The Pursuit of DLPFC: Non-neuronavigated Methods to Target the Left Dorsolateral Pre-frontal Cortex With Symmetric Bicephalic Transcranial Direct Current Stimulation (tDCS)

Efficacy of non-invasive brain stimulation and neuronavigation for major depressive disorder: a systematic review and meta-analysis

INTRODUCTION

Repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) are increasingly used for major depressive disorder (MDD). Most tDCS and rTMS studies target the left dorsolateral prefrontal cortex, either with or without neuronavigation. We examined the effect of rTMS and tDCS, and the added value of neuronavigation in the treatment of MDD.

METHODS

A search on PubMed, Embase, and Cochrane databases for rTMS or tDCS randomized controlled trials of MDD up to 1 February 2023, yielded 89 studies. We then performed meta-analyses comparing tDCS efficacy to non-neuronavigated rTMS, tDCS to neuronavigated rTMS, and neuronavigated rTMS to non-neuronavigated rTMS. We assessed the significance of the effect in subgroups and in the whole meta-analysis with a z-test and subgroup differences with a chi-square test.

RESULTS

We found small-to-medium effects of both tDCS and rTMS on MDD, with a slightly greater effect from rTMS. No significant difference was found between neuronavigation and non-neuronavigation.

CONCLUSION

Although both tDCS and rTMS are effective in treating MDD, many patients do not respond. Additionally, current neuronavigation methods are not significantly improving MDD treatment. It is therefore imperative to seek personalized methods for these interventions.

Electrode positioning errors reduce current dose for focal tDCS set-ups: Evidence from individualized electric field mapping

OBJECTIVE

Electrode positioning errors contribute to variability of transcranial direct current stimulation (tDCS) effects. We investigated the impact of electrode positioning errors on current flow for tDCS set-ups with different focality.

METHODS

Deviations from planned electrode positions were determined using data acquired in an experimental study (N = 240 datasets) that administered conventional and focal tDCS during magnetic resonance imaging (MRI). Comparison of individualized electric field modeling for planned and empirically derived "actual" electrode positions was conducted to quantify the impact of positioning errors on the electric field dose in target regions for tDCS.

RESULTS

Planned electrode positions resulted in higher current dose in the target regions for focal compared to conventional montages (7-12%). Deviations from planned positions significantly reduced current flow in the target regions, selectively for focal set-ups (26-30%). Dose reductions were significantly larger for focal compared to conventional set-ups (29-43%).

CONCLUSIONS

Precise positioning is crucial when using focal tDCS set-ups to avoid significant reductions of current dose in the intended target regions.

SIGNIFICANCE

Our results highlight the urgent need to routinely implement methods for improving electrode positioning, minimization of electrode drift, verification of electrode positions before and/or after tDCS and also to consider positioning errors when investigating dose-response relationships, especially for focal set-ups.

Effects of Transcranial Direct Current Stimulation on Cognitive Function in Older Adults with and without Mild Cognitive Impairment: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

INTRODUCTION

Noninvasive brain stimulation (NIBS) has shown benefits for cognitive function in older adults. However, the effects of transcranial direct current stimulation (tDCS) on cognitive function in older adults are inconsistent across studies, and the evidence for tDCS has limitations. We aim to explore whether tDCS can improve cognitive function and different cognitive domains (i.e., learning and memory and executive function) in adults aged 65 years and older with and without mild cognitive impairment and to further analyze the influencing factors of tDCS.

METHODS

Five English databases (PubMed, Cochrane Library, EMBASE, Web of Science, the cumulative Index to Nursing and Allied Health Literature [CINAHL]) and four Chinese databases were searched from inception to October 14, 2023. Literature screening, data extraction, and quality assessment were completed independently by two reviewers. All statistical analyses were conducted using RevMan software (version 5.3). Standardized mean difference (SMD) along with a 95% confidence interval (CI) was used to express the effect size of the outcomes, and a random-effect model was also used.

RESULTS

A total of 10 RCTs and 1,761 participants were included in the meta-analysis, and the risk of bias in those studies was relatively low. A significant effect favoring tDCS on immediate postintervention cognitive function (SMD = 0.16, Z = 2.36, p = 0.02) was found. However, the effects on immediate postintervention learning and memory (SMD = 0.20, Z = 2.00, p = 0.05) and executive function (SMD = 0.10, Z = 1.22, p = 0.22), and 1-month postintervention cognitive function (SMD = 0.12, Z = 1.50, p = 0.13), learning and memory (SMD = 0.17, Z = 1.39, p = 0.16), and executive function (SMD = 0.08, Z = 0.67, p = 0.51) were not statistically significant.

CONCLUSION

tDCS can significantly improve the immediate postintervention cognitive function of healthy older adults and MCI elderly individuals. Additional longitudinal extensive sample studies are required to clarify the specific effects of tDCS on different cognitive domains, and the optimal tDCS parameters need to be explored to guide clinical practice.

Optimizing electrode placement for transcranial direct current stimulation in nonsuperficial cortical regions: a computational modeling study

Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation technique for modulating neuronal excitability by sending a weak current through electrodes attached to the scalp. For decades, the conventional tDCS electrode for stimulating the superficial cortex has been widely reported. However, the investigation of the optimal electrode to effectively stimulate the nonsuperficial cortex is still lacking. In the current study, the optimal tDCS electrode montage that can deliver the maximum electric field to nonsuperficial cortical regions is investigated. Two finite element head models were used for computational simulation to determine the optimal montage for four different nonsuperficial regions: the left foot motor cortex, the left dorsomedial prefrontal cortex (dmPFC), the left medial orbitofrontal cortex (mOFC), and the primary visual cortex (V1). Our findings showed a good consistency in the optimal montage between two models, which led to the anode and cathode being attached to C4-C3 for the foot motor, F4-F3 for the dmPFC, Fp2-F7 for the mOFC, and Oz-Cz for V1. Our suggested montages are expected to enhance the overall effectiveness of stimulation of nonsuperficial cortical areas.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13534-023-00335-2.

Adjunctive duration-doubled transcranial direct current stimulation for the treatment of depressive patients with suicidal ideation: study protocol for a double-blind, randomized, sham-controlled trial

BACKGROUND

The problem of suicide has become increasingly common in individuals with major depressive disorder (MDD). Transcranial direct current stimulation (tDCS) is an effective treatment for MDD with 2 milliamperes (mA) for at least 30 min per day for 2 weeks. This study aims to investigate the efficacy of daily duration-doubled tDCS as an adjunctive intervention for rapidly reducing suicidal ideation and improving depression in MDD patients.

METHODS

In this double-blind, randomized, sham-controlled study, 76 MDD patients with suicidal ideation are randomly assigned to either active (n=38) or sham (n=38) tDCS group. The anode and cathode are placed over the scalp areas corresponding to left and right dorsolateral prefrontal cortex (DLPFC), respectively, and each stimulation lasts for 60 min. The primary outcome is defined as change of Beck Scale for Suicide Ideation (BSI) after 5 and 10 sessions. The change of other clinical assessments, blood biomarkers related to suicidal ideation and depressive sumptoms are defined as secondary outcomes. Blood biomarkers related to suicidal ideation are collected at baseline and after 10 sessions.

DISCUSSION

This study suggests the adjunctive duration-doubled tDCS might be a novel method to rapidly reduce suicidal ideation and improve depressive symptom. The variation of biomarkers could be potential predictive models of suicide risk.

TRIAL REGISTRATION

The trial protocol is registered with ClinicalTrials.gov under protocol registration number NCT05555927. Registered on September 25, 2022.

Predicting the phase distribution during multi-channel transcranial alternating current stimulation in silico and in vivo

BACKGROUND

Transcranial alternating current stimulation (tACS) is a widely used noninvasive brain stimulation (NIBS) technique to affect neural activity. TACS experiments have been coupled with computational simulations to predict the electromagnetic fields within the brain. However, existing simulations are focused on the magnitude of the field. As the possibility of inducing the phase gradient in the brain using multiple tACS electrodes arises, a simulation framework is necessary to investigate and predict the phase gradient of electric fields during multi-channel tACS.

OBJECTIVE

Here, we develop such a framework for phasor simulation using phasor algebra and evaluate its accuracy using in vivo recordings in monkeys.

METHODS

We extract the phase and amplitude of electric fields from intracranial recordings in two monkeys during multi-channel tACS and compare them to those calculated by phasor analysis using finite element models.

RESULTS

Our findings demonstrate that simulated phases correspond well to measured phases (r = 0.9). Further, we systematically evaluated the impact of accurate electrode placement on modeling and data agreement. Finally, our framework can predict the amplitude distribution in measurements given calibrated tissues' conductivity.

CONCLUSIONS

Our validated general framework for simulating multi-phase, multi-electrode tACS provides a streamlined tool for principled planning of multi-channel tACS experiments.

Outcome measures for electric field modeling in tES and TMS: A systematic review and large-scale modeling study

BACKGROUND

Electric field (E-field) modeling is a potent tool to estimate the amount of transcranial magnetic and electrical stimulation (TMS and tES, respectively) that reaches the cortex and to address the variable behavioral effects observed in the field. However, outcome measures used to quantify E-fields vary considerably and a thorough comparison is missing.

OBJECTIVES

This two-part study aimed to examine the different outcome measures used to report on tES and TMS induced E-fields, including volume- and surface-level gray matter, region of interest (ROI), whole brain, geometrical, structural, and percentile-based approaches. The study aimed to guide future research in informed selection of appropriate outcome measures.

METHODS

Three electronic databases were searched for tES and/or TMS studies quantifying E-fields. The identified outcome measures were compared across volume- and surface-level E-field data in ten tES and TMS modalities targeting two common targets in 100 healthy individuals.

