Premotor transcranial direct current stimulation (tDCS) affects primary motor excitability in humans

Department of Clinical Neurophysiology, Georg-August University, Robert Koch Strasse 40, 37075 Göttingen, Germany.
European Journal of Neuroscience (Impact Factor: 3.67). 04/2008; 27(5):1292-300. DOI: 10.1111/j.1460-9568.2008.06090.x
Source: PubMed

ABSTRACT Recent studies have shown that repetitive transcranial magnetic stimulation (rTMS) over the premotor cortex (PM) modifies the excitability of the ipsilateral primary motor cortex (M1). Transcranial direct current stimulation (tDCS) is a new method to induce neuroplasticity in humans non-invasively. tDCS generates neuroplasticity directly in the cortical area under the electrode, but might also induce effects in distant brain areas, caused by activity modulation of interconnected areas. However, this has not yet been tested electrophysiologically. We aimed to study whether premotor tDCS can modify the excitability of the ipsilateral M1 via cortico-cortical connectivity. Sixteen subjects received cathodal and anodal tDCS of the PM and eight subjects of the dorsolateral prefrontal cortex. Premotor anodal, but not premotor cathodal or prefrontal tDCS, modified selectively short intracortical inhibition/intracortical facilitation (SICI/ICF), while motor thresholds, single test-pulse motor-evoked potential and input-output curves were stable throughout the experiments. Specifically, anodal tDCS decreased intracortical inhibition and increased paired-pulse excitability. The selective influence of premotor tDCS on intracortical excitability of the ipsilateral M1 suggests a connectivity-driven effect of tDCS on remote cortical areas. Moreover, this finding indirectly substantiates the efficacy of tDCS to modulate premotor excitability, which might be of interest for applications in diseases accompanied by pathological premotor activity.

