affects spTMS-motor-evoked potentials (MEPs), LI-ppTMS in rats, as in humans, elicits intracortical inhibition of the MEP, and rat LI-ppTMS inhibition is acutely impaired in a seizure model. Rats were anesthetized with pentobarbital (PB) or ketamine-atropine-xylazine (KAX) and stimulated unilaterally over the motor cortex while recording bilateral brachioradialis MEPs. LI-ppTMS was applied analogous to human long interval intracortical inhibition (LICI) protocols, and acute changes in inhibition were evaluated following injection of the convulsant pentylenetetrazole (PTZ). We find that spTMS-evoked MEPs were reliably present under either anesthetic, and that LI-ppTMS elicits inhibition of the conditioned MEP in rats, similar to human LICI, by as much as 58 ± 12 and 71 ± 11% under PB and KAX anesthesia, respectively. LI-ppTMS inhibition was reduced to as much as 53% of saline controls following PTZ injection, while spTMS-derived measures of corticospinal excitability were unchanged. Our data show that regional inhibition, similar to human LICI, is present in rats, can be elicited under PB or KAX anesthesia, and is reduced following convulsant administration. These results suggest a potential for LI-ppTMS as a biomarker of impaired cortical inhibition in murine disease models.

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Agreement Between Investigators Using Paired-Pulse Transcranial Magnetic Stimulation to Assess Quadriceps Intracortical Excitability

Journal of Sport Rehabilitation ◽

10.1123/jsr.2015-0121 ◽

2016 ◽

Vol 25 (4) ◽

Cited By ~ 5

Author(s):

Abbey C. Thomas ◽

Brian G. Pietrosimone ◽

Carter J. Bayer

Keyword(s):

Transcranial Magnetic Stimulation ◽

Magnetic Stimulation ◽

Intracortical Inhibition ◽

Interrater Agreement ◽

Active Muscle ◽

Intracortical Facilitation ◽

Reliability Study ◽

Maximal Voluntary Isometric Contraction ◽

Paired Pulse ◽

Intracortical Excitability

Context: Transcranial magnetic stimulation (TMS) may provide important information regarding the corticospinal mechanisms that may contribute to the neuromuscular activation impairments. Paired-pulse TMS testing is a reliable method for measuring intracortical facilitation and inhibition; however, little evidence exists regarding agreement of these measures in the quadriceps. Objective: To determine the between-sessions and interrater agreement of intracortical excitability (short- and long-interval intracortical inhibition [SICI, LICI] and intracortical facilitation [ICF]) in the dominant-limb quadriceps. Design: Reliability study. Setting: Research laboratory. Participants: 13 healthy volunteers (n = 6 women; age 24.7 ± 2.1 y; height 1.7 ± 0.1 m; mass 77.1 ± 17.4 kg). Intervention: Participants completed 2 TMS sessions separated by 1 wk. Main Outcome Measures: Two investigators measured quadriceps SICI, LICI, and ICF at rest and actively (5% of maximal voluntary isometric contraction). All participants were seated in a dynamometer with the knee flexed to 90°. Intracortical-excitability paradigm and investigator order were randomized. Bland-Altman analyses were used to establish agreement. Results: Agreement was stronger between sessions within a single investigator than between investigators and for active than resting measures. Agreement was strongest for resting SICI and active ICF and LICI between sessions for each investigator. Conclusions: Quadriceps intracortical excitability may be measured longitudinally by a single investigator, though active muscle contraction should be elicited during testing.

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Characterisation of paired-pulse transcranial magnetic stimulation conditions yielding intracortical inhibition or I-wave facilitation using a threshold-hunting paradigm

Experimental Brain Research ◽

10.1007/s002210050901 ◽

1999 ◽

Vol 129 (2) ◽

pp. 317-324 ◽

Cited By ~ 56

Author(s):

F. Awiszus ◽

Helmut Feistner ◽

Dietmar Urbach ◽

Hugh Bostock

Keyword(s):

Transcranial Magnetic Stimulation ◽

Magnetic Stimulation ◽

Intracortical Inhibition ◽

Paired Pulse

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Desynchronization does not contribute to intracortical inhibition and facilitation: a paired-pulse paradigm study combined with TST

Journal of Neurophysiology ◽

10.1152/jn.00381.2016 ◽

2017 ◽

Vol 117 (3) ◽

pp. 1052-1056 ◽

Cited By ~ 2

Author(s):

L. Caranzano ◽

M. A. Stephan ◽

F. R. Herrmann ◽

D. H. Benninger

Keyword(s):

Clinical Practice ◽

Transcranial Magnetic Stimulation ◽

Magnetic Stimulation ◽

Interindividual Variability ◽

Intracortical Inhibition ◽

Intracortical Facilitation ◽

Paired Pulse ◽

Stimulation Technique ◽

Intracortical Inhibition And Facilitation ◽

Triple Stimulation Technique

The paired-pulse (PP) transcranial magnetic stimulation (TMS) paradigms allow the exploration of the motor cortex physiology. The triple stimulation technique (TST) improves conventional TMS by reducing effects of desynchronization of motor neuron discharges allowing a precise evaluation of the corticospinal conduction. The objective of our study was to explore PP TMS paradigms combined with the TST to study whether the desynchronization contributes to these phenomena and whether the combined TMS-TST protocol could improve the consistency of responses. We investigated the PP paradigms of short intracortical inhibition (SICI) with 2 ms interstimulus interval (ISI) and of intracortical facilitation (ICF) with 10 ms ISI in 22 healthy subjects applying either conventional TMS alone or combined with the TST protocol. The results of the PP paradigms combined with the TST of SICI and ICF do not differ from those with conventional TMS. However, combining the PP paradigm with the TST reduces their variability. These results speak against a contribution of the desynchronization of motor neuron discharges to the PP paradigms of SICI and ICF. Combining the PP TMS paradigm with the TST may improve their consistency, but the interindividual variability remains such that it precludes their utility for clinical practice. NEW & NOTEWORTHY Combining the triple stimulation technique with the paired-pulse stimulation paradigm improves the consistency of short intracortical inhibition and facilitation and could be useful in research, but the interindividual variability precludes their utility for clinical practice. Our findings do not suggest that desynchronization of descending discharges following transcranial magnetic stimulation contributes to short intracortical inhibition or intracortical facilitation.

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