Interaction of BDNF and COMT polymorphisms on paired-associative stimulation-induced cortical plasticity

Contribution of Glutamatergic and GABAergic Mechanisms to the Plasticity-Modulating Effects of Dopamine in the Human Motor Cortex

Dopamine, a key neuromodulator in the central nervous system, regulates cortical excitability and plasticity by interacting with glutamate and GABA receptors, which are affected by dopamine receptor subtypes (D1- and D2-like). Non-invasive brain stimulation techniques can induce plasticity and monitor cortical facilitation and inhibition in humans. In a randomized, placebo-controlled, double-blinded study, we investigated how dopamine and D1- and D2-like receptors impact transcranial direct current stimulation (tDCS)-induced plasticity concerning glutamatergic and GABAergic mechanisms. Eighteen healthy volunteers received 1 mA anodal (13 min) and cathodal tDCS (9 min) over the left motor cortex combined with the dopaminergic agents l-dopa (general dopamine activation), bromocriptine (D2-like receptor agonist), combined D2 antagonism via sulpiride and general dopaminergic activation via l-dopa to activate D1-like receptors, and placebo medication. Glutamate-related cortical facilitation and GABA-related cortical inhibition were monitored using transcranial magnetic stimulation techniques, including I-O curve, intracortical facilitation (ICF), short-interval intracortical inhibition (SICI), and I-wave facilitation protocols. Our results indicate that anodal tDCS alone enhanced the I-O curve and ICF while decreasing SICI. Conversely, cathodal tDCS decreased the I-O curve and ICF while increasing SICI. General dopamine and D2 receptor activation combined with anodal tDCS decreased the I-O curve and ICF, but enhanced SICI compared to tDCS alone. When paired with cathodal tDCS, general Dopamine and D2-like receptor activity enhancement prolonged the cathodal tDCS effect on excitability. After anodal tDCS, D1-like receptor activation increased the I-O curve and ICF while reducing SICI. These effects were abolished with cathodal tDCS. Dopaminergic substances combined with anodal and cathodal tDCS did not have a significant effect on I-wave facilitation. These results suggest that D1-like receptor activation enhanced LTP-like plasticity and abolished LTD-like plasticity via glutamatergic NMDA receptor enhancement, while global dopaminergic and D2-like receptor enhancement weakened LTP-like but strengthened LTD-like plasticity primarily via glutamatergic NMDA receptor activity diminution.

Defining Trajectories of Linguistic, Cognitive-Communicative, and Quality of Life Outcomes in Aphasia: Longitudinal Observational Study Protocol

Objective

To describe the trajectories of linguistic, cognitive-communicative, and health-related quality of life (HRQOL) outcomes after stroke in persons with aphasia.

Design

Longitudinal observational study from inpatient rehabilitation to 18 months after stroke.

Setting

Four US mid-west inpatient rehabilitation facilities (IRFs).

Participants

We plan to recruit 400 adult (older than 21 years) English speakers who meet the following inclusion criteria: (1) Diagnosis of aphasia after a left-hemisphere infarct confirmed by CT scan or magnetic resonance imaging (MRI); (2) first admission for inpatient rehabilitation due to a neurologic event; and (3) sufficient cognitive capacity to provide informed consent and participate in testing. Exclusion criteria include any neurologic condition other than stroke that could affect language, cognition or speech, such as Parkinson's disease, Alzheimer's disease, traumatic brain injury, or the presence of right-hemisphere lesions.

Interventions

Not applicable.

Main Outcome Measures

Subjects are administered a test battery of linguistic, cognitive-communicative, and HRQOL measures. Linguistic measures include the Western Aphasia Battery-Revised and the Apraxia of Speech Rating Scale. Cognitive-communicative measures include the Communication Participation Item Bank, Connor's Continuous Performance Test-3, the Communication Confidence Rating Scale for Aphasia, the Communication Effectiveness Index, the Neurological Quality of Life measurement system (Neuro-QoL) Communication short form, and the Neuro-QoL Cognitive Function short form. HRQOL measures include the 39-item Stroke & Aphasia Quality of Life Scale, Neuro-QoL Fatigue, Sleep Disturbance, Depression, Ability to Participate in Social Roles & Activities, and Satisfaction with Social Roles & Activities tests, and the Patient-Reported Outcome Measurement and Information System 10-item Global Health short form. The test battery is administered initially during inpatient rehabilitation, and at 3-, 6-, 12-, and 18-months post-IRF discharge. Biomarker samples are collected via saliva samples at admission and a subgroup of participants also undergo resting state fMRI scans.

