Modulation of motor cortex neuronal networks by rTMS: comparison of local and remote effects of six different protocols of stimulation

Abstract

Repetitive transcranial magnetic stimulation (rTMS) of human motor cortex can produce long-lasting changes in the excitability of excitatory and inhibitory neuronal networks. The effects of rTMS depend critically on stimulus frequency. The aim of our present study was to compare the effects of different rTMS protocols. We compared the aftereffects of 6 different rTMS protocols [paired associative stimulation at interstimulus intervals of 25 (PAS(25)) and 10 ms (PAS(10)); theta burst stimulation delivered as continuous (cTBS) or intermittent delivery pattern (iTBS); 1- and 5-Hz rTMS] on the excitability of stimulated and contralateral motor cortex in 10 healthy subjects. A pronounced increase of cortical excitability, evaluated by measuring the amplitude of motor evoked potentials (MEPs), was produced by iTBS (+56%) and PAS(25) (+45%). Five-hertz rTMS did not produce a significant increase of MEPs. A pronounced decrease of cortical excitability was produced by PAS(10) (-31%), cTBS (-29%), and 1-Hz rTMS (-20%). Short-interval intracortical inhibition was suppressed by PAS(10). Cortical silent period duration was increased by 1-Hz stimulation. No significant effect was observed in the contralateral hemisphere. Head-to-head comparison of the different protocols enabled us to identify the most effective paradigms for modulating the excitatory and inhibitory circuits activated by TMS.

A comparison of neuroplastic responses to non-invasive brain stimulation protocols and motor learning in healthy adults

“…In light of this result, it is not clear why MEP amplitude was significantly decreased following cTBS but not significantly facilitated following iTBS in the current study. One possible explanation is smaller variability following cTBS than iTBS; previous studies have shown smaller SEM following cTBS than iTBS [2,13] and in the current study, the coefficient of variation was smaller for cTBS than iTBS (Fig. 1).…”

“…Indeed, a recent study demonstrated large variability when comparing the effects of six NBS protocols [2]. The effect of intersubject variability on responses to NBS protocols at the group level has been discussed above.…”

Probing changes in corticospinal excitability following theta burst stimulation of the human primary motor cortex

“…A number of factors have been identified that influence the direction and magnitude of induced effects, including the age of study participants, their genetics, and their history of physical activity (Ridding and Ziemann, 2010). Although initial studies suggested TBS protocols were capable of inducing robust LTP and LTD-like plasticity in the human M1 (Huang et al, 2007;Huang et al, 2005), the response to stimulation can vary considerably between individuals (Hamada et al, 2013) and between studies (Di Lazzaro et al, 2011;Gentner et al, 2008;Goldsworthy et al, 2014a, b;Goldsworthy et al, 2012a, b;Hasan et al, 2012;McAllister et al, 2011;Todd et al, 2009;Vallence et al, 2013;Zafar et al, 2008). Most studies use a standard MEP amplitude of ~1 mV to probe the plasticity response to TBS.…”

Inter- and intra-subject variability of motor cortex plasticity following continuous theta-burst stimulation

“…While many studies report significant changes in corticospinal excitability following application of rTMS (e.g. Di Lazzaro et al 2011;Huang et al 2007;Huang et al 2005;Stefan et al 2000) a number of others do not (Clow et al 2014;Goldsworthy et al 2012a;Hamada et al 2013;McAllister et al 2013;McAllister et al 2011), highlighting that the response to rTMS is rather variable. Large inter-and intra-subject NIBS response variability is a limiting factor in both basic and applied research .…”