Transcranial magnetic stimulation and transcranial direct current stimulation: treatments for cognitive and neuropsychiatric symptoms in the neurodegenerative dementias?

Medial anterior prefrontal cortex stimulation downregulates implicit reactions to threats and prevents the return of fear

Downregulating emotional overreactions toward threats is fundamental for developing treatments for anxiety and post-traumatic disorders. The prefrontal cortex (PFC) is critical for top-down modulatory processes, and despite previous studies adopting repetitive transcranial magnetic stimulation (rTMS) over this region provided encouraging results in enhancing extinction, no studies have hitherto explored the effects of stimulating the medial anterior PFC (aPFC, encompassing the Brodmann area 10) on threat memory and generalization. Here we showed that rTMS over the aPFC applied before threat memory retrieval immediately decreases implicit reactions to learned and novel stimuli in humans. These effects enduringly persisted 1 week later in the absence of rTMS. No effects were detected on explicit recognition. Critically, rTMS over the aPFC resulted in a more pronounced reduction of defensive responses compared to rTMS targeting the dorsolateral PFC. These findings reveal a previously unexplored prefrontal region, the modulation of which can efficiently and durably inhibit implicit reactions to learned threats. This represents a significant advancement toward the long-term deactivation of exaggerated responses to threats.

Cerebello-Parietal Functional Connectivity in Amnestic Mild Cognitive Impairment

The role of the cerebellum in amnestic mild cognitive impairment (aMCI), typically a prodromal stage of Alzheimer's disease, is not fully understood. We studied the lobule-specific cerebello-cerebral connectivity in 15 cognitively normal and 16 aMCI using resting-state functional MRI. Our analysis revealed weaker connectivity between the cognitive cerebellar lobules and parietal lobe in aMCI. However, stronger connectivity was observed in the cognitive cerebellar lobules with certain brain regions, including the precuneus cortex, posterior cingulate gyrus, and caudate nucleus in participants with worse cognition. Leveraging these measurable changes in cerebello-parietal functional networks in aMCI could offer avenues for future therapeutic interventions.

Does Transcranial Direct Current Stimulation Affect Potential P300-Related Events in Vascular Dementia? Considerations from a Pilot Study

Vascular dementia, the second most common type of dementia, currently lacks a definitive cure. In the pursuit of therapies aimed at slowing its progression and alleviating symptoms, transcranial direct current stimulation (tDCS) emerges as a promising approach, characterized by its non-invasive nature and the ability to promote brain plasticity. In this study, the primary objective was to investigate the effects of a two-week cycle of tDCS on the dorsolateral prefrontal cortex (DLPFC) and neurophysiological functioning in thirty patients diagnosed with vascular dementia. Each participant was assigned to one of two groups: the experimental group, which received anodal tDCS to stimulate DPCFL, and the control group, which received sham tDCS. Neurophysiological functions were assessed before and after tDCS using P300 event-related potentials (ERPs), while neuropsychological function was evaluated through a Mini-Mental State Examination (MMSE). The results showed a reduction in P300 latency, indicating a faster cognitive process; an increase in P300 amplitude, suggesting a stronger neural response to cognitive stimuli; and a significant improvement in MMSE scores compared to the control group, indicating an overall enhancement in cognitive functions. These findings suggest that tDCS could represent a promising therapeutic option for improving both neurophysiological and cognitive aspects in patients with vascular dementia.

Depression in Alzheimer's Disease: Epidemiology, Mechanisms, and Treatment

Depression and Alzheimer's disease (AD) are substantial public health concerns. In the past decades, a link between the 2 disease entities has received extensive acknowledgment, yet the complex nature of this relationship demands further clarification. Some evidence indicates that midlife depression may be an AD risk factor, while a chronic course of depression in late life may be a precursor to or symptom of dementia. Recently, multiple pathophysiological mechanisms have been proposed to underlie the bidirectional relationship between depression and AD, including genetic predisposition, immune dysregulation, accumulation of AD-related biomarkers (e.g., amyloid-β and tau), and alterations in brain structure. Accordingly, numerous therapeutic approaches, such as pharmacology treatments, psychotherapy, and lifestyle interventions, have been suggested as potential means of interfering with these pathways. However, the current literature on this topic remains fragmented and lacks a comprehensive review characterizing the association between depression and AD. In this review, we aim to address these gaps by providing an overview of the co-occurrence and temporal relationship between depression and AD, as well as exploring their underlying mechanisms. We also examine the current therapeutic regimens for depression and their implications for AD management and outline key challenges facing the field.

Direct Current Stimulation of Prefrontal Cortex Is Not Effective in Progressive Supranuclear Palsy: A Randomized Trial

BACKGROUND

Progressive supranuclear palsy (PSP) is a rare 4R-tauopathy. Transcranial direct current stimulation (tDCS) may improve specific symptoms.

OBJECTIVES

This randomized, double-blinded, sham-controlled trial aimed at verifying the short-, mid-, and long-term effect of multiple sessions of anodal tDCS over the left dorsolateral prefrontal cortex (DLPFC) cortex in PSP.

METHODS

Twenty-five patients were randomly assigned to active or sham stimulation (2 mA for 20 minute) for 5 days/week for 2 weeks. Participants underwent assessments at baseline, after the 2-week stimulation protocol, then after 45 days and 3 months from baseline. Primary outcomes were verbal and semantic fluency. The efficacy was verified with analysis of covariance.

RESULTS

We failed to detect a significant effect of active stimulation on primary outcomes. Stimulation was associated to worsening of specific behavioral complaints.

CONCLUSIONS

A 2-week protocol of anodal left DLPFC tDCS is not effective in PSP. Specific challenges in running symptomatic clinical trials with classic design are highlighted. © 2024 International Parkinson and Movement Disorder Society.

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.

Transcranial direct current stimulation in semantic variant of primary progressive aphasia: a state-of-the-art review

The semantic variant of primary progressive aphasia (svPPA), known also as "semantic dementia (SD)," is a neurodegenerative disorder that pertains to the frontotemporal lobar degeneration clinical syndromes. There is currently no approved pharmacological therapy for all frontotemporal dementia variants. Transcranial direct current stimulation (tDCS) is a promising non-invasive brain stimulation technique capable of modulating cortical excitability through a sub-threshold shift in neuronal resting potential. This technique has previously been applied as adjunct treatment in Alzheimer's disease, while data for frontotemporal dementia are controversial. In this scoped review, we summarize and critically appraise the currently available evidence regarding the use of tDCS for improving performance in naming and/or matching tasks in patients with svPPA. Clinical trials addressing this topic were identified through MEDLINE (accessed by PubMed) and Web of Science, as of November 2022, week 3. Clinical trials have been unable to show a significant benefit of tDCS in enhancing semantic performance in svPPA patients. The heterogeneity of the studies available in the literature might be a possible explanation. Nevertheless, the results of these studies are promising and may offer valuable insights into methodological differences and overlaps, raising interest among researchers in identifying new non-pharmacological strategies for treating svPPA patients. Further studies are therefore warranted to investigate the potential therapeutic role of tDCS in svPPA.

The neural correlates of apathy in the context of aging and brain disorders: a meta-analysis of neuroimaging studies

Introduction

Apathy is a prevalent mood disturbance that occurs in a wide range of populations, including those with normal cognitive aging, mental disorders, neurodegenerative disorders and traumatic brain injuries. Recently, neuroimaging technologies have been employed to elucidate the neural substrates underlying brain disorders accompanying apathy. However, the consistent neural correlates of apathy across normal aging and brain disorders are still unclear.

Methods

This paper first provides a brief review of the neural mechanism of apathy in healthy elderly individuals, those with mental disorders, neurodegenerative disorders, and traumatic brain injuries. Further, following the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines, the structural and functional neuroimaging meta-analysis using activation likelihood estimation method is performed on the apathy group with brain disorders and the healthy elderly, aiming at exploring the neural correlates of apathy.

Results

The structural neuroimaging meta-analysis showed that gray matter atrophy is associated with apathy in the bilateral precentral gyrus (BA 13/6), bilateral insula (BA 47), bilateral medial frontal gyrus (BA 11), bilateral inferior frontal gyrus, left caudate (putamen) and right anterior cingulate, while the functional neuroimaging meta-analysis suggested that the functional connectivity in putamen and lateral globus pallidus is correlated with apathy.

