Transcranial Direct Current Stimulation Improves Cognitive Function in Mild to Moderate Alzheimer Disease: A Meta-Analysis

Transcranial direct current stimulation for global cognition in Alzheimer's disease: a systemic review and meta-analysis

This meta-analysis was to investigate the efficacy of transcranial direct current stimulation (tDCS) for general cognitive function in Alzheimer's disease (AD) and to investigate the potential influential factors. A systematic literature retrieval until August 2023 was performed by searching the PubMed, Embase, Web of Science, and Cochrane Library. Therapeutic effects of tDCS were evaluated using standardized mean difference (SMD) and 95% confidence interval (CI). Pooled effects of tDCS on AD patients were calculated immediately after treatment and at follow-up periods. Subgroup analyses were conducted to identify the potential prognostic factors. Eleven studies with 12 trials including 451 cases were included in our systemic review, in which 9 studies with 10 trials using Mini-Mental State Examination (MMSE) scales were included in the meta-analysis. tDCS significantly improved global cognition in AD immediately after the treatment (SMD, 0.46; 95% CI, 0.25-0.66; P<0.0001), but not at the shorter or longer follow-up period. Subgroup analyses suggested significant global cognitive improvement in patients receiving stimulation on temporal lobes instead of left dorsolateral prefrontal cortex, and in cases receiving tDCS with current density ≥ 0.08 mA/cm2 rather than <0.08 mA/cm2. Compared with tDCS plus cognitive training (CT), tDCS without CT produced obvious cognitive enhancement. In addition, patients with lower education were more likely to benefit from tDCS. tDCS was effective in improving general cognition in AD after treatment. However, further randomized trials are warranted to validate its longer-term effects as well as our subgroup analyses results.

Nonmedication Devices in Development for the Treatment of Alzheimer's Disease

 Huge investments continue to be made in treatment for Alzheimer's disease (AD), with more than one hundred drugs currently in development. Pharmacological approaches and drug development, particularly those targeting amyloid-β, have dominated the therapeutic landscape. At the same time, there is also a growing interest in devices for treating AD. This review aimed to identify and describe devices under development for AD treatment. In this review, we queried the devices that are in development for the treatment of AD. PubMed was searched through the end of 2021 using the terms "device," "therapeutics," and "Alzheimer's" for articles that report on devices to treat AD. Ten devices with 31 references were identified as actively being developed for the treatment of AD. Many of these devices are far along in development. Device-based therapies are often overlooked when evaluating treatment approaches to AD. However, many devices for treating AD are in development and some show promising results.

The effect of transcranial direct current stimulation (tDCS) on cognitive function recovery in patients with depression following electroconvulsive therapy (ECT): protocol for a randomized controlled trial

BACKGROUND

Electroconvulsive therapy (ECT) is a highly effective treatment for depressive disorder. However, the use of ECT is limited by its cognitive side effects (CSEs), and no specific intervention has been developed to address this problem. As transcranial direct current stimulation (tDCS) is a safe and useful tool for improving cognitive function, the main objective of this study was to explore the ability to use tDCS after ECT to ameliorate the cognitive side effects.

METHODS

60 eligible participants will be recruited within two days after completing ECT course and randomly assigned to receive either active or sham stimulation in a blinded, parallel-design trial and continue their usual pharmacotherapy. The tDCS protocol consists of 30-min sessions at 2 mA, 5 times per week for 2 consecutive weeks, applied through 15-cm2 electrodes. An anode will be placed over the left dorsolateral prefrontal cortex (DLPFC), and a cathode will be placed over the right supraorbital cortex. Cognitive function and depressive symptoms will be assessed before the first stimulation (T0), after the final stimulation (T1), 2 weeks after the final stimulation (T2), and 4 weeks after the final stimulation (T3) using the Cambridge Neuropsychological Test Automated Battery (CANTAB).

DISCUSSION

We describe a novel clinical trial to explore whether the administration of tDCS after completing ECT course can accelerates recovery from the CSEs. We hypothesized that the active group would recover faster from the CSEs and be superior to the sham group. If our hypothesis is supported, the use of tDCS could benefit eligible patients who are reluctant to receive ECT and reduce the risk of self-inflicted or suicide due to delays in treatment.

TRIAL REGISTRATION DETAILS

The trial protocol is registered with https://www.chictr.org.cn/ under protocol registration number ChiCTR2300071147 (date of registration: 05.06.2023). Recruitment will start in November 2023.