RESULTS

In the systematic review, we extracted 308 outcome measures from 202 studies that adopted either a gray matter volume-level (n = 197) or surface-level (n = 111) approach. Volume-level results focused on E-field magnitude, while surface-level data encompassed E-field magnitude (n = 64) and normal/tangential E-field components (n = 47). E-fields were extracted in ROIs, such as brain structures and shapes (spheres, hexahedra and cylinders), or the whole brain. Percentiles or mean values were mostly used to quantify E-fields. Our modeling study, which involved 1,000 E-field models and > 1,000,000 extracted E-field values, revealed that different outcome measures yielded distinct E-field values, analyzed different brain regions, and did not always exhibit strong correlations in the same within-subject E-field model.

CONCLUSIONS

Outcome measure selection significantly impacts the locations and intensities of extracted E-field data in both tES and TMS E-field models. The suitability of different outcome measures depends on the target region, TMS/tES modality, individual anatomy, the analyzed E-field component and the research question. To enhance the quality, rigor, and reproducibility in the E-field modeling domain, we suggest standard reporting practices across studies and provide four recommendations.

White matter predicts tDCS antidepressant effects in a sham-controlled clinical trial study

Transcranial direct current stimulation (tDCS) has been used as treatment for depression, but its effects are heterogeneous. We investigated, in a subsample of the clinical trial Escitalopram versus Electrical Direct Current Therapy for Depression Study (ELECTTDCS), whether white matter areas associated with depression disorder were associated with tDCS response. Baseline diffusion tensor imaging data were analyzed from 49 patients (34 females, mean age 41.9) randomized to escitalopram 20 mg/day, tDCS (2 mA, 30 min, 22 sessions), or placebo. Antidepressant outcomes were assessed by Hamilton Depression Rating Scale-17 (HDRS) after 10-week treatment. We used whole-brain tractography for extracting white matter measures for anterior corpus callosum, and bilaterally for cingulum bundle, striato-frontal, inferior occipito-frontal fasciculus and uncinate. For the rostral body, tDCS group showed higher MD associated with antidepressant effects (estimate = -5.13 ± 1.64, p = 0.002), and tDCS significantly differed from the placebo and the escitalopram group. The left striato-frontal tract showed higher FA associated with antidepressant effects (estimate = -2.14 ± 0.72, p = 0.003), and tDCS differed only from the placebo group. For the right uncinate, the tDCS group lower AD values were associated with higher HDRS decrease (estimate = -1.45 ± 0.67, p = 0.031). Abnormalities in white matter MDD-related areas are associated with tDCS antidepressant effects. Suggested better white matter microstructure of the left prefrontal cortex was associated with tDCS antidepressant effects. Future studies should investigate whether these findings are driven by electric field diffusion and density in these areas.

Home-administered transcranial direct current stimulation is a feasible intervention for depression: an observational cohort study

Transcranial direct current stimulation (tDCS) is an emerging treatment for major depression. We recruited participants with moderate-to-severe major depressive episodes for an observational clinical trial using Soterix Medical's tDCS telehealth platform as a standard of care. The acute intervention consisted of 28 sessions (5 sessions/week, 6 weeks) of the left anodal dorsolateral prefrontal cortex (DLPFC) tDCS (2.0 mA × 30 min) followed by a tapering phase of weekly sessions for 4 weeks (weeks 7-10). The n = 16 completing participants had a significant reduction in depressive symptoms by week 2 of treatment [Montgomery-Åsberg Depression Rating Scale (MADRS), Baseline: 28.00 ± 4.35 vs. Week 2: 17.12 ± 5.32, p < 0.001] with continual improvement across each biweekly timepoint. Acute intervention responder and remission rates were 75 and 63% and 88 and 81% following the taper period (week 10).

Optimizing TMS Coil Placement Approaches for Targeting the Dorsolateral Prefrontal Cortex in Depressed Adolescents: An Electric Field Modeling Study

High-frequency repetitive transcranial magnetic stimulation (rTMS) to the left dorsolateral prefrontal cortex (L-DLPFC) shows promise as a treatment for treatment-resistant depression in adolescents. Conventional rTMS coil placement strategies include the 5 cm, the Beam F3, and the magnetic resonance imaging (MRI) neuronavigation methods. The purpose of this study was to use electric field (E-field) models to compare the three targeting approaches to a computational E-field optimization coil placement method in depressed adolescents. Ten depressed adolescents (4 females, age: 15.9±1.1) participated in an open-label rTMS treatment study and were offered MRI-guided rTMS five times per week over 6-8 weeks. Head models were generated based on individual MRI images, and E-fields were simulated for the four targeting approaches. Results showed a significant difference in the induced E-fields at the L-DLPFC between the four targeting methods (χ2=24.7, p<0.001). Post hoc pairwise comparisons showed that there was a significant difference between any two of the targeting methods (Holm adjusted p<0.05), with the 5 cm rule producing the weakest E-field (46.0±17.4V/m), followed by the F3 method (87.4±35.4V/m), followed by MRI-guided (112.1±14.6V/m), and followed by the computational approach (130.1±18.1V/m). Variance analysis showed that there was a significant difference in sample variance between the groups (K2=8.0, p<0.05), with F3 having the largest variance. Participants who completed the full course of treatment had median E-fields correlated with depression symptom improvement (r=-0.77, p<0.05). E-field models revealed limitations of scalp-based methods compared to MRI guidance, suggesting computational optimization could enhance dose delivery to the target.

Differential effects of remotely supervised transcranial direct current stimulation on recognition memory depending on task order

Background

Prior work has shown positive effects of High Definition transcranial direct current stimulation (HD-tDCS) over the dorsolateral prefrontal cortex (DLPFC) on semantic memory performance and metamemory monitoring accuracy. However, HD-tDCS requires setup by a trained researcher, which is not always feasible. Few studies have used remotely supervised (rs) tDCS in healthy populations, and remote supervision has strong practical benefits.

Objective/hypothesis

The goal of the current study was to test if previously shown effects of HD-tDCS over the left DLPFC on semantic memory performance and metamemory monitoring accuracy extended to conventional rs-tDCS, which is less focal than HD-tDCS, and to episodic memory and metamemory tasks.

Materials and methods

A total of 36 healthy participants completed 6 weeks of rs-tDCS sessions, with either active left or right anodal DLPFC stimulation, or sham. Participants completed semantic and episodic memory and metamemory tasks, which each lasted for three consecutive sessions, and session order was counterbalanced across participants.

Results

Overall, there were no main effects of rs-tDCS on metamemory monitoring accuracy or memory performance for either the semantic or the episodic tasks. However, there were effects of rs-tDCS that depended on the order of completing the episodic and semantic task sessions. When participants completed the semantic task sessions after the episodic task sessions, semantic recognition was greater in the left anodal DLPFC condition. In a parallel effect, when participants completed the episodic task sessions after the semantic task sessions, episodic recognition was greater in the right anodal DLPFC condition.

Conclusion

Prior experience with tDCS is a factor for effects of rs-tDCS on cognition. Additionally, the current experiment provides evidence for the feasibility of fully remotely supervised tDCS in healthy participants.

Home-based tDCS for apathy in Alzheimer's disease: a protocol for a randomized double-blinded controlled pilot study

BACKGROUND

Apathy is among the most common behavioral symptoms in dementia and is consistently associated with negative outcomes in Alzheimer's disease (AD). Despite its prevalence and clinical relevance, available pharmacological and non-pharmacological strategies to treat apathy in AD have been marked, respectively, by potentially severe side effects and/or limited efficacy. Transcranial direct current stimulation (tDCS) is a relatively novel non-pharmacological method of neuromodulation with promising results. Compared to previous tDCS formats, recent technological advances have increased the portability of tDCS, which creates the potential for caregiver-administered, home use. Our study aims to evaluate the feasibility, safety, and efficacy of home-based tDCS for the treatment of apathy in AD.

METHODS/DESIGN

This is an experimenter- and participant-blinded, randomized, sham-controlled, parallel-group (1:1 for two groups) pilot clinical trial, involving 40 subjects with AD. After a brief training, caregivers will administer tDCS for participants at home under remote televideo supervision by research staff to ensure the use of proper technique. Participants will be assessed at baseline, during treatment (week 2, week 4, and week 6), and 6 weeks post-treatment. Dependent measures will cover cognitive performance, apathy, and other behavioral symptoms. Data about side effects and acceptability will also be collected.

DISCUSSION

Our study will address apathy, an overlooked clinical problem in AD. Our findings will advance the field of non-pharmacological strategies for neuropsychiatric symptoms, presenting a great potential for clinical translation.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT04855643.

Experimental validation of computational models for the prediction of phase distribution during multi-channel transcranial alternating current stimulation

Transcranial alternating current stimulation (tACS) is a widely used noninvasive brain stimulation (NIBS) technique to affect neural activity. Neural oscillations exhibit phase-dependent associations with cognitive functions, and tools to manipulate local oscillatory phases can affect communication across remote brain regions. A recent study demonstrated that multi-channel tACS can generate electric fields with a phase gradient or traveling waves in the brain. Computational simulations using phasor algebra can predict the phase distribution inside the brain and aid in informing parameters in tACS experiments. However, experimental validation of computational models for multi-phase tACS is still lacking. Here, we develop such a framework for phasor simulation and evaluate its accuracy using in vivo recordings in nonhuman primates. We extract the phase and amplitude of electric fields from intracranial recordings in two monkeys during multi-channel tACS and compare them to those calculated by phasor analysis using finite element models. Our findings demonstrate that simulated phases correspond well to measured phases (r = 0.9). Further, we systematically evaluated the impact of accurate electrode placement on modeling and data agreement. Finally, our framework can predict the amplitude distribution in measurements given calibrated tissues’ conductivity. Our validated general framework for simulating multi-phase, multi-electrode tACS provides a streamlined tool for principled planning of multi-channel tACS experiments.

