Effect of stimulus orientation and intensity on short-interval intracortical inhibition (SICI) and facilitation (SICF): A multi-channel transcranial magnetic stimulation study

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.

Download Full-text

Cortical excitability varies across different muscles

Journal of Neurophysiology ◽

10.1152/jn.00148.2018 ◽

2018 ◽

Vol 120 (3) ◽

pp. 1397-1403 ◽

Cited By ~ 7

Author(s):

Parvathi Menon ◽

Matthew C. Kiernan ◽

Steve Vucic

Keyword(s):

Transcranial Magnetic Stimulation ◽

Magnetic Stimulation ◽

Functional Organization ◽

Cortical Excitability ◽

Short Interval ◽

Intracortical Inhibition ◽

Body Regions ◽

Threshold Tracking ◽

Resting Motor Threshold ◽

Limb Muscles

The aim of the present study was to determine whether significant differences in cortical excitability were evident across different body regions in healthy humans. Threshold tracking transcranial magnetic stimulation (TMS) was undertaken in 28 healthy controls. Short-interval intracortical inhibition [SICI between interstimulus intervals (ISI) 1–7 ms], intracortical facilitation (ICF, between ISI 10–30 ms), resting motor threshold (RMT), cortical silent period (CSP) duration (generated at stimulus intensity 150% RMT), and motor evoked potential amplitude were recorded from the abductor pollicis brevis (APB), tibialis anterior (TA), and trapezius muscles. These muscles were selected as they are frequently affected in neurodegenerative diseases, such as amyotrophic lateral sclerosis. SICI and ICF are measured as a percentage difference between conditioned and an unconditioned test response. SICI was significantly greater when recorded over the APB (9.9 ± 1.5%) and TA (8.6 ± 1.4%) muscles compared with the trapezius (4.5 ± 1.9%, P < 0.05). The CSP duration was significantly shorter (CSPtrapezius, 131.0 ± 6.3 ms; CSPTA, 175.7 ± 9.9 ms; CSPAPB, 188.3 ± 4.0 ms; P < 0.001) and ICF greater ( P < 0.01) in the trapezius muscle. There were no significant correlations between inhibitory and facilitatory processes recorded across the three muscles. The present study established significant differences in cortical excitability across three body regions, with evidence of more prominent inhibition and less facilitation in the limb muscles. NEW & NOTEWORTHY Cortical excitability of muscles with differing motor functions was assessed using threshold tracking transcranial magnetic stimulation. Significantly greater intracortical inhibition and less facilitation were evident over the limb muscles. These findings could relate to differences in the functional organization of the corticomotoneuronal system innervating different muscle regions.

Download Full-text

Probing the orientation specificity of excitatory and inhibitory circuitries in the primary motor cortex with multi-channel TMS

10.1101/2021.08.20.457101 ◽

2021 ◽

Author(s):

Victor H. Souza ◽

Jaakko O. Nieminen ◽

Sergei Tugin ◽

Lari M. Koponen ◽

Oswaldo Baffa ◽

...

Keyword(s):

Electric Field ◽

Test Stimulus ◽

Primary Motor Cortex ◽

Motor Evoked Potentials ◽

Short Interval ◽

Intracortical Inhibition ◽

Stimulus Orientation ◽

Field Orientation ◽

Resting Motor Threshold ◽

Orientation Specificity

Background: The electric field orientation is a crucial parameter for optimizing the excitation of neuronal tissue in transcranial magnetic stimulation (TMS). Yet, the effects of stimulus orientation on the short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) paradigms are poorly known, mainly due to significant technical challenges in manipulating the TMS-induced stimulus orientation within milliseconds. Objective: Our aim is to assess the effect of the TMS-induced stimulus orientation on the SICI and ICF paradigms and search for the optimal orientations to maximize the facilitation and suppression of the motor evoked potentials (MEP). Methods: We applied paired-pulse multi-channel TMS in healthy subjects to generate SICI and ICF with conditioning and test pulses in the same, opposite, and perpendicular orientations to each other. The conditioning- and test-stimulus intensities were 80% and 110% of the resting motor threshold, respectively. Results: Both SICI and ICF were significantly affected by the conditioning- and test-stimulus orientation. MEP suppression and facilitation were strongest with both pulses delivered in the same direction. SICI with a 2.5-ms and ICF with a 6.0-ms interstimulus interval (ISI) were more sensitive to changes in stimulus orientation compared with SICI at 0.5- and ICF at 8.0-ms ISIs, respectively. Conclusion: Our findings provide evidence that SICI and ICF at specific ISIs are mediated by distinct mechanisms. Such mechanisms exhibit a preferential orientation depending on the anatomical and morphological arrangement of inhibitory and excitatory neuronal populations. We also demonstrate that the SICI and ICF can be maximized by adjusting the TMS-induced electric field orientation.