Results

Not applicable.

Conclusions

This longitudinal observational study will develop trajectory models for recovery of clinically relevant linguistic, cognitive-communicative, and quality of life outcomes over 18 months after inpatient rehabilitation. Models will identify individual differences in the patterns of recovery based on variations in personal, genetic, imaging, and therapy characteristics. The resulting models will provide an unparalleled representation of recovery from aphasia resulting from stroke. This improved understanding of recovery will enable clinicians to better tailor and plan rehabilitation therapies to individual patient's needs.

Genetics of ischemic stroke functional outcome

Ischemic stroke, which accounts for 87% of cerebrovascular accidents, is responsible for massive global burden both in terms of economic cost and personal hardship. Many stroke survivors face long-term disability-a phenotype associated with an increasing number of genetic variants. While clinical variables such as stroke severity greatly impact recovery, genetic polymorphisms linked to functional outcome may offer physicians a unique opportunity to deliver personalized care based on their patient's genetic makeup, leading to improved outcomes. A comprehensive catalogue of the variants at play is required for such an approach. In this review, we compile and describe the polymorphisms associated with outcome scores such as modified Rankin Scale and Barthel Index. Our search identified 74 known genetic polymorphisms spread across 48 features associated with various poststroke disability metrics. The known variants span diverse biological systems and are related to inflammation, vascular homeostasis, growth factors, metabolism, the p53 regulatory pathway, and mitochondrial variation. Understanding how these variants influence functional outcome may be helpful in maximizing poststroke recovery.

Dopamine Alters the Effect of Brain Stimulation on Decision-Making

Noninvasive brain stimulation techniques, such as transcranial direct current stimulation (tDCS), show promise in treating a range of psychiatric and neurologic conditions. However, optimization of such applications requires a better understanding of how tDCS alters cognition and behavior. Existing evidence implicates dopamine in tDCS alterations of brain activity and plasticity; however, there is as yet no causal evidence for a role of dopamine in tDCS effects on cognition and behavior. Here, in a preregistered, double-blinded study, we examined how pharmacologically manipulating dopamine altered the effect of tDCS on the speed-accuracy trade-off, which taps ubiquitous strategic operations. Cathodal tDCS was delivered over the left prefrontal cortex and the superior medial frontal cortex before participants (N = 62, 24 males, 38 females) completed a dot-motion task, making judgments on the direction of a field of moving dots under instructions to emphasize speed, accuracy, or both. We leveraged computational modeling to uncover how our interventions altered latent decisional processes driving the speed-accuracy trade-off. We show that dopamine in combination with tDCS (but not tDCS alone nor dopamine alone) not only impaired decision accuracy but also impaired discriminability, which suggests that these manipulations altered the encoding or representation of discriminative evidence. This is, to the best of our knowledge, the first direct evidence implicating dopamine in the way tDCS affects cognition and behavior.SIGNIFICANCE STATEMENT tDCS can improve cognitive and behavioral impairments in clinical conditions; however, a better understanding of its mechanisms is required to optimize future clinical applications. Here, using a pharmacological approach to manipulate brain dopamine levels in healthy adults, we demonstrate a role for dopamine in the effects of tDCS in the speed-accuracy trade-off, a strategic cognitive process ubiquitous in many contexts. In doing so, we provide direct evidence implicating dopamine in the way tDCS affects cognition and behavior.