A Systematic Review and Large-Scale tES and TMS Electric Field Modeling Study Reveals How Outcome Measure Selection Alters Results in a Person- and Montage-Specific Manner

Background

Electric field (E-field) modeling is a potent tool to examine the cortical effects of transcranial magnetic and electrical stimulation (TMS and tES, respectively) and to address the high variability in efficacy observed in the literature. However, outcome measures used to report E-field magnitude vary considerably and have not yet been compared in detail.

Objectives

The goal of this two-part study, encompassing a systematic review and modeling experiment, was to provide an overview of the different outcome measures used to report the magnitude of tES and TMS E-fields, and to conduct a direct comparison of these measures across different stimulation montages.

Methods

Three electronic databases were searched for tES and/or TMS studies reporting E-field magnitude. We extracted and discussed outcome measures in studies meeting the inclusion criteria. Additionally, outcome measures were compared via models of four common tES and two TMS modalities in 100 healthy younger adults.

Results

In the systematic review, we included 118 studies using 151 outcome measures related to E-field magnitude. Structural and spherical regions of interest (ROI) analyses and percentile-based whole-brain analyses were used most often. In the modeling analyses, we found that there was an average of only 6% overlap between ROI and percentile-based whole-brain analyses in the investigated volumes within the same person. The overlap between ROI and whole-brain percentiles was montage- and person-specific, with more focal montages such as 4Ã-1 and APPS-tES, and figure-of-eight TMS showing up to 73%, 60%, and 52% overlap between ROI and percentile approaches respectively. However, even in these cases, 27% or more of the analyzed volume still differed between outcome measures in every analyses.

Conclusions

The choice of outcome measures meaningfully alters the interpretation of tES and TMS E-field models. Well-considered outcome measure selection is imperative for accurate interpretation of results, valid between-study comparisons, and depends on stimulation focality and study goals. We formulated four recommendations to increase the quality and rigor of E-field modeling outcome measures. With these data and recommendations, we hope to guide future studies towards informed outcome measure selection, and improve the comparability of studies.

Comparison of coil placement approaches targeting dorsolateral prefrontal cortex in depressed adolescents receiving repetitive transcranial magnetic stimulation: an electric field modeling study

Background

A promising treatment option for adolescents with treatment-resistant depression is high-frequency repetitive transcranial magnetic stimulation (rTMS) delivered to the left dorsolateral prefrontal cortex (L-DLPFC). Conventional coil placement strategies for rTMS in adults include the 5-cm rule, the Beam F3 method, and the magnetic resonance imaging (MRI) neuronavigation method. The purpose of this study was to compare the three targeting approaches to a computational E-field optimization coil placement method in depressed adolescents.

Methods

Ten consenting and assenting depressed adolescents (4 females, age: 15.9 ± 1.1) participated in an open-label rTMS treatment study. Participants were offered MRI-guided rTMS 5 times per week over 6-8 weeks. To compute the induced E-field, a head model was generated based on MRI images, and a figure-8 TMS coil (Neuronetics) was placed over the L-DLPFC using the four targeting approaches.

Results

Results show that there was a significant difference in the induced E-field at the L-DLPFC between the four targeting methods ( χ 2 = 24.7, p < 0.001). Post hoc pairwise comparisons show that there was a significant difference between any two of the targeting methods (Holm adjusted p < 0.05), with the 5-cm rule producing the weakest E-field (46.0 ± 17.4 V/m), followed by the F3 method (87.4 ± 35.4 V/m), followed by the MRI-guided (112.1 ± 14.6 V/m), and followed by the computationally optimized method (130.1 ± 18.1 V/m). The Bartlett test of homogeneity of variances show that there was a significant difference in sample variance between the groups ( K 2 = 8.0, p < 0.05), with F3 having the largest variance. In participants who completed the full course of treatment, the median E-field strength in the L-DLPFC was correlated with the change in depression severity ( r = - 0.77, p < 0.05).

Conclusions

The E-field models revealed inadequacies of scalp-based targeting methods compared to MRI-guidance. Computational optimization may further enhance E-field dose delivery to the treatment target.

Neurocognitive, physiological, and biophysical effects of transcranial alternating current stimulation

Transcranial alternating current stimulation (tACS) can modulate human neural activity and behavior. Accordingly, tACS has vast potential for cognitive research and brain disorder therapies. The stimulation generates oscillating electric fields in the brain that can bias neural spike timing, causing changes in local neural oscillatory power and cross-frequency and cross-area coherence. tACS affects cognitive performance by modulating underlying single or nested brain rhythms, local or distal synchronization, and metabolic activity. Clinically, stimulation tailored to abnormal neural oscillations shows promising results in alleviating psychiatric and neurological symptoms. We summarize the findings of tACS mechanisms, its use for cognitive applications, and novel developments for personalized stimulation.

The Neurobase of ambiguity loss aversion about decision making

In our daily decision-making, there are two confusing problems: risk and ambiguity. Many psychological studies and neuroscience studies have shown that the prefrontal cortex (PFC) is an important neural mechanism for modulating the human brain in risk and ambiguity decision-making, especially the dorsolateral prefrontal cortex (DLPFC). We used transcranial direct current stimulation (tDCS) to reveal the causal relationship between the DLPFC and ambiguity decision-making. We design two experimental tasks involving ambiguity to gain and ambiguity to loss. The results of our study show that there is a significant effect on left DLPFC stimulation about ambiguity to loss, there is an insignificant effect on left DLPFC stimulation about ambiguity to gain, and there is an insignificant effect on right DLPFC stimulation about ambiguity to gain and ambiguity to loss. This result indicates that people are more sensitive to ambiguity loss than ambiguity gain. Further analysis found that the degree of participants' attitudes toward ambiguity loss who received anodal simulation was lower than that who received sham stimulation across the left DLPFC, which means that the subjects had a strong ambiguity loss aversion after the participants received the anodal simulation of the left DLPFC.

Efficacy of adjunctive intensive transcranial direct current stimulation of different cortices in treatment-resistant depression: a study protocol for a randomized double-blinded sham-controlled trial

BACKGROUND

Treatment-resistant depression (TRD) carries a high economic burden worldwide. Transcranial direct current stimulation (tDCS) is advantageous for improving cognition and can be safely used in the treatment of depression. The effectiveness of tDCS of the left and right orbitofrontal cortex (OFC) as adjuvant treatment in patients with TRD has rarely been explored. Therefore, the objective of this trial is to evaluate the effectiveness there of when administering left dorsolateral prefrontal cortex (DLPFC) positive stimulation or OFC negative stimulation in patients with TRD.

METHODS

Ninety eligible participants will be recruited to receive intervention at Shanghai Mental Health Center. Treatment will be randomly assigned in a double-blind fashion. Participants will receive either DLPFC (n = 30), OFC (n = 30), or sham (n = 30) tDCS, while continuing their usual pharmacotherapy at a stable dosage for at least 2 weeks before enrollment and throughout the stimulation period. All participants will receive 20 weekday stimulation sessions of 60 minutes duration each. Participants in the active group will be stimulated at 2 mA throughout the session, whereas the sham group will receive only a brief period of stimulation to mimic the sensation. After 20 stimulation sessions, no further treatment will be administered. Measurements will be conducted at regular points throughout and at 8 weeks after trial completion. The primary outcome is the change in the 17-item Hamilton Depression Rating Scale (HAMD-17) score after 20 sessions. Secondary outcomes were defined as changes in other measurement scales, cognitive function, resting-state functional magnetic resonance imaging (rs-fMRI), and serum biomarkers.

DISCUSSION

We hypothesize that, in contrast to the sham group, both the active DLPFC and OFC tDCS groups will show superiority in HAMD-17 score reduction after 5, 10, and 20 sessions. Moreover, associations of the improvement of depressive symptoms with variations in rs-fMRI and TRD-related biomarkers will be evaluated. Our study may suggest that adjunctive intensive tDCS with left DLPFC positive stimulation or right OFC negative stimulation may be effective as a novel method to relieve depressive symptoms in patients with TRD. The variation of rs-fMRI, biomarkers could be used as a potential prediction model of treatment efficacy in TRD.

TRIAL REGISTRATION

The trial protocol is registered with www.chictr.org.cn under protocol registration number ChiCTR2200058030. Date of registration: March 27, 2022. Recruitment started in September 2022 and is ongoing.

Feasibility of epidural temporal interference stimulation for minimally invasive electrical deep brain stimulation: simulation and phantom experimental studies

Objective. Temporal interference stimulation (TIS) has shown the potential as a new method for selective stimulation of deep brain structures in small animal experiments. However, it is challenging to deliver a sufficient temporal interference (TI) current to directly induce an action potential in the deep area of the human brain when electrodes are attached to the scalp because the amount of injection current is generally limited due to safety issues. Thus, we propose a novel method called epidural TIS (eTIS) to address this issue; in this method, the electrodes are attached to the epidural surface under the skull.Approach. We employed finite element method (FEM)-based electric field simulations to demonstrate the feasibility of eTIS. We first optimized the electrode conditions to deliver maximum TI currents to each of the three different targets (anterior hippocampus, subthalamic nucleus, and ventral intermediate nucleus) based on FEM, and compared the stimulation focality between eTIS and transcranial TIS (tTIS). Moreover, we conducted realistic skull-phantom experiments for validating the accuracy of the computational simulation for eTIS.Main results. Our simulation results showed that eTIS has the advantage of avoiding the delivery of TI currents over unwanted neocortical regions compared with tTIS for all three targets. It was shown that the optimized eTIS could induce neural action potentials at each of the three targets when a sufficiently large current equivalent to that for epidural cortical stimulation is injected. Additionally, the simulated results and measured results via the phantom experiments were in good agreement.Significance. We demonstrated the feasibility of eTIS, facilitating more focalized and stronger electrical stimulation of deep brain regions than tTIS, with the relatively less invasive placement of electrodes than conventional deep brain stimulation via computational simulation and realistic skull phantom experiments.

