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

Abstract

<jats:sec> <jats:title>Background</jats:title> <jats:p>Motor 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.</jats:p> </jats:sec> <jats:sec> <jats:title>Methods</jats:title> <jats:p>In 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.</jats:p> </jats:sec> <jats:sec> <jats:title>Results</jats:title> <jats:p>Corticospinal excitability in M1 was significantly greater 15 min after PMd iTBS600 than that after sham-iTBS600 (<jats:italic>p</jats:italic> = 0.012). Compared with that after sham-iTBS600, at 0 (<jats:italic>p</jats:italic> = 0.014) and 15 (<jats:italic>p</jats:italic> = 0.037) min after iTBS600, SICI in M1 was significantly decreased, whereas 15 min after iTBS600, ICF in M1 was significantly increased (<jats:italic>p</jats:italic> = 0.033).</jats:p> </jats:sec> <jats:sec> <jats:title>Conclusion</jats:title> <jats:p>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.</jats:p> </jats:sec>

Modulation of dorsal premotor cortex differentially influences I‐wave excitability in primary motor cortex of young and older adults

“…It was reported that when this intensity was applied directly over M1, it did not influence M1 excitability (Huang et al., 2009). Given that the present study identified the location of PMd similarly to previous studies (Huang et al., 2009, 2018; Meng et al., 2020), it is therefore unlikely that M1 was directly activated during PMd iTBS.…”

“…In accordance with existing literature, iTBS consisted of bursts of three pulses given at a frequency of 50 Hz. Each triplet was repeated 10 times at 200 ms within a 2 s train, and this was repeated every 8 s for 20 cycles, totalling 600 pulses (Huang et al., 2005 , 2008 , 2018 ; Meng et al., 2020 ). The location of left PMd was defined as 8% of the distance between the nasion and inion (∼2.5–3 cm) anterior to the M1 hotspot, consistent with previous work (Huang et al., 2018 ; Koch et al., 2007 ; Meng et al., 2020 ; Münchau et al., 2002 ).…”

“…Each triplet was repeated 10 times at 200 ms within a 2 s train, and this was repeated every 8 s for 20 cycles, totalling 600 pulses (Huang et al., 2005 , 2008 , 2018 ; Meng et al., 2020 ). The location of left PMd was defined as 8% of the distance between the nasion and inion (∼2.5–3 cm) anterior to the M1 hotspot, consistent with previous work (Huang et al., 2018 ; Koch et al., 2007 ; Meng et al., 2020 ; Münchau et al., 2002 ). Both the M1 hotspot and left PMd location were digitally recorded relative to the standard MNI‐ICBM152 template using Brainsight neuronavigation (Rogue Research, Montreal, Quebec, Canada).…”

“…The PMd plans, predicts and corrects movements during motor learning by updating the activity of M1 (Chouinard et al., 2005 ; Nowak et al., 2009 ; Parikh & Santello, 2017 ). Recent studies have reported that modulation of PMd excitability using repetitive TMS (rTMS) techniques such as theta burst stimulation (TBS) is able to modify M1 excitability (Meng et al., 2020 ), as well as alter the neuroplastic response of M1 and influence motor skill learning (Huang et al., 2018 ). The ability to recruit late I‐waves with TMS has also been shown to predict the strength of PMd–M1 connectivity (Volz et al., 2015 ), in addition to the neuroplastic response to M1 TMS interventions (Hamada et al., 2013 ; Volz et al., 2019 ).…”

Cathodal Transcranial Direct Current Stimulation (tDCS) Applied to the Left Premotor Cortex Interferes with Explicit Reproduction of a Motor Sequence

“…Reaction time acceleration following anodal tDCS was found independent of the task (random vs. sequential) suggesting an unspecific stimulation effect. A comparable effect has been shown for the implicit task variant [61] and may occur due to an excitatory effect of anodal tDCS on corticospinal excitability as has been shown for TMS [76,77] yielding a beneficial effect on task performance. The data are summarized in Figure 5.…”