A Critical Review of Noninvasive Brain Stimulation Technologies in Alzheimer's Dementia and Primary Progressive Aphasia

Multiple pharmacologic agents now have been approved in the United States and other countries as treatment to slow disease and clinical progression for Alzheimer's disease. Given these treatments have not been proven to lessen the cognitive deficits already manifested in the Alzheimer's Clinical Syndrome (ACS), and none are aimed for another debilitating dementia syndrome identified as primary progressive aphasia (PPA), there is an urgent need for new, safe, tolerable, and efficacious treatments to mitigate the cognitive deficits experienced in ACS and PPA. Noninvasive brain stimulation has shown promise for enhancing cognitive functioning, and there has been interest in its potential therapeutic value in ACS and PPA. This review critically examines the evidence of five technologies in ACS and PPA: transcranial direct current stimulation (tDCS), transcranial alternating current stimulation (tACS), transcranial random noise stimulation (tRNS), repetitive transcranial magnetic stimulation (rTMS), and noninvasive vagus nerve stimulation (nVNS). Many randomized controlled trials of tDCS and rTMS report positive treatment effects on cognition in ACS and PPA that persist out to at least 8 weeks, whereas there are few trials for tACS and none for tRNS and nVNS. However, most positive trials did not identify clinically meaningful changes, underscoring that clinical efficacy has yet to be established in ACS and PPA. Much is still to be learned about noninvasive brain stimulation in ACS and PPA, and shifting the focus to prioritize clinical significance in addition to statistical significance in trials could yield greater success in understanding its potential cognitive effects and optimal parameters.

Cognitive Effect of Transcranial Direct Current Stimulation on Left Dorsolateral Prefrontal Cortex in Mild Alzheimer's Disease: A Randomized, Double-Blind, Cross-Over Small-Scale Exploratory Study

Background

Transcranial direct current stimulation (tDCS) is considered a potential therapeutic instrument for Alzheimer's disease (AD) because it affects long-term synaptic plasticity through the processes of long-term potentiation and long-term depression, thereby improving cognitive ability. Nevertheless, the efficacy of tDCS in treating AD is still debated. Dorsal lateral prefrontal cortex is the main role in executive functions.

Objective

We investigate the cognitive effects of tDCS on AD patients.

Methods

Thirty mild AD patients aged 66-86 years (mean = 75.6) were included in a double-blind, randomized, sham-controlled crossover study. They were randomly assigned to receive 10 consecutive daily sessions of active tDCS (2 mA for 30 min) or a sham intervention and switched conditions 3 months later. The anodal and cathodal electrodes were placed on the left dorsal lateral prefrontal cortex and the right supraorbital area, respectively. Subjects underwent various neuropsychological assessments before and after the interventions.

Results

The results showed that tDCS significantly improved Cognitive Abilities Screening Instrument scores, especially on the items of "concentration and calculation", "orientation", "language ability", and "categorical verbal fluency". Mini-Mental State Examination and Wisconsin Card Sorting Test scores in all domains of "concept formation", "abstract thinking", "cognitive flexibility", and "accuracy" also improved significantly after tDCS. For the sham condition, no difference was found between the baseline scores and the after-intervention scores on any of the neuropsychological tests.

Conclusion

>: Using tDCS improves the cognition of AD patients. Further large size clinical trials are necessary to validate the data.

The effects of noninvasive brain stimulation on cognitive function in patients with mild cognitive impairment and Alzheimer's disease using resting-state functional magnetic resonance imaging: A systematic review and meta-analysis

OBJECTIVE

The aim of this systematic review and meta-analysis was to evaluate the efficacy of noninvasive brain stimulation (NIBS) on cognition using functional magnetic resonance imaging (fMRI) in patients with mild cognitive impairment (MCI) and Alzheimer's disease (AD), thus providing the neuroimaging mechanism of cognitive intervention.

METHODS

English articles published up to April 30, 2023 were searched in the PubMed, Web of Science, Embase, and Cochrane Library databases. We included randomized controlled trials where resting-state fMRI was used to observe the effect of NIBS in patients with MCI or AD. RevMan software was used to analyze the continuous variables, and SDM-PSI software was used to perform an fMRI data analysis.

RESULTS

A total of 17 studies comprising 258 patients in the treatment group and 256 in the control group were included. After NIBS, MCI patients in the treatment group showed hyperactivation in the right precuneus and decreased activity in the left cuneus and right supplementary motor area. In contrast, patients in the control group showed decreased activity in the right middle frontal gyrus and no hyperactivation. The clinical cognitive scores in MCI patients were significantly improved by NIBS, while not in AD. Some evidence regarding the modulation of NIBS in resting-state brain activity and functional brain networks in patients with AD was found.

CONCLUSIONS

NIBS could improve cognitive function in patients with MCI and AD. fMRI evaluations could be added to evaluate the contribution of specific NIBS treatment therapeutic effectiveness.