Discussion

Through the neuroimaging meta-analysis, this study has identified the potential neural locations of apathy in terms of brain structure and function, which may offer valuable pathophysiological insights for developing more effective therapeutic interventions for affected patients.

A blended neurostimulation protocol to delineate cortico-muscular and spino-muscular dynamics following neuroplastic adaptation

In this paper we propose a novel neurostimulation protocol that provides an intervention-based assessment to distinguish the contributions of different motor control networks in the cortico-spinal system. Specifically, we use a combination of non-invasive brain stimulation and neuromuscular stimulation to probe neuromuscular system behavior with targeted impulse-response system identification. In this protocol, we use an in-house developed human-machine interface (HMI) for an isotonic wrist movement task, where the user controls a cursor on-screen. During the task, we generate unique motor evoked potentials based on triggered cortical or spinal level perturbations. Externally applied brain-level perturbations are triggered through TMS to cause wrist flexion/extension during the volitional task. The resultant contraction output and related reflex responses are measured by the HMI. These movements also include neuromodulation in the excitability of the brain-muscle pathway via transcranial direct current stimulation. Colloquially, spinal-level perturbations are triggered through skin-surface neuromuscular stimulation of the wrist muscles. The resultant brain-muscle and spinal-muscle pathways perturbed by the TMS and NMES, respectively, demonstrate temporal and spatial differences as manifested through the human-machine interface. This then provides a template to measure the specific neural outcomes of the movement tasks, and in decoding differences in the contribution of cortical- (long-latency) and spinal-level (short-latency) motor control. This protocol is part of the development of a diagnostic tool that can be used to better understand how interaction between cortical and spinal motor centers changes with learning, or injury such as that experienced following stroke.

Transcranial direct current stimulation for the treatment of post-stroke depression: A systematic review

Background

Post-stroke depression (PSD) is not only a frequent neuropsychiatric manifestation secondary to stroke but is also associated with disability, poor rehabilitation outcomes, sleep disorders, cognitive impairment, and increased mortality. Transcranial direct current stimulation (tDCS), a primary modality of non-invasive brain stimulation (NIBS), has shown promising clinical results in the rehabilitation of patients with PSD recently. The primary aim of this systematic review is to assess the effects of tDCS on PSD.

Methods

PubMed and Cochrane databases were used for paper identification up to May 2022. Only English language studies and published data were taken into consideration. The methodological quality of selected studies was assessed according to the modified Sackett Scale, based on Physiotherapy Evidence Database (PEDro) scores.

Results

Six experimental studies were included for the PSD treatment of tDCS and all of them reported that, following the intervention of tDCS, the experimental group shows a statistically significant decrease in the depression level in accordance with different assessment scales.

Conclusion

This article simply aims at providing a comprehensive overview of the raw data reported in this field to date. Based on the current evidence, tDCS presents promising results for the treatment of PSD. Moreover, tDCS is also effective in PSD patients with aphasia or CPSP. However, an optimal stimulation protocol is needed to formulate. Thus, the development of robustly controlled, randomized, and high-quality clinical trials to further assess the utility of tDCS as a therapeutic tool for the treatment of PSD survivors is encouraged.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42023322076, identifier: CRD42023322076.

Neuroimaging-Guided Transcranial Magnetic and Direct Current Stimulation in MCI: Toward an Individual, Effective and Disease-Modifying Treatment

The therapeutic approaches currently applied in Alzheimer's disease (AD) and similar neurodegenerative diseases are essentially based on pharmacological strategies. However, despite intensive research, the effectiveness of these treatments is limited to transient symptomatic effects, and they are still far from exhibiting a true therapeutic effect capable of altering prognosis. The lack of success of such pharmacotherapy-based protocols may be derived from the cases in the majority of trials being too advanced to benefit significantly in therapeutic terms at the clinical level. For neurodegenerative diseases, mild cognitive impairment (MCI) may be an early stage of the disease continuum, including Alzheimer's. Noninvasive brain stimulation (NIBS) techniques have been developed to modulate plasticity in the human cortex in the last few decades. NIBS techniques have made it possible to obtain unique findings concerning brain functions, and design novel approaches to treat various neurological and psychiatric conditions. In addition, its synaptic and cellular neurobiological effects, NIBS is an attractive treatment option in the early phases of neurodegenerative diseases, such as MCI, with its beneficial modifying effects on cellular neuroplasticity. However, there is still insufficient evidence about the potential positive clinical effects of NIBS on MCI. Furthermore, the huge variability of the clinical effects of NIBS limits its use. In this article, we reviewed the combined approach of NIBS with various neuroimaging and electrophysiological methods. Such methodologies may provide a new horizon to the path for personalized treatment, including a more individualized pathophysiology approach which might even define new specific targets for specific symptoms of neurodegenerations.

Non-invasive brain stimulation and pain neuroscience education in the cognitive-affective treatment of chronic low back pain: Evidence and future directions

Chronic low back pain (CLBP) is among the leading causes of disability worldwide. Beyond the physical and functional limitations, people's beliefs, cognitions, and perceptions of their pain can negatively influence their prognosis. Altered cognitive and affective behaviors, such as pain catastrophizing and kinesiophobia, are correlated with changes in the brain and share a dynamic and bidirectional relationship. Similarly, in the presence of persistent pain, attentional control mechanisms, which serve to organize relevant task information are impaired. These deficits demonstrate that pain may be a predominant focus of attentional resources, leaving limited reserve for other cognitively demanding tasks. Cognitive dysfunction may limit one's capacity to evaluate, interpret, and revise the maladaptive thoughts and behaviors associated with catastrophizing and fear. As such, interventions targeting the brain and resultant behaviors are compelling. Pain neuroscience education (PNE), a cognitive intervention used to reconceptualize a person's pain experiences, has been shown to reduce the effects of pain catastrophizing and kinesiophobia. However, cognitive deficits associated with chronic pain may impact the efficacy of such interventions. Non-invasive brain stimulation (NIBS), such as transcranial direct current stimulation (tDCS) or repetitive transcranial magnetic stimulation (rTMS) has been shown to be effective in the treatment of anxiety, depression, and pain. In addition, as with the treatment of most physical and psychological diagnoses, an active multimodal approach is considered to be optimal. Therefore, combining the neuromodulatory effects of NIBS with a cognitive intervention such as PNE could be promising. This review highlights the cognitive-affective deficits associated with CLBP while focusing on current evidence for cognition-based therapies and NIBS.

Multi-atlas thalamic nuclei segmentation on standard T1-weighed MRI with application to normal aging

Specific thalamic nuclei are implicated in healthy aging and age-related neurodegenerative diseases. However, few methods are available for robust automated segmentation of thalamic nuclei. The threefold aims of this study were to validate the use of a modified thalamic nuclei segmentation method on standard T1 MRI data, to apply this method to quantify age-related volume declines, and to test functional meaningfulness by predicting performance on motor testing. A modified version of THalamus Optimized Multi-Atlas Segmentation (THOMAS) generated 22 unilateral thalamic nuclei. For validation, we compared nuclear volumes obtained from THOMAS parcellation of white-matter-nulled (WMn) MRI data to T1 MRI data in 45 participants. To examine the effects of age/sex on thalamic nuclear volumes, T1 MRI available from a second data set of 121 men and 117 women, ages 20-86 years, were segmented using THOMAS. To test for functional ramifications, composite regions and constituent nuclei were correlated with Grooved Pegboard test scores. THOMAS on standard T1 data showed significant quantitative agreement with THOMAS from WMn data, especially for larger nuclei. Sex differences revealing larger volumes in men than women were accounted for by adjustment with supratentorial intracranial volume (sICV). Significant sICV-adjusted correlations between age and thalamic nuclear volumes were detected in 20 of the 22 unilateral nuclei and whole thalamus. Composite Posterior and Ventral regions and Ventral Anterior/Pulvinar nuclei correlated selectively with higher scores from the eye-hand coordination task. These results support the use of THOMAS for standard T1-weighted data as adequately robust for thalamic nuclear parcellation.

