Posts Tagged transcranial current stimulation

[Abstract] Realistic modeling of transcranial current stimulation: The electric field in the brain

Highlights

  • Computational models are required to optimize the electric field in the brain.
  • tCS pipelines allow for fast and semi-automatic production of realistic head models.
  • In-vivo validation studies corroborate electric field predictions from tCS models.
  • tCS modeling could help identify the causes for intra and inter-subject variability.
  • Successful application of multi-electrode montages strongly depends on tCS models

Abstract

Computational models of transcranial current stimulation (tCS) derived from MRI predict the electric field distribution in individual brains with reasonable accuracy and should be used to guide the selection of optimal stimulation parameters. Some recent advances that support this claim are: free toolboxes to generate individual head models for electric field calculations, the validation of model predictions in comparison to in-vivomeasurements, and new algorithms to optimize the electric field at the target with multi-electrode stimulation. Electrical impedance tomography may provide subject-specific estimates of the electric conductivity of the scalp and skull, thereby improving the accuracy of the electric field calculations. In the future, electric field models should be coupled with electrophysiological models to predict experimental outcomes.

Graphical abstract

Image 1 

via Realistic modeling of transcranial current stimulation: The electric field in the brain – ScienceDirect

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[ARTICLE] Opportunities for Guided Multichannel Non-invasive Transcranial Current Stimulation in Poststroke Rehabilitation – Full Text HTML

Stroke is a leading cause of serious long-term disability worldwide. Functional outcome depends on stroke location, severity and early intervention. Conventional rehabilitation strategies have limited effectiveness, and new treatments still fail to keep pace, in part due to a lack of understanding of the different stages in brain recovery and the vast heterogeneity in the post-stroke population. Innovative methodologies for restorative neurorehabilitation are required to reduce long-term disability and socioeconomic burden. Neuroplasticity is involved in post-stroke functional disturbances, and also during rehabilitation. Tackling post-stroke neuroplasticity by non-invasive brain stimulation is regarded as promising, but efficacy might be limited because of rather uniform application across patients despite individual heterogeneity of lesions, symptoms and other factors. Transcranial direct current stimulation (tDCS) induces and modulates neuroplasticity, and has been shown to be able to improve motor and cognitive functions. tDCS is suited to improve post-stroke rehabilitation outcomes, but effect sizes are often moderate and suffer from variability. Indeed, the location, extent and pattern of functional network connectivity disruption should be considered when determining the optimal location sites for tDCS therapies. Here, we present potential opportunities for neuroimaging-guided tDCS-based rehabilitation strategies after stroke that could be personalized. We introduce innovative multimodal intervention protocols based on multichannel tDCS montages, neuroimaging methods and real-time closed-loop systems to guide therapy. This might help to overcome current treatment limitations in post-stroke rehabilitation and increase our general understanding of adaptive neuroplasticity leading to neural reorganization after stroke.

Continue —> Frontiers | Opportunities for Guided Multichannel Non-invasive Transcranial Current Stimulation in Poststroke Rehabilitation | Stroke

Figure 1. Stimweaver simulations for (A) guided multichannel tDCS montages vs. (B) classical tDCS montages. (A) Multichannel tDCS representations for distributed cortical targets for (A.1) poststroke lower limb motor rehabilitation (top and back views, see Multichannel tDCS for Poststroke Lower Limb Motor Rehabilitation) and (A.2) poststroke aphasia rehabilitation (left and right views, see Multichannel tDCS for Poststroke Aphasia Rehabilitation). Optimal solution using eight Neuroelectrics Pistim circular electrodes (1 cm radius and Ag/Cl). Total injected current 4 mA. Plots of the normal component of the E-field (V/m) (left), tDCS target region (center left), priority level (center right), and relative error (right) shown on the gray matter. In the left column, positive (red) colors reflect ingoing, excitatory normal electric fields (blue the opposite). In the second column, red areas denote targets to facilitate activation and blue to suppress activation. The third column colors reflect the importance (weight) of each area taking positive values up to 20. A dark blue cortical area reflects minimum/default priority and a red area maximum priority. In-between colors denote the corresponding intermediate priority. The last column provides a visual display of the match of electric fields solution to target [the relative error (10)]. Note that this model may not fit each poststroke patient with lower limb (A.1) or language (A.2) impairment because areas important for restitution are likely to be different according to lesion size and location (see Multichannel tDCS for Poststroke Lower Limb Motor Rehabilitation and Multichannel tDCS for Poststroke Aphasia Rehabilitation for details). (B) Plots of the normal component of the E-field (volts per meter) of classical tDCS montages for (B.1) anodic poststroke motor rehabilitation (top, back, and frontal views) and (B.2) cathodic poststroke aphasia rehabilitation (left, right, and frontal views). Solutions using two Neuroelectrics Pistim circular electrodes. Total injected current 2 mA. (B.1) Anodic stimulation over the M1 affected area: “active” electrode on C1 and cathode (return electrode) over the contralateral supraorbital area (38). (B.2) Cathodic stimulation over the right homolog of Broca’s area: “active” electrode on F6 and anode (return electrode) over the contralateral supraorbital area (47).

