Abstract
Theta-burst stimulation (TBS), a variant of repetitive transcranial magnetic stimulation (rTMS), can potentially benefit the treatment of swallowing disorders. However, the after-effects of TBS on the swallowing motor cortex remain uncertain. The newly developed graph-based analysis of the centrality approach has been increasingly used to explore brain networks. The purpose of this study was to identify degree centrality (DC) alterations in the brain network after different TBS protocols were performed over the suprahyoid muscles motor cortex in healthy subjects. A total of 40 right-handed healthy subjects (mean age: 23.73 ± 2.57 years, range: 21–30, 20 females) were included in this study and randomly assigned to two groups, including the continuous TBS (cTBS) group and the intermittent TBS (iTBS) group. All of the subjects underwent resting-state functional magnetic resonance imaging (rs-fMRI) scanning before and after TBS implementation. Compared to the baseline, cTBS resulted in increased DC values in the left inferior frontal gyrus (P < 0.01). In the iTBS group, decreased DC was observed in the left cerebellum and left medial frontal gyrus; However, increased DC was observed in several brain areas including the right superior temporal gyrus, right superior frontal gyrus, right postcentral gyri and left paracentral lobule (P < 0.01). These results indicated that cTBS mainly results in increasing DC in the ipsilateral. However, iTBS is capable of facilitating the excitability of the swallowing motor cortex and increasing the connectivity of multiple brain regions, including the bilateral sensorimotor network, and might have therapeutic potential in the treatment of swallowing disorders.
Highlights
Swallowing is one of the most complex sensorimotor tasks involving a widely distributed neuronal network, including different levels of the central nervous system from the bilateral cerebral cortex to the medulla oblongata and many of the cranial nerves (Kern et al, 2001; Martin et al, 2001; Ertekin and Aydogdu, 2003; Cicala et al, 2019)
After continuous TBS (cTBS) was applied to the left suprahyoid motor cortex, we observed increased degree centrality (DC) values in the left inferior frontal gyrus (BA 48; P < 0.01; Figure 1, Table 2)
Application of intermittent TBS (iTBS) to the left suprahyoid motor cortex resulted in decreased DC in the left cerebellum and left medial frontal gyrus (BA 11), and increased DC were seen in the right superior temporal gyrus (BA 48), right superior frontal gyrus (BA 10), right postcentral gyrus (BA 3), and left paracentral lobule (BA 4; P < 0.01)
Summary
Swallowing is one of the most complex sensorimotor tasks involving a widely distributed neuronal network, including different levels of the central nervous system from the bilateral cerebral cortex to the medulla oblongata and many of the cranial nerves (Kern et al, 2001; Martin et al, 2001; Ertekin and Aydogdu, 2003; Cicala et al, 2019). Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive neurostimulation technique that is based on the law of electromagnetic induction for delivering electric field pulses into the brain and has been increasingly used to investigate the neural mechanisms of swallowing and dysphagia (Khedr et al, 2009; Vasant et al, 2014; Pisegna et al, 2016). Different patterns of TBS delivery, including continuous TBS (cTBS) and intermittent TBS (iTBS), produced opposite effects on the synaptic efficiency of the stimulated cortex (Huang et al, 2005). Several studies have suggested that TBS is a more effective method than traditional rTMS in improving cerebral function, ability to function, and neurological deficits in stroke patients (Ackerley et al, 2010; Hsu et al, 2012). One other study had confirmed that TBS can improve the motor function obstacle with a sequence of iTBS stimulation on only the affected hemisphere motor cortex (M1; Suppa et al, 2008). Alterations in the aftereffects across the bilateral hemispheres and the connectivity of brain regions following the application of different patterns of TBS remain unclear
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