i-SATA: A MATLAB based toolbox to estimate current density generated by transcranial direct current stimulation in an individual brain.
TL;DR: Researchers can use individual-SATA (-SATA) to extend it to individual head for customizing tDCS-montages and provide estimates of the current-density induced across an individual's cortical lobes and gyri as tested on images from two different scanners.
Abstract: Objective Transcranial Direct Current Stimulation (tDCS) is a technique where a weak current is passed through the electrodes placed on the scalp. The distribution of the electric current induced in the brain due to tDCS is provided by simulation toolbox like Realistic volumetric Approach based Simulator for Transcranial electric stimulation (ROAST). However, the procedure to estimate the total current density induced at the target and the intermediary region of the cortex is complex. The Systematic-Approach-for-tDCS-Analysis (SATA) was developed to overcome this problem. However, SATA is limited to standardized (MNI152) headspace only. Here we develop individual-SATA (i-SATA) to extend it to individual head. Approach T1-weighted images of 15 subjects were taken from two Magnetic Resonance Imaging scanners of different strengths. Across the subjects, the montages were simulated in ROAST. i-SATA converts the ROAST output to Talairach space. The x, y and z coordinates of the anterior commissure (AC), posterior commissure (PC), and Mid-Sagittal (MS) points are necessary for the conversion. AC and PC are detected using the acpcdetect toolbox. We developed a method to determine the MS in the image and cross-verified its location manually using BrainSight®. Main results Determination of points with i-SATA is fast and accurate. The i-SATA provided estimates of the current-density induced across an individual's cortical lobes and gyri as tested on images from two different scanners. Significance Researchers can use i-SATA for customizing tDCS-montages. With i-SATA it is also easier to compute the inter-individual variation in current-density across the target and intermediary regions of the brain. The software is publicly available.
Citations
More filters
TL;DR: In this article, the effects of cortical anatomical parameters (volumes, dimension, and torque) on simulated tDCS current density in healthy young, middle-aged, and older males and females were investigated.
14 citations
TL;DR: In this article , the effects of cortical anatomical parameters (volumes, dimension, and torque) on simulated tDCS current density in healthy young, middle-aged, and older males and females were investigated.
14 citations
TL;DR: In this paper, the authors introduced a dose-target determination index (DTDI) to quantify the focality of tDCS and examined the dose-focality relationship in three different populations.
Abstract: Background: In transcranial direct current stimulation (tDCS), the injected current becomes distributed across the brain areas. The objective is to stimulate the target region of interest (ROI) while minimizing the current in non-target ROIs (the ‘focality’ of tDCS). For this purpose, determining the appropriate current dose for an individual is difficult. Aim: To introduce a dose–target determination index (DTDI) to quantify the focality of tDCS and examine the dose–focality relationship in three different populations. Method: Here, we extended our previous toolbox i-SATA to the MNI reference space. After a tDCS montage is simulated for a current dose, the i-SATA(MNI) computes the average (over voxels) current density for every region in the brain. DTDI is the ratio of the average current density at the target ROI to the ROI with a maximum value (the peak region). Ideally, target ROI should be the peak region, so DTDI shall range from 0 to 1. The higher the value, the better the dose. We estimated the variation of DTDI within and across individuals using T1-weighted brain images of 45 males and females distributed equally across three age groups: (a) young adults (20 ≤ x ˂ 40 years), (b) mid adults (40 ≤ x ˂ 60 years), and (c) older adults (60 ≤ x ˂ 80 years). DTDI’s were evaluated for the frontal montage with electrodes at F3 and the right supraorbital for three current doses of 1 mA, 2 mA, and 3 mA, with the target ROI at the left middle frontal gyrus. Result: As the dose is incremented, DTDI may show (a) increase, (b) decrease, and (c) no change across the individuals depending on the relationship (nonlinear or linear) between the injected tDCS current and the distribution of current density in the target ROI. The nonlinearity is predominant in older adults with a decrease in focality. The decline is stronger in males. Higher current dose at older age can enhance the focality of stimulation. Conclusion: DTDI provides information on which tDCS current dose will optimize the focality of stimulation. The recommended DTDI dose should be prioritized based on the age (>40 years) and sex (especially for males) of an individual. The toolbox i-SATA(MNI) is freely available.
6 citations
TL;DR: In this paper , the authors reviewed 94 clinical TES studies that leveraged ROAST for computational modeling and found that over 1800 individual heads have been modeled by RoAST for more than 30 different clinical applications.
2 citations
TL;DR: The CSF channels the flow of tDCS current between electrodes with focal ROIs acting like reservoirs of current, and was the principal determinant of focality.