Home-Based Transcranial Direct Current Stimulation to Enhance Cognition in Stroke: Randomized Controlled Trial

BACKGROUND

Transcranial direct current stimulation (tDCS) is a promising tool for improving post-stroke cognitive function. Home-based rehabilitation is increasingly required for patients with stroke, and additional benefits are expected if supplemented with remotely supervised tDCS (RS-tDCS). We evaluated the cognitive improvement effect and feasibility of RS-tDCS in patients with chronic stroke.

METHODS

Twenty-six patients with chronic stroke and cognitive impairment (Korean version of the Montreal Cognitive Assessment [K-MoCA] score <26) were randomized into real and sham RS-tDCS groups and underwent concurrent computerized cognitive training and RS-tDCS. Patients and caregivers underwent training to ensure correct tDCS self-application, were monitored, and treated 5 d/wk for 4 weeks. We investigated several cognition tests including K-MoCA, Korean version of the Dementia Rating Scale-2, Korean-Boston Naming Test, Trail Making Test, Go/No Go, and Controlled Oral Word Association Test at the end of the training sessions and one month later. Repeated-measures ANOVA was used for comparison between the groups and within each group. The adherence rate of the appropriate RS-tDCS session was also investigated.

RESULTS

In within-group comparison, unlike the sham group, the real group showed significant improvement in K-MoCA (P_real=0.004 versus P_sham=0.132), particularly in patients with lower baseline K-MoCA (K-MoCA_10-17; P_real=0.001 versus P_sham=0.835, K-MoCA_18-25; P_real=0.060 versus P_sham=0.064) or with left hemispheric lesions (left; P_real=0.010 versus P_sham=0.454, right; P_real=0.106 versus P_sham=0.128). In between-group comparison, a significant difference was observed in K-MoCA in the lower baseline K-MoCA subgroup (K-MoCA_10-17; P_time×group=0.048), but no significant difference was found in other cognitive tests. The adherence rate of successful application of the RS-tDCS was 98.4%, and no serious adverse effects were detected.

CONCLUSIONS

RS-tDCS is a safe and feasible rehabilitation modality for post-stroke cognitive dysfunction. Specifically, RS-tDCS is effective in patients with moderate cognitive decline. Additionally, these data demonstrate the potential to enhance home-based cognitive training, although significant differences were not consistently found in between-group comparisons; therefore, further larger studies are needed.

REGISTRATION

URL: https://cris.nih.go.kr; Unique identifier: KCT0003427.

Transcranial Direct Current Stimulation Combined With Listening to Preferred Music Alters Cortical Speech Processing in Older Adults

Emerging evidence suggests transcranial direct current stimulation (tDCS) can improve cognitive performance in older adults. Similarly, music listening may improve arousal and stimulate subsequent performance on memory-related tasks. We examined the synergistic effects of tDCS paired with music listening on auditory neurobehavioral measures to investigate causal evidence of short-term plasticity in speech processing among older adults. In a randomized sham-controlled crossover study, we measured how combined anodal tDCS over dorsolateral prefrontal cortex (DLPFC) paired with listening to autobiographically salient music alters neural speech processing in older adults compared to either music listening (sham stimulation) or tDCS alone. EEG assays included both frequency-following responses (FFRs) and auditory event-related potentials (ERPs) to trace neuromodulation-related changes at brainstem and cortical levels. Relative to music without tDCS (sham), we found tDCS alone (without music) modulates the early cortical neural encoding of speech in the time frame of ∼100-150 ms. Whereas tDCS by itself appeared to largely produce suppressive effects (i.e., reducing ERP amplitude), concurrent music with tDCS restored responses to those of the music+sham levels. However, the interpretation of this effect is somewhat ambiguous as this neural modulation could be attributable to a true effect of tDCS or presence/absence music. Still, the combined benefit of tDCS+music (above tDCS alone) was correlated with listeners' education level suggesting the benefit of neurostimulation paired with music might depend on listener demographics. tDCS changes in speech-FFRs were not observed with DLPFC stimulation. Improvements in working memory pre to post session were also associated with better speech-in-noise listening skills. Our findings provide new causal evidence that combined tDCS+music relative to tDCS-alone (i) modulates the early (100-150 ms) cortical encoding of speech and (ii) improves working memory, a cognitive skill which may indirectly bolster noise-degraded speech perception in older listeners.

Differences in electric field strength between clinical and non-clinical populations induced by prefrontal tDCS: A cross-diagnostic, individual MRI-based modeling study

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MDD and SCZ showed lower prefrontal tDCS-induced e-field strengths compared to HC.

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Average e-field strengths did not significantly differ between MDD and SCZ patients.

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Inter-individual variability of e-field intensities and distribution was prominent.

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Inter-rater variability emphasizes the importance of standardized positioning.

Introduction

Prefrontal cortex (PFC) regions are promising targets for therapeutic applications of non-invasive brain stimulation, e.g. transcranial direct current stimulation (tDCS), which has been proposed as a novel intervention for major depressive disorder (MDD) and negative symptoms of schizophrenia (SCZ). However, the effects of tDCS vary inter-individually, and dose–response relationships have not been established. Stimulation parameters are often tested in healthy subjects and transferred to clinical populations. The current study investigates the variability of individual MRI-based electric fields (e-fields) of standard bifrontal tDCS across individual subjects and diagnoses.

Method

The study included 74 subjects, i.e. 25 patients with MDD, 24 patients with SCZ, and 25 healthy controls (HC). Individual e-fields of a common tDCS protocol (i.e. 2 mA stimulation intensity, bifrontal anode-F3/cathode-F4 montage) were modeled by two investigators using SimNIBS (2.0.1) based on structural MRI scans.

Result

On a whole-brain level, the average e-field strength was significantly reduced in MDD and SCZ compared to HC, but MDD and SCZ did not differ significantly. Regions of interest (ROI) analysis for PFC subregions showed reduced e-fields in Sallet areas 8B and 9 for MDD and SCZ compared to HC, whereas there was again no difference between MDD and SCZ. Within groups, we generally observed high inter-individual variability of e-field intensities at a higher percentile of voxels.

Conclusion

MRI-based e-field modeling revealed significant differences in e-field strengths between clinical and non-clinical populations in addition to a general inter-individual variability. These findings support the notion that dose–response relationships for tDCS cannot be simply transferred from healthy to clinical cohorts and need to be individually established for clinical groups. In this respect, MRI-based e-field modeling may serve as a proxy for individualized dosing.

The effects of noninvasive brain stimulation on heart rate and heart rate variability: A systematic review and meta-analysis

Noninvasive brain stimulation (NIBS) techniques such as transcranial magnetic stimulation and transcranial direct current stimulation are widely used to test the involvement of specific cortical regions in various domains such as cognition and emotion. Despite the capability of stimulation techniques to test causal directions, this approach has been only sparsely used to examine the cortical regulation of autonomic nervous system (ANS) functions such as heart rate (HR) and heart rate variability (HRV) and to test current models in this regard. In this preregistered (PROSPERO) systematic review and meta-analysis, we aimed to investigate, based on meta-regression, whether NIBS represents an effective method for modulating HR and HRV measures, and to evaluate whether the ANS is modulated by cortical mechanisms affected by NIBS. Here we have adhered to the PRISMA guidelines. In a series of four meta-analyses, a total of 131 effect sizes from 35 sham-controlled trials were analyzed using robust variance estimation random-effects meta-regression technique. NIBS was found to effectively modulate HR and HRV with small to medium effect sizes. Moderator analyses yielded significant differences in effects between stimulation of distinct cortical areas. Our results show that NIBS is a promising tool to investigate the cortical regulation of ANS, which may add to the existing brain imaging and animal study literature. Future research is needed to identify further factors modulating the size of effects. As many of the studies reviewed were found to be at high risk of bias, we recommend that methods to reduce potential risk of bias be used in the design and conduct of future studies.

Multipair transcranial temporal interference stimulation for improved focalized stimulation of deep brain regions: A simulation study

Temporal interference stimulation (TIS) has been proved to be effective in stimulating deep brain regions while avoiding the stimulation of neocortical regions in animal experiments. In the traditional TIS, two alternating currents are injected with different frequencies via two electrode pairs attached to the scalp. In the human brain, however, it is difficult to achieve a focal stimulation of deep brain structures due to the high complexity of human brain structures. In this study, we hypothesized that the use of multiple electrode pairs may contribute to the more focalized delivery of temporal interference (TI) currents to the target site in the deep area of the brain. Based on this hypothesis, we proposed a novel multipair TIS method that employs more than two electrode pairs for improved focalized stimulation of the deep brain region (in this study, the head of the right hippocampus). Three realistic finite element models were used to validate the feasibility of the proposed multipair TIS. Additional electrode pairs were sequentially added to the conventional two-electrode pairs with the aim of maximizing the delivery of TI currents to the target while minimizing TI currents in the neocortical regions. The results confirmed that the multipair TIS provides better focalized stimulation than the conventional two-pair TIS for all three head models. It is expected that the proposed multipair TIS can be used to enhance the effectiveness of noninvasive deep brain stimulation.