Exploratory genome-wide analyses of cortical inhibition, facilitation, and plasticity in late-life depression

Late-life depression (LLD) is a heterogenous mood disorder influenced by genetic factors. Cortical physiological processes such as cortical inhibition, facilitation, and plasticity may be markers of illness that are more strongly associated with genetic factors than the clinical phenotype. Thus, exploring the relationship between genetic factors and these physiological processes may help to characterize the biological mechanisms underlying LLD and improve diagnosis and treatment selection. Transcranial magnetic stimulation (TMS) combined with electromyography was used to measure short interval intracortical inhibition (SICI), cortical silent period (CSP), intracortical facilitation (ICF), and paired associative stimulation (PAS) in 79 participants with LLD. We used exploratory genome-wide association and gene-based analyses to assess for genetic correlations of these TMS measures. MARK4 (which encodes microtubule affinity-regulating kinase 4) and PPP1R37 (which encodes protein phosphatase 1 regulatory subunit 37) showed genome-wide significant association with SICI. EGFLAM (which encodes EGF-like fibronectin type III and laminin G domain) showed genome-wide significant association with CSP. No genes met genome-wide significant association with ICF or PAS. We observed genetic influences on cortical inhibition in older adults with LLD. Replication with larger sample sizes, exploration of clinical phenotype subgroups, and functional analysis of relevant genotypes is warranted to better characterize genetic influences on cortical physiology in LLD. This work is needed to determine whether cortical inhibition may serve as a biomarker to improve diagnostic precision and guide treatment selection in LLD.

Neuronavigated Repetitive Transcranial Stimulation Improves Neurocognitive Functioning in Veterans with Schizophrenia: A Possible Role of BDNF Polymorphism

It has been reported in the previous literatures that high-frequency (HF) neuronavigated repetitive transcranial magnetic stimulation (rTMS) may improve neurocognitive functioning in patients with schizophrenia. Nonetheless, the heterogeneity of the research findings with regards to the effectiveness of HF-rTMS on the neurocognitive functioning in patients with schizophrenia greatly hinders its clinical application. The current study was designed to determine the predictive role of BDNF variants for neurocognitive improvements after rTMS administration in veterans with schizophrenia. 109 hospitalized veterans with schizophrenia were randomly allocated to active HF-rTMS (n=63) or sham stimulation (n=46) over left DLPFC for 4 consecutive weeks. Neurocognitive functions were assessed by using the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) at baseline and at the end of week 4. BDNF polymorphism was genotyped by the technicians. Compared with sham stimulation sessions, the immediate memory performance was significantly increased in active sessions after neuronavigated HF-rTMS administration. In addition, patients with the CC homozygotes demonstrated greater improvement of immediate memory after rTMS treatment, while T allele carriers showed no significant improvement in immediate memory domain relative to baseline performance of immediate memory. Our findings suggest that add-on neuronavigated HF-rTMS is beneficial on immediate memory only in patients with CC homozygotes, but not in T allele carriers. This pilot study provides further evidence for BDNF as a promise biomarker in predicting the clinical response to rTMS stimulation.

BDNF Therapeutic Mechanisms in Neuropsychiatric Disorders

Brain-derived neurotrophic factor (BDNF) is the most abundant neurotrophin in the adult brain and functions as both a primary neurotrophic signal and a neuromodulator. It serves essential roles in neuronal development, maintenance, transmission, and plasticity, thereby influencing aging, cognition, and behavior. Accumulating evidence associates reduced central and peripheral BDNF levels with various neuropsychiatric disorders, supporting its potential utilization as a biomarker of central pathologies. Subsequently, extensive research has been conducted to evaluate restoring, or otherwise augmenting, BDNF transmission as a potential therapeutic approach. Promising results were indeed observed for genetic BDNF upregulation or exogenous administration using a multitude of murine models of neurological and psychiatric diseases. However, varying mechanisms have been proposed to underlie the observed therapeutic effects, and many findings indicate the engagement of disease-specific and other non-specific mechanisms. This is because BDNF essentially affects all aspects of neuronal cellular function through tropomyosin receptor kinase B (TrkB) receptor signaling, the disruptions of which vary between brain regions across different pathologies leading to diversified consequences on cognition and behavior. Herein, we review the neurophysiology of BDNF transmission and signaling and classify the converging and diverging molecular mechanisms underlying its therapeutic potentials in neuropsychiatric disorders. These include neuroprotection, synaptic maintenance, immunomodulation, plasticity facilitation, secondary neuromodulation, and preservation of neurovascular unit integrity and cellular viability. Lastly, we discuss several findings suggesting BDNF as a common mediator of the therapeutic actions of centrally acting pharmacological agents used in the treatment of neurological and psychiatric illness.

