Impact of 3-Day Combined Anodal Transcranial Direct Current Stimulation-Visuospatial Training on Object-Location Memory in Healthy Older Adults and Patients with Mild Cognitive Impairment

The impact of transcranial direct current stimulation combined with interim testing on spatial route learning in patients with schizophrenia

BACKGROUND

Cognitive deficits in patients with schizophrenia have drawn widespread attention. Transcranial direct current stimulation (tDCS) can modulate cognitive processes by altering neuronal excitability. Previous studies have found that interim testing can enhance spatial route learning and memory in patients with schizophrenia. However, there has been limited research on the combined effects of these two methods on spatial route learning in these patients.

OBJECTIVE

To investigate whether the combination of tDCS and interim testing can effectively contribute to the maintenance of spatial route memory in patients with schizophrenia. The study involved conducting route learning using interim testing after anodal tDCS treatment on the left dorsolateral prefrontal cortex (L-DLPFC).

METHODS

Ninety-two patients with schizophrenia were recruited and divided into groups receiving anodal, sham, or no stimulation. The anodal group received L-DLPFC tDCS treatment 10 times over 5 days (twice daily for 20 min). After treatment, spatial route learning was assessed in interim testing. Correct recall rates of landmark positions and proactive interference from prior learning were compared among the groups.

RESULTS

Regardless of stimulation type, the interim testing group outperformed the relearning group. Additionally, recall scores were higher following anodal stimulation, indicating the efficacy of tDCS.

CONCLUSIONS

Both tDCS and interim testing independently enhance the ability to learn new information in spatial route learning for patients with schizophrenia, indicating that tDCS of the left DLPFC significantly improves memory in these patients.

The cognitive effect of non-invasive brain stimulation combined with cognitive training in Alzheimer's disease and mild cognitive impairment: a systematic review and meta-analysis

BACKGROUND

Non-invasive brain stimulation (NIBS) combined with cognitive training (CT) may have shown some prospects on improving cognitive function in patients with Alzheimer's disease (AD) and mild cognitive impairment (MCI). However, data from clinical trials or meta-analysis involving NIBS combined with CT have shown controversial results. The aim of this systematic review and meta-analysis was to evaluate short-term and long-term effects of NIBS combined with CT on improving global cognition and other specific cognitive domains in patients with AD and MCI.

METHODS

This systematic review and meta-analysis was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Five electronic databases including PubMed, Web of Science, EBSCO, Cochrane Library and Embase were searched up from inception to 20 November 2023. The PEDro scale and the Cochrane's risk of bias assessment were used to evaluate risk of bias and methodological quality of included studies. All statistical analyses were conducted with Review Manager 5.3.

RESULTS

We included 15 studies with 685 patients. The PEDro scale was used to assess methodological quality with a mean score of 7.9. The results of meta-analysis showed that NIBS combined with CT was effective on improving global cognition in AD and MCI (SMD = 0.52, 95% CI (0.18, 0.87), p = 0.003), especially for patients accepting repetitive transcranial magnetic stimulation (rTMS) combined with CT (SMD = 0.46, 95% CI (0.14, 0.78), p = 0.005). AD could achieve global cognition improvement from NIBS combined with CT group (SMD = 0.77, 95% CI (0.19, 1.35), p = 0.01). Transcranial direct current stimulation (tDCS) combined with CT could improve language function in AD and MCI (SMD = 0.29, 95% CI (0.03, 0.55), p = 0.03). At evaluation follow-up, rTMS combined with CT exhibited larger therapeutic responses to AD and MCI in global cognition (SMD = 0.55, 95% CI (0.09, 1.02), p = 0.02). AD could achieve global cognition (SMD = 0.40, 95% CI (0.03, 0.77), p = 0.03) and attention/working memory (SMD = 0.72, 95% CI (0.23, 1.20), p = 0.004) improvement after evaluation follow-up from NIBS combined with CT group.

CONCLUSIONS

Overall, NIBS combined with CT, particularly rTMS combined with CT, has both short-term and follow-up effects on improving global cognition, mainly in patients with AD. tDCS combined with CT has advantages on improving language function in AD and MCI. Future more studies need evaluate cognitive effects of NIBS combined with CT on other specific cognitive domain in patients with cognitive deterioration.