Prefrontal photobiomodulation produces beneficial mitochondrial and oxygenation effects in older adults with bipolar disorder

There is growing evidence of mitochondrial dysfunction and prefrontal cortex (PFC) hypometabolism in bipolar disorder (BD). Older adults with BD exhibit greater decline in PFC-related neurocognitive functions than is expected for age-matched controls, and clinical interventions intended for mood stabilization are not targeted to prevent or ameliorate mitochondrial deficits and neurocognitive decline in this population. Transcranial infrared laser stimulation (TILS) is a non-invasive form of photobiomodulation, in which photons delivered to the PFC photo-oxidize the mitochondrial respiratory enzyme, cytochrome-c-oxidase (CCO), a major intracellular photon acceptor in photobiomodulation. TILS at 1064-nm can significantly upregulate oxidized CCO concentrations to promote differential levels of oxygenated vs. deoxygenated hemoglobin (HbD), an index of cerebral oxygenation. The objective of this controlled study was to use non-invasive broadband near-infrared spectroscopy to assess if TILS to bilateral PFC (Brodmann area 10) produces beneficial effects on mitochondrial oxidative energy metabolism (oxidized CCO) and cerebral oxygenation (HbD) in older (≥50 years old) euthymic adults with BD (N = 15). As compared to sham, TILS to the PFC in adults with BD increased oxidized CCO both during and after TILS, and increased HbD concentrations after TILS. By significantly increasing oxidized CCO and HbD concentrations above sham levels, TILS has the potential ability to stabilize mitochondrial oxidative energy production and prevent oxidative damage in the PFC of adults with BD. In conclusion, TILS was both safe and effective in enhancing metabolic function and subsequent hemodynamic responses in the PFC, which might help alleviate the accelerated neurocognitive decline and dysfunctional mitochondria present in BD.

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.

The beneficial effect on cognition of noninvasive brain stimulation intervention in patients with dementia: a network meta-analysis of randomized controlled trials

BACKGROUND

Dementia [i.e., Alzheimer disease (AD)], the most common neurodegenerative disease, causes profound negative impacts on executive function and quality of life. Available pharmacological treatments often fail to achieve satisfactory outcomes. Noninvasive brain stimulation (NIBS) techniques, which focally modify cortical function and enhance synaptic long-term potentiation, are potentially beneficial for the cognition in patients with AD. The aim of the current network meta-analysis (NMA) was to evaluate the efficacy and safety of different NIBS interventions in patients with AD through NMA.

METHODS

Only randomized controlled trials (RCTs) examining NIBS interventions in patients with AD had been included. All NMA procedures were performed under the frequentist model. The primary and secondary outcomes were changes in cognitive function and quality of life, respectively.

RESULTS

Nineteen RCTs (639 participants) were included. The mean treatment and follow-up durations were 5.7 and 10.5 weeks, respectively. The combination of cathodal tDCS of the left dorsolateral prefrontal cortex and anodal tDCS over the right supraorbital region (c-tDCS-F3 + a-tDCS-Fp2) was associated with a significant beneficial effect on cognition compared with sham controls (standardized mean difference=2.43, 95% confidence interval=0.61-4.26, n=12 and 11). It was also associated with the greatest beneficial effect on cognition among all the investigated NIBS approaches. All the methods were well tolerated with regard to the safety profile, as reflected in the rates of adverse events or local discomfort, as well as acceptability, as indicated by dropout rate.

CONCLUSIONS

The present findings provide evidence of the benefits of NIBS, especially tDCS, for beneficial effect on cognition in patients with AD. However, because of few studies included, this effect was not replicated yet in the other studies. Therefore, future larger-scale and longer follow-up duration RCTs should be warranted.

TRIAL REGISTRATION

PROSPERO CRD42020209516. The current study had been approved by the Institutional Review Board of the Tri-Service General Hospital, National Defense Medical Center (TSGHIRB No. B-109-29).

Therapeutic approaches for improving cognitive function in the aging brain

The rapid aging of populations around the world has become an unprecedented challenge. Aging is associated with cognitive impairment, including dementia and mild cognitive impairment. Successful drug development for improving or maintaining cognition in the elderly is critically important. Although 4 drugs for improving cognition in Alzheimer's disease have been approved, a variety of potential drugs targeting age-related cognitive impairment are still in development. In addition, non-pharmacological interventions, including cognition-oriented treatments, non-invasive brain stimulation physical exercise, and lifestyle-related interventions, have also been suggested as cognitive enhancers in the last decade. In this paper, we reviewed the recent evidence of pharmacological and non-pharmacological interventions aimed at improving or maintaining cognition in the elderly.

Can brain stimulation enhance cognition in clinical populations? A critical review

Many psychiatric and neurological conditions are associated with cognitive impairment for which there are very limited treatment options. Brain stimulation methodologies show promise as novel therapeutics and have cognitive effects. Electroconvulsive therapy (ECT), known more for its related transient adverse cognitive effects, can produce significant cognitive improvement in the weeks following acute treatment. Transcranial magnetic stimulation (TMS) is increasingly used as a treatment for major depression and has acute cognitive effects. Emerging research from controlled studies suggests that repeated TMS treatments may additionally have cognitive benefit. ECT and TMS treatment cause neurotrophic changes, although whether these are associated with cognitive effects remains unclear. Transcranial electrical stimulation methods including transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS) are in development as novel treatments for multiple psychiatric conditions. These treatments may also produce cognitive enhancement particularly when stimulation occurs concurrently with a cognitive task. This review summarizes the current clinical evidence for these brain stimulation treatments as therapeutics for enhancing cognition. Acute, or short-lasting, effects as well as longer-term effects from repeated treatments are reviewed, together with potential putative neural mechanisms. Areas of future research are highlighted to assist with optimization of these approaches for enhancing cognition.