Abstract: Background Conventionally, transcranial direct current stimulation (tDCS) aims to focalize the current reaching the target region-of-interest (ROI). The focality can be quantified by the dose-target-determination-index (DTDI). Despite having a uniform tDCS setup, some individuals receive focal stimulation (high DTDI) while others show reduced focality (“non-focal”). The volume of cerebrospinal fluid (CSF), gray matter (GM), and white matter (WM) underlying each ROI govern the tDCS current distribution inside the brain, thereby regulating focality. Aim To determine the regional volume parameters that differentiate the focal and non-focal groups. Methods T1-weighted images of the brain from 300 age-sex matched adults were divided into three equal groups- (a) Young (20 ≤ × < 40 years), (b) Middle (40 ≤ × < 60 years), and (c) Older (60 ≤ × < 80 years). For each group, inter and intra-hemispheric montages with electrodes at (1) F3 and right supraorbital region (F3-RSO), and (2) CP5 and Cz (CP5-Cz) were simulated, targeting the left- Dorsolateral Prefrontal Cortex (DLPFC) and -Inferior Parietal Lobule (IPL), respectively. Both montages were simulated for two current doses (1 and 2 mA). For each individual head simulated for a tDCS configuration (montage and dose), the current density at each region-of-interest (ROI) and their DTDI were calculated. The individuals were categorized into two groups- (1) Focal (DTDI ≥ 0.75), and (2) Non-focal (DTDI < 0.75). The regional volume of CSF, GM, and WM of all the ROIs was determined. For each tDCS configuration and ROI, three 3-way analysis of variance was performed considering- (i) GM, (ii) WM, and (iii) CSF as the dependent variable (DV). The age group, sex, and focality group were the between-subject factors. For a given ROI, if any of the 3 DV’s showed a significant main effect or interaction involving the focality group, then that ROI was classified as a “focal ROI.” Results Regional CSF was the principal determinant of focality. For interhemispheric F3-RSO montage, interaction effect (p < 0.05) of age and focality was observed at Left Caudate Nucleus, with the focal group exhibiting higher CSF volume. The CSF volume of focal ROI correlated positively (r ∼ 0.16, p < 0.05) with the current density at the target ROI (DLPFC). For intrahemispheric CP5-Cz montage, a significant (p < 0.05) main effect was observed at the left pre- and post-central gyrus, with the focal group showing lower CSF volume. The CSF volume correlated negatively (r ∼ –0.16, p < 0.05) with current density at left IPL. The results were consistent for both current doses. Conclusion The CSF channels the flow of tDCS current between electrodes with focal ROIs acting like reservoirs of current. The position of focal ROI in the channel determines the stimulation intensity at the target ROI. For focal stimulation in interhemispheric F3-RSO, the proximity of focal ROI reserves the current density at the target ROI (DLPFC). In contrast, for intrahemispheric montage (CP5-Cz), the far-end location of focal ROI reduces the current density at the target (IPL).
1 citations
References
More filters
TL;DR: It is proposed that cognitive control stems from the active maintenance of patterns of activity in the prefrontal cortex that represent goals and the means to achieve them, which provide bias signals to other brain structures whose net effect is to guide the flow of activity along neural pathways that establish the proper mappings between inputs, internal states, and outputs needed to perform a given task.
Abstract: ▪ Abstract The prefrontal cortex has long been suspected to play an important role in cognitive control, in the ability to orchestrate thought and action in accordance with internal goals. Its neural basis, however, has remained a mystery. Here, we propose that cognitive control stems from the active maintenance of patterns of activity in the prefrontal cortex that represent goals and the means to achieve them. They provide bias signals to other brain structures whose net effect is to guide the flow of activity along neural pathways that establish the proper mappings between inputs, internal states, and outputs needed to perform a given task. We review neurophysiological, neurobiological, neuroimaging, and computational studies that support this theory and discuss its implications as well as further issues to be addressed
10,943 citations
TL;DR: FieldTrip is an open source software package that is implemented as a MATLAB toolbox and includes a complete set of consistent and user-friendly high-level functions that allow experimental neuroscientists to analyze experimental data.
Abstract: This paper describes FieldTrip, an open source software package that we developed for the analysis of MEG, EEG, and other electrophysiological data. The software is implemented as a MATLAB toolbox and includes a complete set of consistent and user-friendly high-level functions that allow experimental neuroscientists to analyze experimental data. It includes algorithms for simple and advanced analysis, such as time-frequency analysis using multitapers, source reconstruction using dipoles, distributed sources and beamformers, connectivity analysis, and nonparametric statistical permutation tests at the channel and source level. The implementation as toolbox allows the user to perform elaborate and structured analyses of large data sets using the MATLAB command line and batch scripting. Furthermore, users and developers can easily extend the functionality and implement new algorithms. The modular design facilitates the reuse in other software packages.