No Object-Location Memory Improvement through Focal Transcranial Direct Current Stimulation over the Right Temporoparietal Cortex

Remembering objects and their associated location (object-location memory; OLM), is a fundamental cognitive function, mediated by cortical and subcortical brain regions. Previously, the combination of OLM training and transcranial direct current stimulation (tDCS) suggested beneficial effects, but the evidence remains heterogeneous. Here, we applied focal tDCS over the right temporoparietal cortex in 52 participants during a two-day OLM training, with anodal tDCS (2 mA, 20 min) or sham (40 s) on the first day. The focal stimulation did not enhance OLM performance on either training day (stimulation effect: -0.09, 95%CI: [-0.19; 0.02], p = 0.08). Higher electric field magnitudes in the target region were not associated with individual performance benefits. Participants with content-related learning strategies showed slightly superior performance compared to participants with position-related strategies. Additionally, training gains were associated with individual verbal learning skills. Consequently, the lack of behavioral benefits through focal tDCS might be due to the involvement of different cognitive processes and brain regions, reflected by participant's learning strategies. Future studies should evaluate whether other brain regions or memory-relevant networks may be involved in the modulation of object-location associations, investigating other target regions, and further exploring individualized stimulation parameters.

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.

Prefrontal theta-gamma transcranial alternating current stimulation improves non-declarative visuomotor learning in older adults

The rise in the global population of older adults underscores the significance to investigate age-related cognitive disorders and develop early treatment modalities. Previous research suggests that non-invasive transcranial Alternating Current Stimulation (tACS) can moderately improve cognitive decline in older adults. However, non-declarative cognition has received relatively less attention. This study investigates whether repeated (16-day) bilateral theta-gamma cross-frequency tACS targeting the Dorsolateral Prefrontal Cortex (DLPFC) enhances non-declarative memory. Computerized cognitive training was applied alongside stimulation to control for the state-of-the-brain. The Alternating Serial Reaction Time (ASRT) task was employed to assess non-declarative functions such as visuomotor skill and probabilistic sequence learning. Results from 35 participants aged 55-82 indicated that active tACS led to more substantial improvements in visuomotor skills immediately after treatment, which persisted 3 months later, compared to sham tACS. Treatment benefit was more pronounced in older adults of younger age and those with pre-existing cognitive decline. However, neither intervention group exhibited modulation of probabilistic sequence learning. These results suggest that repeated theta-gamma tACS can selectively improve distinct non-declarative cognitive aspects when targeting the DLPFC. Our findings highlight the therapeutic potential of tACS in addressing deficits in learning and retaining general skills, which could have a positive impact on the quality of life for cognitively impaired older individuals by preserving independence in daily activities.

Transcranial Direct Current Stimulation in neurogenetic syndromes: new treatment perspectives for Down syndrome?

This perspective review aims to explore the potential neurobiological mechanisms involved in the application of transcranial Direct Current Stimulation (tDCS) for Down syndrome (DS), the leading cause of genetically-based intellectual disability. The neural mechanisms underlying tDCS interventions in genetic disorders, typically characterized by cognitive deficits, are grounded in the concept of brain plasticity. We initially present the neurobiological and functional effects elicited by tDCS applications in enhancing neuroplasticity and in regulating the excitatory/inhibitory balance, both associated with cognitive improvement in the general population. The review begins with evidence on tDCS applications in five neurogenetic disorders, including Rett, Prader-Willi, Phelan-McDermid, and Neurofibromatosis 1 syndromes, as well as DS. Available evidence supports tDCS as a potential intervention tool and underscores the importance of advancing neurobiological research into the mechanisms of tDCS action in these conditions. We then discuss the potential of tDCS as a promising non-invasive strategy to mitigate deficits in plasticity and promote fine-tuning of the excitatory/inhibitory balance in DS, exploring implications for cognitive treatment perspectives in this population.

Efficacy analysis of three brain stimulation techniques for Alzheimer's disease: a meta-analysis of repeated transcranial magnetic stimulation, transcranial direct current stimulation, and deep brain stimulation

INTRODUCTION

This systematic review and meta-analysis study investigates the efficacy of repeated transcranial magnetic stimulation (rTMS), transcranial direct current stimulation (tDCS), and deep brain stimulation (DBS) using neuropsychological assessments as a potential treatment option for Alzheimer's disease (AD).

METHODS

PubMed, Embase, and the Cochrane Library were searched for studies on rTMS, tDCS, and DBS for the treatment of patients with AD between April 1970 and October 2022. The mini-Mental State Examination (MMSE) and AD Assessment Scale - Cognitive Subscale (ADAS-Cog) were adopted as the efficacy index.

