The effects of prolonged cathodal direct current stimulation on the excitatory and inhibitory circuits of the ipsilateral and contralateral motor cortex

Abstract

Weak cathodal transcranial direct current stimulation (tDCS) of the human hand area modulates corticospinal excitability with a suppression of motor-evoked potentials (MEPs) evoked by transcranial magnetic stimulation (TMS). The changes in excitability persist beyond the time of stimulation if tDCS is given for several minutes and can remain stable for an hour or more. The aim of present study was to evaluate whether a long-lasting suppression of cortical excitability could be induced by prolonged cathodal tDCS (20 min of stimulation). We also explored the impact of brain-derived neurotrophic factor (BDNF) gene polymorphisms, on tDCS after-effects. Cortical excitability to single and paired-pulse TMS was evaluated both for the stimulated and contralateral hemisphere, before and up to 24 h after 20 min of cathodal tDCS. We evaluated threshold and amplitude of MEPs, short interval intracortical inhibition (SICI), and intracortical facilitation (ICF). tDCS produced a pronounced suppression of MEP amplitude that was still significant at 3 h after the end of stimulation. The BDNF genotype had not influence on tDCS after-effects. Thresholds for MEPs, SICI and ICF were not affected. No significant effect was observed in the contralateral hemisphere. Twenty minutes of cathodal tDCS is capable of inducing a long-lasting suppression of the excitability of the human motor cortex.

Delayed pain decrease following M1 tDCS in spinal cord injury: A randomized controlled clinical trial

“…Delayed tDCS-response has been observed in previous studies assessing the effect of tDCS on pain and MEP in patients with migraine and elderly people, respectively [48,49]. tDCS mechanisms are related to its influence on sodium and calcium channels opening and NMDA receptors excitability [50], while longlasting effects are analogous to activity-dependent synaptic plasticity, namely long-term potentiation (LTP) and long-term depression (LTD) [51][52][53]. Structural, functional and connectivity alterations at the cortical level have been described in patients with SCI, especially in the somatosensory cortex, consequently to the injury itself, as well as a result of the lack of sensory and motor inputs [54][55][56]; these changes being related to neuropathic pain [57].…”

Noninvasive Neuromodulation in Poststroke Gait Disorders

“…[84][85][86] In general, a single session of NIBS induces reversible effects that last from a few minutes up to about 3 hours, depending on the stimulation type and parameters. 87,88 Data on healthy individuals suggest a long-lasting enhancement of cognitive and motor skills acquisitions with multiple daily stimulation sessions, through an effect on consolidation, 89,90 but more experiments are required to assess the effects of repeated applications of TMS or tDCS in association with multiple training sessions in patients. 91 2.…”

Preconditioning tDCS facilitates subsequent tDCS effect on skill acquisition in older adults

“…It is assumed that the neuronal changes associated with the persisting effects of tDCS are analogous to activity-dependent synaptic plasticity (i.e., LTP and LTD;Di Lazzarro et al 2012) which is N-methyl-D-aspartate (NMDA) receptor dependent (Di Lazzaro et al 2012). The application of tDCS over the primary motor cortex (M1) elicits changes in corticospinal excitability in a polarity specific manner: motor evoked potentials (MEPs) evoked by transcranial magnetic stimulation (TMS) are potentiated by tDCS with the anodal electrode placed over M1and suppressed by tDCS with the cathodal electrode placed over M1 (Nitsche and Paulus 2000), suggesting the facilitatory and inhibitory nature of anodal and cathodal under the stimulation site, respectively.…”