Parietal-hippocampal rTMS improves cognitive function in Alzheimer's disease and increases dynamic functional connectivity of default mode network

Parietal-hippocampal repetitive transcranial magnetic stimulation (rTMS) improves cognitive function in Alzheimer's disease (AD), however, the underlying therapeutic mechanism has not been elucidated. A double-blind, randomized, sham-controlled parietal-hippocampal rTMS trial (five sessions/week for a total of 10 sessions) of mild-to-moderate AD patients was conducted in the study. High-frequency rTMS was applied to a subject-specific left lateral parietal region with the highest functional connectivity with the hippocampus based on resting-state fMRI. A multimodal MRI scan and a complete neuropsychological battery of tests were conducted at baseline, immediately after the intervention and 12-week follow-up after the rTMS treatment. Compared to sham treatment (n = 27), patients undergoing active rTMS treatment (n = 29) showed higher Mini Mental State Examination (MMSE) score and dynamic functional connectivity (dFC) magnitude of the default mode network (DMN) after two weeks of rTMS treatment, but not at 12-week follow-up. A significant positive correlation was observed between changes in MMSE and changes in the dFC magnitude of DMN in patients who underwent active-rTMS treatment, but not in those who received sham-rTMS treatment. The findings of the current study indicate that fMRI-guided rTMS treatment improves cognitive function of AD patients in the short term, and DMN functional connectivity contributes to therapeutic effectiveness of rTMS.

Transcranial Current Stimulation as a Tool of Neuromodulation of Cognitive Functions in Parkinson’s Disease

Decrease in cognitive function is one of the most common causes of poor life quality and early disability in patients with Parkinson’s disease (PD). Existing methods of treatment are aimed at both correction of motor and non-motor symptoms. Methods of adjuvant therapy (or complementary therapy) for maintaining cognitive functions in patients with PD are of interest. A promising subject of research in this regard is the method of transcranial electric current stimulation (tES). Here we reviewed the current understanding of the pathogenesis of cognitive impairment in PD and of the effects of transcranial direct current stimulation and transcranial alternating current stimulation on the cognitive function of patients with PD-MCI (Parkinson’s Disease–Mild Cognitive Impairment).

Transcranial Direct Current Stimulation (tDCS) as a Useful Rehabilitation Strategy to Improve Cognition in Patients With Alzheimer's Disease and Parkinson's Disease: An Updated Systematic Review of Randomized Controlled Trials

Alzheimer's disease (AD) and Parkinson's disease (PD) are neurodegenerative disorders characterized by cognitive impairment and functional decline increasing with disease progression. Within non-pharmacological interventions, transcranial direct current stimulation (tDCS) might represent a cost-effective rehabilitation strategy to implement cognitive abilities with positive implications for functional autonomy and quality-of-life of patients. Our systematic review aimed at evaluating the effects of tDCS upon cognition in people suffering from AD and PD. We searched for randomized controlled trials (RCTs) into PubMed, Web of Science, and Cochrane Library. Three review authors extracted data of interest, with neuropsychological tests or experimental cognitive tasks scores as outcome measures. A total of 17 RCTs (10 trials for AD and 7 trials for PD) were included. Compared with sham stimulation, tDCS may improve global cognition and recognition memory in patients with AD and also some executive functions (i.e., divided attention, verbal fluency, and reduction of sensitivity to interference) in patients with PD. Criticism remains about benefits for the other investigated cognitive domains. Despite preliminary emerging evidences, larger RCTs with common neuropsychological measures and long-term follow-ups establishing longevity of the observed effects are necessary for future research in applied psychology field, alongside improved clinical guidelines on the neurodegenerative disorders pertaining electrodes montage, sessions number, duration and intensity of the stimulation, and cognitive battery to be used.

Quantifying test-retest reliability of repeated objective attentional measures in Lewy body dementia

Objective cognitive impairment is a feature of Lewy body dementia (LBD), and computerised attentional tasks are commonly used as outcome measures in interventional trials. However, the reliability of these measures, in the absence of interventions, are unknown. This study examined the reliability of these attentional measures at short-term and longer-term follow-up stages. LBD patients (n = 36) completed computerised attentional tasks [simple and choice reaction time, and digit vigilance (SRT, CRT, DV)] at short-term (Day 0–Day 5) and longer-term (4 and 12 weeks) follow-up. Intra-class correlations (ICCs) were calculated to assess test–retest reliability. At short-term, the reciprocal SRT, CRT and DV mean reaction time to correct answers, the reciprocal DV coefficient of variation, and reciprocal power of attention (PoA) all showed excellent levels of reliability (all ICCs > 0.90). The reciprocal PoA showed the highest level of reliability (ICC = 0.978). At longer-term follow-up, only the reciprocal PoA had excellent levels of reliability (ICC = 0.927). Reciprocal SRT, CRT and DV reaction time to correct answers, and the CRT coefficient of variation values, showed good levels of test–retest reliability (ICCs ≥ 0.85). Contrary to expectations, most attentional measures demonstrated high levels of test–retest reliability at both short-term and longer-term follow-up time points. The reciprocal PoA composite measure demonstrated excellent levels of test–retest reliability, both in the short-term and long-term. This indicates that objective attentional tasks are suitable outcome measures in LBD studies and that the composite PoA measure may offer the highest levels of reliability.

The Effect of Adding Transcranial Direct Current Stimulation to Hyperbaric Oxygen Therapy in Patients With Delayed Encephalopathy After Carbon Monoxide Poisoning: A Randomised Controlled Trial

Objective: To investigate the effect of transcranial direct current stimulation (tDCS) combined with hyperbaric oxygen therapy (HBOT) in patients with delayed encephalopathy after carbon monoxide poisoning (DEACMP).

Design: A parallel-group, open-label randomised controlled study.

Setting: Hyperbaric Oxygen Therapy Room of the Second Hospital of Hebei Medical University.

Subjects: A total of 40 patients were recruited for the current study. Patients were randomly divided into a treatment group and a control group (20 cases/group).

Interventions: Control group: conventional, individualised rehabilitation therapy. Treatment group: conventional, individualised rehabilitation therapy and tDCS.

Main Measures: cognitive function of patients, the Barthel Index (BI).

Results: After treatment, significantly higher MMSE and BI scores, as well as a greater reduction in P300 latency and an increase in P300 amplitude, were observed in the treatment group compared to the control group (MMSE: 13 ± 7 vs. 9 ± 5; P300 latency: 342 ± 29 vs. 363 ± 17 ms; P300 amplitude: 7.0 ± 3.3 vs. 5.1 ± 2.7 μV; all P < 0.05). In both groups, however, MMSE and BI scores, in addition to P300 amplitude, were significantly improved; in contrast, there was a decrease in P300 latency in both groups after treatment compared to before treatment (all P < 0.05).

Conclusion: Combined with HBOT, tDCS can help improve cognitive function and ADL in patients with DEACMP. This combination therapy might be a helpful method to enhance the recovery of patients with DEACMP.

Modulation of Long-Term Potentiation by Gamma Frequency Transcranial Alternating Current Stimulation in Transgenic Mouse Models of Alzheimer's Disease

Transcranial alternating current stimulation (tACS) is a neuromodulation procedure that is currently studied for the purpose of improving cognitive function in various diseases. A few studies have shown positive effects of tACS in Alzheimer's disease (AD). However, the mechanism underlying tACS has not been established. The purpose of this study was to investigate the mechanism of tACS in five familial AD mutation (5xFAD) mouse models. We prepared twenty 4-month-old mice and divided them into four groups: wild-type mice without stimulation (WT-NT group), wild-type mice with tACS (WT-T group), 5xFAD mice without stimulation (AD-NT group), and 5xFAD mice with tACS (AD-T group). The protocol implemented was as follows: gamma frequency 200 μA over the bilateral frontal lobe for 20 min over 2 weeks. The following tests were conducted: excitatory postsynaptic potential (EPSP) recording, Western blot analysis (cyclic AMP response element-binding (CREB) proteins, phosphorylated CREB proteins, brain-derived neurotrophic factor, and parvalbumin) to examine the synaptic plasticity. The EPSP was remarkably increased in the AD-T group compared with in the AD-NT group. In the Western blot analysis, the differences among the groups were not significant. Hence, tACS can affect the long-lasting enhancement of synaptic transmission in mice models of AD.