RESULTS

The analysis yielded 17 eligible studies. rTMS greatly improved the cognition of patients with AD (immediate post-treatment WMD of MMSE score: 2.06, p < 0.00001; short-term follow-up WMD of MMSE score: 2.12, p = 0.006; WMD of ADAS-Cog score in single-arm studies: -4.97, p = 0.001). DBS did not reverse the progression of cognitive decline (WMD of ADAS-Cog score in single-arm studies: 7.40, p < 0.00001). Furthermore, tDCS demonstrated no significant efficacy in improving cognition in random clinical trials or single-arm studies.

CONCLUSION

rTMS is a promising non-medicinal alternative for cognitive improvement inpatients with AD.

The Effects of Transcranial Direct Current Stimulation in Patients with Mild Cognitive Impairment

Transcranial direct current stimulation (tDCS) came into consideration in recent years as a promising, non-invasive form of neuromodulation for individuals suffering from mild cognitive impairment (MCI). MCI represents a transitional stage between normal cognitive aging and more severe cognitive decline, which appears in neurodegenerative diseases, such as Alzheimer's disease. Numerous studies have shown that tDCS can have several useful effects in patients with MCI. It is believed to enhance cognitive functions, including memory and attention, potentially slowing down the progression of neurodegeneration and cognitive decline. tDCS is believed to work by modulating neuronal activity and promoting synaptic plasticity in the brain regions associated with cognition. Moreover, tDCS is generally considered safe and well-tolerated, making it an attractive option for long-term therapeutic use in MCI. However, further research is needed to determine the optimal stimulation parameters and long-term effects of tDCS in this population, as well as its potential to serve as a complementary therapy alongside other interventions for MCI. In this review, we included 16 randomized clinical trials containing patients with MCI who were treated with tDCS. We aim to provide important evidence for the cognitive enhancement using tDCS in patients with MCI, summarizing the effects and conclusions found in several clinical trials, and discuss its main mechanisms.

The effects of transcranial direct current stimulation on cognitive function for mild cognitive impairment: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Transcranial direct current stimulation (tDCS) emerged as a potential modality for enhancing cognitive functions in patients with cognitive decline, including mild cognitive impairment (MCI). Our systematic review and meta-analysis aim to synthesize the available randomized controlled trials (RCTs) on the effects of tDCS on cognitive functions in patients with MCI.

METHODS

Our review protocol was registered on PROSPERO with ID: CRD42022360587. We conducted a systematic database search until September 2022. Standardized mean difference (SMD) and pooled effect size (ES) for robust variance estimation (RVE) method were used as effect estimates for our meta-analysis.

RESULTS

We included 11 RCTs with a total of 429 participants. The meta-analysis showed that, compared to sham groups, tDCS did not improve global functioning (measured by MOCA) (SMD = 0.02, CI =  - 0.30 to 0.35; p = 0.88), memory domain (ES = 0.681, CI =  - 2.15 to 3.51, p = 0.576), sustained attention (measured by TMT-A) (SMD =  - 0.21, CI =  - 0.52 to 0.10, p = 0.19), and executive function (measured by TMT-B) (SMD =  - 0.53, CI =  - 1.56 to 0.50, p = 0.20).

CONCLUSION

Our meta-analysis found no significant effect of tDCS on cognitive functions in MCI patients, including effects on global functioning, memory, sustained attention, and executive function. Therefore, an important change to be tested in future studies is to look for a better combination with tDCS for patients with MCI.

Tolerability and blinding of high-definition transcranial direct current stimulation among older adults at intensities of up to 4 mA per electrode

BACKGROUND

Few studies have investigated tolerability, blinding, and double-blinding of High-Definition transcranial Direct Current Stimulation (HD-tDCS) at amplitudes above 2 milliamps (mA).

OBJECTIVE

We examined a) tolerability of HD-tDCS during stimulation sessions and b) blinding and double blinding of participants and study team members.

METHODS

Data from a mixed neurologic sample of 292 older adults were pooled from 3046 HD-tDCS sessions (2329 active; 717 sham). Per electrode amplitudes ranged from 1 mA to 4 mA with total currents up to 10 mA. Participants completed a standardized sensation (tolerability) questionnaire after each session. Participants and study team members stated whether the participant received active or sham stimulation at the end of various sessions. Data were collapsed into the presence/absence of a symptom due to low rates of positive responding and were analyzed for both differences and bioequivalency.