Therapeutic potential of brain stimulation techniques in the treatment of mental, psychiatric, and cognitive disorders

Treatment for brain diseases has been disappointing because available medications have failed to produce clinical response across all the patients. Many patients either do not respond or show partial and inconsistent effect, and even in patients who respond to the medications have high relapse rates. Brain stimulation has been seen as an alternative and effective remedy. As a result, brain stimulation has become one of the most valuable therapeutic tools for combating against brain diseases. In last decade, studies with the application of brain stimulation techniques not only have grown exponentially but also have expanded to wide range of brain disorders. Brain stimulation involves passing electric currents into the cortical and subcortical area brain cells with the use of noninvasive as well as invasive methods to amend brain functions. Over time, technological advancements have evolved into the development of precise devices; however, at present, most used noninvasive techniques are repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS), whereas the most common invasive technique is deep brain stimulation (DBS). In the current review, we will provide an overview of the potential of noninvasive (rTMS and tDCS) and invasive (DBS) brain stimulation techniques focusing on the treatment of mental, psychiatric, and cognitive disorders.

A four-month home-based tDCS study on patients with Alzheimer's disease

In the present open-label study, our first aim was to study the tolerability and feasibility of long-term treatment with transcranial direct current stimulation (tDCS) and the second aim was to measure whether the treatment led to cognitive improvement. Participants with AD used a tDCS home-treatment kit inducing a low current (2 mA) via two scalp electrodes 30 minutes daily for 4 months. A total of 8 participants were recruited. The treatment technique was manageable for the participants and their spouses, and no troublesome side effects were reported. No significant effects of treatment were found after 4 months.

Transcranial Direct Current Stimulation Enhances Cognitive Function in Patients with Mild Cognitive Impairment and Early/Mid Alzheimer’s Disease: A Systematic Review and Meta-Analysis

Transcranial direct current stimulation (tDCS) i a non-invasive brain stimulation which is considered to have the potential to improve cognitive impairment in patients with mild cognitive impairment (MCI) and Alzheimer’s disease (AD). However, previous studies have been controversial on the therapeutic effect of tDCS. This meta-analysis aimed to evaluate the effects of tDCS on cognitive impairment in patients with MCI and mild-to-moderate AD. Five databases, namely PubMed, EMBASE, MEDLINE, Web of Science and The Cochrane Library, were searched with relative terms to extract the cognitive function changes measured by an objective cognitive scale in the included studies. The meta-analysis results showed that, compared with sham tDCS treatment, the overall cognitive function of patients with AD and MCI was significantly improved (weighted mean difference = 0.99; 95% confidence interval, 0.32 to 1.66; p = 0.004) after tDCS treatment, but the behavioral symptoms, recognition memory function, attention and executive function were not significantly improved. The subgroup analysis showed that the treatment would be more efficacious if the temporal-lobe-related brain areas were stimulated, the number of stimulations was greater than or equal to 10 and the current density was 2.5 mA/cm2. Among them, AD patients benefited more than MCI patients. No cognitive improvement was observed in patients with MCI or AD at different follow-up times after treatment. Our meta-analysis provided important evidence for the cognitive enhancement of tDCS in patients with MCI and mild-to-moderate AD and discussed its underlying mechanisms.

A systematic review and meta-analysis of transcranial direct-current stimulation effects on cognitive function in patients with Alzheimer's disease

Transcranial direct-current stimulation (tDCS) appears to enhance cognitive function in Alzheimer's disease (AD). Accordingly, over the last two decades, the number of studies using tDCS for AD has grown. This study aimed to provide a quantitative assessment of the efficacy of tDCS in improving cognitive function in patients with AD. We systematically searched the literature until May 2021 to identify relevant publications for inclusion in our systematic review and meta-analysis. Eligible studies were sham-controlled trials assessing the impacts of anodal or cathodal tDCS on cognitive function in patients with AD. The outcome measure of this study was the effects of tDCS on distinct cognitive domains including memory, attention, and global cognitive function. The initial search yielded a total of 323 records. Five other articles were found using manual search of the databases. Of these, 13 publications (14 different studies) with a total of 211 patients of various degrees of AD severity underwent meta-analysis. Meta-analysis revealed the non-significant effects of tDCS on attention (0.425 SMD, 95% CI, -0.254 to 1.104, p = 0.220), and significant positive impacts on the amelioration of general cognitive measures (1.640 SMD, 95% CI, 0.782 to 2.498, p < 0.000), and memory (1.031 SMD, 95% CI, 0.688 to 1.373, p < 0.000) dysfunction in patients with AD. However, the heterogeneity of the studies were high in all subdomains of cognition (ϰ² = 22.810, T² = 0.55², d.f. = 5, I² = 78.80%, p < 0.000 for attention, ϰ² = 96.29, T² = 1.727, d.f. = 10, I² = 89.61%, p < 0.000 for general cognition, and ϰ² = 7.253, T² = 0.085, d.f. = 5, I² = 31.06%, p = 0.203 for memory). Improved memory and general cognitive function in patients with AD was shown in this meta-analysis. However, due to the small number of studies and the high heterogeneity of the data, more high-quality studies using standardized parameters and measures are needed before tDCS can be considered as a treatment for AD.