7,963 citations
TL;DR: Transcranial electrical stimulation using weak current may be a promising tool to modulate cerebral excitability in a non‐invasive, painless, reversible, selective and focal way.
Abstract: The approach taken in this study to produce localised changes of cerebral excitability in the intact human was modulation of neuronal excitability by weak electric currents applied transcranially. So far, this technique has mainly been used in animal research, primarily through modulation of the resting membrane potential (Terzuolo & Bullock, 1956; Creutzfeld et al. 1962; Eccles et al. 1962; Bindman et al. 1964; Purpura & McMurtry, 1965; Artola et al. 1990; Malenka & Nicoll, 1999). In general, cerebral excitability was diminished by cathodal stimulation, which hyperpolarises neurones. Anodal stimulation caused neuronal depolarisation, leading to an increase in excitability (Bindman et al. 1962; Purpura & McMurtry, 1965), as was shown by spontaneous neuronal discharges and the amplitudes of evoked potentials (Landau et al. 1964; Purpura & McMurtry, 1965; Gorman, 1966). However, in single cortical layers opposite effects were seen (Purpura & McMurtry, 1965), underlining the fact that the effects of DC stimulation depend on the interaction of electric flow direction and neuronal geometry. Enduring effects of 5 h and longer have been described if the stimulation itself lasts sufficiently long, about 10–30 min. These prolonged effects are not simply due to prolonged membrane potential shifts or recurrent excitation, because intermittent complete cancellation of electrical brain activity by hypothermia does not abolish them (Gartside, 1968a,b). Long-term potentiation (LTP) and long-term depression (LTD) have been proposed as the likely candidates for this phenomenon (Hattori et al. 1990; Moriwaki, 1991; Islam et al. 1995; Malenka & Nicoll, 1999).
The concept described here was an attempt to induce neuronal excitability changes in man by application of weak DC stimulation through the intact skull. It has already been demonstrated within invasive presurgical epilepsy diagnostics that intracranial currents of sufficient strength can be achieved in humans by stimulation with surface electrodes at intensities of up to 1.5 mA (Dymond et al. 1975). A suitable candidate for evaluating cortical excitability changes is transcranial magnetic stimulation (TMS), because it allows the quantification of motor-cortical neurone responses in a painless and non-invasive manner. The amplitude of the resulting motor-evoked potential (MEP) represents the excitability of the motor system. In the following, we confirm the principal possibility of altering cortical excitability by applying weak DC. Furthermore we show that systematic DC stimulation with minimum stimulation duration and intensity is necessary for an effective application of weak current in humans. This is of particular importance for inducing effects which outlast the duration of stimulation.
4,672 citations
TL;DR: When used in concert with authors' deeper knowledge of an experiment, the TD system provides consistent and comprehensive labels for brain activation foci, which is better than that of the expert group.
Abstract: An automated coordinate-based system to retrieve brain labels from the 1988 Talairach Atlas, called the Talairach Daemon (TD), was previously introduced (Lancaster et al., 1997). In the present study, the TD system and its 3-D database of labels for the 1988 Talairach atlas were tested for labeling of functional activation foci. TD system labels were compared with author-designated labels of activation coordinates from over 250 published functional brain-mapping studies and with manual atlas-derived labels from an expert group using a subset of these activation coordinates. Automated labeling by the TD system compared well with authors' labels, with a 70% or greater label match averaged over all locations. Author-label matching improved to greater than 90% within a search range of 65 mm for most sites. An adaptive grey matter (GM) range-search utility was evaluated using individual activations from the M1 mouth region (30 subjects, 52 sites). It provided an 87% label match to Brodmann area labels (B A4&B A 6) within a search range of 65 mm. Using the adaptive GM range search, the TD system's overall match with authors' labels (90%) was better than that of the expert group (80%). When used in concert with authors' deeper knowledge of an experiment, the TD system provides consistent and comprehensive labels for brain activation foci. Additional suggested applications of the TD system include interactive labeling, anatomical grouping of activation foci, lesion-deficit analysis, and neuroanatomy education. Hum. Brain Mapping 10:120 -131, 2000. © 2000 Wiley-Liss, Inc.
3,380 citations
TL;DR: It is shown that electric fields may be clustered at distinct gyri/sulci sites because of details in tissue architecture/conductivity, notably cerebrospinal fluid (CSF).
1,071 citations