Siwei Bai

A computational modelling study of transcranial direct current stimulation montages used in depression.

Transcranial direct current stimulation (tDCS) is a neuromodulatory technique which involves passing a mild electric current to the brain through electrodes placed on the scalp. Several clinical studies suggest that tDCS may have clinically meaningful efficacy in the treatment of depression. The objective of this study was to simulate and compare the effects of several tDCS montages either used in clinical trials or proposed, for the treatment of depression, in different high-resolution anatomically-accurate head models. Detailed segmented finite element head models of two subjects were presented, and a total of eleven tDCS electrode montages were simulated. Sensitivity analysis on the effects of changing the size of the anode, rotating both electrodes and displacing the anode was also conducted on selected montages. The F3-F8 and F3-F4 montages have been used in clinical trials reporting significant antidepressant effects and both result in relatively high electric fields in dorsolateral prefrontal cortices. Other montages using a fronto-extracephalic or fronto-occipital approach result in greater stimulation of central structures (e.g. anterior cingulate cortex) which may be advantageous in treating depression, but their efficacy has yet to be tested in randomised controlled trials. Results from sensitivity analysis suggest that electrode position and size may be adjusted slightly to accommodate other priorities, such as skin discomfort and damage.

A computational model of direct brain excitation induced by electroconvulsive therapy: Comparison among three conventional electrode placements

BACKGROUND Electroconvulsive therapy (ECT) is a highly effective treatment for severe depressive disorder. Efficacy and cognitive outcomes have been shown to depend on variations in electrode placement and other stimulus parameters, presumably because of differences in the pattern of neuronal activation. This latter effect, however, is poorly understood. OBJECTIVE In this study, we present an anatomically accurate human head computational model to stimulate neuronal excitation during ECT, to better understand the effects of varying electrode placement and stimulus parameters. METHODS Electric field and current density throughout the head, as well as direct neural activation within the brain, were computed using the finite element method. Regions representing passive volume conductors (skin, skull, cerebrospinal fluid) were extracellularly coupled to an excitable neural continuum region representing the brain. The skull was modeled with anistropic electrical conductivity. RESULTS Simulation results indicated that direct activation of the brain occurred immediately beneath the electrodes on the scalp, consistent with existing imaging studies. In addition, we found that the brainstem was also activated using a right unilateral electrode configuration. Simulation also demonstrated that a reduction in stimulus amplitude or pulse width led to a reduction in the spatial extent of brain activation. CONCLUSIONS The novel model described in this study was able to simulate direct excitation of the brain during ECT, was useful in characterizing differences in neuronal activation as electrode placement, pulse width, and amplitude were altered, and is proposed as a tool for further exploring the effects of variations in ECT stimulation approaches. Results from the simulations assist in understanding recently described clinical phenomena, in particular, the reduction in cognitive side effects with ultrabrief pulse width stimulation, and greater effects of the ECT stimulus on cardiovascular function with unilateral electrode placement.

A pilot study of alternative transcranial direct current stimulation electrode montages for the treatment of major depression

BACKGROUND Typically, transcranial direct current stimulation (tDCS) treatments for depression have used bifrontal montages with anodal (excitatory) stimulation targeting the left dorsolateral prefrontal cortex (DLPFC). There is limited research examining the effects of alternative electrode montages. OBJECTIVE/HYPOTHESIS This pilot study aimed to examine the feasibility, tolerability and safety of two alternative electrode montages and provide preliminary data on efficacy. The montages, Fronto-Occipital (F-O) and Fronto-Cerebellar (F-C), were designed respectively to target midline brain structures and the cerebellum. METHODS The anode was placed over the left supraorbital region and the cathode over the occipital and cerebellar region for the F-O and F-C montages respectively. Computational modelling was used to determine the electric fields produced in the brain regions of interest compared to a standard bifrontal montage. The two montages were evaluated in an open label study of depressed participants (N=14). Mood and neuropsychological functioning were assessed at baseline and after four weeks of tDCS. RESULTS Computational modelling revealed that the novel montages resulted in greater activation in the anterior cingulate cortices and cerebellum than the bifrontal montage, while activation of the DLPFCs was higher for the bifrontal montage. After four weeks of tDCS, overall mood improvement rates of 43.8% and 15.9% were observed under the F-O and F-C conditions, respectively. No significant neuropsychological changes were found. LIMITATIONS The clinical pilot was open-label, without a control condition and computational modelling was based on one healthy participant. CONCLUSIONS Results found both montages safe and feasible. The F-O montage showed promising antidepressant potential.

Clinical Pilot Study and Computational Modeling of Bitemporal Transcranial Direct Current Stimulation, and Safety of Repeated Courses of Treatment, in Major Depression.

Objectives This study aimed to examine a bitemporal (BT) transcranial direct current stimulation (tDCS) electrode montage for the treatment of depression through a clinical pilot study and computational modeling. The safety of repeated courses of stimulation was also examined. Methods Four participants with depression who had previously received multiple courses of tDCS received a 4-week course of BT tDCS. Mood and neuropsychological function were assessed. The results were compared with previous courses of tDCS given to the same participants using different electrode montages. Computational modeling examined the electric field maps produced by the different montages. Results Three participants showed clinical improvement with BT tDCS (mean [SD] improvement, 49.6% [33.7%]). There were no adverse neuropsychological effects. Computational modeling showed that the BT montage activates the anterior cingulate cortices and brainstem, which are deep brain regions that are important for depression. However, a fronto-extracephalic montage stimulated these areas more effectively. No adverse effects were found in participants receiving up to 6 courses of tDCS. Conclusions Bitemporal tDCS was safe and led to clinically meaningful efficacy in 3 of 4 participants. However, computational modeling suggests that the BT montage may not activate key brain regions in depression more effectively than another novel montage—fronto-extracephalic tDCS. There is also preliminary evidence to support the safety of up to 6 repeated courses of tDCS.

