a-tDCS Differential Modulation of Corticospinal Excitability: The Effects of Electrode Size (original) (raw)
Related papers
Clinical Neurophysiology, 2014
Transcranial pulsed current stimulation (tPCS) is a novel non-invasive neuromodulatory paradigm with less side effects compared to the conventional transcranial direct current stimulation (tDCS). Despite tDCS which modifies neuronal excitability by tonic depolarization of the resting membrane potential, tPCS modifies neuronal excitability by a combination of tonic and phasic effects. tPCS appears to be a promising tool for clinical neuroplasticity research as a new method of delivering transcranial stimulation for modulation of corticospinal excitability.
Revista Pesquisa em Fisioterapia, 2017
Transcranial Direct Current Stimulation (tDCS) uses a direct electrical current to modulate the activity of cortical neurons. Anodal tDCS (positive pole) increases the excitability of cortical neurons, while cathodic tDCS (negative pole) reduces it. However, when applied in the peripheral nervous system the effects are the opposite of cranial application. Furthermore, when central and peripheral stimuli are used concomitantly, their effects can be summed up. This has been demonstrated by combining tDCS with other forms of sensory peripheral stimulation. We propose a new electrode configuration to potentiate the excitatory and inhibitory effects of tDCS on neuronal excitability and increase upper limb motor function. Our hypothesis is that placement of the electrodes in the primary motor cortex (M1) and the contralateral brachial plexus (BP) would promote this potentiation by central and peripheral synaptic summation. We will test our hypothesis in two proof-of-concept studies. Study...
Anodal transcranial direct current stimulation (a-tDCS) of the primary motor cortex (M1) has been shown to be effective in increasing corticomotor excitability. Methods: We investigated whether longer applications of a-tDCS coincide with greater increases in corticomotor excitability compared to shorter application of a-tDCS. Ten right-handed healthy participants received one session of a-tDCS (1mA current) with shorter (10 min) and longer (10+10 min) stimulation durations applied to the left M1 of extensor carpi radialis muscle (ECR). Corticomotor excitability following application of a-tDCS was assessed at rest with transcranial magnetic stimulation (TMS) elicited motor evoked potentials (MEP) and compared with baseline data for each participant. Results: MEP amplitudes were increased following 10 min of a-tDCS by 67% (p = 0.001) with a further increase (32%) after the second 10 min of a-tDCS (p = 0.005). MEP amplitudes remained elevated at 15 min post stimulation compared to baseline values by 65% (p = 0.02). Discussion: The results demonstrate that longer application of a-tDCS within the recommended safety limits, increases corticomotor excitability with after effects of up to 15 minutes post stimulation.
A pilot study on effects of 4×1 High-Definition tDCS on motor cortex excitability
2012 Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2012
High-Definition transcranial Direct Current Stimulation (HD-tDCS) using specialized small electrodes has been proposed as a focal, non-invasive neuromodulatory technique. Here we provide the first evidence of a change in cortical excitability after HD-tDCS of the motor cortex, using TMS motor evoked potential (MEP) as the measure of excitability. Stimulation for 20 minutes at 1 mA with an anode centered over the hand area of the motor cortex and four surrounding return electrodes (anodal 4×1 montage) produced a significant increase in MEP amplitude and variability after stimulation, compared to sham stimulation. Stimulation was well tolerated by all subjects with adverse effects limited to transient sensation under the electrodes. A high-resolution computational model confirmed predictions of increased focality using the 4×1 HD tDCS montage compared to conventional tDCS. Simulations also indicated that variability in placement of the center electrode relative to the location of the target (central sulcus) could account for increasing variability. These results provide support for the careful use of this technique where focal tDCS is desired.
Archives of Physical Medicine and Rehabilitation, 2015
Objective-To investigate the effects of anodal transcranial direct current stimulation (a-tDCS) intensity on corticospinal excitability and affected muscle activation in individuals with chronic spinal cord injury (SCI). Design-Single blind, randomized, sham-controlled, crossover study. Setting-Medical Research Institute and Rehabilitation Hospital. Participants-Nine volunteers with chronic SCI and motor dysfunction in wrist extensor muscles. Intervention-Three single session exposures to 20 minutes of a-tDCS (anode over the extensor carpi radialis (ECR) muscle representation on the left primary motor cortex, cathode over the right supraorbital area), using 1 mA, 2 mA or sham stimulation, delivered at rest, with at least one week between sessions. Outcome Measures-Corticospinal excitability was assessed with motor evoked potentials (MEPs) from the ECR muscle using surface electromyography (EMG) following transcranial magnetic stimulation. Changes in spinal excitability, sensory threshold and muscle strength were also investigated. Results-Mean MEP amplitude significantly increased by ~40% immediately following 2 mA a-tDCS (Pre 0.36±0.1 mV; Post 0.47±0.11 mV; p=0.001), but not with 1 mA or sham. Maximal voluntary EMG measures remained unaltered across all conditions. Sensory threshold significantly decreased over time following 1 mA (p=0.002) and 2 mA (p=0.039) a-tDCS, and did not change with sham. F-wave persistence showed a non-significant trend for increase (Pre: 32±12%; Post: 41±10%; Follow-up: 46±12%) following 2 mA stimulation. No adverse effects were reported with any of the experimental conditions. Conclusion-Anodal-tDCS can transiently raise corticospinal excitability to affected muscles in chronic SCI patients following 2 mA stimulation. Sensory perception can improve with both 1 and 2 mA stimulation. This study gives support to the safe and effective use of a-tDCS using small electrodes in SCI patients, and highlights the importance of stimulation intensity.