Effect of brain-derived neurotrophic factor gene polymorphisms on motor performance and motor learning: A systematic review and meta-analysis

Brain-derived neurotrophic factor (BDNF) gene polymorphisms may modulate neurotransmitter efficiency, thereby influencing motor performance and motor learning. However, studies to date have provided no consensus regarding the genetic influence of BDNF genotypes (i.e., Val/Val, Val/Met, or Met/Met type). This study aimed to investigate the effect of BDNF genotype on motor performance and motor learning in healthy human adults via a systematic review and meta-analysis. A total of 19 relevant studies were identified using PubMed and Web of Science search for articles published between 2000 and 2021 with motor performance or motor learning as the primary outcome measures. The results of our systematic review suggest that the BDNF genotype is unlikely to contribute to motor performance and motor learning abilities because only 2/32 datasets (6.3%) from 16 studies on motor performance and 3/19 datasets (17.6%) from 13 studies on motor learning indicated a significant genetic effect. Moreover, a meta-analysis of motor learning publications involving 17 datasets from 11 studies revealed that there was no significant difference in the learning score normalized using baseline data between Val/Val and Met carriers (Val/Met + Met/Met or Val/Met; standardized mean differences = 0.08, P = 0.37) with zero heterogeneity (I² = 0) and a relatively low risk of publication bias. Taken together, the BDNF genotype may have only a minor impact on individual motor performance and motor learning abilities.

Do Brain-Derived Neurotrophic Factor Genetic Polymorphisms Modulate the Efficacy of Motor Cortex Plasticity Induced by Non-invasive Brain Stimulation? A Systematic Review

Techniques of non-invasive brain stimulation (NIBS) of the human primary motor cortex (M1) are widely used in basic and clinical research to induce neural plasticity. The induction of neural plasticity in the M1 may improve motor performance ability in healthy individuals and patients with motor deficit caused by brain disorders. However, several recent studies revealed that various NIBS techniques yield high interindividual variability in the response, and that the brain-derived neurotrophic factor (BDNF) genotype (i.e., Val/Val and Met carrier types) may be a factor contributing to this variability. Here, we conducted a systematic review of all published studies that investigated the effects of the BDNF genotype on various forms of NIBS techniques applied to the human M1. The motor-evoked potential (MEP) amplitudes elicited by single-pulse transcranial magnetic stimulation (TMS), which can evaluate M1 excitability, were investigated as the main outcome. A total of 1,827 articles were identified, of which 17 (facilitatory NIBS protocol, 27 data) and 10 (inhibitory NIBS protocol, 14 data) were included in this review. More than two-thirds of the data (70.4–78.6%) on both NIBS protocols did not show a significant genotype effect of NIBS on MEP changes. Conversely, most of the remaining data revealed that the Val/Val type is likely to yield a greater MEP response after NIBS than the Met carrier type in both NIBS protocols (21.4–25.9%). Finally, to aid future investigation, we discuss the potential effect of the BDNF genotype based on mechanisms and methodological issues.

Modulation of motor cortical excitability by continuous theta-burst stimulation in adults with autism spectrum disorder

OBJECTIVE

To test whether change in motor evoked potential (ΔMEP) induced by continuous theta-burst stimulation (cTBS) of motor cortex (M1) distinguishes adults with autism spectrum disorder (ASD) from neurotypicals, and to explore the contribution of two common polymorphisms related to neuroplasticity.

METHODS

44 adult neurotypical (NT) participants (age 21-65, 34 males) and 19 adults with ASD (age 21-58, 17 males) prospectively underwent M1 cTBS. Their data were combined with previously obtained results from 35 NT and 35 ASD adults.

