Pre-treatment attentional processing speed and antidepressant response to transcranial direct current stimulation: Results from an international randomized controlled trial

Brain-Derived Neurotrophic Factor (BDNF) as a Predictor of Treatment Response in Major Depressive Disorder (MDD): A Systematic Review

Brain-derived neurotrophic factor (BDNF) has been studied as a biomarker of major depressive disorder (MDD). Besides diagnostic biomarkers, clinically useful biomarkers can inform response to treatment. We aimed to review all studies that sought to relate BDNF baseline levels, or BDNF polymorphisms, with response to treatment in MDD. In order to achieve this, we performed a systematic review of studies that explored the relation of BDNF with both pharmacological and non-pharmacological treatment. Finally, we reviewed the evidence that relates peripheral levels of BDNF and BDNF polymorphisms with the development and management of treatment-resistant depression.

Transcranial direct current stimulation for bipolar depression: systematic reviews of clinical evidence and biological underpinnings

Despite multiple available treatments for bipolar depression (BD), many patients face sub-optimal responses. Transcranial direct current stimulation (tDCS) has been advocated in the management of different conditions, including BD, especially in treatment-resistant cases. The optimal dose and timing of tDCS, the mutual influence with other concurrently administered interventions, long-term efficacy, overall safety, and biological underpinnings nonetheless deserve additional assessment. The present study appraised the existing clinical evidence about tDCS for bipolar depression, delving into the putative biological underpinnings with a special emphasis on cellular and molecular levels, with the ultimate goal of providing a translational perspective on the matter. Two separate systematic reviews across the PubMed database since inception up to August 8^th 2022 were performed, with fourteen clinical and nineteen neurobiological eligible studies. The included clinical studies encompass 207 bipolar depression patients overall and consistently document the efficacy of tDCS, with a reduction in depression scores after treatment ranging from 18% to 92%. The RCT with the largest sample clearly showed a significant superiority of active stimulation over sham. Mild-to-moderate and transient adverse effects are attributed to tDCS across these studies. The review of neurobiological literature indicates that several molecular mechanisms may account for the antidepressant effect of tDCS in BD patients, including the action on calcium homeostasis in glial cells, the enhancement of LTP, the regulation of neurotrophic factors and inflammatory mediators, and the modulation of the expression of plasticity-related genes. To the best of our knowledge, this is the first study on the matter to concurrently provide a synthesis of the clinical evidence and an in-depth appraisal of the putative biological underpinnings, providing consistent support for the efficacy, safety, and tolerability of tDCS.

Is transcranial direct current stimulation, alone or in combination with antidepressant medications or psychotherapies, effective in treating major depressive disorder? A systematic review and meta-analysis

BACKGROUND

Transcranial direct current stimulation (tDCS) has shown mixed results for depression treatment. The efficacies of tDCS combination therapies have not been investigated deliberately. This review aims to evaluate the clinical efficacy of tDCS as a monotherapy and in combination with medication, psychotherapy, and ECT for treating adult patients with major depressive disorder (MDD) and identified the factors influencing treatment outcome measures (i.e. depression score, dropout, response, and remission rates).

METHODS

The systematic review was performed in PubMed/Medline, EMBASE, PsycINFO, Web of Sciences, and OpenGrey. Two authors performed independent literature screening and data extraction. The primary outcomes were the standardized mean difference (SMD) for continuous depression scores after treatment and odds ratio (OR) dropout rate; secondary outcomes included ORs for response and remission rates. Random effects models with 95% confidence intervals were employed in all outcomes. The overall effect of tDCS was investigated by meta-analysis. Sources of heterogeneity were explored via subgroup analyses, meta-regression, sensitivity analyses, and assessment of publication bias.

RESULTS

Twelve randomised, sham-controlled trials (active group: N = 251, sham group: N = 204) were included. Overall, the integrated depression score of the active group after treatment was significantly lower than that of the sham group (g = - 0.442, p = 0.017), and further analysis showed that only tDCS + medication achieved a significant lower score (g = - 0.855, p < 0.001). Moreover, this combination achieved a significantly higher response rate than sham intervention (OR = 2.7, p = 0.006), while the response rate remained unchanged for the other three therapies. Dropout and remission rates were similar in the active and sham groups for each therapy and also for the overall intervention. The meta-regression results showed that current intensity is the only predictor for the response rate. None of publication bias was identified.

CONCLUSION

The effect size of tDCS treatment was obviously larger in depression score compared with sham stimulation. The tDCS combined selective serotonin re-uptake inhibitors is the optimized therapy that is effective on depression score and response rate. tDCS monotherapy and combined psychotherapy have no significant effects. The most important parameter for optimization in future trials is treatment strategy.

