Transcranial Magnetic Stimulation in Different Current Directions Activates Separate Cortical Circuits

Transcranial magnetic stimulation (TMS) to the primary motor cortex (M1) produces a series of corticospinal descending waves, with a direct (D) wave followed by several indirect (I) waves. TMS inducing posterior–anterior (PA) current in the brain predominantly recruits the early I1-wave, whereas anterior–posterior (AP) directed current preferentially recruits the late I3-wave. However, it is not known whether I-waves elicited by different current directions are mediated by the same neuronal populations. We studied the neuronal mechanisms mediating I-waves by examining the influence of short-latency afferent inhibition (SAI) on various I-waves. SAI was tested with electrical median nerve stimulation at the wrist followed by TMS to the contralateral M1 at different current directions. Surface electromyograms and single motor units were recorded from the first dorsal interosseous muscle. SAI was weaker for the AP compared with that for the PA current direction. With increasing median nerve stimulation intensities, SAI increased for the PA direction but showed a U-shaped relationship for the AP direction. SAI produced more inhibition of late I-waves generated by PA than those generated by AP current direction. We conclude that late I-waves generated by PA and AP current directions are mediated by different neuronal mechanisms.

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Motor Cortical Plasticity Induced by Volitional Muscle Activity-Triggered Transcranial Magnetic Stimulation and Median Nerve Stimulation

10.21203/rs.3.rs-89368/v1 ◽

2020 ◽

Author(s):

Pramudika Nirmani Kariyawasam ◽

Shinya Suzuki ◽

Susumu Yoshida

Keyword(s):

Transcranial Magnetic Stimulation ◽

Median Nerve ◽

Nerve Stimulation ◽

Magnetic Stimulation ◽

Primary Motor Cortex ◽

Short Interval ◽

Corticospinal Excitability ◽

Post Intervention ◽

Median Nerve Stimulation ◽

Resting Motor Threshold

Abstract BackgroundBilateral motor training (BMT) is a useful method to modify the excitability of the corticospinal system. The effects of artificial symmetrical movement on corticospinal excitability through functional electrical stimulation (FES) or transcranial magnetic stimulation (TMS) have not been reported. Therefore, we compared motor-evoked potentials (MEPs) following TMS over the ipsilateral primary motor cortex (M1) of voluntary movements after conventional BMT and repetitive artificial symmetrical movements generated through FES and TMS.MethodsSurface electromyograms of the abductor pollicis brevis (APB) muscles were recorded bilaterally in 12 healthy participants. Three sessions with different protocols were conducted: (1) bilateral finger training (BFT) involving bilateral thumb abduction, (2) right APB-triggered TMS of the ipsilateral M1 (APB-triggered i-TMS), and (3) right APB-triggered contralateral median nerve stimulation (APB-triggered c-MNS). Each protocol consisted of 360 trials for 30 min. Resting motor threshold (RMT), MEPs induced by single-pulse TMS, short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF) induced by paired-pulse TMS were assessed as outcome measures at baseline and at 0, 20, 40, and 60 min after intervention.ResultsRMT showed no significant effect of intervention, time, or interaction. MEP amplitude showed a significant effect with time. MEP amplitude significantly increased at 0, 20, and 40 min post-intervention in BFT; at 0, 20, 40, and 60 min post-intervention in APB-triggered i-TMS; and at 20 and 40 min post-intervention in APB-triggered c-MNS in comparison to the baseline values. SICI was significantly decreased at 0 min post-intervention in the BFT and APB-triggered i-TMS protocols. ICF was significantly increased at 0 min post-intervention in the BFT and at 20 min post-intervention in the APB-triggered c-MNS protocol.ConclusionThe main finding of the present study was the long-lasting increase in MEP amplitude in all three mirror-symmetrical movement protocols. The observed changes are long-lasting and comparatively strong. However, the underlying neural mechanisms seem to be slightly different across the three protocols. Thus, whether voluntarily or artificially caused, repetitive symmetrical mirror movements enhance corticospinal excitability.

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Sustained increase of somatosensory cortex excitability by 5 Hz repetitive transcranial magnetic stimulation studied by paired median nerve stimulation in humans

Neuroscience Letters ◽

10.1016/j.neulet.2003.11.034 ◽

2004 ◽

Vol 356 (2) ◽

pp. 91-94 ◽

Cited By ~ 49

Author(s):

Patrick Ragert ◽

Michael Becker ◽

Martin Tegenthoff ◽

Burkhard Pleger ◽

Hubert R. Dinse

Keyword(s):

Transcranial Magnetic Stimulation ◽

Median Nerve ◽

Somatosensory Cortex ◽

Nerve Stimulation ◽

Magnetic Stimulation ◽

Repetitive Transcranial Magnetic Stimulation ◽

Median Nerve Stimulation ◽

Sustained Increase

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Motor Cortical Plasticity Induced by Volitional Muscle Activity-Triggered Transcranial Magnetic Stimulation and Median Nerve Stimulation

Brain Sciences ◽

10.3390/brainsci12010061 ◽

2021 ◽

Vol 12 (1) ◽

pp. 61

Author(s):

Pramudika Nirmani Kariyawasam ◽

Shinya Suzuki ◽

Susumu Yoshida

Keyword(s):

Transcranial Magnetic Stimulation ◽

Nerve Stimulation ◽

Magnetic Stimulation ◽

Primary Motor Cortex ◽

Motor Evoked Potentials ◽

Short Interval ◽

Corticospinal Excitability ◽

Motor Training ◽

Median Nerve Stimulation ◽

Bilateral Movement

Bilateral motor training is a useful method for modifying corticospinal excitability. The effects of bilateral movement that are caused by artificial stimulation on corticospinal excitability have not been reported. We compared motor-evoked potentials (MEPs) of the primary motor cortex (M1) after conventional bilateral motor training and artificial bilateral movements generated by electromyogram activity of abductor pollicis brevis (APB) muscle-triggered peripheral nerve stimulation (c-MNS) and transcranial magnetic stimulation of the ipsilateral M1 (i-TMS). A total of three protocols with different interventions—bilateral finger training, APB-triggered c-MNS, and APB-triggered i-TMS—were administered to 12 healthy participants. Each protocol consisted of 360 trials of 30 min for each trial. MEPs that were induced by single-pulse TMS, short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF) that were induced by paired-pulse TMS were assessed as outcome measures at baseline and at 0, 20, 40, and 60 min after intervention. MEP amplitude significantly increased up to 40 min post-intervention in all protocols compared to that at the baseline, although there were some differences in the changing pattern of ICF and SICI in each protocol. These findings suggest that artificial bilateral movement has the potential to increase the ipsilateral cortical excitability of the moving finger.

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