Brain stimulation: a therapeutic approach for the treatment of neurological disorders

Brain stimulation has become one of the most acceptable therapeutic approaches in recent years and a powerful tool in the remedy against neurological diseases. Brain stimulation is achieved through the application of electric currents using non-invasive as well as invasive techniques. Recent technological advancements have evolved into the development of precise devices with capacity to produce well-controlled and effective brain stimulation. Currently, most used non-invasive techniques are repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS), whereas the most common invasive technique is deep brain stimulation (DBS). In last decade, application of these brain stimulation techniques has not only exploded but also expanded to wide variety of neurological disorders. Therefore, in the current review, we will provide an overview of the potential of both non-invasive (rTMS and tDCS) and invasive (DBS) brain stimulation techniques in the treatment of such brain diseases.

Exercise priming with transcranial direct current stimulation: a study protocol for a randomized, parallel-design, sham-controlled trial in mild cognitive impairment and Alzheimer's disease

Background

Transcranial direct current stimulation (tDCS) is a non-invasive type of brain stimulation that uses electrical currents to modulate neuronal activity. A small number of studies have investigated the effects of tDCS on cognition in patients with Mild Cognitive Impairment (MCI) and Alzheimer’s disease (AD), and have demonstrated variable effects. Emerging evidence suggests that tDCS is most effective when applied to active brain circuits. Aerobic exercise is known to increase cortical excitability and improve brain network connectivity. Exercise may therefore be an effective, yet previously unexplored primer for tDCS to improve cognition in MCI and mild AD.

Methods

Participants with MCI or AD will be randomized to receive 10 sessions over 2 weeks of either exercise primed tDCS, exercise primed sham tDCS, or tDCS alone in a blinded, parallel-design trial. Those randomized to an exercise intervention will receive individualized 30-min aerobic exercise prescriptions to achieve a moderate-intensity dosage, equivalent to the ventilatory anaerobic threshold determined by cardiopulmonary assessment, to sufficiently increase cortical excitability. The tDCS protocol consists of 20 min sessions at 2 mA, 5 times per week for 2 weeks applied through 35 cm² bitemporal electrodes. Our primary aim is to assess the efficacy of exercise primed tDCS for improving global cognition using the Montreal Cognitive Assessment (MoCA). Our secondary aims are to evaluate the efficacy of exercise primed tDCS for improving specific cognitive domains using various cognitive tests (n-back, Word Recall and Word Recognition Tasks from the Alzheimer’s Disease Assessment Scale-Cognitive subscale) and neuropsychiatric symptoms (Neuropsychiatric Inventory). We will also explore whether exercise primed tDCS is associated with an increase in markers of neurogenesis, oxidative stress and angiogenesis, and if changes in these markers are correlated with cognitive improvement.

Discussion

We describe a novel clinical trial to investigate the effects of exercise priming before tDCS in patients with MCI or mild AD. This proof-of-concept study may identify a previously unexplored, non-invasive, non-pharmacological combination intervention that improves cognitive symptoms in patients. Findings from this study may also identify potential mechanistic actions of tDCS in MCI and mild AD.

Trial registration

Clinicaltrials.gov, NCT03670615. Registered on September 13, 2018.

Efficacy of non-invasive brain stimulation on global cognition and neuropsychiatric symptoms in Alzheimer's disease and mild cognitive impairment: A meta-analysis and systematic review

BACKGROUND

Non-invasive brain stimulation (NIBS) techniques have shown some promise in improving cognitive and neuropsychiatric symptoms (NPS) in people with Alzheimer's disease (AD) and its prodromal stage, mild cognitive impairment (MCI). However, data from clinical trials involving NIBS have shown inconsistent results. This meta-analysis investigated the efficacy of NIBS, specifically repetitive transcranial magnetic stimulation (rTMS), and transcranial direct current stimulation (tDCS) compared to sham stimulation on global cognition and NPS in people with AD and MCI.

METHOD

Multi-session randomized sham-controlled clinical trials were identified through MEDLINE, PsycINFO, and Embase until June 2021. Standardized mean difference (SMD) and 95% confidence interval (CI) between the active and sham treatments were calculated using random-effects meta-analyses. Included studies reported outcome measures for global cognition and/or NPS. Heterogeneity, from different NIBS techniques, disease populations, or tests used to assess global cognition or NPS, was measured using chi-square and I², and investigated using subgroup analyses. Possible effects of covariates were also investigated using meta-regressions.

