Transcranial alternating current stimulation and its effects on cognition and the treatment of psychiatric disorders: a systematic review and meta-analysis

Cognitive and Neuropsychiatric Effects of 40 Hz tACS Simultaneously with Cognitive Exercises for Dementia: A Randomized, Crossover, Double-Blind, Sham-Controlled Study

Background and Objectives: Transcranial alternating current stimulation (tACS) at 40 Hz has shown potential to enhance cognitive function. However, research on its combination with cognitive exercises, particularly its long-term effects in a dementia population, remains limited. This study investigated the effects of 40 Hz tACS paired with simultaneous cognitive exercises on cognition, neuropsychiatric symptoms, and the depression status of individuals with dementia in a sham-controlled, double-blind crossover design. Materials and Methods: A total of 42 participants with dementia were randomized into two groups: (1) the R1S2 group received 40 Hz real tACS with cognitive exercises, followed by a ≥8-week washout period, and then sham tACS with cognitive exercises; (2) the S1R2 group received the reversed sequence. tACS was applied at 1.5 mA peak-to-peak with electrodes over the left dorsolateral prefrontal cortex and contralateral supraorbital area. Participants received two 30 min stimulation sessions per day, 5 days per week, for 4 consecutive weeks, paired with cognitive exercises using the MindTriggers app (2.9.1). The primary outcome was the Alzheimer's Disease Assessment Scale-Cognitive Subscale (ADAS-Cog) and the secondary outcomes included the Montgomery-Åsberg Depression Rating Scale (MADRS) and the Neuropsychiatric Inventory Questionnaire (NPI-Q). All outcome measures were assessed before and after each treatment block. Results: Real tACS paired with cognitive exercises significantly improved ADAS-Cog scores post-treatment compared to pre-treatment (p-value = 0.019), whereas sham tACS did not. Furthermore, real tACS produced significant long-term improvements approximately 2-3 months post-treatment in ADAS-Cog scores compared to sham (p-value = 0.048). Both real (p-value = 0.003) and sham (p-value = 0.015) tACS significantly reduced NPI-Q scores post-treatment. MADRS scores significantly improved (p-value = 0.007) post-treatment for real tACS but not sham. Conclusions: The 40 Hz tACS paired with cognitive exercises improves cognition, neuropsychiatric symptoms, and depression post-treatment in dementia, with sustained cognitive effects. The findings highlight its potential as a non-invasive therapeutic intervention for dementia.

Normative characterization of age-related periodic and aperiodic activity in resting-state real-world clinical EEG recordings

Introduction

The relevance of electroencephalographic (EEG) biomarkers is increasing, as advancements in spectral analysis enable computational decomposition of complex neural signals into quantitative EEG (qEEG) parameters. Especially the differentiation of periodic and aperiodic components can reveal insights into neural function, disease biomarkers, and therapeutic efficacy. The aim of these analyses from real-world clinical routine EEG recordings was to provide normative values of physiological age-related oscillatory (periodic) and non-rhythmic (aperiodic) activity.

Methods

We analyzed 532 physiological EEGs of patients between 8 and 92 years of age. EEG segments were preprocessed, and the power spectrum was computed using a multitaper method. We decomposed the power spectrum into periodic (peak power, frequency, and bandwidth) and aperiodic (intercept and exponent) components. Linear regression models were used to investigate age-related changes in these parameters.

Results

We observed significant global age-related changes in the periodic alpha (-0.015 Hz/year) and gamma (+0.013 to +0.031 Hz/year) peak frequency as well as in the aperiodic exponent (-0.003 to -0.004 μV2/Hz/year). In the other parameters there were solely regional or no significant age-related changes.

Conclusion

Decomposing the power spectrum into periodic and aperiodic components allows for the characterization of age-related changes.

Significance

This study provides the first spectrum-wide normative characterization of age-related changes in periodic and aperiodic activity, relevant for non-invasive brain stimulation with alternating current targeting ongoing oscillatory activity.

Personalized Theta Transcranial Alternating Current Stimulation and Gamma Transcranial Alternating Current Stimulation Bring Differential Neuromodulatory Effects on the Resting Electroencephalogram: Characterizing the Temporal, Spatial, and Spectral Dimensions of Transcranial Alternating Current Stimulation

OBJECTIVES

The neuromodulatory effects of transcranial alternating current stimulation (tACS) on electroencephalogram (EEG) dynamics are quite heterogenous. The primary objective of the study is to comprehensively characterize the effects of two tACS protocols on resting-state EEG.