Download Full-text

Effects of the motor cortical quadripulse transcranial magnetic stimulation (QPS) on the contralateral motor cortex and interhemispheric interactions

Journal of Neurophysiology ◽

10.1152/jn.00515.2013 ◽

2014 ◽

Vol 111 (1) ◽

pp. 26-35 ◽

Cited By ~ 17

Author(s):

Ryosuke Tsutsumi ◽

Ritsuko Hanajima ◽

Yasuo Terao ◽

Yuichiro Shirota ◽

Shinya Ohminami ◽

...

Keyword(s):

Transcranial Magnetic Stimulation ◽

Corpus Callosum ◽

Magnetic Stimulation ◽

Motor Evoked Potentials ◽

Short Interval ◽

Long Term Potentiation ◽

Intracortical Inhibition ◽

Motor Threshold ◽

Resting Motor Threshold

Corpus callosum connects the bilateral primary motor cortices (M1s) and plays an important role in motor control. Using the paired-pulse transcranial magnetic stimulation (TMS) paradigm, we can measure interhemispheric inhibition (IHI) and interhemispheric facilitation (IHF) as indexes of the interhemispheric interactions in humans. We investigated how quadripulse transcranial magnetic stimulation (QPS), one form of repetitive TMS (rTMS), on M1 affects the contralateral M1 and the interhemispheric interactions. QPS is able to induce bidirectional plastic changes in M1 depending on the interstimulus intervals (ISIs) of TMS pulses: long-term potentiation (LTP)-like effect by QPS-5 protocol, and long-term depression-like effect by QPS-50, whose numbers indicate the ISI (ms). Twelve healthy subjects were enrolled. We applied QPS over the left M1 and recorded several parameters before and 30 min after QPS. QPS-5, which increased motor-evoked potentials (MEPs) induced by left M1 activation, also increased MEPs induced by right M1 activation. Meanwhile, QPS-50, which decreased MEPs elicited by left M1 activation, did not induce any significant changes in MEPs elicited by right M1 activation. None of the resting motor threshold, active motor threshold, short-interval intracortical inhibition, long-interval intracortical inhibition, intracortical facilitation, and short-interval intracortical inhibition in right M1 were affected by QPS. IHI and IHF from left to right M1 significantly increased after left M1 QPS-5. The degree of left first dorsal interosseous MEP amplitude change by QPS-5 significantly correlated with the degree of IHF change. We suppose that the LTP-like effect on the contralateral M1 may be produced by some interhemispheric interactions through the corpus callosum.

Download Full-text

F147. Absolute and relative reliability of short-interval intracortical inhibition measured by threshold tracking transcranial magnetic stimulation

Clinical Neurophysiology ◽

10.1016/j.clinph.2018.04.310 ◽

2018 ◽

Vol 129 ◽

pp. e122-e123

Author(s):

Jose M. Matamala ◽

James Howells ◽

Thanuja Dharmadasa ◽

Terry Trinh ◽

Yan Ma ◽

...

Keyword(s):

Transcranial Magnetic Stimulation ◽

Magnetic Stimulation ◽

Short Interval ◽

Intracortical Inhibition ◽

Relative Reliability ◽

Threshold Tracking

Download Full-text

Threshold Tracked Short-Interval Intracortical Inhibition More Closely Predicts the Cortical Response to Transcranial Magnetic Stimulation

Neuromodulation Technology at the Neural Interface ◽

10.1016/j.neurom.2021.11.004 ◽

2022 ◽

Author(s):

Ryoki Sasaki ◽

John G. Semmler ◽

George M. Opie

Keyword(s):