RESULT

The pooled meta-analyses included 19 studies measuring global cognition (N_active=288, N_sham=264), and 9 studies investigating NPS (N_active=165, N_sham=140). NIBS significantly improved global cognition (SMD=1.14; 95% CI=0.49,1.78; p = 0.001; I² = 90.2%) and NPS (SMD=0.82; 95% CI=0.13, 1.50; p = 0.019; I² = 86.1%) relative to sham stimulation in patients with AD and MCI. Subgroup analyses found these effects were restricted to rTMS but not tDCS, and to patients with AD but not MCI. Meta-regression showed that age was significantly associated with global cognition response (N_studies=16, p = 0.020, I² = 89.51%, R² = 28.96%), with larger effects sizes in younger populations. All significant meta-analyses had large effect sizes (SMD ≥0.8), suggesting clinical utility of NIBS in the short term. There remained substantial heterogeneity across all subgroup analyses and meta-regressions (all I² > 50%). Egger's tests showed no evidence of publication biases.

CONCLUSION

rTMS improved global cognition and NPS in those with AD. Further studies in MCI and using tDCS will help to fully evaluate the specific NIBS techniques and populations most likely to benefit on global cognition and NPS measures. Additional research should investigate the long term clinical utility of NIBS in these populations.

Role of Transcranial Direct Current Stimulation in the Management of Alzheimer's Disease: A Meta-analysis of Effects, Adherence and Adverse Effects

Transcranial direct current stimulation (tDCS) is a form of novel brain stimulating method that has attracted interest owing to its relative inexpensiveness and ease of administration. It has been evaluated in many studies for its effectiveness in improving cognitive symptoms in Alzheimer's disease (AD). However, our understanding regarding its efficacy and the most effective way of administering tDCS (in terms of lead placement to achieve response and prevent harmful consequences) is still evolving. The current meta-analysis was conducted to resolve the above issues. A search using appropriate keywords and medical subject headings was conducted on PubMed, Scopus and DOAJ database. Studies were analysed on pre-defined inclusion and exclusion criteria. Finally 11 studies were included for quantitative analysis from 1,021 obtained from initial search. All the studies included were methodologically of high quality, though an asymmetrical funnel plot raised the possibility of publication bias. tDCS was found to significantly improve the scores on cognition as compared to sham. Anodal tDCS was found to be significantly beneficial in this regards, whereas cathodal and dual stimulation were not. There were no significant difference in the number of drop-outs and adverse reaction in tDCS and sham group. The quality of evidence that we have reviewed in this study is robust. tDCS, particularly anodal tDCS is an effective treatment modality in AD. It is well tolerated in patients with AD. However, further studies are warranted to probe the role of tDCS in other domains of AD.

High-Definition Transcranial Direct Current Stimulation Improves Delayed Memory in Alzheimer's Disease Patients: A Pilot Study Using Computational Modeling to Optimize Electrode Position

BACKGROUND

The optimal stimulation parameters when using transcranial direct current stimulation (tDCS) to improve memory performance in patients with Alzheimer's disease (AD) are lacking. In healthy individuals, inter-individual differences in brain anatomy significantly influence current distribution during tDCS, an effect that might be aggravated by variations in cortical atrophy in AD patients.

OBJECTIVE

To measure the effect of individualized HD-tDCS in AD patients.

METHODS

Nineteen AD patients were randomly assigned to receive active or sham high-definition tDCS (HD-tDCS). Computational modeling of the HD-tDCS-induced electric field in each patient's brain was analyzed based on magnetic resonance imaging (MRI) scans. The chosen montage provided the highest net anodal electric field in the left dorsolateral prefrontal cortex (DLPFC). An accelerated HD-tDCS design was conducted (2 mA for 3×20 min) on two separate days. Pre- and post-intervention cognitive tests and T1 and T2-weighted MRI and diffusion tensor imaging data at baseline were analyzed.

RESULTS

Different montages were optimal for individual patients. The active HD-tDCS group improved significantly in delayed memory and MMSE performance compared to the sham group. Five participants in the active group had higher scores on delayed memory post HD-tDCS, four remained stable and one declined. The active HD-tDCS group had a significant positive correlation between fractional anisotropy in the anterior thalamic radiation and delayed memory score.

CONCLUSION

HD-tDCS significantly improved delayed memory in AD. Our study can be regarded as a proof-of-concept attempt to increase tDCS efficacy. The present findings should be confirmed in larger samples.

Revisiting Apathy in Alzheimer's Disease: From Conceptualization to Therapeutic Approaches

Apathy is a neurobehavioral syndrome characterized by impaired motivation for goal-directed behaviors and cognitive activity, alongside blunted affect. Apathy is a common neuropsychiatric syndrome in Alzheimer's disease (AD), with a 5-year prevalence over 70%. Apathy also serves as a prognostic indicator, correlating with the progression of AD. Despite advances in its conceptualization and understanding of its neural basis, there is very limited empirical evidence to support the available strategies for the treatment of apathy in AD. Given its complex pathophysiology, including distinct substrates for different apathy dimensions (affective, cognitive, and behavioral), it is unlikely that a single pharmacological or nonpharmacological strategy will be effective for all cases of apathy in AD. High-quality evidence research is needed to better understand the role of specific strategies aiming at a personalized approach.