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[BLOG POST] A window into the brain networks: magnetoencephalography (MEG) and simultaneous Transcranial Current Stimulation (tCS). | Blog Neuroelectrics

A window into the brain networks: magnetoencephalography (MEG) and simultaneous Transcranial Current Stimulation (tCS).

Based on already published large evidence, non-invasive brain stimulation (NIBS) techniques like tdCS represent very important approach for the improvement of abnormal brain functions in various conditions (psychiatric and neurological). NIBS can induce temporary changes of neural oscillations and performance on various functional tasks. One of the key-points in understanding a mechanism of NIBS is the knowledge about the brains response to current stimulation and underlying brain network dynamics changes. Until recently, concurrent observation of the effect of NIBS on multiple brain networks interactions and most importantly, how current stimulation modifies these networks remained unknown because of difficulties in simultaneous recording and current stimulation. Recently, in Neuroelectrics wireless hybrid EEG/tCS 8-channel neurostimulator system has been developed that allows simultaneous EEG recording and current stimulation. Now, a relatively new imaging technique called magnetoencephalography (MEG) has emerged as a procedure that can bring new inside into brain dynamics. In this context, our group conducted a successfully proof of concept test to ensure the feasibility of concurrent MEG recording and current stimulation using Starstim and a set of non-ferrous electrodes (Figure 1). But first of all, what actually is MEG? Magnetoencephalography (MEG) is a noninvasive recording method of the magnetic flux from the head surface. Magnetic flux is associated with intracranial electrical currents produced by neural activity (the neural currents are caused by a flow of ions through postsynaptic dendritic membranes). From Maxwell equations, magnetic fields are found whenever there is a current flow, whether in a wire or a neuronal element. Hence, MEG detects these magnetic fields generated by spontaneous or evoked brain activity.

Continue —> A window into the brain networks: magnetoencephalography (MEG) and simultaneous Transcranial Current Stimulation (tCS). | Blog Neuroelectrics

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[Blog Post] Quick and Dirty Guide on Transcranial Current Stimulation

18 December, 2014

by Aureli Soria-Frisch

While heading to Petronas Technology University where I will give a course on transcranial current stimulation (tCS) basics I summarized the basics of the technology and particularly on Starstim, the device we envisioned and started to develop within the HIVE project. tCS devices allow the controlled injection of low-amplitude electrical currents into the cerebral cortex through the electrodes, which are non-invasively placed on the scalp.

brain_pic1

In this sense they play the opposite role to EEG, i.e. not for monitoring brain activity but for modifying it. There has been some advancement in the tCS field, but the technology and its effects on the brain are still not fully understood. Well, the effects are showing up more and more as studies and clinical trials increase. As a matter of fact, publications on tCS have multiplied by a factor of 4 in the last 4 years, and the clinical trials involving it, even by a factor of 10. But what is still not really understood is what causes this effect from both an electrophysiological as well as therapeutic point of view. I would like to comment on the electrophysiological effects giving some quick hints on what makes the applied electrical current affect the brain activity at the neuronal level. The state of the art is far from this understanding on its effects at neuronal population level and at a global brain level, i.e. connectivity, which have been much less studied.

Different types of tCS

Continue —> Quick and Dirty Guide on Transcranial Current Stimulation | Blog Neuroelectrics.

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[WHITE PAPER] tDCS clinical research – highlights: Depression – Full Text PDF

Is transcranial current stimulation (tCS, including direct current, tDCS, alternating current, tACS, or random noise stimulation tRNS) effective for the treatment of depression?

Under what conditions? With what montages? We focus here on a review of the recent literature on this topic. We have relied on Google Scholar and also PubMed to carry out the search, including the terms of tDCS, tACS, tRNS as well as Depression (from March 2012 and till Sep 2013).

As you can read below, there quite a few encouraging results in this area, and study group sizes (the famous N) are moderately large. We try to indicate group size and the use of a sham-controlled, double-blind experimental technique. Most studies are careful about these crucial aspects. In addition, it is worth mentioning that there continues to be a lack of bad news from the safety point of view. This seems to be a common pattern of tDCS research (or tCS, in fact). I will discuss this further in a future post on an update on tCS Safety.

The typical target for treatment is anodal on the left DLPFC (F3 in the 10-20 EEG system) with the cathode over the contralateral orbit or, sometimes, over the right DLPFC. As in prior posts, in what follows we concentrate on relevant, study-oriented papers with patients, and leave reviews to the end. In order to make the reading lighter, we have edited the abstracts a bit (please click on the title link if you are interested in the paper)… Full Text PDF

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