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    • "The primary effect is a polaritydependent shift in resting membrane potentials, and sufficiently long stimulation results in long-lasting excitability enhancements or reductions which depend on the glutamatergic and GABAergic systems (Nitsche & Paulus, 2001, 2011; Nitsche et al., 2003a,b, 2005; Stagg et al., 2009). tDCS is suited to the exploration of plasticity of interregional cortical connectivity, as shown by its ability to induce plasticity of premotor–motor cortex connections (Boros et al., 2008), and has been shown to improve motor learning (Nitsche et al., 2003c; Reis et al., 2009). We hypothesized that excitabilityenhancing anodal tDCS applied to the posterior parietal cortex (P3) will enhance M1 excitability, while cathodal tDCS over the same area will result in antagonistic effects. "
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    ABSTRACT: The posterior parietal cortex is part of the cortical network involved in motor learning and is structurally and functionally connected with the primary motor cortex (M1). Neuroplastic alterations of neuronal connectivity might be an important basis for learning processes. These have however not been explored for parieto-motor connections in humans by transcranial direct current stimulation (tDCS). Exploring tDCS effects on parieto-motor cortical connectivity might be functionally relevant, because tDCS has been shown to improve motor learning. We aimed to explore plastic alterations of parieto-motor cortical connections by tDCS in healthy humans. We measured neuroplastic changes of corticospinal excitability via motor evoked potentials (MEP) elicited by single-pulse transcranial magnetic stimulation (TMS) before and after tDCS over the left posterior parietal cortex (P3), and 3 cm posterior or lateral to P3, to explore the spatial specificity of the effects. Furthermore, short-interval intracortical inhibition/intracortical facilitation (SICI/ICF) over M1, and parieto-motor cortical connectivity were obtained before and after P3 tDCS. The results show polarity-dependent M1 excitability alterations primarily after P3 tDCS. Single-pulse TMS-elicited MEPs, M1 SICI/ICF at 5 and 7 ms and 10 and 15 ms interstimulus intervals (ISIs), and parieto-motor connectivity at 10 and 15 ms ISIs were all enhanced by anodal stimulation. Single pulse-TMS-elicited MEPs, and parieto-motor connectivity at 10 and 15 ms ISIs were reduced by cathodal tDCS. The respective corticospinal excitability alterations lasted for at least 120 min after stimulation. These results show an effect of remote stimulation of parietal areas on M1 excitability. The spatial specificity of the effects and the impact on parietal cortex-motor cortex connections suggest a relevant connectivity-driven effect. © 2015 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.
    European Journal of Neuroscience 02/2015; 41(6). DOI:10.1111/ejn.12840 · 3.67 Impact Factor
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    • "Stimulation of PM using unilateral tDCS montages has been investigated in three studies with mixed results (Boros et al. 2008; Kirimoto et al. 2009, 2011). Kirimoto et al. (2009, 2011) found PM anodal and cathodal stimulation suppressed and facilitated cMEPs, respectively, but only with an electrode Ն18 cm 2 , whereas Boros et al. (2008) found no change after PM anodal or cathodal tDCS on MEP amplitude with singlepulse TMS. The effects of direct current stimulation targeting PM appear less robust than M1 stimulation. "
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    ABSTRACT: Propriospinal neurons (PN) are essential for accurate control of the upper limb, receiving bilateral input from premotor (PM) and primary motor (M1) cortices. In humans, excitability of PNs can be estimated from motor evoked potentials (MEPs) using transcranial magnetic stimulation (TMS) and peripheral nerve stimulation to summate at the C3-C4 level of the spinal cord. Transcranial direct current stimulation (tDCS) alters excitability of cortical and subcortical areas. A recent study demonstrated that cathodal-tDCS can suppress facilitatory (FAC) and inhibitory (INH) components of PN excitability, presumably via effects on cortico-reticulospinal neurons (Bradnam et al., 2011b). The present study investigated the effects of bilateral tDCS with healthy subjects. The cathode was placed over left dorsal PM or M1, and the anode over right M1 in separate sessions (PM-M1, M1-M1 or Sham). TMS of right M1 elicited MEPs in left Biceps Brachii across a range of TMS intensities chosen to examine PN-mediated FAC and INH. Conditioning was applied using median nerve stimulation to coincide with TMS and peripheral volleys summating at the C3-C4 level. All participants showed FAC at TMS intensities near active motor threshold and INH at slightly higher intensities. After tDCS, FAC was reduced for M1-M1 compared to Sham but not after PM-M1 stimulation. Contrary to an earlier study with cathodal-tDCS, INH was unchanged across all sessions. The difference between these and earlier findings may relate to dual vs single hemisphere M1 stimulation. M1-M1 tDCS may be a useful adjuvant to techniques that aim to reduce upper limb impairment after stroke.
    Journal of Neurophysiology 03/2014; 111(11). DOI:10.1152/jn.00879.2013 · 3.04 Impact Factor
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    • "Apart from transcranial magnetic stimulation (TMS) and repetitive transcranial magnetic stimulation, which are neurostimulatory techniques, transcranial direct current stimulation (tDCS) is a well-known neuromodulatory technique. This technique has been involved in a number of important discoveries in the field of human cortical function and has become a well-established method for enhancing brain function in healthy participants (Antal et al., 2007; Boggio et al., 2006; Boros et al., 2008; Uy and Ridding, 2003) and patients with neurological conditions (Boggio et al., 2007; Fregni et al., 2005; Hummel et al., 2005; Benninger et al., 2010). The direction of corticospinal excitability (CSE) changes depends on the polarity of the active electrode. "
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    ABSTRACT: We aimed to compare the effects of anodal-transcranial pulsed current stimulation (a-tPCS) with conventional anodal transcranial direct current stimulation (a-tDCS) on corticospinal excitability (CSE) in healthy individuals. CSE of the dominant primary motor cortex of the resting right extensor carpi radialis muscle was assessed before, immediately, 10, 20 and 30min after application of four experimental conditions: (1) a-tDCS, (2) a-tPCS with short inter-pulse interval (a-tPCSSIPI, 50ms), (3) a-tPCS with long inter-pulse interval (a-tPCSLIPI., 650ms) and (4) sham a-tPCS. The total charges were kept constant in all experimental conditions except sham condition. The outcome measure in this study was motor evoked potentials. Only a-tDCS and a-tPCSSIPI (P<0.05) induced significant increases in CSE, lasted for at least 30min. Post-hoc tests indicated that this increase was larger in a-tPCSSIPI (P<0.05). There were no significant changes following application of a-tPCSLIPI and sham a-tPCS. All participants tolerated the applied currents in all experimental conditions very well. Compared to a-tDCS, a-tPCSSIPI is a better technique for enhancement of CSE. There were no sham effects for application of a-tPCS. However, unlike a-tDCS which modifies neuronal excitability by tonic depolarization of the resting membrane potential, a-tPCS modifies neuronal excitability by a combination of tonic and phasic effects. a-tPCS could be considered as a promising neuromodulatory tool in basic neuroscience and as a therapeutic technique in neurorehabilitation.
    Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 09/2013; 125(2). DOI:10.1016/j.clinph.2013.08.025 · 2.98 Impact Factor
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