Inter-Individual Variability in Motor Output Is Driven by Recruitment Gain in the Corticospinal Tract Rather Than Motor Threshold

Sarkar, Arkaprovo; Dipani, Alish; Leodori, Giorgio; Popa, Traian; Kassavetis, Panagiotis; Hallett, Mark; Thirugnanasambandam, Nivethida

doi:10.3390/brainsci12101401

Cited by 3 publications

(2 citation statements)

References 50 publications

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“…Whereas the RMT has been reported to be increased in some studies [22,24], this finding has not been confirmed by other authors [16,18], who also found normal MEP amplitudes in FP [17,18]. In this regard, it is worth noticing that a single TMS intensity was used instead of MEP recruitment with multiple stimulation intensities, which may reflect M1 excitability more accurately [37][38][39]. A certain variability in results has also been found in intracortical inhibition processes, with SICI reported to be either normal [16,18] or increased in the affected and decreased in the unaffected hemisphere [22].…”

Section: Discussionmentioning

confidence: 86%

Pathophysiology and Treatment of Functional Paralysis: Insight from Transcranial Magnetic Stimulation

et al. 2023

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Functional paralysis (FP) or limb weakness is a common presentation of functional movement disorders (FMD), accounting for 18.1% of the clinical manifestations of FMD. The pathophysiology of FP is not known, but imaging studies have identified changes in structural and functional connectivity in multiple brain networks. It has been proposed that noninvasive brain stimulation techniques may be used to understand the pathophysiology of FP and may represent a possible therapeutic option. In this paper, we reviewed transcranial magnetic stimulation studies on functional paralysis, focusing on their pathophysiological and therapeutical implications. Overall, there is general agreement on the integrity of corticospinal pathways in FP, while conflicting results have been found about the net excitability of the primary motor cortex and its excitatory/inhibitory circuitry in resting conditions. The possible involvement of spinal cord circuits remains an under-investigated area. Repetitive transcranial magnetic stimulation appears to have a potential role as a safe and viable option for the treatment of functional paralysis, but more studies are needed to investigate optimal stimulation parameters and clarify its role in the context of other therapeutical options.

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Section: Discussionmentioning

confidence: 86%

Pathophysiology and Treatment of Functional Paralysis: Insight from Transcranial Magnetic Stimulation

et al. 2023

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“…In the literature, associations between the effects of NIBS and neurophysiological parameters, including short-interval intracortical inhibition (SICI), intracortical facilitation (ICF), and the coefficient of variation of the MEP (MEP-CV), have been reported ( Hordacre et al, 2017 ; Li et al, 2019 ; Katagiri et al, 2020 ). Additionally, the slope of the recruitment curve (RC) is a predictor of variability in the amplitude of the test MEP ( Sarkar et al, 2022 ). By incorporating these factors, machine-learning techniques may effectively identify responders and nonresponders, subsequently complementing the traditional linear regression approach used in previous studies.…”

Section: Introductionmentioning

confidence: 99%

Predicting interindividual response to theta burst stimulation in the lower limb motor cortex using machine learning

Katagiri,

Saho,

Shibukawa

et al. 2024

Front. Neurosci.

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Using theta burst stimulation (TBS) to induce neural plasticity has played an important role in improving the treatment of neurological disorders. However, the variability of TBS-induced synaptic plasticity in the primary motor cortex prevents its clinical application. Thus, factors associated with this variability should be explored to enable the creation of a predictive model. Statistical approaches, such as regression analysis, have been used to predict the effects of TBS. Machine learning may potentially uncover previously unexplored predictive factors due to its increased capacity for capturing nonlinear changes. In this study, we used our prior dataset (Katagiri et al., 2020) to determine the factors that predict variability in TBS-induced synaptic plasticity in the lower limb motor cortex for both intermittent (iTBS) and continuous (cTBS) TBS using machine learning. Validation of the created model showed an area under the curve (AUC) of 0.85 and 0.69 and positive predictive values of 77.7 and 70.0% for iTBS and cTBS, respectively; the negative predictive value was 75.5% for both patterns. Additionally, the accuracy was 0.76 and 0.72, precision was 0.82 and 0.67, recall was 0.82 and 0.67, and F1 scores were 0.82 and 0.67 for iTBS and cTBS, respectively. The most important predictor of iTBS was the motor evoked potential amplitude, whereas it was the intracortical facilitation for cTBS. Our results provide additional insights into the prediction of the effects of TBS variability according to baseline neurophysiological factors.

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Efficacy of High-Definition Transcranial Alternating Current Stimulation (HD-tACS) at the M1 Hotspot Versus C3 Site in Modulating Corticospinal Tract Excitability

Meng,

Houston,

Dias

et al. 2024

Biomedicines

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Previous studies have shown that beta-band transcranial alternating current stimulation (tACS) applied at the M1 hotspot can modulate corticospinal excitability. However, it remains controversial whether tACS can influence motor unit activities at the spinal cord level. This study aims to compare the efficacy of applying tACS over the hotspot versus the conventional C3 site on motor unit activities and subsequent behavioral changes. This study used a randomized crossover trial design, where fifteen healthy participants performed a paced ball-squeezing exercise while receiving high-definition tACS (HD-tACS) at 21 Hz and 2 mA for 20 min. HD-tACS targeted either the flexor digitorum superficialis (FDS) hotspot or the C3 site, with the order of stimulation randomized for each participant and a 1-week washout period between sessions. Motor unit activities were recorded from the FDS. HD-tACS intervention significantly reduced the variability of motor unit firing rates and increased force variability during isometric force production. The significant modulation effects were seen only when the intervention was applied at the hotspot, but not at the C3 site. Our findings demonstrate that HD-tACS significantly modulates motor unit activities and force variability. The results indicate that cortical-level entrainment by tACS can lead to the modulation of spinal motor neuron activities. Additionally, this study provides further evidence that the C3 site may not be the optimal target for tACS intervention for hand muscles, highlighting the need for personalized neuromodulation strategies.

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Inter-Individual Variability in Motor Output Is Driven by Recruitment Gain in the Corticospinal Tract Rather Than Motor Threshold

Cited by 3 publications

References 50 publications

Pathophysiology and Treatment of Functional Paralysis: Insight from Transcranial Magnetic Stimulation

Pathophysiology and Treatment of Functional Paralysis: Insight from Transcranial Magnetic Stimulation

Predicting interindividual response to theta burst stimulation in the lower limb motor cortex using machine learning

Efficacy of High-Definition Transcranial Alternating Current Stimulation (HD-tACS) at the M1 Hotspot Versus C3 Site in Modulating Corticospinal Tract Excitability

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