Effects of Noninvasive Brain Stimulation (NIBS) on Cognitive Impairment in Mild Cognitive Impairment and Alzheimer Disease: A Meta-analysis

OBJECTIVE

The purpose of this meta-analysis was to evaluate the beneficial effects and optimal stimulation protocol of noninvasive brain stimulation (NIBS) including repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) on patients with mild cognitive impairment and Alzheimer disease.

MATERIALS AND METHODS

PubMed, Web of Science, Embase, and the Cochrane Library were searched until March 2020. The cognitive outcomes were extracted and the standardized mean difference with 95% confidence interval was calculated.

RESULTS

Twenty-eight studies were included. The result of NIBS showed significant effect on global cognition (P<0.05). Low-frequency rTMS over right dorsolateral prefrontal cortex (DLPFC), high-frequency rTMS (HF-rTMS) over left DLPFC, and the tDCS over left DLPFC and temporal lobe can significantly improve the memory function (P<0.05). HF-rTMS over left, right, or bilateral DLPFC can significantly improve the language function (P<0.05). Both HF-rTMS and tDCS over left DLPFC can obviously improve the executive function (P<0.05). Multiple sessions of rTMS with 80% to 100% intensity and anode tDCS with 2 mA current density are more suitable for all these functions.

CONCLUSIONS

NIBS has a beneficial effect on cognitive performance in both mild cognitive impairment and Alzheimer disease patients. Distinct optimal stimulation parameters were observed for different cognitive functions.

Impact of Transcranial Direct Current Stimulation on Cognitive Function, Brain Functional Segregation, and Integration in Patients with Mild Cognitive Impairment According to Amyloid-Beta Deposition and APOE ε4-Allele: A Pilot Study

Anodal transcranial direct current stimulation (anodal-tDCS) is known to improve cognition and normalize abnormal network configuration during resting-state functional magnetic resonance imaging (fMRI) in patients with mild cognitive impairment (MCI). We aimed to evaluate the impact of sequential anodal-tDCS on cognitive functions, functional segregation, and integration parameters in patients with MCI, according to high-risk factors for Alzheimer’s disease (AD): amyloid-beta (Aβ) deposition and APOE ε4-allele status. In 32 patients with MCI ([¹⁸ F] flutemetamol-: n = 10, [¹⁸ F] flutemetamol+: n = 22; APOE ε4-: n = 13, APOE ε4+: n = 19), we delivered anodal-tDCS (2 mA/day, five times/week, for 2 weeks) over the left dorsolateral prefrontal cortex and assessed the neuropsychological test battery and resting-state fMRI measurements before and after 2 weeks stimulation. We observed a non-significant impact of an anodal-tDCS on changes in neuropsychological battery scores between MCI patients with and without high-risk factors of AD, Aβ retention and APOE ε4-allele. However, there was a significant difference in brain functional segregation and integration parameters between MCI patients with and without AD high-risk factors. We also found a significant effect of tDCS-by-APOE ε4-allele interaction on changes in the functional segregation parameter of the temporal pole. In addition, baseline Aβ deposition significantly associated negatively with change in global functional integrity of hippocampal formation. Anodal-tDCS might help to enhance restorative and compensatory intrinsic functional changes in MCI patients, modulated by the presence of Aβ retention and the APOE ε4-allele.

tDCS-induced modulation of GABA concentration and dopamine release in the human brain: A combination study of magnetic resonance spectroscopy and positron emission tomography

BACKGROUND

Transcranial direct current stimulation (tDCS) to the dorsolateral prefrontal cortex (DLPFC) hypothetically modulates cognitive functions by facilitating or inhibiting neuronal activities chiefly in the cerebral cortex. The effect of tDCS in the deeper brain region, the basal ganglia-cortical circuit, remains unknown.

OBJECTIVE

To investigate the interaction between γ-aminobutyric acid (GABA) concentrations and dopamine release following tDCS.

METHOD

This study used a randomized, placebo-controlled, double-blind, crossover design. Seventeen healthy male subjects underwent active and sham tDCS (13 min twice at an interval of 20 min) with the anode placed at the left DLPFC and the cathode at the right DLPFC, followed by examinations with [¹¹C]-raclopride positron emission topography (PET) and GABA-magnetic resonance spectroscopy (MRS). MRS voxels were set in the left DLPFC and bilateral striata. Paired t-tests and regression analyses were performed for PET and MRS parameters.

RESULTS

MRS data analyses showed elevations in GABA in the left striatum along with moderate reductions in the right striatum and the left DLPFC after active tDCS. PET data analyses showed that reductions in [¹¹C]-raclopride binding potentials (increase in dopamine release) in the right striatum were inversely correlated with those in the left striatum after active tDCS. GABA reductions in the left DLPFC positively correlated with elevations in GABA in the left striatum and with increases in right striatal dopamine release and negatively correlated with increases in left striatal dopamine release.

CONCLUSION

The present results suggest that tDCS to the DLPFC modulates dopamine-GABA functions in the basal ganglia-cortical circuit.