The use of noninvasive brain stimulation techniques to improve reading difficulties in dyslexia: A systematic review

Noninvasive brain stimulation (NIBS) allows to actively and noninvasively modulate brain function. Aside from inhibiting specific processes, NIBS may also enhance cognitive functions, which might be used for the prevention and intervention of learning disabilities such as dyslexia. However, despite the growing interest in modulating learning abilities, a comprehensive, up-to-date review synthesizing NIBS studies with dyslexics is missing. Here, we fill this gap and elucidate the potential of NIBS as treatment option in dyslexia. The findings of the 15 included studies suggest that repeated sessions of reading training combined with different NIBS protocols may induce long-lasting improvements of reading performance in child and adult dyslexics, opening promising avenues for future research. In particular, the "classical" reading areas seem to be most successfully modulated through NIBS, and facilitatory protocols can improve various reading-related subprocesses. Moreover, we emphasize the need to further explore the potential to modulate auditory cortex function as a preintervention and intervention approach for affected children, for example, to avoid the development of auditory and phonological difficulties at the core of dyslexia. Finally, we outline how future studies may increase our understanding of the neurobiological basis of NIBS-induced improvements in dyslexia.

Transcranial direct current stimulation modulates working memory and prefrontal-insula connectivity after mild-moderate traumatic brain injury

Background: Persistent posttraumatic symptoms (PPS) may manifest after a mild-moderate traumatic brain injury (mmTBI) even when standard brain imaging appears normal. Transcranial direct current stimulation (tDCS) represents a promising treatment that may ameliorate pathophysiological processes contributing to PPS. Objective/Hypothesis: We hypothesized that in a mmTBI population, active tDCS combined with training would result in greater improvement in executive functions and post-TBI cognitive symptoms and increased resting state connectivity of the stimulated region, i.e., left dorsolateral prefrontal cortex (DLPFC) compared to control tDCS. Methods: Thirty-four subjects with mmTBI underwent baseline assessments of demographics, symptoms, and cognitive function as well as resting state functional magnetic resonance imaging (rsfMRI) in a subset of patients (n = 24). Primary outcome measures included NIH EXAMINER composite scores, and the Neurobehavioral Symptom Inventory (NSI). All participants received 10 daily sessions of 30 min of executive function training coupled with active or control tDCS (2 mA, anode F3, cathode right deltoid). Imaging and assessments were re-obtained after the final training session, and assessments were repeated after 1 month. Mixed-models linear regression and repeated measures analyses of variance were calculated for main effects and interactions. Results: Both active and control groups demonstrated improvements in executive function (EXAMINER composite: p < 0.001) and posttraumatic symptoms (NSI cognitive: p = 0.01) from baseline to 1 month. Active anodal tDCS was associated with greater improvements in working memory reaction time compared to control (p = 0.007). Reaction time improvement correlated significantly with the degree of connectivity change between the right DLPFC and the left anterior insula (p = 0.02). Conclusion: Anodal tDCS improved reaction time on an online working memory task in a mmTBI population, and decreased connectivity between executive network and salience network nodes. These findings generate important hypotheses for the mechanism of recovery from PPS after mild-moderate TBI.

Anatomical and fMRI-network comparison of multiple DLPFC targeting strategies for repetitive transcranial magnetic stimulation treatment of depression

BACKGROUND

The efficacy of repetitive transcranial magnetic stimulation (rTMS) for depression may vary depending on the subregion stimulated within the dorsolateral prefrontal cortex (DLPFC). Clinical TMS typically uses scalp-based landmarks for DLPFC targeting, rather than individualized MRI guidance.

OBJECTIVE

In rTMS patients, determine the brain systems targeted by multiple DLPFC stimulation rules by computing several surrogate measures: underlying brain targets labeled with connectivity-based atlases, subgenual cingulate anticorrelation strength, and functionally connected networks.

METHODS

Forty-nine patients in a randomized controlled trial of rTMS therapy for treatment resistant major depression underwent structural and functional MRI. DLPFC rules were applied virtually using MR-image guidance. Underlying cortical regions were labeled, and connectivity with the subgenual cingulate and whole-brain computed.

RESULTS

Scalp-targeting rules applied post hoc to these MRIs that adjusted for head size, including Beam F3, were comparably precise, successful in directly targeting classical DLPFC and frontal networks, and anticorrelated with the subgenual cingulate. In contrast, all rules involving fixed distances introduced variability in regions and networks targeted. The 5 cm rule targeted a transitional DLPFC region with a different connectivity profile from the adjusted rules. Seed-based connectivity analyses identified multiple regions, such as posterior cingulate and inferior parietal lobe, that warrant further study in order to understand their potential contribution to clinical response.

CONCLUSION

EEG-based rules consistently targeted DLPFC brain regions with resting-state fMRI features known to be associated with depression response. These results provide a bridge from lab to clinic by enabling clinicians to relate scalp-targeting rules to functionally connected brain systems.

Universal Transcranial Direct Current Stimulation (tDCS) Headset for targeting the bilateral Dorsolateral Prefrontal Cortex: Towards facilitating broader adoption

Electrode position affects the brain current flow intensity and distribution induced by transcranial direct current stimulation (tDCS). The dorsolateral pre-frontal cortex (DLPFC) is a common target in neuropsychology and neuropsychiatry applications. A positioning scheme and subsequently a headgear has previously been developed to target the DLPFC automatically - devoid of any scalp ruler or neuronavigation method. This approach minimizes the time cost for pre-treatment measurements without compromising targeting accuracy and induced electric field focality. The goal of this study was to further develop this headgear to facilitate broader adoption while maintaining its core design elements intact. Briefly, we developed the headset to accommodate all adult head sizes (52-62 cm) rather than having multiple sizes, to have increased robustness, enhanced visual aesthetics, and have improved usability.We recruited 8 subjects and tested the accuracy of electrode placement on various head sizes. We also tested usability with the System Usability Scale (SUS) and asked the subjects to rate visual appeal. Our study demonstrated that the newly developed headset had greater usability and was more visually appealing than its predecessor without compromising targeting accuracy.Clinical Relevance- This study introduces a headset for routine tDCS administration targeting bilateral DLPFC. The headset is highly usable, robust, and is expected to facilitate home and high-volume use.

A novel technique for accurate electrode placement over cortical targets for transcranial electrical stimulation (tES) clinical trials

Objective. We present an easy-to-implement technique for accurate electrode placement over repeated transcranial electrical stimulation (tES) sessions across participants and time. tES is an emerging, non-invasive neuromodulation technique that delivers electrical stimulation using scalp electrodes.Approach.The tES electrode placement technique was developed during an exploratory clinical trial aimed at targeting a specific MNI-atlas cortical coordinate inN= 59 depressed participants (32 F, mean age: 31.1 ± 8.3 SD). Each participant completed 12 sessions of active or sham stimulation, administered using high-definition (HD) or conventional sized electrode montages placed according to the proposed technique. Neuronavigation data measuring the distances between the identified and the intended stimulation site, simulations, and cerebral blood flow (CBF) data at baseline and post-treatment were acquired to evaluate the targeting characteristics of the proposed technique.Main results.Neuronavigation measurements indicate accurate electrode placement to within 1 cm of the stimulation target on average across repeated sessions. Simulations predict that these placement characteristics result in minimal electric field differences at the stimulation target (>0.90 correlation, and <10% change in the modal electric field and targeted volume). Additionally, significant changes in %CBF (relative to baseline) under the stimulation target in the active stimulation group relative to sham confirmed that the proposed placement technique introduces minimal bias in the spatial location of the cortical coordinate ultimately targeted. Finally, we show proof of concept that the proposed technique provides similar accuracy of electrode placement at other cortical targets.Significance.For voxel-level cortical targets, existing techniques based on cranial landmarks are suboptimal. Our results show that the proposed electrode placement approach provides high consistency for the accurate targeting of such specific cortical regions. Overall, the proposed technique now enables the accurate targeting of locations not accessible with the existing 10-20 system such as scalp-projections of clinically-relevant cortical coordinates identified by brain mapping studies. Clinical trial ID: NCT03556124.

Effects of transcranial direct current stimulation combined with listening to preferred music on memory in older adults

Listening to autobiographically-salient music (i.e., music evoking personal memories from the past), and transcranial direct current stimulation (tDCS) have each been suggested to temporarily improve older adults' subsequent performance on memory tasks. Limited research has investigated the effects of combining both tDCS and music listening together on cognition. The present study examined whether anodal tDCS stimulation over the left dorsolateral prefrontal cortex (2 mA, 20 min) with concurrent listening to autobiographically-salient music amplified subsequent changes in working memory and recognition memory in older adults than either tDCS or music listening alone. In a randomized sham-controlled crossover study, 14 healthy older adults (64-81 years) participated in three neurostimulation conditions: tDCS with music listening (tDCS + Music), tDCS in silence (tDCS-only), or sham-tDCS with music listening (Sham + Music), each separated by at least a week. Working memory was assessed pre- and post-stimulation using a digit span task, and recognition memory was assessed post-stimulation using an auditory word recognition task (WRT) during which electroencephalography (EEG) was recorded. Performance on the backwards digit span showed improvement in tDCS + Music, but not in tDCS-only or Sham + Music conditions. Although no differences in behavioural performance were observed in the auditory WRT, changes in neural correlates underlying recognition memory were observed following tDCS + Music compared to Sham + Music. Findings suggest listening to autobiographically-salient music may amplify the effects of tDCS for working memory, and highlight the potential utility of neurostimulation combined with personalized music to improve cognitive performance in the aging population.