MATERIALS AND METHODS

A total of 36 healthy participants were recruited and were randomized into three groups. Two groups received either personalized theta (4-8 Hz) or gamma (40 Hz) stimulation bilaterally in the frontal regions for 20 minutes (4 minutes ON, 1 minute OFF, four cycles). The third group performed relaxed breath watching for 20 minutes. Artifact-free, 1-minute EEG segments from the baseline, during tACS, and after stimulation resting EEG were characterized to see the effects of tACS. Threshold-free cluster enhanced permutation tests (for spectral measures) and two-way mixed analysis of variance (for aperiodic slope) were used for statistical inferences.

RESULTS

Current modeling simulation using ROAST with preset parameters (800 μA, AF3 AF4 locations) showed that induced electric fields can activate frontal cortical regions. During the stimulation period, personalized theta tACS entrained theta band power in the centro-parietal areas. There was a compensatory power decrease in the beta and gamma bands after theta tACS. No entrainment effects were observed for gamma tACS during stimulation, but a significant entrainment was observed in the theta and beta bands in the parieto-occipital regions after stimulation. The delta band power decreased in the central regions. No spectral modulations were seen after breath watching. The spectral slope, which measures aperiodic activity, was not affected by either breath watching or tACS.

CONCLUSIONS

Characterizing the effects of multiple tACS protocols is critical to effectively target specific neural oscillatory patterns and to personalize the protocols. The study can be extended to target specific oscillatory patterns associated with cognitive deficits in neuro-psychiatric conditions.

Transcranial alternating current stimulation for neuropsychiatric disorders: a systematic review of treatment parameters and outcomes

Background

Transcranial alternating current stimulation (tACS) alters cortical excitability with low-intensity alternating current and thereby modulates aberrant brain oscillations. Despite the recent increase in studies investigating the feasibility and efficacy of tACS in treating neuropsychiatric disorders, its mechanisms, as well as optimal stimulation parameters, are not fully understood.

Objectives

This systematic review aimed to compile human research on tACS for neuropsychiatric disorders to delineate typical treatment parameters for these conditions and evaluate its outcomes.

Methods

A search for published studies and unpublished registered clinical trials was conducted through OVID (MEDLINE, PsycINFO, and Embase), ClinicalTrials.gov, and the International Clinical Trials Registry Platform. Studies utilizing tACS to treat neuropsychiatric disorders in a clinical trial setting were included.

Results

In total, 783 published studies and 373 clinical trials were screened; 53 published studies and 70 clinical trials were included. Published studies demonstrated a low risk of bias, as assessed by the Joanna Briggs Institute Critical Appraisal Tools. Neurocognitive, psychotic, and depressive disorders were the most common disorders treated with tACS. Both published studies (58.5%) and registered clinical trials (52%) most commonly utilized gamma frequency bands and tACS was typically administered at an intensity of 2 mA peak-to-peak, once daily for 20 or fewer sessions. Although the targeted brain locations and tACS montages varied across studies based on the outcome measures and specific pathophysiology of the disorders, the dorsolateral prefrontal cortex (DLPFC) was the most common target in both published studies (30.2%) and registered clinical trials (25.6%). Across studies that published results on tACS outcome measures, tACS resulted in enhanced symptoms and/or improvements in overall psychopathology for neurocognitive (all 11 studies), psychotic (11 out of 14 studies), and depressive (7 out of 8 studies) disorders. Additionally, 17 studies reported alterations in the power spectrum of the electroencephalogram around the entrained frequency band at the targeted locations following tACS.

Conclusion

Behavioral and cognitive symptoms have been positively impacted by tACS. The most consistent changes were reported in cognitive symptoms following gamma-tACS over the DLPFC. However, the paucity of neuroimaging studies for each neuropsychiatric condition highlights the necessity for replication studies employing biomarker- and mechanism-centric approaches.

Non-invasive brain stimulation and vision rehabilitation: a clinical perspective

Non-invasive brain stimulation techniques allow targeted modulation of brain regions and have emerged as a promising tool for vision rehabilitation. This review presents an overview of studies that have examined the use of non-invasive brain stimulation techniques for improving vision and visual functions. A description of the proposed neural mechanisms that underpin non-invasive brain stimulation effects is also provided. The clinical implications of non-invasive brain stimulation in vision rehabilitation are examined, including their safety, effectiveness, and potential applications in specific conditions such as amblyopia, post-stroke hemianopia, and central vision loss associated with age-related macular degeneration. Additionally, the future directions of research in this field are considered, including the need for larger and more rigorous clinical trials to validate the efficacy of these techniques. Overall, this review highlights the potential for brain stimulation techniques as a promising avenue for improving visual function in individuals with impaired vision and underscores the importance of continued research in this field.