Dataset of concurrent EEG, ECG, and behavior with multiple doses of transcranial electrical stimulation

We present a dataset combining human-participant high-density electroencephalography (EEG) with physiological and continuous behavioral metrics during transcranial electrical stimulation (tES). Data include within participant application of nine High-Definition tES (HD-tES) types, targeting three cortical regions (frontal, motor, parietal) with three stimulation waveforms (DC, 5 Hz, 30 Hz); more than 783 total stimulation trials over 62 sessions with EEG, physiological (ECG, EOG), and continuous behavioral vigilance/alertness metrics. Experiment 1 and 2 consisted of participants performing a continuous vigilance/alertness task over three 70-minute and two 70.5-minute sessions, respectively. Demographic data were collected, as well as self-reported wellness questionnaires before and after each session. Participants received all 9 stimulation types in Experiment 1, with each session including three stimulation types, with 4 trials per type. Participants received two stimulation types in Experiment 2, with 20 trials of a given stimulation type per session. Within-participant reliability was tested by repeating select sessions. This unique dataset supports a range of hypothesis testing including interactions of tDCS/tACS location and frequency, brain-state, physiology, fatigue, and cognitive performance.

Transcranial Direct Current Stimulation and Cognition in Neuropsychiatric Disorders: Systematic Review of the Evidence and Future Directions

Transcranial direct current stimulation (tDCS) has been implemented in neuropsychiatric disorders characterized by cognitive impairment. However, methodological heterogeneity challenges conclusive remarks. Through a critical analysis of previous conflicting findings and in the light of current neurobiological models of pathophysiology, we qualitatively assessed the effects of tDCS in neuropsychiatric disorders that share neurobiological underpinnings, as to evaluate whether stimulation can improve cognitive deficits in patients' cohorts. We performed a systematic review of tDCS studies targeting cognitive functions in mental disorders and pathological cognitive aging. Data from 41 studies, comprising patients with diagnosis of mood disorders, schizophrenia-spectrum disorders, Alzheimer's disease (AD), and mild cognitive impairment (MCI), were included. Results indicate that tDCS has the capacity to enhance processing speed, working memory, and executive functions in patients with mood and schizophrenia-spectrum disorders. The evidence of a positive effect on general cognitive functioning and memory is either inconclusive in AD, or weak in MCI. Future directions are discussed for developing standardized stimulation protocols and for translating the technique therapeutic potential into effective clinical practice.

A systematic review and meta-analysis on the effects of transcranial direct current stimulation in depressive episodes

BACKGROUND

Transcranial direct current stimulation (tDCS) has shown mixed results for depression treatment.

OBJECTIVE

To perform a systematic review and meta-analysis of trials using tDCS to improve depressive symptoms.

METHODS

A systematic review was performed from the first date available to January 06, 2020 in PubMed, EMBASE, Cochrane Library, and additional sources. We included randomized, sham-controlled clinical trials (RCTs) enrolling participants with an acute depressive episode and compared the efficacy of active versus sham tDCS, including association with other interventions. The primary outcome was the Hedges' g for continuous depression scores; secondary outcomes included odds ratios (ORs) and number needed to treat (NNT) for response, remission, and acceptability. Random effects models were employed. Sources of heterogeneity were explored via metaregression, sensitivity analyses, subgroup analyses, and bias assessment.

RESULTS

We included 23 RCTs (25 datasets, 1,092 participants), most (57%) presenting a low risk of bias. Active tDCS was superior to sham regarding endpoint depression scores (k = 25, g = 0.46, 95% confidence interval [CI]: 0.22-0.70), and also achieved superior response (k = 18, 33.3% vs. 16.56%, OR = 2.28 [1.52-3.42], NNT = 6) and remission (k = 18, 19.12% vs. 9.78%, OR = 2.12 [1.42-3.16], NNT = 10.7) rates. Moreover, active tDCS was as acceptable as sham. No risk of publication bias was identified. Cumulative meta-analysis showed that effect sizes are basically unchanged since total sample reached 439 participants.

CONCLUSIONS

TDCS is modestly effective in treating depressive episodes. Further well-designed, large-scale RCTs are warranted.

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.

Association of BDNF, HTR2A, TPH1, SLC6A4, and COMT polymorphisms with tDCS and escitalopram efficacy: ancillary analysis of a double-blind, placebo-controlled trial

OBJECTIVE

We investigated whether single nucleotide polymorphisms (SNPs) associated with neuroplasticity and activity of monoamine neurotransmitters, such as the brain-derived neurotrophic factor (BDNF, rs6265), the serotonin transporter (SLC6A4, rs25531), the tryptophan hydroxylase 1 (TPH1, rs1800532), the 5-hydroxytryptamine receptor 2A (HTR2A, rs6311, rs6313, rs7997012), and the catechol-O-methyltransferase (COMT, rs4680) genes, are associated with efficacy of transcranial direct current stimulation (tDCS) in major depression.

METHODS

Data from the Escitalopram vs. Electrical Current Therapy for Treating Depression Clinical Study (ELECT-TDCS) were used. Participants were antidepressant-free at baseline and presented with an acute, moderate-to-severe unipolar depressive episode. They were randomized to receive escitalopram/tDCS-sham (n=75), tDCS/placebo-pill (n=75), or placebo-pill/sham-tDCS (n=45). General linear models assessed the interaction between treatment group and allele-wise carriers. Additional analyses were performed for each group and each genotype separately.

RESULTS

Pairwise group comparisons (tDCS vs. placebo, tDCS vs. escitalopram, and escitalopram vs. placebo) did not identify alleles associated with depression improvement. In addition, exploratory analyses also did not identify any SNP unequivocally associated with improvement of depression in any treatment group.

CONCLUSION

Larger, combined datasets are necessary to identify candidate genes for tDCS response.