Abstract
Mirror training (MT) is an observation-based motor learning strategy. Intermittent theta burst stimulation (iTBS) is an accelerated form of excitatory repetitive transcranial magnetic stimulation (rTMS) that has been used to enhance the cortical excitability of the motor cortices. This study aims to investigate the combined effects of iTBS with MT on the resting state functional connectivity at alpha frequency band in healthy adults. Eighteen healthy adults were randomized into one of three groups—Group 1: iTBS plus MT, Group 2: iTBS plus sham MT, and Group 3: sham iTBS plus MT. Participants in Groups 1 and 3 observed the mirror illusion of the moving (right) hand in a plain mirror for four consecutive sessions, one session/day, while participants in Group 2 received the same training with a covered mirror. Real or sham iTBS was applied daily over right motor cortex prior to the training. Resting state electroencephalography (EEG) at baseline and post-training was recorded when participants closed their eyes. The mixed-effects model demonstrated a significant interaction effect in the coherence between FC4 and C4 channels, favoring participants in Group 1 over Group 3 (Δβ = −0.84, p = 0.048). A similar effect was also found in the coherence between FC3 and FC4 channels favoring Group 1 over Group 3 (Δβ = −0.43, p = 0.049). In contrast to sham iTBS combined with MT, iTBS combined with MT may strengthen the functional connectivity between bilateral premotor cortices and ipsilaterally within the motor cortex of the stimulated hemisphere. In contrast to sham MT, real MT, when combined with iTBS, might diminish the connectivity among the contralateral parietal–frontal areas.
Highlights
Mirror training (MT), in which participants are required to move one side of their hand while simultaneously observing the mirror visual feedback (MVF) from a mirror placed in the midsagittal plane, has been investigated with healthy adults to study the process of observation-based motor learning (Zult et al, 2016; Chen et al, 2019) and applied in stroke rehabilitation to Intermittent theta burst stimulation (iTBS) With Mirror Visual Feedback improve the upper extremity motor relearning in patients with hemiplegia (Fong et al, 2019)
The present study investigated the combined effect of iTBS with MT on modulating the resting state functional connectivity at alpha frequency band, in healthy adults
Our experiment found that the combination of iTBS with MT strengthened intrahemispheric connectivity between premotor and motor areas in the ipsilateral side, as indicated by the increased coherence between FC4 and C4 channels, as well as the interhemispheric connectivity of bilateral premotor cortices, as indicated by the increased coherence between FC3 and FC4 channels
Summary
Mirror training (MT), in which participants are required to move one side of their hand while simultaneously observing the mirror visual feedback (MVF) from a mirror placed in the midsagittal plane, has been investigated with healthy adults to study the process of observation-based motor learning (Zult et al, 2016; Chen et al, 2019) and applied in stroke rehabilitation to iTBS With Mirror Visual Feedback improve the upper extremity motor relearning in patients with hemiplegia (Fong et al, 2019). Facilitating the motor cortex by excitatory NIBS, including high-frequency rTMS or anodal tDCS, prior or concurrently to MT showed a greater effect on enhancing motor performance (measured using a two-ball rotation task) in healthy adults (von Rein et al, 2015) and motor recovery (measured using the box and block test or the action research arm test) in patients with stroke (Kim and Yim, 2018; Jin et al, 2019), indicating a synergistic effect when combining these two treatment modalities. There is evidence to support that iTBS delivered to the motor cortex could enhance the efficacy of motor training in healthy individuals (Platz et al, 2018) and patients with stroke (Ackerley et al, 2016) It is still unclear whether iTBS could enhance observation-based motor learning via MT, and what its underpinning neural correlates are
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