RESULTS

There were no safety-related adverse events. HD-tDCS was well tolerated with mostly no ("none") or "mild" sensations reported across sessions, regardless of active or sham condition and in both stimulation naïve and experienced participants. There were no significant differences in side effects between active and sham, with some achieving bioequivalence. Tingling and itching were significantly more common after lower (<2 mA) than higher (≥3 mA) amplitude active sessions, while skin redness was significantly more common after higher amplitudes. Blinding was effective at the participant and study team levels.

CONCLUSIONS

HD-tDCS was well tolerated with center electrode amplitudes up to 4 mA. The bimodal ramp-up/down format of the sham was effective for blinding. These results support higher scalp-based amplitudes that enable greater brain-based current intensities in older adults.

Transcranial Electrical Stimulation for Associative Memory Enhancement: State-of-the-Art from Basic to Clinical Research

Associative memory (AM) is the ability to bind new information into complex memory representations. Noninvasive brain stimulation (NIBS), especially transcranial electric stimulation (tES), has gained increased interest in research of associative memory (AM) and its impairments. To provide an overview of the current state of knowledge, we conducted a systematic review following PRISMA guidelines covering basic and clinical research. Out of 374 identified records, 41 studies were analyzed-twenty-nine in healthy young adults, six in the aging population, three comparing older and younger adults, as well as two studies on people with MCI, and one in people with Alzheimer's dementia. Studies using transcranial direct current stimulation (tDCS), transcranial alternating current stimulation (tACS) as well as oscillatory (otDCS) and high-definition protocols (HD-tDCS, HD-tACS) have been included. The results showed methodological heterogeneity in terms of study design, stimulation type, and parameters, as well as outcome measures. Overall, the results show that tES is a promising method for AM enhancement, especially if the stimulation is applied over the parietal cortex and the effects are assessed in cued recall paradigms.

Identifying factors influencing cognitive outcomes after anodal transcranial direct current stimulation in older adults with and without cognitive impairment: A systematic review

Anodal transcranial direct current stimulation (tDCS) can improve cognition in healthy older adults, those with Alzheimer's disease (AD) and mild cognitive impairment (MCI), albeit with considerable variability in response. This systematic review identifies interindividual factors that may influence tDCS outcomes in older individuals with or without cognitive impairment. Peer-reviewed articles were included if they assessed whether cognitive outcomes (memory or global cognition) after tDCS were associated with pre-intervention factors in healthy older adults or individuals with AD/MCI. We identified eight factors that may affect cognitive outcomes after tDCS. Improved tDCS outcomes were predicted by lower baseline cognitive function when tDCS was combined with a co-intervention (but not when used alone). Preserved brain structure and better baseline functional connectivity, genetic polymorphisms, and the use of concomitant medications may predict better tDCS outcomes, but further research is warranted. tDCS outcomes were not consistently associated with age, cognitive reserve, sex, and AD risk factors. Accounting for individual differences in baseline cognition, particularly for combined interventions, may thus maximize the therapeutic potential of tDCS.

Combined Cognitive Training and Transcranial Direct Current Stimulation in Neuropsychiatric Disorders: A Systematic Review and Meta-analysis

BACKGROUND

Treatments for cognitive dysfunction in neuropsychiatric conditions are urgently needed. Cognitive training and transcranial direct current stimulation (tDCS) hold promise, and there is growing interest in combined or multimodal treatments, though studies to date have had small samples and inconsistent results.

METHODS

A systematic review and meta-analysis was completed. Retained studies included cognitive training combined with active or sham tDCS in a neuropsychiatric population and reported a posttreatment cognitive outcome. Meta-analyses included effect sizes comparing cognitive training plus active tDCS and cognitive training plus sham tDCS in 5 cognitive domains. Risk of bias in included studies and across studies was explored.

RESULTS

Fifteen studies were included: 10 in neurodegenerative disorders and 5 in psychiatric disorders (n = 629). There were several tDCS montages, though two-thirds of studies placed the anode over the left dorsolateral prefrontal cortex. A wide variety of cognitive training types and outcome measures were reported. There was a small, statistically significant effect of combined treatment on measures of attention/working memory, as well as small and non-statistically significant effects favoring combined treatment on global cognition and language. There was no evidence of bias in individual studies but some evidence of nonreporting or small-study bias across studies.

CONCLUSIONS

These results may provide preliminary support for the efficacy of combined cognitive training and tDCS on measures of attention/working memory. More data are needed, particularly via studies that explicitly align the cognitive ability of interest, stimulation target, training type, and outcome measures.

