Intermittent theta burst stimulation facilitates functional connectivity from the dorsal premotor cortex to primary motor cortex

Hai-Jiang Meng,Yan-Ling Pi,Na Cao,Jian Zhang

doi:10.7717/peerj.9253

Abstract

BackgroundMotor information in the brain is transmitted from the dorsal premotor cortex (PMd) to the primary motor cortex (M1), where it is further processed and relayed to the spinal cord to eventually generate muscle movement. However, how information from the PMd affects M1 processing and the final output is unclear. Here, we applied intermittent theta burst stimulation (iTBS) to the PMd to alter cortical excitability not only at the application site but also at the PMd projection site of M1. We aimed to determine how PMd iTBS–altered information changed M1 processing and the corticospinal output.MethodsIn total, 16 young, healthy participants underwent PMd iTBS with 600 pulses (iTBS600) or sham-iTBS600. Corticospinal excitability, short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF) were measured using transcranial magnetic stimulation before and up to 60 min after stimulation.ResultsCorticospinal excitability in M1 was significantly greater 15 min after PMd iTBS600 than that after sham-iTBS600 (p = 0.012). Compared with that after sham-iTBS600, at 0 (p = 0.014) and 15 (p = 0.037) min after iTBS600, SICI in M1 was significantly decreased, whereas 15 min after iTBS600, ICF in M1 was significantly increased (p = 0.033).ConclusionOur results suggested that projections from the PMd to M1 facilitated M1 corticospinal output and that this facilitation may be attributable in part to decreased intracortical inhibition and increased intracortical facilitation in M1. Such a facilitatory network may inform future understanding of the allocation of resources to achieve optimal motion output.

Highlights

After a period of noninvasive brain stimulation or certain patterns of activity, the function as well as the very structure of the cortex of the brain changes
We examined whether the level of corticospinal M1 excitability was altered when iTBS with 600 pulses (iTBS600) was applied to the PMd by measuring the change in motor-evoked potentials (MEPs) amplitude at the target first dorsal interosseous (FDI) muscle after the application
Compared with the baseline, application of iTBS600 to the PMd significantly increased MEP amplitude in M1 15 min after the intervention (p = 0.004). These results suggested that corticospinal M1 excitability was significantly increased by iTBS600 applied to the PMd (Fig. 2)

Summary

Introduction

After a period of noninvasive brain stimulation or certain patterns of activity, the function as well as the very structure of the cortex of the brain changes. A growing body of research has shown that a broad set of key brain regions, known as the motor system network, are functionally involved in motor performance and motor control This motor system network is not restricted to the motor cortex but dynamically extends into parietal, temporal, and prefrontal areas, depending on task complexity and an individual’s experience (Swinnen & Wenderoth, 2004). Our results suggested that projections from the PMd to M1 facilitated M1 corticospinal output and that this facilitation may be attributable in part to decreased intracortical inhibition and increased intracortical facilitation in M1. Such a facilitatory network may inform future understanding of the allocation of resources to achieve optimal motion output

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