Effect of γ-tACS on prefrontal hemodynamics in bipolar disorder: A functional near-infrared study

OBJECTIVES

Transcranial alternating current stimulation (tACS) is a potential therapeutic psychiatric tool that has been shown to modulate clinical symptoms and brain function by inducing brain oscillations. However, direct evidence on the effects of gamma-tACS (γ-tACS) on Bipolar I Disorder (BD-I) is limited. In the present study we used functional near-infrared spectroscopy to explore prefrontal hemodynamic changes in BD-I patients receiving combined γ-tACS intervention in addition to pharmacological treatment.

METHODS

Only 39 male patients with BD-I in the acute manic phase were included, and they were randomly divided into an intervention group (n = 18) and a control group (n = 21). The intervention group received γ-tACS treatment on a weekday for a total of 10 sessions in the right prefrontal cortex and left prefrontal cortex. All participants were pretested (baseline) and posttested (2 weeks after) with questionnaires to assess clinical symptoms and cognitive abilities, and with functional near infrared spectroscopy (fNIRS) to assess spontaneous cortical hemodynamic activities.

RESULTS

Compared to the control group, the intervention group had greater increases in Montreal Cognitive Assessment (MoCA) scores, and greater decreases in Bech-Rafaelsen Mania Rating Scale (BRMS) scores. In the intervention group, functional connectivity (FC) was significantly greater in the left hemisphere. γ-tACS treatment resulted in a left hemispheric lateralization effect of resting state FC in BD-I patients, increasing the hemodynamic activity of the patient's left prefrontal cortex.

CONCLUSIONS

γ-tACS can improve cognitive impairment and mood symptoms with BD-I patients in an acute manic episode by enhancing FC in the patients' left prefrontal cortex.

An experimental examination of neurostimulation and cognitive restructuring as potential components for Misophonia interventions

Misophonia is a disorder of decreased tolerance to certain aversive, repetitive common sounds, or to stimuli associated with these sounds. Two matched groups of adults (29 participants with misophonia and 30 clinical controls with high emotion dysregulation) received inhibitory neurostimulation (1 Hz) over a personalized medial prefrontal cortex (mPFC) target functionally connected to the left insula; excitatory neurostimulation (10 Hz) over a personalized dorsolateral PFC (dlPFC) target; and sham stimulation over either target. Stimulations were applied while participants were either listening or cognitively downregulating emotions associated with personalized aversive, misophonic, or neutral sounds. Subjective units of distress (SUDS) and psychophysiological measurements (e.g., skin conductance response [SCR] and level [SCL]) were collected. Compared to controls, participants with misophonia reported higher distress (∆SUDS = 1.91-1.93, ps < 0.001) when listening to and when downregulating misophonic distress. Both types of neurostimulation reduced distress significantly more than sham, with excitatory rTMS providing the most benefit (Cohen's dSUDS = 0.53; dSCL = 0.14). Excitatory rTMS also enhanced the regulation of emotions associated with misophonic sounds in both groups when measured by SUDS (dcontrol = 1.28; dMisophonia = 0.94), and in the misophonia group alone when measured with SCL (d = 0.20). Both types of neurostimulation were well tolerated. Engaging in cognitive restructuring enhanced with high-frequency neurostimulation led to the lowest misophonic distress, highlighting the best path forward for misophonia interventions.

Treatment of apathy in Parkinson's disease: A bayesian network meta-analysis of randomised controlled trials

Background

Apathy is an important but unrecognised aspect of Parkinson's disease (PD). The optimal therapeutic options for apathy remain unclear. Early recognition and treatment of apathy can reduce the significant burden of disease for patients and their caregivers. Here we conducted a meta-analysis to evaluate the comparative efficacy of different treatment modalities of apathy in PD (CRD42021292099).

Methods

We screened Medline, Embase, and PsycINFO databases for articles on therapies for apathy in PD. The outcome of interest is the reduction in apathy scores post-intervention and is measured by standardised mean differences (SMD) with 95% credible intervals (CrI). We included only randomised controlled trials examining interventions targeted at reducing apathy.

Results

Nineteen studies involving 2372 patients were included in the quantitative analysis. The network meta-analysis found pharmacotherapy to be the most efficacious treatment, significantly better than brain stimulation (SMD -0.43, 95% CrI -0.78 to -0.07), exercise-based interventions (SMD -0.66, 95% CrI -1.25 to -0.08), supplements (SMD -0.33, 95% CrI -0.67 to 0), and placebo (SMD -0.38, 95% CrI -0.56 to -0.23). Subgroup analysis of pharmacotherapy versus placebo found similar efficacy of dopamine agonists (SMD -0.36, 95% CI -0.59 to -0.12, P = 0.003) and alternative medications (SMD -0.42, 95% CI -0.61 to -0.23, P < 0.001). The remaining comparisons and subgroup analyses did not demonstrate any significant treatment effects.