Is non-invasive brain stimulation effective for cognitive enhancement in Alzheimer's disease? An updated meta-analysis

OBJECTIVE

Alzheimer's disease dementia (AD) and its preclinical stage, mild cognitive impairment (MCI), are critical issues confronting the aging society. Non-invasive brain stimulation (NIBS) techniques have the potential to be effective tools for enhancing cognitive functioning. The main objective of our meta-analysis was to quantify and update the status of the efficacy of repetitive Transcranial Magnetic Stimulation (rTMS) and Transcranial Direct Current Stimulation (tDCS) when applied in AD and MCI.

METHODS

The systematic literature search was conducted in PubMed and Web of Science according to PRISMA statement.

RESULTS

Pooled effect sizes (Hedges' g) from 32 studies were analyzed using random effect models. We found both, rTMS and tDCS to have significant immediate cognition-enhancing effect in AD with rTMS inducing also beneficial long-term effects. We found no evidence for synergistic effect of cognitive training with NIBS.

CONCLUSIONS

In AD a clinical recommendation can be made for NEURO-AD^TM system and for high-frequency rTMS over the left dorsolateral prefrontal cortex (DLPFC) as probably effective protocols (B-level of evidence) and for anodal tDCS over the left DLPFC as a possibly effective.

SIGNIFICANCE

According to scientific literature, NIBS may be an effective method for improving cognition in AD and possibly in MCI.

Modulation of network centrality and gray matter microstructure using multi-session brain stimulation and memory training

Neural mechanisms of behavioral improvement induced by repeated transcranial direct current stimulation (tDCS) combined with cognitive training are yet unclear. Previously, we reported behavioral effects of a 3-day visuospatial memory training with concurrent anodal tDCS over the right temporoparietal cortex in older adults. To investigate intervention-induced neural alterations we here used functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) datasets available from 35 participants of this previous study, acquired before and after the intervention. To delineate changes in whole-brain functional network architecture, we employed eigenvector centrality mapping. Gray matter alterations were analyzed using DTI-derived mean diffusivity (MD). Network centrality in the bilateral posterior temporooccipital cortex was reduced after anodal compared to sham stimulation. This focal effect is indicative of decreased functional connectivity of the brain region underneath the anodal electrode and its left-hemispheric homolog with other "relevant" (i.e., highly connected) brain regions, thereby providing evidence for reorganizational processes within the brain's network architecture. Examining local MD changes in these clusters, an interaction between stimulation condition and training success indicated a decrease of MD in the right (stimulated) temporooccipital cluster in individuals who showed superior behavioral training benefits. Using a data-driven whole-brain network approach, we provide evidence for targeted neuromodulatory effects of a combined tDCS-and-training intervention. We show for the first time that gray matter alterations of microstructure (assessed by DTI-derived MD) may be involved in tDCS-enhanced cognitive training. Increased knowledge on how combined interventions modulate neural networks in older adults, will help the development of specific therapeutic interventions against age-associated cognitive decline.

Non-invasive brain stimulation and neuroenhancement

Attempts to enhance human memory and learning ability have a long tradition in science. This topic has recently gained substantial attention because of the increasing percentage of older individuals worldwide and the predicted rise of age-associated cognitive decline in brain functions. Transcranial brain stimulation methods, such as transcranial magnetic (TMS) and transcranial electric (tES) stimulation, have been extensively used in an effort to improve cognitive functions in humans. Here we summarize the available data on low-intensity tES for this purpose, in comparison to repetitive TMS and some pharmacological agents, such as caffeine and nicotine. There is no single area in the brain stimulation field in which only positive outcomes have been reported. For self-directed tES devices, how to restrict variability with regard to efficacy is an essential aspect of device design and function. As with any technique, reproducible outcomes depend on the equipment and how well this is matched to the experience and skill of the operator. For self-administered non-invasive brain stimulation, this requires device designs that rigorously incorporate human operator factors. The wide parameter space of non-invasive brain stimulation, including dose (e.g., duration, intensity (current density), number of repetitions), inclusion/exclusion (e.g., subject's age), and homeostatic effects, administration of tasks before and during stimulation, and, most importantly, placebo or nocebo effects, have to be taken into account. The outcomes of stimulation are expected to depend on these parameters and should be strictly controlled. The consensus among experts is that low-intensity tES is safe as long as tested and accepted protocols (including, for example, dose, inclusion/exclusion) are followed and devices are used which follow established engineering risk-management procedures. Devices and protocols that allow stimulation outside these parameters cannot claim to be "safe" where they are applying stimulation beyond that examined in published studies that also investigated potential side effects. Brain stimulation devices marketed for consumer use are distinct from medical devices because they do not make medical claims and are therefore not necessarily subject to the same level of regulation as medical devices (i.e., by government agencies tasked with regulating medical devices). Manufacturers must follow ethical and best practices in marketing tES stimulators, including not misleading users by referencing effects from human trials using devices and protocols not similar to theirs.