Non-invasive brain stimulation for enhancement of corticospinal excitability and motor performance
Basic and clinical neuroscience, 2013
During the past 20 years, non-invasive brain stimulation has become an emerging field in clinical neuroscience due to its capability to transiently modulate corticospinal excitability, motor and cognitive functions. Whereas transcranial magnetic stimulation has been used extensively since more than two decades ago as a potential "neuromodulator", transcranial current stimulation (tCS) has more recently gathered increased scientific interests. The primary aim of this narrative review is to describe characteristics of different tCS paradigms. tCS is an umbrella term for a number of brain modulating paradigms such as transcranial direct current stimulation (tDCS), transcranial alternative current stimulation (tACS), and transcranial random noise stimulation (tRNS). Their efficacy is dependent on two current parameters: intensity and length of application. Unlike tACS and tRNS, tDCS is polarity dependent. These techniques could be used as stand-alone techniques or can be used ...
No robust online effects of transcranial direct current stimulation on corticospinal excitability
Brain Stimulation
Transcranial direct current stimulation (tDCS) has been used for over twenty years to modulate cortical (particularly motor corticospinal) excitability both during (online) and outlasting (offline) the stimulation, with the former effects associated to the latter. However, tDCS effects are highly variable, partially because stimulation intensity is commonly not adjusted individually (in contrast to transcranial magnetic stimulation, TMS). In Experiment 1, we therefore explored an empirical approach of personalizing tDCS intensity for the primary motor cortex (M1) based on dose-response curves (DRCs), individually relating tDCS Intensity (in steps from 0.3 to 2.0 mA) and Polarity (anodal, cathodal) to the online modulation of concurrent TMS motor evoked potentials (MEP), assessing DRC reliability across two separate days. No robust DRCs could be observed, neither at the individual nor at the group level, with the only robust effect being a (paradoxical) MEP facilitation during cathodal tDCS at 2.0 mA, but no modulation at traditional intensities of or near 1 mA. In Experiment 2, we therefore attempted to replicate the classical bidirectional online MEP modulation during 1 mA tDCS that had been reported by several of the early seminal tDCS papers. We either closely recreated stimulation parameters and temporal protocol of these original studies (Experiment 2A) or slightly modernized them according to current standards (Experiment 2B). In neither experiment did we observed any significant online MEP modulation. We conclude that an empirical titration of individually effective tDCS intensities may not be feasible as online tDCS effects do not appear to be sufficiently robust.
Variability in Response to Transcranial Direct Current Stimulation of the Motor Cortex
Brain Stimulation, 2014
Background: Responses to a number of different plasticity-inducing brain stimulation protocols are highly variable. However there is little data available on the variability of response to transcranial direct current stimulation (TDCS). Objective: We tested the effects of TDCS over the motor cortex on corticospinal excitability. We also examined whether an individual's response could be predicted from measurements of onset latency of motor evoked potential (MEP) following stimulation with different orientations of monophasic transcranial magnetic stimulation (TMS). Methods: Fifty-three healthy subjects participated in a crossover-design. Baseline latency measurements with different coil orientations and MEPs were recorded from the first dorsal interosseous muscle prior to the application of 10 min of 2 mA TDCS (0.057 mA/cm 2 ). Thirty MEPs were measured every 5 min for up to half an hour after the intervention to assess after-effects on corticospinal excitability. Results: Anodal TDCS at 2 mA facilitated MEPs whereas there was no significant effect of 2 mA cathodal TDCS. A two-step cluster analysis suggested that approximately 50% individuals had only a minor, or no response to TDCS whereas the remainder had a facilitatory effect to both forms of stimulation. There was a significant correlation between the latency difference of MEPs (anterioreposterior stimulation minus latero-medial stimulation) and the response to anodal, but not cathodal TDCS. Conclusions: The large variability in response to these TDCS protocols is in line with similar studies using other forms of non-invasive brain stimulation. The effects highlight the need to develop more robust protocols, and understand the individual factors that determine responsiveness.