RESULTS

ΔMEP at 15 minutes post-cTBS (T15) was a significant predictor of diagnosis (p = 0.04) in the present sample (n=63). T15 remained a significant predictor in a larger sample (n=91) and when partially imputed based on T10-T20 from a yet-greater sample (N=133). T15 also remained a significant predictor of diagnosis among brain-derived neurotrophic factor (BDNF) Met+ and apolipoprotein E (APOE) ε4- subjects (p's < 0.05), but not among Met- or ε4+ subjects (p's > 0.19).

CONCLUSIONS

ΔMEP at T15 post-cTBS is a significant biomarker for adults with ASD, and its utility is modulated by BDNF and APOE polymorphisms.

SIGNIFICANCE

M1 cTBS response is a physiologic biomarker for adults with ASD in large samples, and controlling for BDNF and APOE polymorphisms can improve its diagnostic utility.

Potential Prognostic Impact of Dopamine Receptor D1 (rs4532) Polymorphism in Post-stroke Outcome in the Elderly

Background: Single-nucleotide polymorphisms (SNPs) may affect post-stroke motor recovery, and some SNPs have been implicated in swallowing disturbances after stroke. Certain SNPs may also have altered influences according to different age. Objective: This post-hoc study investigated whether SNPs have different effects on dysphagia recovery between the elderly vs. young stroke patients. Methods: Analysis was conducted from a previous study including 218 stroke subjects with dysphagia. They were stratified into two groups, aged <65 and aged ≥65 years. The primary outcome was persistence of nil per mouth (NPM) at 3 months post-stroke onset. Association between outcome and nine different SNPs were investigated. Results: The elderly group (50%, n = 103) showed poorer swallowing outcomes than the young group. The minor allele of the dopamine receptor D1 (DRD1, rs4532) polymorphism showed potential association (p = 0.022) with an increased risk of NPM at 12 weeks post-stroke in the elderly, both in the additive (OR, 2.94; 95% CI, 1.17-7.37) and dominant models (OR, 2.93; 95% CI, 1.04-8.23) but did not reach statistical significance after Bonferonni correction. Logistic regression analysis showed that in those aged ≥65 years, models including the minor allele of rs4532 predicted the risk of the poor outcome with good accuracies even after adjustment of clinical factors, such as previous pneumonia episodes (AUROC, 0.86; 95% CI, 0.79-0.93) or the National Institutes of Health Stroke Scale (AUROC, 0.82; 95% CI, 0.67-0.92). In contrast, those aged <65 years seemed not to be affected by the presence of the rs4532 polymorphism, and models that included intubation history (AUROC, 0.81; 95% CI, 0.73-0.90) or previous pneumonia episodes (AUROC, 0.77; 95% CI, 0.68-0.87) showed modest levels of accuracies in predicting NPM at 12 weeks poststroke. Conclusions: Our study suggests a possible association between the rs4532 and post-stroke swallowing recovery, primarily in those aged ≥65 years. Certain SNPs may lead to less favorable outcomes in the elderly. The gene-age interaction should be considered in post-stroke swallowing recovery. Clinical Trial Registration: https://www.clinicaltrials.gov, Unique identifier [NCT03577444].

Variability in cTBS Aftereffects Attributed to the Interaction of Stimulus Intensity With BDNF Val66Met Polymorphism

Objective: To evaluate whether a common polymorphism (Val66Met) in the gene for brain-derived neurotrophic factor (BDNF)-a gene thought to influence plasticity-contributes to inter-individual variability in responses to continuous theta-burst stimulation (cTBS), and explore whether variability in stimulation-induced plasticity among Val66Met carriers relates to differences in stimulation intensity (SI) used to probe plasticity. Methods: Motor evoked potentials (MEPs) were collected from 33 healthy individuals (11 Val66Met) prior to cTBS (baseline) and in 10 min intervals immediately following cTBS for a total of 30 min post-cTBS (0 min post-cTBS, 10 min post-cTBS, 20 min post cTBS, and 30 min post-cTBS) of the left primary motor cortex. Analyses assessed changes in cortical excitability as a function of BDNF (Val66Val vs. Val66Met) and SI. Results: For both BDNF groups, MEP-suppression from baseline to post-cTBS time points decreased as a function of increasing SI. However, the effect of SI on MEPs was more pronounced for Val66Met vs. Val66Val carriers, whereby individuals probed with higher vs. lower SIs resulted in paradoxical cTBS aftereffects (MEP-facilitation), which persisted at least 30 min post-cTBS administration. Conclusions: cTBS aftereffects among BDNF Met allele carriers are more variable depending on the SI used to probe cortical excitability when compared to homozygous Val allele carriers, which could, to some extent, account for the inconsistency of previously reported cTBS effects. Significance: These data provide insight into the sources of cTBS response variability, which can inform how best to stratify and optimize its use in investigational and clinical contexts.