Conclusion

Our meta-analysis of randomised controlled trials showed that pharmacotherapy is the most efficacious treatment option, with dopamine agonists having similar efficacy as other medications. Further research is needed to determine the optimal management strategy.

Transcranial alternating current stimulation for schizophrenia: a systematic review of randomized controlled studies

Background

In randomized clinical trials (RCTs) investigating the application of transcranial alternating current stimulation (tACS) in schizophrenia, inconsistent results have been reported. The purpose of this exploratory systematic review of RCTs was to evaluate tACS as an adjunct treatment for patients with schizophrenia based on its therapeutic effects, tolerability, and safety.

Methods

Our analysis included RCTs that evaluated adjunctive tACS' effectiveness, tolerability, and safety in schizophrenia patients. Three independent authors extracted data and synthesized it using RevMan 5.3 software.

Results

Three RCTs involving 76 patients with schizophrenia were encompassed in the analysis, with 40 participants receiving active tACS and 36 receiving sham tACS. Our study revealed a significant superiority of active tACS over sham tACS in improving total psychopathology (standardized mean difference [SMD] = -0.61, 95% confidence interval [CI]: -1.12, -0.10; I2 = 16%, p = 0.02) and negative psychopathology (SMD = -0.65, 95% CI: -1.11, -0.18; I2 = 0%, p = 0.007) in schizophrenia. The two groups, however, showed no significant differences in positive psychopathology, general psychopathology, or auditory hallucinations (all p > 0.05). Two RCTs examined the neurocognitive effects of tACS, yielding varied findings. Both groups demonstrated similar rates of discontinuation due to any reason and adverse events (all p > 0.05).

Conclusion

Adjunctive tACS is promising as a viable approach for mitigating total and negative psychopathology in individuals diagnosed with schizophrenia. However, to gain a more comprehensive understanding of tACS's therapeutic effects in schizophrenia, it is imperative to conduct extensive, meticulously planned, and well-documented RCTs.

Brain State-Dependent Non-Invasive Neurostimulation with EEG Feedback: Achievements and Prospects (Review)

Non-invasive brain stimulation with electroencephalogram (EEG) feedback is an intensively developing and promising area of neurophysiology. The review considers the literature data over the past 5 years on the achievements and promising directions for the further development of this research line. Modern data on the developed approaches to the practical use of various types of brain state-dependent adaptive neurostimulation with EEG feedback were analyzed. The main attention is paid to the studies using non-invasive magnetic and electrical stimulation, as well as acoustic and audiovisual stimulation. The paper considers the possibilities and prospects for using these technologies in clinical medicine. The results of the authors' own research are presented.

Severity and Longitudinal Course of Depression, Anxiety and Post-Traumatic Stress in Paediatric and Young Adult Cancer Patients: A Systematic Review and Meta-Analysis

BACKGROUND

A diagnosis of cancer and treatment may constitute a highly traumatic period for paediatric cancer patients (PYACPs). However, no review has comprehensively analysed how the mental health of PYACPs is acutely affected and the longitudinal course.

METHODS

This systematic review followed PRISMA guidelines. Comprehensive searches of databases were conducted to identify studies of depression, anxiety and post-traumatic stress symptoms in PYACPs. Random effects meta-analyses were used for the primary analysis.

RESULTS

From 4898 records, 13 studies were included. Acutely after diagnosis, depressive and anxiety symptoms were significantly elevated in PYACPs. Depressive symptoms only significantly decreased after 12 months (standardised mean difference, SMD = -0.88; 95% CI: -0.92, -0.84). This downward trajectory persisted to 18 months (SMD = -1.862; 95% CI: -1.29, -1.09). Anxiety symptoms similarly only decreased after 12 (SMD = -0.34; 95% CI: -0.42, -0.27) up to 18 months (SMD = -0.49; 95% CI: -0.60, -0.39) after the cancer diagnosis. Post-traumatic stress symptoms showed protracted elevations throughout follow-up. Overall, significant predictors of poorer psychological outcomes included unhealthy family functioning, concomitant depression or anxiety, poor cancer prognosis or experiencing cancer and treatment-related side effects.

CONCLUSIONS

While depression and anxiety may improve over time with a favourable environment, post-traumatic stress may have a protracted course. Timely identification and psycho-oncological intervention are critical.