Abstract
Noninvasive brain stimulation techniques such as transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) can induce long-term potentiation-like facilitation, but whether the combination of TMS and tDCS has additive effects is unclear. To address this issue, in this randomized crossover study, we investigated the effect of preconditioning with cathodal high-definition (HD) tDCS on intermittent theta burst stimulation- (iTBS-) induced plasticity in the left motor cortex. A total of 24 healthy volunteers received preconditioning with cathodal HD-tDCS or sham intervention prior to iTBS in a random order with a washout period of 1 week. The amplitude of motor evoked potentials (MEPs) was measured at baseline and at several time points (5, 10, 15, and 30 min) after iTBS to determine the effects of the intervention on cortical plasticity. Preconditioning with cathodal HD-tDCS followed by iTBS showed a greater increase in MEP amplitude than sham cathodal HD-tDCS preconditioning and iTBS at each time postintervention point, with longer-lasting after-effects on cortical excitability. These results demonstrate that preintervention with cathodal HD-tDCS primes the motor cortex for long-term potentiation induced by iTBS and is a potential strategy for improving the clinical outcome to guide therapeutic decisions.
Highlights
Noninvasive brain stimulation (NIBS) techniques such as transcranial magnetic stimulation (TMS) and transcranial direct current stimulation can induce a long-term potentiation- (LTP-) like facilitation or long-term depression- (LTD-) like suppression [1,2,3]
When applied to the primary motor cortex (M1), inhibitory preconditioning with cathodal transcranial direct current stimulation (tDCS) and subsequent 5-Hz rTMS significantly increased the excitability of the corticospinal tract, whereas facilitatory preconditioning with anodal tDCS and subsequent 5-Hz rTMS decreased excitability [7, 9]
Subjects showed an increase in motor evoked potentials (MEPs) amplitude at 5 min postintervention compared to the respective baseline values in both intervention groups
Summary
Noninvasive brain stimulation (NIBS) techniques such as transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) can induce a long-term potentiation- (LTP-) like facilitation or long-term depression- (LTD-) like suppression [1,2,3]. Depending on the stimulus frequency of repetitive (r)TMS or the polarity of electrodes placed on the scalp in tDCS, these 2 types of stimulation can bidirectionally regulate the excitability of neurons in neural networks [4,5,6]. Whether a greater effect can be achieved by combining TMS and tDCS is an open question. Preconditioning with tDCS can alter the functional state of the motor cortex, resulting in TMS-induced changes in cortical plasticity [7,8,9]. The preconditioning effects of tDCS may be related to synaptic homeostatic plasticity which is thought to maintain neural activity within a certain physiological range and ensure the stability of neural network activity [10]. As described in the Bienenstock–Cooper–Munro (BCM) theory of bidirectional synaptic
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