Exploring the neurobiology of reading through non-invasive brain stimulation: A review

Non-invasive brain stimulation (NIBS) has gained increasing popularity as a modulatory tool for drawing causal inferences and exploring task-specific network interactions. Yet, a comprehensive synthesis of reading-related NIBS studies is still missing. We fill this gap by synthesizing the results of 78 NIBS studies investigating the causal involvement of brain regions for reading processing, and then link these results to a neurobiological model of reading. The included studies provide evidence for a functional-anatomical double dissociation for phonology versus semantics during reading-related processes within left inferior frontal and parietal areas. Additionally, the posterior parietal cortex and the anterior temporal lobe are identified as critical regions for reading-related processes. Overall, the findings provide some evidence for a dual-stream neurobiological model of reading, in which a dorsal stream (left temporo-parietal and inferior frontal areas) processes unfamiliar words and pseudowords, and a ventral stream (left occipito-temporal and inferior frontal areas, with assistance from the angular gyrus and the anterior temporal lobe) processes known words. However, individual differences in reading abilities and strategies, as well as differences in stimulation parameters, may impact the neuromodulatory effects induced by NIBS. We emphasize the need to investigate task-specific network interactions in future studies by combining NIBS with neuroimaging.

Parsing the antidepressant effects of non-invasive brain stimulation and pharmacotherapy: A symptom clustering approach on ELECT-TDCS

BACKGROUND

Transcranial direct current stimulation (tDCS) presents small antidepressant efficacy at group level and considerable inter-individual variability of response. Its heterogeneous effects bring the need to investigate whether specific groups of patients submitted to tDCS could present comparable or larger improvement compared to pharmacotherapy. Aggregate measurements might be insufficient to address its effects.

OBJECTIVE

/Hypothesis: To determine the efficacy of tDCS, compared to pharmacotherapy and placebo, in depressive symptom clusters.

METHODS

Data from ELECT-TDCS (Escitalopram versus Electrical Direct-Current Therapy for Treating Depression Clinical Study, ClinicalTrials.gov, NCT01894815), in which antidepressant-free, depressed patients were randomized to receive 22 bifrontal tDCS (2 mA, 30 min) sessions (n = 94), escitalopram 20 mg/day (n = 91), or placebo (n = 60) over 10 weeks. Agglomerative hierarchical clustering identified "sleep/insomnia", "core depressive", "guilt/anxiety", and "atypical" clusters that were the dependent measure. Trajectories were estimated using linear mixed regression models. Effect sizes are expressed in raw HAM-D units. P-values were adjusted for multiple comparisons.

RESULTS

For core depressive symptoms, escitalopram was superior to tDCS (ES = -0.56; CI_95% = -0.94 to -0.17, p = .009), which was superior to placebo (ES = 0.49; CI_95% = 0.06 to 0.92, p = .042). TDCS but not escitalopram was superior to placebo in sleep/insomnia symptoms (ES = 0.87; CI_95% = 0.22 to 1.52, p = .015). Escitalopram but not tDCS was superior to placebo in guilt/anxiety symptoms (ES = 1.66; CI_95% = 0.58 to 2.75, p = .006). No active intervention was superior to placebo for atypical symptoms.

CONCLUSIONS

Pharmacotherapy and non-invasive brain stimulation produce distinct effects in depressive symptoms. TDCS or escitalopram could be chosen according to specific clusters of symptoms for a bigger response.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT01894815.

Transcranial Direct Current Stimulation (tDCS) Augments the Effects of Gamified, Mobile Attention Bias Modification

Anxiety-related attention bias (AB) is the preferential processing of threat observed in clinical and sub-clinical anxiety. Attention bias modification training (ABMT) is a computerized cognitive training technique designed to systematically direct attention away from threat and ameliorate AB, but mixed and null findings have highlighted gaps in our understanding of mechanisms underlying ABMT and how to design the most effective delivery systems. One neuromodulation technique, transcranial direct current stimulation (tDCS) across the pre-frontal cortex (PFC) may augment the effects of ABMT by strengthening top-down cognitive control processes, but the evidence base is limited and has not been generalized to current approaches in digital therapeutics, such as mobile applications. The present study was a single-blind randomized sham-controlled design. We tested whether tDCS across the PFC, vs. sham stimulation, effectively augments the beneficial effects of a gamified ABMT mobile app. Thirty-eight adults (Mage = 23.92, SD = 4.75; 18 females) evidencing low-to-moderate anxiety symptoms were randomly assigned to active or sham tDCS for 30-min while receiving ABMT via a mobile app. Participants reported on potential moderators of ABMT, including life stress and trait anxiety. ECG was recorded during a subsequent stressor to generate respiratory sinus arrhythmia (RSA) suppression as a metric of stress resilience. ABMT delivered via the app combined with tDCS (compared to sham) reduced AB and boosted stress resilience measured via RSA suppression, particularly for those reporting low life stress. Our results integrating tDCS with ABMT provide insight into the mechanisms of AB modulation and support ongoing evaluations of enhanced ABMT reliability and effectiveness via tDCS.

Cognitive Telerehabilitation with Transcranial Direct Current Stimulation Improves Cognitive and Emotional Functioning Following a Traumatic Brain Injury: A Case Study

OBJECTIVE

Cognitive deficits following a traumatic brain injury (TBI) are a leading cause of disability in young adults and there is a critical need for novel approaches to improve cognitive outcomes in TBI survivors. Transcranial direct current stimulation (tDCS) paired with cognitive remediation has emerged as a viable, cost-effective, noninvasive approach for treating cognitive impairments in a wide variety of neurological conditions. Here, we report the first case study utilizing remotely supervised tDCS (RS-tDCS) protocol paired with cognitive remediation in a 29-year-old man with persisting cognitive and emotional sequelae following TBI.

METHOD

Neuropsychological measures were administered before and after the patient completed 20 daily sessions of RS-tDCS (2.0 mA × 20 minutes, left anodal dorsolateral prefrontal cortex montage). During the daily stimulation period, he completed adaptive cognitive training. All treatment procedures were delivered at home and monitored in real time via videoconference with a study technician.

RESULTS

Following 20 RS-tDCS and cognitive training sessions, he had significant improvements (>1 SD) on tests of attention and working memory, semantic fluency, and information processing speed. Mood was also improved.

CONCLUSIONS

This is the first demonstration of at-home telerehabilitation with RS-tDCS and cognitive training to improve cognitive outcomes following TBI.

The intervention, the patient and the illness - Personalizing non-invasive brain stimulation in psychiatry

Current hypotheses on the therapeutic action of non-invasive brain stimulation (NIBS) in psychiatric disorders build on the abundant data from neuroimaging studies. This makes NIBS a very promising tool for developing personalized interventions within a precision medicine framework. NIBS methods fundamentally vary in their neurophysiological properties. They comprise repetitive transcranial magnetic stimulation (rTMS) and its variants (e.g. theta burst stimulation - TBS) as well as different types of transcranial electrical stimulation (tES), with the largest body of evidence for transcranial direct current stimulation (tDCS). In the last two decades, significant conceptual progress has been made in terms of NIBS targets, i.e. from single brain regions to neural circuits and to functional connectivity as well as their states, recently leading to brain state modulating closed-loop approaches. Regarding structural and functional brain anatomy, NIBS meets an individually unique constellation, which varies across normal and pathophysiological states. Thus, individual constitutions and signatures of disorders may be indistinguishable at a given time point, but can theoretically be parsed along course- and treatment-related trajectories. We address precision interventions on three levels: 1) the NIBS intervention, 2) the constitutional factors of a single patient, and 3) the phenotypes and pathophysiology of illness. With examples from research on depressive disorders, we propose solutions and discuss future perspectives, e.g. individual MRI-based electrical field strength as a proxy for NIBS dosage, and also symptoms, their clusters, or biotypes instead of disorder focused NIBS. In conclusion, we propose interleaved research on these three levels along a general track of reverse and forward translation including both clinically directed research in preclinical model systems, and biomarker guided controlled clinical trials. Besides driving the development of safe and efficacious interventions, this framework could also deepen our understanding of psychiatric disorders at their neurophysiological underpinnings.

Effects of tDCS on neuroplasticity and inflammatory biomarkers in bipolar depression: Results from a sham-controlled study

OBJECTIVES

We investigated the role of peripheral biomarkers associated with neuroplasticity and immune-inflammatory processes on the effects of transcranial direct current stimulation (tDCS), a safe, affordable, and portable non-invasive neuromodulatory treatment, in bipolar depression.

METHODS

This is an exploratory analysis using a dataset from the sham-controlled study the Bipolar Depression Electrical Treatment Trial (BETTER)(clinicaltrials.govNCT02152878). Participants were 52 adults with type I or II bipolar disorder in a moderate-to-severe depressive episode, randomized to 12 bifrontal active or sham tDCS sessions over a 6-week treatment course. Plasma levels of brain derived neurotrophic factor (BDNF), glial cell derived neurotrophic factor (GDNF), interleukins (IL) 2, 4, 6, 8, 10, 18, 33, 1β, 12p70, 17a, interferon gamma (IFN), tumor necrosis factor alpha (TNF) and its soluble receptors 1 and 2, ST2, and KLOTHO were investigated at baseline and endpoint. We performed analyses unadjusted for multiple testing to evaluate whether baseline biomarkers were predictive for depression improvement and changed during treatment using linear regression models.

RESULTS

A time x group interaction (Cohen's d: -1.16, 95% CI = -1.96 to -0.3, p = .005) was found for IL-8, with greater reductions after active tDCS. Higher baseline IL-6 plasma levels was associated with symptomatic improvement after tDCS (F_(1,43) = 5.43; p = .025). Other associations were not significant.