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.

Protocols for cognitive enhancement. A user manual for Brain Health Services-part 5 of 6

Cognitive complaints in the absence of objective cognitive impairment, observed in patients with subjective cognitive decline (SCD), are common in old age. The first step to postpone cognitive decline is to use techniques known to improve cognition, i.e., cognitive enhancement techniques.We aimed to provide clinical recommendations to improve cognitive performance in cognitively unimpaired individuals, by using cognitive, mental, or physical training (CMPT), non-invasive brain stimulations (NIBS), drugs, or nutrients. We made a systematic review of CMPT studies based on the GRADE method rating the strength of evidence.CMPT have clinically relevant effects on cognitive and non-cognitive outcomes. The quality of evidence supporting the improvement of outcomes following a CMPT was high for metamemory; moderate for executive functions, attention, global cognition, and generalization in daily life; and low for objective memory, subjective memory, motivation, mood, and quality of life, as well as a transfer to other cognitive functions. Regarding specific interventions, CMPT based on repeated practice (e.g., video games or mindfulness, but not physical training) improved attention and executive functions significantly, while CMPT based on strategic learning significantly improved objective memory.We found encouraging evidence supporting the potential effect of NIBS in improving memory performance, and reducing the perception of self-perceived memory decline in SCD. Yet, the high heterogeneity of stimulation protocols in the different studies prevent the issuing of clear-cut recommendations for implementation in a clinical setting. No conclusive argument was found to recommend any of the main pharmacological cognitive enhancement drugs ("smart drugs", acetylcholinesterase inhibitors, memantine, antidepressant) or herbal extracts (Panax ginseng, Gingko biloba, and Bacopa monnieri) in people without cognitive impairment.Altogether, this systematic review provides evidence for CMPT to improve cognition, encouraging results for NIBS although more studies are needed, while it does not support the use of drugs or nutrients.

Noninvasive brain stimulation for the treatment of neurocognitive disorders: right for prime time?

PURPOSE OF REVIEW

Neurocognitive disorders are associated with tremendous burden at the level of the individual, the care giver, and society at large. No effective treatments have been discovered to date.

RECENT FINDINGS

Noninvasive brain stimulation (NIBS) comprises several promising interventions that have been studied in Alzheimer's disease and related dementias. Most recent studies have tested transcranial direct current stimulation or repetitive transcranial magnetic stimulation on their own or in combination with other interventions, particularly cognitive training. While most studies were proof-of-principle studies with small sample sizes, combination and long-duration protocols seem to be promising approaches to pursue. Some studies also investigated novel neurophysiological markers as predictors of response to NIBS.

SUMMARY

NIBS presents several interventional options that are ready to be evaluated using well powered, long-duration trials. These future studies should build on the promising leads from the current literature, including the potential advantage of combining NIBS with other interventions; the delivery of interventions for long durations to assess long-term impact; and the use of neurophysiological markers that could optimize the personalization and efficacy of NIBS.

Transcranial Direct Current Stimulation Enhances Episodic Memory in Healthy Older Adults by Modulating Retrieval-Specific Activation

Memory decline has become an issue of major importance in the aging society. Anodal transcranial direct current stimulation (atDCS) is a viable tool to counteract age-associated episodic memory deterioration. However, the underlying neural mechanisms are unclear. In this single-blind, sham-controlled study, we combined atDCS and functional magnetic resonance imaging to assess the behavioral and neural consequences of multiple-session atDCS in older adults. Forty-nine healthy older adults received either 10 sessions of anodal or sham stimulation over the left dorsolateral prefrontal cortex. Before and after stimulation, participants performed a source memory task in the MRI scanner. Compared to sham stimulation, atDCS significantly improved item memory performance. Additionally, atDCS significantly increased regional brain activity around the stimulation area in the prefrontal cortex and extended to the bilateral anterior cingulate cortex. Neural changes in the prefrontal cortex correlated with memory gains. Our findings therefore indicate that multiple-session offline atDCS may improve memory in older adults by inducing neural alterations.