neuronavigated-focalized-transcranial-direct-current-stimulation

Neuronavigated Focalized Transcranial Direct Current Stimulation Administered During Functional Magnetic Resonance Imaging

Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation technique that allows the modulation of the excitability and plasticity ...

University Medicine Greifswald

Subjective cognitive decline (SCD) is considered a risk factor for Alzheimer's disease (AD), highlighting the need for identifying and ranking effective interventions. This was addressed in a systematic review and network meta-analysis (NMA) of pharmacological and non-pharmacological interventions for SCD.

A systematic review and network meta-analysis of interventions for subjective cognitive decline.

Trajectories of decline across different socio-cognitive domains in healthy older adults and in pathological aging conditions have not been investigated. This was addressed in the present systematic review and meta-analysis.

Progression of socio-cognitive impairment from healthy aging to Alzheimer's dementia: A systematic review and meta-analysis.

The ventromedial prefrontal cortex (vmPFC) mediates the inhibition of defensive responses upon encounters of cues, that had lost their attribute as a threat signal via previous extinction learning. Here, we investigated whether such fear extinction recall can be facilitated by anodal transcranial direct current stimulation (tDCS). Extinction recall was tested twenty-four hours after previously acquired fear was extinguished. Either anodal tDCS or sham stimulation targeting the vmPFC was applied during this test. After stimulation ceased, we examined return of fear after subjects had been re-exposed to aversive events. Fear was assessed by reports of threat expectancy and modulations of autonomic (skin conductance, heart rate) and protective reflex (startle potentiation) measures, the latter of which are mediated by subcortical defense circuits. While tDCS did not affect initial extinction recall, it abolished the return of startle potentiation and autonomic components of the fear response. Results suggest hierarchical multi-level vmPFC functions in human fear inhibition and indicate, that its stimulation might immunize against relapses into pathological subcortically mediated defensive activation.

Stimulation of the ventromedial prefrontal cortex blocks the return of subcortically mediated fear responses.

Electrode positioning errors contribute to variability of transcranial direct current stimulation (tDCS) effects. We investigated the impact of electrode positioning errors on current flow for tDCS set-ups with different focality.

Electrode positioning errors reduce current dose for focal tDCS set-ups: Evidence from individualized electric field mapping.

Primary progressive aphasia (PPA) accounts for approximately 43% of frontotemporal dementias and is mainly characterised by a progressive impairment of speech and communication abilities. Three clinical variants have been identified: (a) non-fluent/agrammatic, (b) semantic, and (c) logopenic/phonological PPA variants. There is currently no curative treatment for PPA, and the disease progresses inexorably over time, with devastating effects on speech and communication ability, functional status, and quality of life. Several non-pharmacological interventions that may improve symptoms (e.g. different forms of language training and non-invasive brain stimulation) have been investigated in people with PPA.

Non-pharmacological interventions for improving language and communication in people with primary progressive aphasia.

Previous studies have demonstrated that conventional transcranial direct current stimulation (tDCS) can enhance novel-word learning. However, because of the widespread current that is induced by these setups and lack of appropriate control conditions, little is known about the underlying neural mechanisms. In the present double-blinded and sham-tDCS controlled study, we investigated for the first time if regionally precise focal tDCS targeting two key nodes of the novel-word learning network at different time points would result in regionally and temporally distinct effects. 156 participants completed a contextual novel-word-learning paradigm and learning success was probed immediately after the acquisition period and 30-min later. Participants were randomly assigned to six stimulation conditions: Active tDCS (1.5 mA) was administered to left inferior frontal (IFG) or middle temporal gyrus (MTG), either during acquisition or delayed recall. Control groups received sham-tDCS either during acquisition or delayed recall (50% IFG/MTG). Data were analyzed with a generalized linear mixed model with a binomial link function in a Bayesian framework. Our results showed that frontal tDCS selectively increased accuracy gains from immediate to delayed recall, irrespective of timing of the stimulation. There was no evidence for beneficial effects of middle temporal gyrus tDCS. Our findings confirm that IFG tDCS can enhance novel-word learning in a regionally, but not timing specific way. Tentatively, this may be explained by enhancement of semantic selection processes resulting in more effective consolidation and/or retrieval. Future studies using longer time intervals between assessments are required to clarify the potential contribution of neurophysiological after-effects of IFG tDCS administered during acquisition to enhanced consolidation.

The role of frontal cortex in novel-word learning and consolidation: Evidence from focal transcranial direct current stimulation.

Transcranial direct current stimulation (tDCS) has been studied extensively for its potential to enhance human cognitive functions in healthy individuals and to treat cognitive impairment in various clinical populations. However, little is known about how tDCS modulates the neural networks supporting cognition and the complex interplay with mediating factors that may explain the frequently observed variability of stimulation effects within and between studies. Moreover, research in this field has been characterized by substantial methodological variability, frequent lack of rigorous experimental control and small sample sizes, thereby limiting the generalizability of findings and translational potential of tDCS. The present manuscript aims to delineate how these important issues can be addressed within a neuroimaging context, to reveal the neural underpinnings, predictors and mediators of tDCS-induced behavioral modulation. We will focus on functional magnetic resonance imaging (fMRI), because it allows the investigation of tDCS effects with excellent spatial precision and sufficient temporal resolution across the entire brain. Moreover, high resolution structural imaging data can be acquired for precise localization of stimulation effects, verification of electrode positions on the scalp and realistic current modeling based on individual head and brain anatomy. However, the general principles outlined in this review will also be applicable to other imaging modalities. Following an introduction to the overall state-of-the-art in this field, we will discuss in more detail the underlying causes of variability in previous tDCS studies. Moreover, we will elaborate on design considerations for tDCS-fMRI studies, optimization of tDCS and imaging protocols and how to assure high-level experimental control. Two additional sections address the pressing need for more systematic investigation of tDCS effects across the healthy human lifespan and implications for tDCS studies in age-associated disease, and potential benefits of establishing large-scale, multidisciplinary consortia for more coordinated tDCS research in the future. We hope that this review will contribute to more coordinated, methodologically sound, transparent and reproducible research in this field. Ultimately, our aim is to facilitate a better understanding of the underlying mechanisms by which tDCS modulates human cognitive functions and more effective and individually tailored translational and clinical applications of this technique in the future.

Article	Year
A systematic review and network meta-analysis of interventions for subjective cognitive decline. Alzheimer's & dementia (New York, N. Y.)\| PubMed ID: 34268448	2021
Progression of socio-cognitive impairment from healthy aging to Alzheimer's dementia: A systematic review and meta-analysis. Neuroscience and biobehavioral reviews\| PubMed ID: 35905800	2022
Stimulation of the ventromedial prefrontal cortex blocks the return of subcortically mediated fear responses. Translational psychiatry\| PubMed ID: 36127327	2022
Electrode positioning errors reduce current dose for focal tDCS set-ups: Evidence from individualized electric field mapping. Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology\| PubMed ID: 38643613	2024
Non-pharmacological interventions for improving language and communication in people with primary progressive aphasia. The Cochrane database of systematic reviews\| PubMed ID: 38808659	2024
The role of frontal cortex in novel-word learning and consolidation: Evidence from focal transcranial direct current stimulation. Cortex; a journal devoted to the study of the nervous system and behavior\| PubMed ID: 38824804	2024
Investigating the neural mechanisms of transcranial direct current stimulation effects on human cognition: current issues and potential solutions. Frontiers in neuroscience\| PubMed ID: 38957187	2024

Steffen Riemann

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