CONCLUSIONS

Our exploratory findings suggested that IL-6 is a potential predictor of tDCS response and IL-8 might decrease after tDCS; although confirmatory studies are warranted due to the multiplicity of comparisons.

In-vivo imaging of targeting and modulation of depression-relevant circuitry by transcranial direct current stimulation: a randomized clinical trial

Recent clinical trials of transcranial direct current stimulation (tDCS) in depression have shown contrasting results. Consequently, we used in-vivo neuroimaging to confirm targeting and modulation of depression-relevant neural circuitry by tDCS. Depressed participants (N = 66, Baseline Hamilton Depression Rating Scale (HDRS) 17-item scores ≥14 and <24) were randomized into Active/Sham and High-definition (HD)/Conventional (Conv) tDCS groups using a double-blind, parallel design, and received tDCS individually targeted at the left dorsolateral prefrontal cortex (DLPFC). In accordance with Ampere's Law, tDCS currents were hypothesized to induce magnetic fields at the stimulation-target, measured in real-time using dual-echo echo-planar-imaging (DE-EPI) MRI. Additionally, the tDCS treatment trial (consisting of 12 daily 20-min sessions) was hypothesized to induce cerebral blood flow (CBF) changes post-treatment at the DLPFC target and in the reciprocally connected anterior cingulate cortex (ACC), measured using pseudo-continuous arterial spin labeling (pCASL) MRI. Significant tDCS current-induced magnetic fields were observed at the left DLPFC target for both active stimulation montages (Brodmann's area (BA) 46: p_HD = 0.048, Cohen's d_HD = 0.73; p_Conv = 0.018, d_Conv = 0.86; BA 9: p_HD = 0.011, d_HD = 0.92; p_Conv = 0.022, d_Conv = 0.83). Significant longitudinal CBF increases were observed (a) at the left DLPFC stimulation-target for both active montages (p_HD = 3.5E-3, d_HD = 0.98; p_Conv = 2.8E-3, d_Conv = 1.08), and (b) at ACC for the HD-montage only (p_HD = 2.4E-3, d_HD = 1.06; p_Conv = 0.075, d_Conv = 0.64). These results confirm that tDCS-treatment (a) engages the stimulation-target, and (b) modulates depression-relevant neural circuitry in depressed participants, with stronger network-modulations induced by the HD-montage. Although not primary outcomes, active HD-tDCS showed significant improvements of anhedonia relative to sham, though HDRS scores did not differ significantly between montages post-treatment.

Prefrontal resting-state connectivity and antidepressant response: no associations in the ELECT-TDCS trial

Functional and structural MRI of prefrontal cortex (PFC) may provide putative biomarkers for predicting the treatment response to transcranial direct current stimulation (tDCS) in depression. A recent MRI study from ELECT-TDCS (Escitalopram versus Electrical Direct-Current Theror Depression Study) showed that depression improvement after tDCS was associated with gray matter volumes of PFC subregions. Based thereon, we investigated whether antidepressant effects of tDCS are similarly associated with baseline resting-state functional connectivity (rsFC). A subgroup of 51 patients underwent baseline rsFC-MRI. All patients of ELECT-TDCS were randomized to three treatment arms for 10 weeks (anodal-left, cathodal-right PFC tDCS plus placebo medication; escitalopram 10 mg/day for 3 weeks and 20 mg/day thereafter plus sham tDCS; and placebo medication plus sham tDCS). RsFC was calculated for various PFC regions and analyzed in relation to the individual antidepressant response. There was no significant association between baseline PFC connectivity of essential structural regions, nor any other PFC regions (after correction for multiple comparisons) and patients' individual antidepressant response. This study did not reveal an association between antidepressants effects of tDCS and baseline rsFC, unlike the gray matter volume findings. Thus, the antidepressant effects of tDCS may be differentially related to structural and functional MRI measurements.

Association between tDCS computational modeling and clinical outcomes in depression: data from the ELECT-TDCS trial

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation intervention investigated for the treatment of depression. Clinical results have been heterogeneous, partly due to the variability of electric field (EF) strength in the brain owing to interindividual differences in head anatomy. Therefore, we investigated whether EF strength was correlated with behavioral changes in 16 depressed patients using simulated electric fields in real patient data from a controlled clinical trial. We hypothesized that EF strength in the dorsolateral prefrontal cortex (DLPFC) and anterior cingulate cortex (ACC), brain regions implicated in depression pathophysiology, would be associated with changes in depression, mood and anxiety scores. SimNIBS were used to simulate individual electric fields based on the MRI structural T1-weighted brain scans of depressed subjects. Linear regression models showed, at the end of the acute treatment phase, that simulated EF strength was inversely associated with negative affect in the bilateral ACC (left: β = - 160.463, CI [- 291.541, - 29.385], p = 0.021; right: β = - 189.194, CI [- 289.479, - 88.910], p = 0.001) and DLPFC (left: β = - 93.210, CI [- 154.960, - 31.461], p = 0.006; right: β = - 82.564, CI [- 142.867, - 22.262], p = 0.011) and with depression scores in the left ACC (β = - 156.91, CI [- 298.51, - 15.30], p = 0.033). No association between positive affect or anxiety scores, and simulated EF strength in the investigated brain regions was found. To conclude, our findings show preliminary evidence that EF strength simulations might be associated with further behavioral changes in depressed patients, unveiling a potential mechanism of action for tDCS. Further studies should investigate whether individualization of EF strength in key brain regions impact clinical response.

Cognitive outcomes of the bipolar depression electrical treatment trial (BETTER): a randomized, double-blind, sham-controlled study

Bipolar depression is associated with marked cognitive deficits. Pharmacological treatments for this condition are limited and may aggravate depressive and cognitive symptoms. Therefore, therapeutic interventions that preserve adequate cognitive functioning are necessary. Our previous results demonstrated significant clinical efficacy of transcranial direct current stimulation (tDCS) in the Bipolar Depression Electrical Treatment Trial (BETTER). Here, cognitive outcomes of this study are reported. We randomized 59 patients with bipolar disorder I or II in an acute depressive episode to receive active (12 2 mA, 30-min, anodal-left, cathodal-right prefrontal cortex tDCS sessions) or sham tDCS. Patients were on stable pharmacological regimen for at least 2 weeks. A battery of 12 neuropsychological assessments in five cognitive domains (attention and processing speed, memory, language, inhibitory control, and working memory and executive function) was performed at baseline, after two weeks and at endpoint (week 6). No significant differences between groups over 6 weeks of treatment were observed for any cognitive outcomes. Moreover, no decrease in cognitive performance was observed. Our findings warrant further replication in larger studies. Trial Registration: clinicaltrials.gov Identifier: NCT02152878.

Effect of Anodal Transcranial Direct Current Stimulation Combined With Cognitive Training for Improving Cognition and Language Among Children With Cerebral Palsy With Cognitive Impairment: A Pilot, Randomized, Controlled, Double-Blind, and Clinical Trial

About 30-45% of cerebral palsy (CP) patients have cognitive impairment. Previous studies showed the evidence that transcranial direct current stimulation (tDCS) may have some benefits in attention-deficit/hyperactivity disorder, autism spectrum disorder, and motor development in CP. The aim of this study is to evaluate the effect of tDCS on cognition, language, and activities of daily living (ADL) among children with CP with cognitive impairment. It was a pilot, randomized, controlled, double-blind, clinical trial in a tertiary pediatric hospital, and 13 children with CP and a cognitive age under 42 months were enrolled. tDCS group (n = 8) had active tDCS and cognitive training (20 min/session, total 20 sessions, for 12 weeks) and sham group (n = 5) had sham tDCS and cognitive training. Primary outcome was the Bayley Scales of Infant Development II (BSID II). Secondary outcomes were the Pediatric Evaluation of Disability Inventory (PEDI), the Laboratory Temperament Assessment Battery (Lab-TAB), the Early Childhood Behavior Questionnaire (ECBQ), the Korean version of MacArthur-Bates Communicative Development Inventories (M-B CDI-K), the Sequenced Language Scale for Infants (SELSI) and the Preschool Receptive-Expressive Language Scale (PRES). After intervention, the tDCS group showed significant improvements in all measurements (p < 0.05) except the M-B CDI-K (grammar), whereas the sham group only showed significant improvements in the Lab-TAB (manipulation domain), the ECBQ (attentional shifting), and the M-B CDI-K (comprehension). The between-group differences in the degree of post-intervention improvement were not statistically significant. The degree of improvement was associated with better baseline cognitive function and younger age (p < 0.05). There were no major adverse events after tDCS. The combined application of tDCS and cognitive training was feasible and associated with improvements in cognitive function, ADL, and language among children with CP with cognitive impairment. However, considering that it is a pilot study, further larger-scale systematic investigation is needed. Clinical Trial Registration: The trial was registered in the Clinical Research Information Service database, identifier: KCT0003023.

