Abstract
BackgroundTranscranial direct current stimulation (TDCS) targeting the primary motor hand area (M1-HAND) may induce lasting shifts in corticospinal excitability, but after-effects show substantial inter-individual variability. Functional magnetic resonance imaging (fMRI) can probe after-effects of TDCS on regional neural activity on a whole-brain level.ObjectiveUsing a double-blinded cross-over design, we investigated whether the individual change in corticospinal excitability after TDCS of M1-HAND is associated with changes in task-related regional activity in cortical motor areas.MethodsSeventeen healthy volunteers (10 women) received 20 min of real (0.75 mA) or sham TDCS on separate days in randomized order. Real and sham TDCS used the classic bipolar set-up with the anode placed over right M1-HAND. Before and after each TDCS session, we recorded motor evoked potentials (MEP) from the relaxed left first dorsal interosseus muscle after single-pulse transcranial magnetic stimulation(TMS) of left M1-HAND and performed whole-brain fMRI at 3 Tesla while participants completed a visuomotor tracking task with their left hand. We also assessed the difference in MEP latency when applying anterior-posterior and latero-medial TMS pulses to the precentral hand knob (AP-LM MEP latency).ResultsReal TDCS had no consistent aftereffects on mean MEP amplitude, task-related activity or motor performance. Individual changes in MEP amplitude, measured directly after real TDCS showed a positive linear relationship with individual changes in task-related activity in the supplementary motor area and AP-LM MEP latency.ConclusionFunctional aftereffects of classical bipolar anodal TDCS of M1-HAND on the motor system vary substantially across individuals. Physiological features upstream from the primary motor cortex may determine how anodal TDCS changes corticospinal excitability.
Highlights
Transcranial Direct Current Stimulation (TDCS) can noninvasively induce plasticity in the human brain by de- or hyperpolarizing neuronal membranes through the application of weak direct, electrical current
Using the amplitude of the motor evoked potential (MEP) as a measure of corticospinal excitability, many studies have demonstrated that corticospinal excitability increases when the anodal electrode is placed over the primary motor hand area (M1-HAND) while it decreases when the cathodal electrode is placed over primary motor cortex (M1)-HAND (Nitsche and Paulus, 2000; Liebetanz et al, 2002)
Using a double-blinded cross-over design, we investigated how individual TDCS-induced changes in corticospinal excitability, as reflected by MEP amplitude evoked by single-pulse transcranial magnetic stimulation (TMS), are associated with individual changes in regional cortical activity, as reflected by task-related blood oxygenation level dependent (BOLD)-Functional magnetic resonance imaging (fMRI)
Summary
Transcranial Direct Current Stimulation (TDCS) can noninvasively induce plasticity in the human brain by de- or hyperpolarizing neuronal membranes through the application of weak direct, electrical current. Even though TDCS induced MEP changes have been replicated various times (for review Nitsche and Paulus, 2011), many recent reports, including a large doubleblind, placebo-controlled trial, did not show significant effects of anodal TDCS on corticospinal excitability These recent studies consistently found that the individual change in MEP amplitude was highly variable (Horvath et al, 2014; Lopez-Alonso et al, 2014; Wiethoff et al, 2014; Chew et al, 2015; Strube et al, 2016; Ammann et al, 2017; Lefebvre et al, 2019; Jonker et al, 2020). Functional magnetic resonance imaging (fMRI) can probe after-effects of TDCS on regional neural activity on a whole-brain level
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