New Methods, Old Brains-A Systematic Review on the Effects of tDCS on the Cognition of Elderly People

The world's population is aging. With this comes an increase in the prevalence of age-associated diseases, which amplifies the need for novel treatments to counteract cognitive decline in the elderly. One of the recently discussed non-pharmacological approaches is transcranial direct current stimulation (tDCS). TDCS delivers weak electric currents to the brain, thereby modulating cortical excitability and activity. Recent evidence suggests that tDCS, mainly with anodal currents, can be a powerful means to non-invasively enhance cognitive functions in elderly people with age-related cognitive decline. Here, we screened a recently developed tDCS database (http://tdcsdatabase.com) that is an open access source of published tDCS papers and reviewed 16 studies that applied tDCS to healthy older subjects or patients suffering from Alzheimer's Disease or pre-stages. Evaluating potential changes in cognitive abilities we focus on declarative and working memory. Aiming for more standardized protocols, repeated tDCS applications (2 mA, 30 min) over the left dorso-lateral prefrontal cortex (LDLPFC) of elderly people seem to be one of the most efficient non-invasive brain stimulation (NIBS) approaches to slow progressive cognitive deterioration. However, inter-subject variability and brain state differences in health and disease restrict the possibility to generalize stimulation methodology and increase the necessity of personalized protocol adjustment by means of improved neuroimaging techniques and electrical field modeling.

Analyzing the Effect of Weak External Transcranial Magnetic Stimulation on the Primary Dominant Frequencies of Alzheimer Patients Brain by Using MEG Recordings

Backround and Objectives: Alternative, non-invasive, and non-pharmaceutical options are gaining place in the battle of Alzheimer’s Disease treatment control. Lately, the magnetic stimulation of the brain is the most prevalent technique with encouraging results. The aim of this study is to establish any possible change on the Primary Dominant Frequencies (PDF) (range 2–7 Hz) of the affected brain regions in Alzheimer Disease (AD) patients after applying extremely weak Transcranial Magnetic Stimulation. Materials and Methods: For this purpose, all AD patients were scanned with the use of MagnetoEncephaloGraphy (MEG) recordings through a whole-head 122–channel MEG system. Results: Our results exerted statistically significant PDF changes due to weak TMS accompanied by rabid attenuation of clinical symptoms. Conclusion: Thus, this is the first time that a positive therapeutic effect is being demonstrated even at pico-Tesla range magnetic fields in a small clinical group of studies for AD.

Diagnostic contribution and therapeutic perspectives of transcranial magnetic stimulation in dementia

Transcranial magnetic stimulation (TMS) is a powerful tool to probe in vivo brain circuits, as it allows to assess several cortical properties such asexcitability, plasticity and connectivity in humans. In the last 20 years, TMS has been applied to patients with dementia, enabling the identification of potential markers of thepathophysiology and predictors of cognitive decline; moreover, applied repetitively, TMS holds promise as a potential therapeutic intervention. The objective of this paper is to present a comprehensive review of studies that have employed TMS in dementia and to discuss potential clinical applications, from the diagnosis to the treatment. To provide a technical and theoretical framework, we first present an overview of the basic physiological mechanisms of the application of TMS to assess cortical excitability, excitation and inhibition balance, mechanisms of plasticity and cortico-cortical connectivity in the human brain. We then review the insights gained by TMS techniques into the pathophysiology and predictors of progression and response to treatment in dementias, including Alzheimer's disease (AD)-related dementias and secondary dementias. We show that while a single TMS measure offers low specificity, the use of a panel of measures and/or neurophysiological index can support the clinical diagnosis and predict progression. In the last part of the article, we discuss the therapeutic uses of TMS. So far, only repetitive TMS (rTMS) over the left dorsolateral prefrontal cortex and multisite rTMS associated with cognitive training have been shown to be, respectively, possibly (Level C of evidence) and probably (Level B of evidence) effective to improve cognition, apathy, memory, and language in AD patients, especially at a mild/early stage of the disease. The clinical use of this type of treatment warrants the combination of brain imaging techniques and/or electrophysiological tools to elucidate neurobiological effects of neurostimulation and to optimally tailor rTMS treatment protocols in individual patients or specific patient subgroups with dementia or mild cognitive impairment.

Transcranial Magnetic Stimulation as a Diagnostic and Therapeutic Tool in Various Types of Dementia

Dementia is recognized as a healthcare and social burden and remains challenging in terms of proper diagnosis and treatment. Transcranial magnetic stimulation (TMS) is a diagnostic and therapeutic tool in various neurological diseases that noninvasively investigates cortical excitability and connectivity and can induce brain plasticity. This article reviews findings on TMS in common dementia types as well as therapeutic results. Alzheimer’s disease (AD) is characterized by increased cortical excitability and reduced cortical inhibition, especially as mediated by cholinergic neurons and as documented by impairment of short latency inhibition (SAI). In vascular dementia, excitability is also increased. SAI may have various outcomes, which probably reflects its frequent overlap with AD. Dementia with Lewy bodies (DLB) is associated with SAI decrease. Motor cortical excitability is usually normal, reflecting the lack of corticospinal tract involvement. DLB and other dementia types are also characterized by impairment of short interval intracortical inhibition. In frontotemporal dementia, cortical excitability is increased, but SAI is normal. Repetitive transcranial magnetic stimulation has the potential to improve cognitive function. It has been extensively studied in AD, showing promising results after multisite stimulation. TMS with electroencephalography recording opens new possibilities for improving diagnostic accuracy; however, more studies are needed to support the existing data.

Does participant's age impact on tDCS induced fields? Insights from computational simulations

Objective: Understanding the induced current flow from transcranial direct current stimulation (tDCS) is essential for determining the optimal dose and treatment. Head tissue conductivities play a key role in the resulting electromagnetic fields. However, there exists a complicated relationship between skull conductivity and participant age, that remains unclear. We explored how variations in skull electrical conductivities, particularly as a suggested function of age, affected tDCS induced electric fields.Approach: Simulations were employed to compare tDCS outcomes for different intensities across head atlases of varying age. Three databases were chosen to demonstrate differing variability in skull conductivity with age and how this may affect induced fields. Differences in tDCS electric fields due to proposed age-dependent skull conductivity variation, as well as deviations in grey matter, white matter and scalp, were compared and the most influential tissues determined.Main results: tDCS induced peak electric fields significantly negatively correlated with age, exacerbated by employing proposed age-appropriate skull conductivity (according to all three datasets). Uncertainty in skull conductivity was the most sensitive to changes in peak fields with increasing age. These results were revealed to be directly due to changing skull conductivity, rather than head geometry alone. There was no correlation between tDCS focality and age.Significance: Accurate and individualised head anatomy andin vivoskull conductivity measurements are essential for modelling tDCS induced fields. In particular, age should be taken into account when considering stimulation dose to precisely predict outcomes.

The effect of repetitive transcranial magnetic stimulation on cognitive impairment in Parkinson's disease with dementia: Pilot study

BACKGROUND

The exact mechanism of cognitive impairment in PD is not known. Repetitive transcranial magnetic stimulation (rTMS) has been proposed as a possible treatment for cognitive impairment and to treat the motor symptoms in Parkinson's disease (PD) where its effects seem additive to those of dopaminergic medications.

OBJECTIVE

In this pilot study we investigated whether repeated sessions of rTMS have an effect on measures of cognitive impairment in patients with PD dementia.

METHODS

33 patients with PD dementia were randomly assigned sham or real rTMS (2000 pulses; 20 Hz; 90% RMT; 10 trains of 10 s with 25 s between each train) over the hand area of each motor cortex (5 min between hemispheres) for 10 days (5 days/week) followed by 5 booster sessions every month for 3 months. Assessments included the Unified Parkinson's Disease Rating Scale part III (UPDRS), Montreal Cognitive Assessment (MoCA); Mini Mental State Examination (MMSE), Clinical Dementia Rating Scale (CDR); Memory and Executive Screening (MES) and Instrumental activity of Daily Living (IADL). Event related potentials (P300) and cortical excitability were measured before treatment and after the last session.

RESULTS

There were no significant differences in the effects of rTMS between groups. Although rTMS improved motor function in the active group it had only a minor effect on two of the dementia rating scores (the MMSE and MoCA) but not the others (CDR and MES). There was also a reduction in the latency of the P300 in the active group.

CONCLUSIONS

rTMS over M1 is useful for motor function and may have a small positive effect on cognition. However, better approaches for the latter are necessary, may be require multisite rTMS to target both motor and frontal cortical region.