Cognitive Function Improvement in Mouse Model of Alzheimer's Disease Following Transcranial Direct Current Stimulation

Anodal transcranial direct current stimulation (tDCS) is a painless noninvasive method that reportedly improves cognitive function in Alzheimer’s disease (AD) by stimulating the brain. However, its underlying mechanism remains unclear. Thus, the present study investigates the cognitive effects in a 5xFAD AD mouse model using electrophysiological and pathological methods. We used male 5xFAD C57BL/6J and male C57BL/6J wild-type mice; the dementia model was confirmed through DNA sequencing. The verified AD and wild-type mice were randomly assigned into four groups of five mice each: an induced AD group receiving tDCS treatment (Stim-AD), an induced AD group not receiving tDCS (noStim-AD), a non-induction group receiving tDCS (Stim-WT), and a non-induction group not receiving tDCS (noStim-WT). In the Stim group, mice received tDCS in the frontal bregma areas at an intensity of 200 µA for 20 min. After 2 weeks of treatment, we decapitated the mice, removed the hippocampus from the brain, confirmed its neuronal activation through excitatory postsynaptic potential (EPSP) recording, and performed molecular experiments on the remaining tissue using western blots. EPSP significantly increased in the Stim-AD group compared to that in the noStim-AD, which was comparable to that in the non-induced groups, Stim-WT and noStim-WT. There were no significant differences in cyclic amp-response element binding protein (CREB), phosphorylated CREB (pCREB), and Brain-derived neurotrophic factor (BDNF) levels in the Stim-AD group compared to those in the noStim-AD group. This study demonstrated that a tDCS in both frontal lobes of a transgenic 5xFAD mouse model affects long-term potentiation, indicating possible enhancement of cognitive function.

The role of noninvasive brain stimulation for behavioral and psychological symptoms of dementia: a systematic review and meta-analysis

OBJECTIVE

This meta-analysis aimed at evaluating and comparing the efficacy of noninvasive brain stimulation (NIBS) techniques on the behavioral and psychological symptoms of dementia (BPSD).

METHODS

An exhaustive literature retrieval was performed on PubMed, Embase, Cochrane Library, and Web of Science until October 2019. The primary outcome was the relative changes in BPSD severity scores immediately after NIBS and at the last follow-up visit. Subgroup analyses were conducted to compare the efficacy of repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS). Changes in the severity scores after NIBS were also analyzed with restriction to patients with Alzheimer's disease (AD).

RESULTS

Ten studies with 324 patients were included, out of which 7 studies involved patients with AD. The analysis results indicated that NIBS significantly improved the BPSD outcome immediately after stimulation (SMD, 0.31; 95% CI, 0.10-0.52; P = 0.005), but not at the last follow-up visit (0.15; - 0.11-0.41; 0.25). Our subgroup analyses suggested that the favorable effects of rTMS remained significant at the last follow-up visit (0.57; 0.18-0.96; 0.004). This discrepancy maybe caused by the continuously insignificant outcomes of tDCS on the whole data. The results for AD patients immediately after stimulation (0.37; 0.12-0.61; 0.003) and at the last follow-up visit (0.29; - 0.19-0.76; 0.24) were both largely similar to those in the whole patient group with dementia.

CONCLUSIONS

rTMS, rather than tDCS, was capable of persistently improving the BPSD at an early stage after treatment. More trials are warranted to confirm our results before the establishment of final conclusions.

Repetitive transcranial magnetic stimulation for cognitive impairment in Alzheimer's disease: a meta-analysis of randomized controlled trials

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive brain stimulation technique for Alzheimer's disease (AD). rTMS, with high- or low-frequency, is thought to enhance or inhibit the cortical activities, respectively. This meta-analysis of randomized controlled trials (RCTs) was to summarize the efficacy of the rTMS on the cognition of AD patients and to identify its potential influential factors.

METHODS

Literature from the Pubmed, Embase, Cochrane Library and Web of Science were searched and screened to identify eligible studies. Standardized mean difference (SMD) and 95% confidence interval were used to evaluate the therapeutic effects of rTMS. Subgroup analyses were performed to investigate the influential factors.

RESULTS

Ten studies with 15 trials involving 240 patients were included. Compared with sham stimulation, rTMS could significantly improve cognition in AD (SMD, 0.42; 95% CI 0.18-0.67; P = 0.0006). Subgroup analysis suggested significant cognitive enhancement in participants receiving rTMS on multiple sites rather than on single site, and in patients receiving rTMS of more than 10 sessions, but not ≤ 10 sessions. Compared with rTMS as the single therapeutic method, rTMS with concurrent cognitive training seemed to produce greater improvement. Moreover, 20 Hz rTMS, seemed to be more effective than 10 Hz or 1 Hz rTMS. Furthermore, patients with higher education, or with mild-to-moderate AD were more likely to benefit from rTMS than patients with lower education, or with severe dementia, respectively.

CONCLUSIONS

Based on the current evidence, rTMS was an effective therapy for cognitive impairment in AD. Large RCTs are warranted to further validate the results of our subgroup analyses.