Hybrid soft computing systems for electromyographic signals analysis: a review

Electromyographic (EMG) is a bio-signal collected on human skeletal muscle. Analysis of EMG signals has been widely used to detect human movement intent, control various human-machine interfaces, diagnose neuromuscular diseases, and model neuromusculoskeletal system. With the advances of artificial intelligence and soft computing, many sophisticated techniques have been proposed for such purpose. Hybrid soft computing system (HSCS), the integration of these different techniques, aims to further improve the effectiveness, efficiency, and accuracy of EMG analysis. This paper reviews and compares key combinations of neural network, support vector machine, fuzzy logic, evolutionary computing, and swarm intelligence for EMG analysis. Our suggestions on the possible future development of HSCS in EMG analysis are also given in terms of basic soft computing techniques, further combination of these techniques, and their other applications in EMG analysis.

A computational model of direct brain stimulation by electroconvulsive therapy

Electroconvulsive therapy (ECT) is the most effective treatment for severe depressive disorder, and yet the mechanisms of its therapeutic effects remain largely unknown. A novel computational model is presented in this study to simulate and investigate direct cortical excitation caused by bitemporal electroconvulsive therapy (BT ECT), using a finite element model (FEM) of the human head. The skull was modeled with anisotropic conductivity, with an excitable ionic neural model incorporated into the brain based on the classic Hodgkin-Huxley formulation. Results suggested that this model is able to reproduce direct stimulation of the cortex during the application of ECT.

Revisiting frontoparietal montage in electroconvulsive therapy: clinical observations and computer modeling: a future treatment option for unilateral electroconvulsive therapy.

Objectives The aim of this study was to compare the clinical effects of frontoparietal electrode placement, an alternative montage for right unilateral electroconvulsive therapy (ECT), with the commonly used temporoparietal montage. Methods In a single patient who received alternate treatments with the abovementioned right unilateral montages, within a treatment course of ECT, time-to-reorientation after each treatment and seizure expression were compared. Computer modeling was used to simulate and compare differences in electrical stimulation patterns in key cerebral regions, with the 2 montages. These simulations were done in an anatomically realistic head model recreated from magnetic resonance imaging scans of the patient’s head. Results Time-to-reorientation was shorter after treatment with frontoparietal ECT (mean, 28.3 minutes; SD, 2.9 minutes) than after temporoparietal ECT (mean, 50.0 minutes; SD, 11.5 minutes), suggesting less retrograde memory impairment. Seizure duration and expression were similar for the 2 montages. Computer modeling demonstrated less hippocampal and right inferior frontal cortical stimulation but comparable anterior cingulate cortex stimulation with the frontoparietal montage. Conclusions These results, although preliminary, suggest that the frontoparietal montage may result in less memory side effects, but comparable efficacy, to the temporoparietal montage.

Effect of white matter anisotropy in modeling electroconvulsive therapy

White matter in the brain exhibits strong anisotropic conductivity. Modeling studies on electroen-cephalography have found that such anisotropic conductivity greatly influences the estimated dipole source. In this study, we made a detailed comparison of the effects of conductivity anisotropy using a computational model of electroconvulsive therapy (ECT). The human head model was a high resolution finite element model generated from MRI scans, implemented with tissue heterogeneity and an excitable neural model incorporated in the brain. Results showed that anisotropy in conductivity had minimal effects on the location of the brain region that was maximally activated, but it had relatively large effects on deep brain structures.

Computational models of Bitemporal, Bifrontal and Right Unilateral ECT predict differential stimulation of brain regions associated with efficacy and cognitive side effects

BACKGROUND Extensive clinical research has shown that the efficacy and cognitive outcomes of electroconvulsive therapy (ECT) are determined, in part, by the type of electrode placement used. Bitemporal ECT (BT, stimulating electrodes placed bilaterally in the frontotemporal region) is the form of ECT with relatively potent clinical and cognitive side effects. However, the reasons for this are poorly understood. OBJECTIVE This study used computational modelling to examine regional differences in brain excitation between BT, Bifrontal (BF) and Right Unilateral (RUL) ECT, currently the most clinically-used ECT placements. Specifically, by comparing similarities and differences in current distribution patterns between BT ECT and the other two placements, the study aimed to create an explanatory model of critical brain sites that mediate antidepressant efficacy and sites associated with cognitive, particularly memory, adverse effects. METHODS High resolution finite element human head models were generated from MRI scans of three subjects. The models were used to compare differences in activation between the three ECT placements, using subtraction maps. RESULTS AND CONCLUSION In this exploratory study on three realistic head models, Bitemporal ECT resulted in greater direct stimulation of deep midline structures and also left temporal and inferior frontal regions. Interpreted in light of existing knowledge on depressive pathophysiology and cognitive neuroanatomy, it is suggested that the former sites are related to efficacy and the latter to cognitive deficits. We hereby propose an approach using binarised subtraction models that can be used to optimise, and even individualise, ECT therapies.

Effects of electroconvulsive therapy stimulus pulsewidth and amplitude computed with an anatomically-realistic head model

The efficacy and cognitive outcomes of electro-convulsive therapy (ECT) on psychiatric disorders have been shown to depend on variations in treatment technique. In order to investigate this, a high resolution finite element human head model was generated from MRI scans and implemented with tissue heterogeneity and an excitable ionic neural formulations in the brain. The model was used to compare the effects of altered ECT stimulus amplitude and pulse width on the spatial extent of directly activated brain regions. The results showed that decreases in both amplitude and pulse width could effectively lead to reductions in the size of activated brain regions.