Left lateral parietal rTMS improves cognition and modulates resting brain connectivity in patients with Alzheimer's disease: Possible role of BDNF and oxidative stress

Repetitive Transcranial Magnetic Stimulation (rTMS) is a non-invasive neuromodulation technique which is increasingly used for cognitive impairment in Alzheimer's Disease (AD). Although rTMS has been shown to modify Brain-Derived Neurotrophic Factor (BDNF) and oxidative stress levels in many neurological and psychiatric diseases, there is still no study evaluating the relationship between memory performance, BDNF, oxidative stress, and resting brain connectivity following rTMS in Alzheimer's patients. Furthermore, there are increasing clinical data showing that the stimulation of strategic brain regions may lead to more robust improvements in memory functions compared to conventional rTMS. In this study, we aimed to evaluate the possible disease-modifying effects of rTMS on the lateral parietal cortex in AD patients who have the highest connectivity with the hippocampus. To fill the mentioned research gaps, we have evaluated the relationships between resting-state Functional Magnetic Resonance Imaging (fMRI), cognitive scores, blood BDNF levels, and total oxidative/antioxidant status to explain the therapeutic and potential disease-modifying effects of rTMS which has been applied at 20 Hz frequencies for two weeks. Our results showed significantly increased visual recognition memory functions and clock drawing test scores which were associated with elevated peripheral BDNF levels, and decreased oxidant status after two weeks of left lateral parietal TMS stimulation. Clinically our findings suggest that the left parietal region targeted rTMS application leads to significant improvement in familiarity-based cognition associated with the network connections between the left parietal region and the hippocampus.

High definition transcranial direct current stimulation (HD-tDCS): A systematic review on the treatment of neuropsychiatric disorders

HD-tDCS (High-definition transcranial direct current stimulation) is a novel non-invasive brain stimulation (NIBS) technique based on the principle that when weak intensity electric currents are targeted on specific areas of the scalp, they cause underlying cortical stimulation. HD-tDCS shares its technical methodology with conventional tDCS (montage comprising of one anode and one cathode) except for a few modifications that are believed to have focal and longer-lasting neuromodulation effects. Although HD-tDCS is a recently available NIBS technique, impactful studies, case reports, and few controlled trials have been conducted in this context, facilitating an understanding of its neurobiological effects and the clinical translation of the same in health care set-up. The current article narratively reviews the mechanism of action of HD-tDCS, and it systematically examines the cognitive, clinical, and neurobiological effects of HD-tDCS in healthy volunteers as well as patients with neuropsychiatric conditions. Thus, this review attempts to explore the role of HD-tDCS in present-day practice and the future in the context of various neurological and psychiatric disorders.

Past, Present, and Future of Non-invasive Brain Stimulation Approaches to Treat Cognitive Impairment in Neurodegenerative Diseases: Time for a Comprehensive Critical Review

Low birth rates and increasing life expectancy experienced by developed societies have placed an unprecedented pressure on governments and the health system to deal effectively with the human, social and financial burden associated to aging-related diseases. At present, ∼24 million people worldwide suffer from cognitive neurodegenerative diseases, a prevalence that doubles every five years. Pharmacological therapies and cognitive training/rehabilitation have generated temporary hope and, occasionally, proof of mild relief. Nonetheless, these approaches are yet to demonstrate a meaningful therapeutic impact and changes in prognosis. We here review evidence gathered for nearly a decade on non-invasive brain stimulation (NIBS), a less known therapeutic strategy aiming to limit cognitive decline associated with neurodegenerative conditions. Transcranial Magnetic Stimulation and Transcranial Direct Current Stimulation, two of the most popular NIBS technologies, use electrical fields generated non-invasively in the brain to long-lastingly enhance the excitability/activity of key brain regions contributing to relevant cognitive processes. The current comprehensive critical review presents proof-of-concept evidence and meaningful cognitive outcomes of NIBS in eight of the most prevalent neurodegenerative pathologies affecting cognition: Alzheimer's Disease, Parkinson's Disease, Dementia with Lewy Bodies, Primary Progressive Aphasias (PPA), behavioral variant of Frontotemporal Dementia, Corticobasal Syndrome, Progressive Supranuclear Palsy, and Posterior Cortical Atrophy. We analyzed a total of 70 internationally published studies: 33 focusing on Alzheimer's disease, 19 on PPA and 18 on the remaining neurodegenerative pathologies. The therapeutic benefit and clinical significance of NIBS remains inconclusive, in particular given the lack of a sufficient number of double-blind placebo-controlled randomized clinical trials using multiday stimulation regimes, the heterogeneity of the protocols, and adequate behavioral and neuroimaging response biomarkers, able to show lasting effects and an impact on prognosis. The field remains promising but, to make further progress, research efforts need to take in account the latest evidence of the anatomical and neurophysiological features underlying cognitive deficits in these patient populations. Moreover, as the development of in vivo biomarkers are ongoing, allowing for an early diagnosis of these neuro-cognitive conditions, one could consider a scenario in which NIBS treatment will be personalized and made part of a cognitive rehabilitation program, or useful as a potential adjunct to drug therapies since the earliest stages of suh diseases. Research should also integrate novel knowledge on the mechanisms and constraints guiding the impact of electrical and magnetic fields on cerebral tissues and brain activity, and incorporate the principles of information-based neurostimulation.

Novel Heat-Mitigating Chip-on-Probe for Brain Stimulation Behavior Experiments

This paper proposes a novel design for a chip-on-probe with the aim of overcoming the heat dissipation effect during brain stimulations using modulated microwave signals. The temperature of the stimulus chip during normal operation is generally 40 °C–60 °C, which is sufficient to cause unintended temperature effects during stimulation. This effect is particularly fatal in brain stimulation applications that require repeated stimulation. This paper proposes, for the first time, a topology that vertically separates the stimulus chip generating the stimulus signal and the probe delivering the signal into the brain to suppress the heat transfer while simultaneously minimizing the radio frequency (RF) transmission loss. As the proposed chip-on-probe should be attached to the head of a small animal, an auxiliary board with a heat sink was carefully designed considering the weight that does not affect the behavior experiment. When the transition structures are properly designed, a heat sink can be mounted to maximize the cooling effect, reducing the temperature by more than 13 °C in a simulation when the heat generated by the chip is transferred to the brain, while the transition from the chip to the probe experiences a loss of 1.2 dB. Finally, the effectiveness of the proposed design is demonstrated by fabricating a chip with the 0.28 μm silicon-on-insulator (SOI) complementary metal–oxide–semiconductor (CMOS) process and a probe with a RT6010 printed-circuit board (PCB), showing a temperature reduction of 49.8 °C with a maximum output power of 11 dBm. In the proposed chip-on-probe device, the temperature formed in the area in contact with the brain is measured at 31.1 °C.

Cerebellar Volume Is Associated with Cognitive Decline in Mild Cognitive Impairment: Results from ADNI

Alzheimer's disease (AD) is a disease with dysfunctional brain network. Previous studies found the cerebellar volume changes over the course of AD disease progression; however, whether cerebellar volume change contributes to the cognitive decline in AD, or its earlier disease stage (i.e., mild cognitive impairment [MCI]) remains unclear. In ADNI, cognitive function was assessed using Alzheimer's Disease Assessment Scale-Cognitive Behavior section (ADAS-Cog). We used linear regression and linear mixed effects models to examine whether cerebellar volume is associated with either baseline cognition or with cognitive changes over time in MCI or in AD. We used logistic regression to assess the relationship between cerebellar volume and disease progression to MCI and AD. We found that cerebellar volume is associated with cognition in patients with MCI, after adjusting for age, gender, education, hippocampal volume, and APOE4 status. Consistently, cerebellar volume is associated with increased odds of the disease stages of MCI and AD when compared to controls. However, cerebellar volume is not associated with cognitive changes over time in either MCI or AD. In summary, cerebellar volume may contribute to cognition level in MCI, but not in AD, indicating that the cerebellar network might modulate the cognitive function in the early stage of the disease. The cerebellum may be a potential target for neuromodulation in treating MCI.

Evaluation and Treatment of Vascular Cognitive Impairment by Transcranial Magnetic Stimulation

The exact relationship between cognitive functioning, cortical excitability, and synaptic plasticity in dementia is not completely understood. Vascular cognitive impairment (VCI) is deemed to be the most common cognitive disorder in the elderly since it encompasses any degree of vascular-based cognitive decline. In different cognitive disorders, including VCI, transcranial magnetic stimulation (TMS) can be exploited as a noninvasive tool able to evaluate in vivo the cortical excitability, the propension to undergo neural plastic phenomena, and the underlying transmission pathways. Overall, TMS in VCI revealed enhanced cortical excitability and synaptic plasticity that seem to correlate with the disease process and progression. In some patients, such plasticity may be considered as an adaptive response to disease progression, thus allowing the preservation of motor programming and execution. Recent findings also point out the possibility to employ TMS to predict cognitive deterioration in the so-called "brains at risk" for dementia, which may be those patients who benefit more of disease-modifying drugs and rehabilitative or neuromodulatory approaches, such as those based on repetitive TMS (rTMS). Finally, TMS can be exploited to select the responders to specific drugs in the attempt to maximize the response and to restore maladaptive plasticity. While no single TMS index owns enough specificity, a panel of TMS-derived measures can support VCI diagnosis and identify early markers of progression into dementia. This work reviews all TMS and rTMS studies on VCI. The aim is to evaluate how cortical excitability, plasticity, and connectivity interact in the pathophysiology of the impairment and to provide a translational perspective towards novel treatments of these patients. Current pitfalls and limitations of both studies and techniques are also discussed, together with possible solutions and future research agenda.