Transcranial Magnetic Stimulation ◽

Magnetic Stimulation ◽

Short Interval ◽

Intracortical Inhibition ◽

Cortical Response

Download Full-text

The effects of 30 Hz, 50 Hz AND 100 Hz continuous theta burst stimulation via transcranial magnetic stimulation on the electrophysiological parameters in healthy individuals

Ideggyógyászati Szemle ◽

10.18071/isz.74.0041 ◽

2021 ◽

Vol 74 (1-2) ◽

pp. 41-49

Author(s):

Zeynep Ozdemir ◽

Erkan Acar ◽

Aysun Soysal

Keyword(s):

Transcranial Magnetic Stimulation ◽

Magnetic Stimulation ◽

Short Interval ◽

Motor Evoked Potential ◽

Individual Variability ◽

Theta Burst Stimulation ◽

Burst Stimulation ◽

Resting Motor Threshold ◽

Theta Burst ◽

Continuous Theta Burst Stimulation

Transcranial magnetic stimulation is a non-invasive procedure that uses robust magnetic fields to create an electrical current in the cerebral cortex. Dual stimulation consists of administering subthreshold conditioning stimulation (CS), then suprathreshold test stimulation (TS). When the interstimulus interval (ISI) is 1-6 msec, the motor evoked potential (MEP) decreases in amplitude; this decrease is termed “short interval intracortical inhibition” (SICI); when the ISI is 7-30 msec, an increase in MEP amplitude occurs, termed “short interval intracortical facilitation” (SICF). Continuous theta burst stimulation (cTBS), often applied at a frequency of 50 Hz, has been shown to decrease cortical excitability. The primary objective is to determine which duration of cTBS achieves better inhibition or excitation. The secondary objective is to compare 50 Hz cTBS to 30 Hz and 100 Hz cTBS. The resting motor threshold (rMT), MEP, SICI, and SICF were studied in 30 healthy volunteers. CS and TS were administered at 80%-120% and 70%-140% of rMT at 2 and 3-millisecond (msec) intervals for SICI, and 10- and 12-msec intervals for SICF. Ten individuals in each group received 30, 50, or 100 Hz, followed by administration of rMT, MT-MEP, SICI, SICF immediately and at 30 minutes. Greater inhibition was achieved with 3 msec than 2 msec in SICI, whereas better facilitation occurred at 12 msec than 10 msec in SICF. At 30 Hz, cTBS augmented inhibition and suppressed facilitation, while 50 Hz yielded less inhibition and greater inter-individual variability. At 100 Hz, cTBS provided slight facilitation in MEP amplitudes with less interindividual variability. SICI and SICF did not differ significantly between 50 Hz and 100 Hz cTBS. Our results suggest that performing SICI and SICF for 3 and 12 msec, respectively, and CS and TS at 80%-120% of rMT, demonstrate safer inhibition and facilitation. Recently, TBS has been used in the treatment of various neurological diseases, and we recommend preferentially 30 Hz over 50 Hz cTBS for better inhibition with greater safety and less inter-individual variability.

Download Full-text

Fatigue-induced changes in short-interval intracortical inhibition and the silent period with stimulus intensities evoking maximal versus submaximal responses

Journal of Applied Physiology ◽

10.1152/japplphysiol.00282.2020 ◽

2020 ◽

Vol 129 (2) ◽

pp. 205-217

Author(s):

Callum G. Brownstein ◽

Loïc Espeit ◽

Nicolas Royer ◽

Thomas Lapole ◽

Guillaume Y. Millet

Keyword(s):

Transcranial Magnetic Stimulation ◽

Magnetic Stimulation ◽

Short Interval ◽

Conditioning Stimulus ◽

Silent Period ◽

Single Pulse ◽

Intracortical Inhibition ◽

Fatiguing Exercise ◽

Induced Changes

This study compared the change in silent period (SP) and short-interval intracortical inhibition (SICI) with conditioning stimulus and single-pulse transcranial magnetic stimulation (TMS) intensities (for SICI and SP, respectively) eliciting maximal and submaximal SICI and SP during fatiguing exercise. The results showed that changes in SICI were only detectable with intensities evoking maximal responses, with no difference between intensities for SP. These findings highlight the importance of maximizing SICI with appropriate intensities before measuring SICI during fatiguing exercise.

Download Full-text