Effects of transcranial direct current stimulation over human motor cortex on corticospinal and transcallosal excitability
ABSTRACT Weak transcranial direct current stimulation (tDCS) can induce long lasting changes in cortical excitability. In the present study we asked whether tDCS applied to the left primary motor cortex (M1) also produces aftereffects distant from the site of the stimulating electrodes. We therefore tested corticospinal excitability in the left and the right M1 and transcallosal excitability between the two cortices using transcranial magnetic stimulation (TMS) before and after applying tDCS. Eight healthy subjects received 10 min of anodal or cathodal tDCS (1 mA) to the left M1. We examined the amplitude of contralateral motor evoked potentials (MEPs) and the onset latency and duration of transcallosal inhibition with single pulse TMS. MEPs evoked from the tDCS stimulated (left) M1 were increased by 32% after anodal and decreased by 27% after cathodal tDCS, while transcallosal inhibition evoked from the left M1 remained unchanged. The effect on MEPs evoked from the left M1 lasted longer for cathodal than for anodal tDCS. MEPs evoked from the right M1 were unchanged whilst the duration of transcallosal inhibition evoked from the right M1 was shortened after cathodal tDCS and prolonged after anodal tDCS. The duration of transcallosal inhibition returned to control values before the effect on the MEPs from the left M1 had recovered. These findings are compatible with the idea that tDCS-induced aftereffects in the cortical motor system are limited to the stimulated hemisphere, and that tDCS not only affects corticospinal circuits involved in producing MEPs but also inhibitory interneurons mediating transcallosal inhibition from the contralateral hemisphere.
- SourceAvailable from: Gianpiero Liuzzi
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- "The cathode was placed on the skin overlying the contralateral supraorbital region (Nitsche and Paulus, 2000). Anodal tDCS applied in this way results in an increase in excitability of the underlying MI that outlasts the period of stimulation (Lang et al., 2004). Sham stimulation was administered according to a well-established protocol (Gandiga et al., 2006). "
ABSTRACT: Changes in γ-aminobutyric acid (GABA) mediated synaptic transmission have been associated with age-related motor and cognitive functional decline. Since anodal transcranial direct current stimulation (atDCS) has been suggested to target cortical GABAergic inhibitory interneurons, its potential for the treatment of deficient inhibitory activity and functional decline is being increasingly discussed. Therefore, after-effects of a single session of atDCS on resting-state and event-related short-interval intracortical inhibition (SICI) as evaluated with double-pulse TMS and dexterous manual performance were examined using a sham-controlled cross-over design in a sample of older and younger participants. The atDCS effect on resting-state inhibition differed in direction, magnitude, and timing, i.e., late relative release of inhibition in the younger and early relative increase in inhibition in the older. More pronounced release of event-related inhibition after atDCS was exclusively seen in the older. Event-related modulation of inhibition prior to stimulation predicted the magnitude of atDCS-induced effects on resting-state inhibition. Specifically, older participants with high modulatory capacity showed a disinhibitory effect comparable to the younger. Beneficial effects on behavior were mainly seen in the older and in tasks requiring higher dexterity, no clear association with physiological changes was found. Differential effects of atDCS on SICI, discussed to reflect GABAergic inhibition at the level of the primary motor cortex, might be distinct in older and younger participants depending on the functional integrity of the underlying neural network. Older participants with preserved modulatory capacity, i.e., a physiologically "young" motor network, were more likely to show a disinhibitory effect of atDCS. These results favor individually tailored application of tDCS with respect to specific target groups.Frontiers in Aging Neuroscience 07/2014; 6:146. DOI:10.3389/fnagi.2014.00146 · 2.84 Impact Factor
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- "Nitsche and Paulus (2000) were able to demonstrate that anodal stimulation of the motor cortex enhances cortical excitability, whereas cathodal stimulation reduces it. Moreover, several tDCS experiments have shown to be significantly dependent on the polarity of the electrodes (Antal et al 2003, Lang et al 2004). Our results clearly showed the strong influence of, especially, the compartments CSF and white matter on the brain current density orientation component, underpinning the necessity of modeling these tissue compartments (at least in a homogenized isotropic way) for accurate tDCS modeling. "
ABSTRACT: Objective. We investigate volume conduction effects in transcranial direct current stimulation (tDCS) and present a guideline for efficient and yet accurate volume conductor modeling in tDCS using our newly-developed finite element (FE) approach. Approach. We developed a new, accurate and fast isoparametric FE approach for high-resolution geometry-adapted hexahedral meshes and tissue anisotropy. To attain a deeper insight into tDCS, we performed computer simulations, starting with a homogenized three-compartment head model and extending this step by step to a six-compartment anisotropic model. Main results. We are able to demonstrate important tDCS effects. First, we find channeling effects of the skin, the skull spongiosa and the cerebrospinal fluid compartments. Second, current vectors tend to be oriented towards the closest higher conducting region. Third, anisotropic WM conductivity causes current flow in directions more parallel to the WM fiber tracts. Fourth, the highest cortical current magnitudes are not only found close to the stimulation sites. Fifth, the median brain current density decreases with increasing distance from the electrodes. Significance. Our results allow us to formulate a guideline for volume conductor modeling in tDCS. We recommend to accurately model the major tissues between the stimulating electrodes and the target areas, while for efficient yet accurate modeling, an exact representation of other tissues is less important. Because for the low-frequency regime in electrophysiology the quasi-static approach is justified, our results should also be valid for at least low-frequency (e.g., below 100 Hz) transcranial alternating current stimulation.Journal of Neural Engineering 12/2013; 11(1):016002. DOI:10.1088/1741-2560/11/1/016002 · 3.42 Impact Factor
Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 10/2013; 125(3). DOI:10.1016/j.clinph.2013.10.003 · 2.98 Impact Factor
- "Like most modeling studies of tDCS, Parazzini et al. (2014) rely on the ''quasi-uniform'' assumption (Bikson et al., 2013) to suggest electric field (or current density) intensity in any given region indicates the relative neuromodulation of that region. None-the-less, an open question is given that both cortical architecture and cell morphology of the cerebellum differ from cortical targets investigated in a majority of tDCS studies, for example motor regions (Nitsche and Paulus, 2000; Lang et al., 2004). Will the cerebellum respond distinctly to an applied electric field? "