Tau-Mediated Dysregulation of Neuroplasticity and Glial Plasticity

The inability of individual neurons to compensate for aging-related damage leads to a gradual loss of functional plasticity in the brain accompanied by progressive impairment in learning and memory. Whereas this loss in neuroplasticity is gradual during normal aging, in neurodegenerative diseases such as Alzheimer’s disease (AD), this loss is accelerated dramatically, leading to the incapacitation of patients within a decade of onset of cognitive symptoms. The mechanisms that underlie this accelerated loss of neuroplasticity in AD are still not completely understood. While the progressively increasing proteinopathy burden, such as amyloid β (Aβ) plaques and tau tangles, definitely contribute directly to a neuron’s functional demise, the role of non-neuronal cells in controlling neuroplasticity is slowly being recognized as another major factor. These non-neuronal cells include astrocytes, microglia, and oligodendrocytes, which through regulating brain homeostasis, structural stability, and trophic support, play a key role in maintaining normal functioning and resilience of the neuronal network. It is believed that chronic signaling from these cells affects the homeostatic network of neuronal and non-neuronal cells to an extent to destabilize this harmonious milieu in neurodegenerative diseases like AD. Here, we will examine the experimental evidence regarding the direct and indirect pathways through which astrocytes and microglia can alter brain plasticity in AD, specifically as they relate to the development and progression of tauopathy. In this review article, we describe the concepts of neuroplasticity and glial plasticity in healthy aging, delineate possible mechanisms underlying tau-induced plasticity dysfunction, and discuss current clinical trials as well as future disease-modifying approaches.

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

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

Occupational Neuroplasticity in the Human Brain: A Critical Review and Meta-Analysis of Neuroimaging Studies

Many studies have revealed the structural or functional brain changes induced by occupational factors. However, it remains largely unknown how occupation-related connectivity shapes the brain. In this paper, we denote occupational neuroplasticity as the neuroplasticity that takes place to satisfy the occupational requirements by extensively professional training and to accommodate the long-term, professional work of daily life, and a critical review of occupational neuroplasticity related to the changes in brain structure and functional networks has been primarily presented. Furthermore, meta-analysis revealed a neurophysiological mechanism of occupational neuroplasticity caused by professional experience. This meta-analysis of functional neuroimaging studies showed that experts displayed stronger activation in the left precentral gyrus [Brodmann area (BA)6], left middle frontal gyrus (BA6), and right inferior frontal gyrus (BA9) than novices, while meta-analysis of structural studies suggested that experts had a greater gray matter volume in the bilateral superior temporal gyrus (BA22) and right putamen than novices. Together, these findings not only expand the current understanding of the common neurophysiological basis of occupational neuroplasticity across different occupations and highlight some possible targets for neural modulation of occupational neuroplasticity but also provide a new perspective for occupational science research.

Guidelines for TMS/tES clinical services and research through the COVID-19 pandemic

BACKGROUND

The COVID-19 pandemic has broadly disrupted biomedical treatment and research including non-invasive brain stimulation (NIBS). Moreover, the rapid onset of societal disruption and evolving regulatory restrictions may not have allowed for systematic planning of how clinical and research work may continue throughout the pandemic or be restarted as restrictions are abated. The urgency to provide and develop NIBS as an intervention for diverse neurological and mental health indications, and as a catalyst of fundamental brain research, is not dampened by the parallel efforts to address the most life-threatening aspects of COVID-19; rather in many cases the need for NIBS is heightened including the potential to mitigate mental health consequences related to COVID-19.

OBJECTIVE

To facilitate the re-establishment of access to NIBS clinical services and research operations during the current COVID-19 pandemic and possible future outbreaks, we develop and discuss a framework for balancing the importance of NIBS operations with safety considerations, while addressing the needs of all stakeholders. We focus on Transcranial Magnetic Stimulation (TMS) and low intensity transcranial Electrical Stimulation (tES) - including transcranial Direct Current Stimulation (tDCS) and transcranial Alternating Current Stimulation (tACS).

METHODS

The present consensus paper provides guidelines and good practices for managing and reopening NIBS clinics and laboratories through the immediate and ongoing stages of COVID-19. The document reflects the analysis of experts with domain-relevant expertise spanning NIBS technology, clinical services, and basic and clinical research - with an international perspective. We outline regulatory aspects, human resources, NIBS optimization, as well as accommodations for specific demographics.

RESULTS

A model based on three phases (early COVID-19 impact, current practices, and future preparation) with an 11-step checklist (spanning removing or streamlining in-person protocols, incorporating telemedicine, and addressing COVID-19-associated adverse events) is proposed. Recommendations on implementing social distancing and sterilization of NIBS related equipment, specific considerations of COVID-19 positive populations including mental health comorbidities, as well as considerations regarding regulatory and human resource in the era of COVID-19 are outlined. We discuss COVID-19 considerations specifically for clinical (sub-)populations including pediatric, stroke, addiction, and the elderly. Numerous case-examples across the world are described.

CONCLUSION

There is an evident, and in cases urgent, need to maintain NIBS operations through the COVID-19 pandemic, including anticipating future pandemic waves and addressing effects of COVID-19 on brain and mind. The proposed robust and structured strategy aims to address the current and anticipated future challenges while maintaining scientific rigor and managing risk.

Transcranial Direct Current Stimulation to Optimise Participation in Stroke Rehabilitation - A Sham-Controlled Cross-Over Feasibility Study

Background

Fatigue and attentional decline limit the duration of many therapy sessions in older adults poststroke. Transcranial direct current stimulation (tDCS) may facilitate participation in rehabilitation, potentially via reduced fatigue and improved sustained attention poststroke.

Objective

To evaluate whether tDCS results in an increase in the number of completed rehabilitation therapy sessions in stroke survivors.

Methods

Nineteen participants were randomly allocated to receive 10 sessions of 2-mA anodal (excitatory) tDCS, or sham tDCS, applied to the left dorsolateral prefrontal cortex (DLPFC) for 20 minutes within 1 hour prior to the first rehabilitation therapy session of the day. After a 2-day washout period, participants then crossed-over. Researchers applying the tDCS, and those recording measures were blinded to group allocation. The number of first rehabilitation therapy sessions completed as planned, as well as the total duration of rehabilitation therapy, were used to determine the influence of tDCS on participation in stroke rehabilitation.

Results

The total number of first therapy sessions completed as planned did not vary according to group allocation (111 of 139 sessions for tDCS, 110 of 147 sessions for sham treatment; chi-square 1.0; P = .31).

Conclusions

Our results suggest that, while tDCS to the DLPFC was well tolerated, it did not significantly influence the number of completed rehabilitation therapy sessions in stroke survivors.

Non-invasive Brain Stimulation in Alzheimer's Disease and Mild Cognitive Impairment-A State-of-the-Art Review on Methodological Characteristics and Stimulation Parameters

Background: Transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) have been proposed as a new therapeutic way to enhance the cognition of patients with dementia. However, serious methodological limitations appear to affect the estimates of their efficacy. We reviewed the stimulation parameters and methods of studies that used TMS or tDCS to alleviate the cognitive symptoms of patients with Alzheimer's disease (AD) and mild cognitive impairment (MCI). Moreover, we evaluated the risk of bias in these studies. Our aim was to highlight the current vulnerabilities of the field and to formulate recommendations on how to manage these issues when designing studies.

Methods: Electronic databases and citation searching were used to identify studies administering TMS or tDCS on patients with AD or MCI to enhance cognitive function. Data were extracted by one review author into summary tables with the supervision of the authors. The risk of bias analysis of randomized-controlled trials was conducted by two independent assessors with version 2 of the Cochrane risk-of-bias tool for randomized trials.