Effects of bifrontal transcranial direct current stimulation on brain glutamate levels and resting state connectivity: multimodal MRI data for the cathodal stimulation site

Transcranial direct current stimulation (tDCS) over prefrontal cortex (PFC) regions is currently proposed as therapeutic intervention for major depression and other psychiatric disorders. The in-depth mechanistic understanding of this bipolar and non-focal stimulation technique is still incomplete. In a pilot study, we investigated the effects of bifrontal stimulation on brain metabolite levels and resting state connectivity under the cathode using multiparametric MRI techniques and computational tDCS modeling. Within a double-blind cross-over design, 20 subjects (12 women, 23.7 ± 2 years) were randomized to active tDCS with standard bifrontal montage with the anode over the left dorsolateral prefrontal cortex (DLPFC) and the cathode over the right DLPFC. Magnetic resonance spectroscopy (MRS) was acquired before, during, and after prefrontal tDCS to quantify glutamate (Glu), Glu + glutamine (Glx) and gamma aminobutyric acid (GABA) concentration in these areas. Resting-state functional connectivity MRI (rsfcMRI) was acquired before and after the stimulation. The individual distribution of tDCS induced electric fields (efields) within the MRS voxel was computationally modelled using SimNIBS 2.0. There were no significant changes of Glu, Glx and GABA levels across conditions but marked differences in the course of Glu levels between female and male participants were observed. Further investigation yielded a significantly stronger Glu reduction after active compared to sham stimulation in female participants, but not in male participants. For rsfcMRI neither significant changes nor correlations with MRS data were observed. Exploratory analyses of the effect of efield intensity distribution on Glu changes showed distinct effects in different efield groups. Our findings are limited by the small sample size, but correspond to previously published results of cathodal tDCS. Future studies should address gender and efield intensity as moderators of tDCS induced effects.

Improving emotion regulation of social exclusion in depression-prone individuals: a tDCS study targeting right VLPFC

BACKGROUND

Growing evidence has indicated that right ventrolateral prefrontal cortex (RVLPFC) is critical in down-regulating emotional responses to social exclusion, and that depression is accompanied by social emotional dysregulation associated with reduced lateral prefrontal engagement. This study used anodal transcranial direct current stimulation (tDCS) to examine whether stimulating RVLPFC could improve emotional down-regulation of social exclusion in individuals with high depressive mood (DM).

METHODS

A total of 96 high and 94 low DM individuals received active or sham tDCS while viewing social exclusion or individual negative pictures under no-reappraisal (passive viewing) and reappraisal conditions. Participants rate their negative emotional experience following the presentation of each image. Pupil diameter and visual fixation duration were also recorded during the task.

RESULTS

It was found that tDCS-activated RVLPFC induced a stronger regulation effect on social exclusion than individual negative emotions. The effect of tDCS on regulation of social exclusion was more pronounced in low v. high DM individuals.

CONCLUSIONS

These findings demonstrate the specific role of RVLPFC on social emotion regulation, which has implications for refining target areas for the treatment of social emotion dysregulation in depression. However the findings do not suggest that high DM individuals benefit from a single-tDCS session on the emotion regulation of social exclusion. Thus we suggest to use multiple tDCS sessions or transcranial magnetic stimulation to further explore the therapeutic proposal in the future.

Cerebral Perfusion Effects of Cognitive Training and Transcranial Direct Current Stimulation in Mild-Moderate TBI

Background: Persistent post-traumatic symptoms (PPS) after traumatic brain injury (TBI) can lead to significant chronic functional impairment. Pseudocontinuous arterial spin labeling (pCASL) has been used in multiple studies to explore changes in cerebral blood flow (CBF) that may result in acute and chronic TBI, and is a promising neuroimaging modality for assessing response to therapies. Methods: Twenty-four subjects with chronic mild-moderate TBI (mmTBI) were enrolled in a pilot study of 10 days of computerized executive function training combined with active or sham anodal transcranial direct current stimulation (tDCS) for treatment of cognitive PPS. Behavioral surveys, neuropsychological testing, and magnetic resonance imaging (MRI) with pCASL sequences to assess global and regional CBF were obtained before and after the training protocol. Results: Robust improvements in depression, anxiety, complex attention, and executive function were seen in both active and sham groups between the baseline and post-treatment visits. Global CBF decreased over time, with differences in regional CBF noted in the right inferior frontal gyrus (IFG). Active stimulation was associated with static or increased CBF in the right IFG, whereas sham was associated with reduced CBF. Neuropsychological performance and behavioral symptoms were not associated with changes in CBF. Discussion: The current study suggests a complex picture between mmTBI, cerebral perfusion, and recovery. Changes in CBF may result from physiologic effect of the intervention, compensatory neural mechanisms, or confounding factors. Limitations include a small sample size and heterogenous injury sample, but these findings suggest promising directions for future studies of cognitive training paradigms in mmTBI.

Individually customized transcranial temporal interference stimulation for focused modulation of deep brain structures: a simulation study with different head models

Temporal interference (TI) stimulation was recently proposed that allows for the stimulation of deep brain structures with neocortical regions being minimally stimulated. For human brain modulation, TI current patterns are known to be considerably affected by the complex structures of the human head, and thus, it is hard to deliver TI current to a specific deep brain region. In this study, we optimized scalp electrode configurations and injection currents that can deliver maximum TI stimulation currents to a specific deep brain region, the head of the right hippocampus in this study, considering the real anatomical head structures of each individual. Three realistic finite element (FE) head models were employed for the optimization of TI stimulation. To generate TI current patterns, two pairs of scalp electrodes were selected, which carry two sinusoidally alternating currents with a small frequency difference. For every possible combination of electrode pairs, optimal injection currents delivering the maximal TI currents to the head of the right hippocampus were determined. The distribution of the optimized TI currents was then compared with that of the unoptimized TI currents and the conventional single frequency alternating current stimulation. Optimization of TI stimulation parameters allows for the delivery of the desired amount of TI current to the target region while effectively reducing the TI currents delivered to cortical regions compared to the other stimulation approaches. Inconsistency of the optimal stimulation conditions suggest that customized stimulation, considering the individual anatomical differences, is necessary for more effective transcranial TI stimulation. Customized transcranial TI stimulation based on the numerical field analysis is expected to enhance the overall effectiveness of noninvasive stimulation of the human deep brain structures.

Electrical stimulation of cranial nerves in cognition and disease

The cranial nerves are the pathways through which environmental information (sensation) is directly communicated to the brain, leading to perception, and giving rise to higher cognition. Because cranial nerves determine and modulate brain function, invasive and non-invasive cranial nerve electrical stimulation methods have applications in the clinical, behavioral, and cognitive domains. Among other neuromodulation approaches such as peripheral, transcranial and deep brain stimulation, cranial nerve stimulation is unique in allowing axon pathway-specific engagement of brain circuits, including thalamo-cortical networks. In this review we amalgamate relevant knowledge of 1) cranial nerve anatomy and biophysics; 2) evidence of the modulatory effects of cranial nerves on cognition; 3) clinical and behavioral outcomes of cranial nerve stimulation; and 4) biomarkers of nerve target engagement including physiology, electroencephalography, neuroimaging, and behavioral metrics. Existing non-invasive stimulation methods cannot feasibly activate the axons of only individual cranial nerves. Even with invasive stimulation methods, selective targeting of one nerve fiber type requires nuance since each nerve is composed of functionally distinct axon-types that differentially branch and can anastomose onto other nerves. None-the-less, precisely controlling stimulation parameters can aid in affecting distinct sets of axons, thus supporting specific actions on cognition and behavior. To this end, a rubric for reproducible dose-response stimulation parameters is defined here. Given that afferent cranial nerve axons project directly to the brain, targeting structures (e.g. thalamus, cortex) that are critical nodes in higher order brain networks, potent effects on cognition are plausible. We propose an intervention design framework based on driving cranial nerve pathways in targeted brain circuits, which are in turn linked to specific higher cognitive processes. State-of-the-art current flow models that are used to explain and design cranial-nerve-activating stimulation technology require multi-scale detail that includes: gross anatomy; skull foramina and superficial tissue layers; and precise nerve morphology. Detailed simulations also predict that some non-invasive electrical or magnetic stimulation approaches that do not intend to modulate cranial nerves per se, such as transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS), may also modulate activity of specific cranial nerves. Much prior cranial nerve stimulation work was conceptually limited to the production of sensory perception, with individual titration of intensity based on the level of perception and tolerability. However, disregarding sensory emulation allows consideration of temporal stimulation patterns (axon recruitment) that modulate the tone of cortical networks independent of sensory cortices, without necessarily titrating perception. For example, leveraging the role of the thalamus as a gatekeeper for information to the cerebral cortex, preventing or enhancing the passage of specific information depending on the behavioral state. We show that properly parameterized computational models at multiple scales are needed to rationally optimize neuromodulation that target sets of cranial nerves, determining which and how specific brain circuitries are modulated, which can in turn influence cognition in a designed manner.

Precision non-implantable neuromodulation therapies: a perspective for the depressed brain

Current first-line treatments for major depressive disorder (MDD) include pharmacotherapy and cognitive-behavioral therapy. However, one-third of depressed patients do not achieve remission after multiple medication trials, and psychotherapy can be costly and time-consuming. Although non-implantable neuromodulation (NIN) techniques such as transcranial magnetic stimulation, transcranial direct current stimulation, electroconvulsive therapy, and magnetic seizure therapy are gaining momentum for treating MDD, the efficacy of non-convulsive techniques is still modest, whereas use of convulsive modalities is limited by their cognitive side effects. In this context, we propose that NIN techniques could benefit from a precision-oriented approach. In this review, we discuss the challenges and opportunities in implementing such a framework, focusing on enhancing NIN effects via a combination of individualized cognitive interventions, using closed-loop approaches, identifying multimodal biomarkers, using computer electric field modeling to guide targeting and quantify dosage, and using machine learning algorithms to integrate data collected at multiple biological levels and identify clinical responders. Though promising, this framework is currently limited, as previous studies have employed small samples and did not sufficiently explore pathophysiological mechanisms associated with NIN response and side effects. Moreover, cost-effectiveness analyses have not been performed. Nevertheless, further advancements in clinical trials of NIN could shift the field toward a more “precision-oriented” practice.