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Effect of conditioning and test stimulus intensity on cortical excitability using triad-conditioning transcranial magnetic stimulation.

ABSTRACT: Cortical facilitation assessed with triad conditioning transcranial magnetic stimulation has been termed triad-conditioned facilitation (TCF). TCF has been supposed to reflect increased intracortical facilitation (ICF) at short interstimulus intervals (ISI) around 10 ms and an intrinsic rhythm of the motor cortex at longer ISI around 25 ms. To gain further insight into the pathophysiological mechanism of TCF, we systematically studied the effect of suprathreshold conditioning stimulus (CS) and test stimulus (TS) intensity on TCF. Various CS intensities and TS intensities were used in a triad-conditioning paradigm that was applied to 11 healthy subjects. ISI between pulses were studied between 5 and 200 ms. TCF at 10 ms ISI enhanced with increasing CS intensity but decreased with increasing TS intensity. The duration of facilitation was longer with higher CS intensity. However, TCF at 25 ms ISI could not be elicited with none of the CS and TS intensities addressed here. Our results are consistent with the notion of TCF at short ISI reflecting ICF. The enhanced and prolonged facilitation with increase of CS without additional isolated facilitation at longer ISI suggest a prolongation of ICF.

SUBMITTER: Hassan SS

PROVIDER: S-EPMC7237525 | biostudies-literature | 2020 May

REPOSITORIES: biostudies-literature

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Effect of conditioning and test stimulus intensity on cortical excitability using triad-conditioning transcranial magnetic stimulation.

Hassan Shady Safwat SS Trenado Carlos C Rageh Tarek Ali TA Schnitzler Alfons A Groiss Stefan Jun SJ

Experimental brain research 20200422 5

Cortical facilitation assessed with triad conditioning transcranial magnetic stimulation has been termed triad-conditioned facilitation (TCF). TCF has been supposed to reflect increased intracortical facilitation (ICF) at short interstimulus intervals (ISI) around 10 ms and an intrinsic rhythm of the motor cortex at longer ISI around 25 ms. To gain further insight into the pathophysiological mechanism of TCF, we systematically studied the effect of suprathreshold conditioning stimulus (CS) and t ...[more]

PMID: 32322929

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Project description:Corticospinal output pathways have typically been considered to be the primary driver for voluntary movements of the hand/forearm; however, more recently, reticulospinal drive has also been implicated in the production of these movements. Although both pathways may play a role, the reticulospinal tract is thought to have stronger connections to flexor muscles than to extensors. Similarly, movements involuntarily triggered via a startling acoustic stimulus (SAS) are believed to receive greater reticular input than voluntary movements. To investigate a differential role of reticulospinal drive depending on movement type or acoustic stimulus, corticospinal drive was transiently interrupted using high-intensity transcranial magnetic stimulation (TMS) applied during the reaction time (RT) interval. This TMS-induced suppression of cortical drive leads to RT delays that can be used to assess cortical contributions to movement. Participants completed targeted flexion and extension movements of the wrist in a simple RT paradigm in response to a control auditory go signal or SAS. Occasionally, suprathreshold TMS was applied over the motor cortical representation for the prime mover. Results revealed that TMS significantly increased RT in all conditions. There was a significantly longer TMS-induced RT delay seen in extension movements than in flexion movements and a greater RT delay in movements initiated in response to control stimuli compared with SAS. These results suggest that the contribution of reticulospinal drive is larger for wrist flexion than for extension. Similarly, movements triggered involuntarily by an SAS appear to involve greater reticulospinal drive, and relatively less corticospinal drive, than those that are voluntarily initiated. NEW & NOTEWORTHY Through the use of the transcranial magnetic stimulation-induced silent period, we provide novel evidence for a greater contribution of reticulospinal drive, and a relative decrease in corticospinal drive, to movements involuntarily triggered by a startle compared with voluntary movements. These results also provide support for the notion that both cortical and reticular structures are involved in the neural pathway underlying startle-triggered movements. Furthermore, our results indicate greater reticulospinal contribution to wrist flexion than extension movements.

Dataset Information

Effect of conditioning and test stimulus intensity on cortical excitability using triad-conditioning transcranial magnetic stimulation.

Publications

Effect of conditioning and test stimulus intensity on cortical excitability using triad-conditioning transcranial magnetic stimulation.

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