Results: Overall, 36 trials were identified of which 23 randomized-controlled trials underwent a risk of bias assessment. More than 75% of randomized-controlled trials involved some levels of bias in at least one domain. Stimulation parameters were highly variable with some ranges of effectiveness emerging. Studies with low risk of bias indicated TMS to be potentially effective for patients with AD or MCI while questioned the efficacy of tDCS.

Conclusions: The presence and extent of methodical issues affecting TMS and tDCS research involving patients with AD and MCI were examined for the first time. The risk of bias frequently affected the domains of the randomization process and selection of the reported data while missing outcome was rare. Unclear reporting was present involving randomization, allocation concealment, and blinding. Methodological awareness can potentially reduce the high variability of the estimates regarding the effectiveness of TMS and tDCS. Studies with low risk of bias delineate a range within TMS parameters seem to be effective but question the efficacy of tDCS.

Early-stage dysfunction of hippocampal theta and gamma oscillations and its modulation of neural network in a transgenic 5xFAD mouse model

Alzheimer's disease (AD) is pathologically characterized by amyloid-β (Aβ) accumulation, which induces Aβ-dependent neuronal dysfunctions. We focused on the early-stage disease progression and examined the neuronal network functioning in the 5xFAD mice. The simultaneous intracranial recordings were obtained from the hippocampal perforant path (PP) and the dentate gyrus (DG). Concomitant to Aβ accumulation, theta power was strongly attenuated in the PP and DG regions of 5xFAD mice compared to those in nontransgenic littermates. For either theta rhythm or gamma oscillation, the phase synchronization on the PP-DG pathway was impaired, evidenced by decreased phase locking value and diminished coherency index. To alleviate the neural oscillatory deficits in early-stage AD, a neural modulation approach (rTMS) was used to activate gamma oscillations and strengthen the synchronicity of neuronal activity on the PP-DG pathway. In brief, there was a significant neuronal network dysfunction at an early-stage AD-like pathology, which preceded the onset of cognitive deficits and was likely driven by Aβ accumulation, suggesting that the neural oscillation analysis played an important role in early AD diagnosis.

Transcranial Direct Current Stimulation Ameliorates Cognitive Impairment via Modulating Oxidative Stress, Inflammation, and Autophagy in a Rat Model of Vascular Dementia

To investigate the potential applications and the molecular mechanisms of transcranial direct current stimulation (tDCS) on cognitive impairment in a vascular dementia (VD) animal model. Sprague-Dawley rats were used in this study. VD rat model was induced by modified permanent bilateral common carotid artery occlusion (2-VO) approach. Anodal tDCS was applied to the animals. Morris water maze was used to analyze spatial memory and navigation ability. The pathological changes in the hippocampal CA1 region and cerebral cortex were examined via Hematoxylin-Eosin staining. The rats were sacrificed for the measurement of the level of superoxide (SOD), glutathione (GSH), reactive oxidative species (ROS), malondialdehyd (MDA), Interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α level in the hippocampus. Western blot was carried out to measure the hippocampal expression of microtubule-associated protein 1 light chain 3 (LC-3) and p62. Rats with VD have decreased number of neurons in the hippocampus and cerebral cortex, as well as worse cognitive impairment. The proliferation of activated microglia and astroglia, accompanied with attenuation of myelination were observed in the white matter about 1 month after 2-VO operation. These abnormalities were significantly ameliorated by tDCS treatment. Further study revealed that anodal tDCS could suppress the MDA and ROS level, while enhance the SOD and GSH level to reduce the oxidative stress. Anodal tDCS could inhibit hypoperfusion-induced IL-1β, IL-6, and TNF-α expression to attenuate inflammatory response in hippocampus. Moreover, anodal tDCS treatment could alleviate autophagy level. The study has demonstrated a possible therapeutic role of tDCS in the treatment of cognitive impairment in VD.

Evaluation and Treatment of Vascular Cognitive Impairment by Transcranial Magnetic Stimulation

The exact relationship between cognitive functioning, cortical excitability, and synaptic plasticity in dementia is not completely understood. Vascular cognitive impairment (VCI) is deemed to be the most common cognitive disorder in the elderly since it encompasses any degree of vascular-based cognitive decline. In different cognitive disorders, including VCI, transcranial magnetic stimulation (TMS) can be exploited as a noninvasive tool able to evaluate in vivo the cortical excitability, the propension to undergo neural plastic phenomena, and the underlying transmission pathways. Overall, TMS in VCI revealed enhanced cortical excitability and synaptic plasticity that seem to correlate with the disease process and progression. In some patients, such plasticity may be considered as an adaptive response to disease progression, thus allowing the preservation of motor programming and execution. Recent findings also point out the possibility to employ TMS to predict cognitive deterioration in the so-called "brains at risk" for dementia, which may be those patients who benefit more of disease-modifying drugs and rehabilitative or neuromodulatory approaches, such as those based on repetitive TMS (rTMS). Finally, TMS can be exploited to select the responders to specific drugs in the attempt to maximize the response and to restore maladaptive plasticity. While no single TMS index owns enough specificity, a panel of TMS-derived measures can support VCI diagnosis and identify early markers of progression into dementia. This work reviews all TMS and rTMS studies on VCI. The aim is to evaluate how cortical excitability, plasticity, and connectivity interact in the pathophysiology of the impairment and to provide a translational perspective towards novel treatments of these patients. Current pitfalls and limitations of both studies and techniques are also discussed, together with possible solutions and future research agenda.

Testing the therapeutic effects of transcranial direct current stimulation (tDCS) in semantic dementia: a double blind, sham controlled, randomized clinical trial

BACKGROUND

Semantic dementia is a neurodegenerative disease that primarily affects the left anterior temporal lobe, resulting in a gradual loss of conceptual knowledge. There is currently no validated treatment. Transcranial stimulation has provided evidence for long-lasting language effects presumably linked to stimulation-induced neuroplasticity in post-stroke aphasia. However, studies evaluating its effects in neurodegenerative diseases such as semantic dementia are still rare and evidence from double-blind, prospective, therapeutic trials is required.

OBJECTIVE

The primary objective of the present clinical trial (STIM-SD) is to evaluate the therapeutic efficacy of a multiday transcranial direct current stimulation (tDCS) regime on language impairment in patients with semantic dementia. The study also explores the time course of potential tDCS-driven improvements and uses imaging biomarkers that could reflect stimulation-induced neuroplasticity.

METHODS

This is a double-blind, sham-controlled, randomized study using transcranial Direct Current Stimulation (tDCS) applied daily for 10 days, and language/semantic and imaging assessments at four time points: baseline, 3 days, 2 weeks and 4 months after 10 stimulation sessions. Language/semantic assessments will be carried out at these same 4 time points. Fluorodeoxyglucose positron emission tomography (FDG-PET), resting-state functional magnetic resonance imaging (rs-fMRI), T1-weighted images and white matter diffusion tensor imaging (DTI) will be applied at baseline and at the 2-week time point. According to the principle of inter-hemispheric inhibition between left (language-related) and right homotopic regions we will use two stimulation modalities - left-anodal and right-cathodal tDCS over the anterior temporal lobes. Accordingly, the patient population (n = 60) will be subdivided into three subgroups: left-anodal tDCS (n = 20), right-cathodal tDCS (n = 20) and sham tDCS (n = 20). The stimulation will be sustained for 20 min at an intensity of 1.59 mA. It will be delivered through 25cm²-round stimulation electrodes (current density of 0.06 mA/cm²) placed over the left and right anterior temporal lobes for anodal and cathodal stimulation, respectively. A group of healthy participants (n = 20) matched by age, gender and education will also be recruited and tested to provide normative values for the language/semantic tasks and imaging measures.

DISCUSSION

The aim of this study is to assess the efficacy of tDCS for language/semantic disorders in semantic dementia. A potential treatment would be easily applicable, inexpensive, and renewable when therapeutic effects disappear due to disease progression.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03481933. Registered on March 2018.

Improved Target Specificity of Transcranial Focused Ultrasound Stimulation (TFUS) using Double-Crossed Ultrasound Transducers

Ultrasound neuromodulation is a promising stimulation modality because of its non-invasiveness, focusing and steering capability, and relatively high spatial resolution compared to the other stimulation modalities. However, despite the high lateral resolution, the ultrasound beam in the axial direction is relatively long, especially when compared to the small size of the mouse brain. Here, we report a new ultrasound focusing technique for small animal in vivo experiments where a high spatial resolution in both lateral and axial directions is achieved by crossing two ultrasound beams. The focal volume of a full width half maximum (FWHM) of our proposed system is only 0.161 mm3 and the focal diameter in the axial direction is about 1 mm, which is ten times smaller than the previously reported ultrasound neuromodulation system. Thus, the proposed system enables targeting a sub-region of a mouse brain using ultrasound for the first time. We also demonstrate successful stimulation of the motor cortex through in vivo mice experiments where the movement of forepaw of the mouse was observed using the double-crossed ultrasound transducers. Moreover, by sweeping the focal point in the z-axis and measuring the success rate of stimulated movements, we show that our double-transducer system targeted a region with 2 mmresolution in the dorsal-ventral (DV) coordinates. The success rate of the double-crossed ultrasound stimulation was quantified by recording the electromyography (EMG) signals during the stimulation. Our results show that the double-crossed ultrasound transducer system with a ten times higher spatial resolution enables highly specific and noninvasive stimulation of small animals and thus enables versatile in vivo experiments to study functional connectivities of brain circuits.

New Perspective for Non-invasive Brain Stimulation Site Selection in Mild Cognitive Impairment: Based on Meta- and Functional Connectivity Analyses

Background

Non-invasive brain stimulation (NIBS) has been widely used to treat mild cognitive impairment (MCI). However, there exists no consensus on the best stimulation sites.

Objective

To explore potential stimulation locations for NIBS treatment in patients with MCI, combining meta- and resting state functional connectivity (rsFC) analyses.

Methods

The meta-analysis was conducted to identify brain regions associated with MCI. Regions of interest (ROIs) were extracted based on this meta-analysis. The rsFC analysis was applied to 45 MCI patients to determine brain surface regions that are functionally connected with the above ROIs.

Results

We found that the dorsolateral prefrontal cortex (DLPFC) and inferior frontal gyrus (IFG) were the overlapping brain regions between our results and those of previous studies. In addition, we recommend that the temporoparietal junction (including the angular gyrus), which was found in both the meta- and rsFC analysis, should be considered in NIBS treatment of MCI. Furthermore, the bilateral orbital prefrontal gyrus, inferior temporal gyrus, medial superior frontal gyrus, and right inferior occipital gyrus may be potential brain stimulation sites for NIBS treatment of MCI.

Conclusion

Our results provide several potential sites for NIBS, such as the DLFPC and IFG, and may shed light on the locations of NIBS sites in the treatment of patients with MCI.

Optogenetics in Brain Research: From a Strategy to Investigate Physiological Function to a Therapeutic Tool

Dissecting the functional roles of neuronal circuits and their interaction is a crucial step in basic neuroscience and in all the biomedical field. Optogenetics is well-suited to this purpose since it allows us to study the functionality of neuronal networks on multiple scales in living organisms. This tool was recently used in a plethora of studies to investigate physiological neuronal circuit function in addition to dysfunctional or pathological conditions. Moreover, optogenetics is emerging as a crucial technique to develop new rehabilitative and therapeutic strategies for many neurodegenerative diseases in pre-clinical models. In this review, we discuss recent applications of optogenetics, starting from fundamental research to pre-clinical applications. Firstly, we described the fundamental components of optogenetics, from light-activated proteins to light delivery systems. Secondly, we showed its applications to study neuronal circuits in physiological or pathological conditions at the cortical and subcortical level, in vivo. Furthermore, the interesting findings achieved using optogenetics as a therapeutic and rehabilitative tool highlighted the potential of this technique for understanding and treating neurological diseases in pre-clinical models. Finally, we showed encouraging results recently obtained by applying optogenetics in human neuronal cells in-vitro.

Development of wirelessly-powered, extracranial brain activator (ECBA) in a large animal model for the future non-invasive human neuromodulation

As transcranial electrical stimulation (tES) is an emerging and promising technique for neuromodulation, we developed a novel device; wirelessly-powered, extracranial brain activator (ECBA), which is mounted subcutaneously, and its neuromodulation effect was investigated. The oscillatory changes in electrocorticography (EcoG) were analyzed from two types of stimulation. Two weeks prior to the recording experiment, we underwent surgery for implantation of subdural strips and ECBA module over centroparietal regions of anesthetized beagles. Low-frequency stimulation (LFS) and subsequent high-frequency stimulation (HFS) protocols (600 pulses respectively) were applied. Then, the power changes before and after each stimulation in five different bands were compared. A significantly larger voltage difference with subcutaneous than transcutaneous stimulation measured at EcoG channels indicated a substantial current attenuation between the skin and skull. Compared with the baseline, all subjects showed consistently decreased delta power and increased gamma power after HFS. LFS also induced a similar, but opposite, pattern of power change in four beagles. The results from this study indicate that LFS and HFS with our novel ECBA can consistently and effectively modulate neural activity of the cortex, inducing neural inhibition and facilitation functions, respectively. Future studies are necessary to further ensuring a consistent efficacy and long-term safety.

Cognitive Training and Transcranial Direct Current Stimulation in Mild Cognitive Impairment: A Randomized Pilot Trial

Background

Transcranial direct current stimulation (tDCS), a non-invasive stimulation, represents a potential intervention to enhance cognition across clinical populations including Alzheimer’s disease and mild cognitive impairment (MCI). This randomized clinical trial in MCI investigated the effects of anodal tDCS (a-tDCS) delivered to left inferior frontal gyrus (IFG) combined with gist-reasoning training (SMART) versus sham tDCS (s-tDCS) plus SMART on measures of cognitive and neural changes in resting cerebral blood flow (rCBF). We were also interested in SMART effects on cognitive performance regardless of the tDCS group.

Methods

Twenty-two MCI participants, who completed the baseline cognitive assessment (T1), were randomized into one of two groups: a-tDCS + SMART and s-tDCS + SMART. Of which, 20 participants completed resting pCASL MRI scan to measure rCBF. Eight SMART sessions were administered over 4 weeks with a-tDCS or s-tDCS stimulation for 20 min before each session. Participants were assessed immediately (T2) and 3-months after training (T3).

Results

Significant group × time interactions showed cognitive gains at T2 in executive function (EF) measure of inhibition [DKEFS- Color word (p = 0.047)], innovation [TOSL (p = 0.01)] and on episodic memory [TOSL (p = 0.048)] in s-tDCS + SMART but not in a-tDCS + SMART group. Nonetheless, the gains did not persist for 3 months (T3) after the training. A voxel-based analysis showed significant increase in regional rCBF in the right middle frontal cortex (MFC) (cluster-wise p = 0.05, k = 1,168 mm³) in a-tDCS + SMART compared to s-tDCS + SMART. No significant relationship was observed between the increased CBF with cognition. Irrespective of group, the combined MCI showed gains at T2 in EF of conceptual reasoning [DKEFS card sort (p = 0.033)] and category fluency [COWAT (p = 0.055)], along with gains at T3 in EF of verbal fluency [COWAT (p = 0.009)].

Conclusion

One intriguing finding is a-tDCS to left IFG plus SMART increased blood flow to right MFC, however, the stimulation seemingly blocked cognitive benefits of SMART on EF (inhibition and innovation) and episodic memory compared to s-tDCS + SMART group. Although the sample size is small, this paper contributes to growing evidence that cognitive training provides a way to significantly enhance cognitive performance in adults showing memory loss, where the role of a-tDCS in augmenting these effects need further study.

Neurophysiological markers of network dysfunction in neurodegenerative diseases

There is strong clinical, imaging and pathological evidence that neurodegeneration is associated with altered brain connectivity. While functional imaging (fMRI) can detect resting and activated states of metabolic activity, its use is limited by poor temporal resolution, cost and confounding vascular parameters. By contrast, electrophysiological (e.g. EEG/MEG) recordings provide direct measures of neural activity with excellent temporal resolution, and source localization methodologies can address problems of spatial resolution, permitting measurement of functional activity of brain networks with a spatial resolution similar to that of fMRI. This opens an exciting therapeutic approach focussed on pharmacological and physiological modulation of brain network activity. This review describes current neurophysiological approaches towards evaluating cortical network dysfunction in common neurodegenerative disorders. It explores how modern neurophysiologic tools can provide markers for diagnosis, prognosis, subcategorization and clinical trial outcome measures, and how modulation of brain networks can contribute to new therapeutic approaches.