Sex effects for the interaction of dopamine related genetic variants for COMT and BDNF on declarative memory performance

Genetic factors are assumed to contribute to memory performance, especially genes affecting the dopaminergic neurotransmission. We aimed to evaluate leading functional genetic variants of the dopamine system, Catechol-O-methyltransferase (COMT) SNP rs4680 and Brain-derived neurotropic factor (BDNF) SNP rs6265, previously found to be associated with memory performance. In two independent general population cohorts (total N = 5937) we investigated direct and interaction effects between COMT and BDNF SNPs on declarative memory performance. We found significant two-way interactions for COMT and BDNF in both cohorts but no direct genetic effects. Sensitivity analyses revealed that an interaction between COMT and BDNF was mainly carried by females. While direct associations of COMT and BDNF on memory have been reported previously, we could demonstrate that the interaction of COMT and BDNF is sex-dependent and more complex and needs further investigation. Our results could be demonstrated in two independent cohorts of valuable size.

Impact of COMT val158met on tDCS-induced cognitive enhancement in older adults

BACKGROUND

Previous studies suggest that genetic polymorphisms and aging modulate inter-individual variability in brain stimulation-induced plasticity. However, the relationship between genetic polymorphisms and behavioral modulation through transcranial direct current stimulation (tDCS) in older adults remains poorly understood.

OBJECTIVE

Link individual tDCS responsiveness, operationalized as performance difference between tDCS and sham condition, to common genetic polymorphisms in healthy older adults.

METHODS

106 healthy older participants from five tDCS-studies were re-invited to donate blood for genotyping of apoliproprotein E (APOE: ε4 carriers and ε4 non-carriers), catechol-O-methyltransferase (COMT: val/val, val/met, met/met), brain-derived neurotrophic factor (BDNF: val/val, val/met, met/met) and KIdney/BRAin encoding gene (KIBRA: C/C, C/T, T/T). Studies had assessed cognitive performance during tDCS and sham in cross-over designs. We now asked whether the tDCS responsiveness was related to the four genotypes using a linear regression models.

RESULTS

We found that tDCS responsiveness was significantly associated with COMT polymorphism; i.e., COMT val carriers (compared to met/met) showed higher tDCS responsiveness. No other significant associations emerged.

CONCLUSION

Using data from five brain stimulation studies conducted in our group, we showed that only individual variation of COMT genotypes modulated behavioral response to tDCS. These findings contribute to the understanding of inherent factors that explain inter-individual variability in functional tDCS effects in older adults, and might help to better stratify participants for future clinical trials.

Within-session verbal learning slope is predictive of lifespan delayed recall, hippocampal volume, and memory training benefit, and is heritable

Memory performance results from plasticity, the ability to change with experience. We show that benefit from practice over a few trials, learning slope, is predictive of long-term recall and hippocampal volume across a broad age range and a long period of time, relates to memory training benefit, and is heritable. First, in a healthy lifespan sample (n = 1825, age 4-93 years), comprising 3483 occasions of combined magnetic resonance imaging (MRI) scans and memory tests over a period of up to 11 years, learning slope across 5 trials was uniquely related to performance on a delayed free recall test, as well as hippocampal volume, independent from first trial memory or total memory performance across the five learning trials. Second, learning slope was predictive of benefit from memory training across ten weeks in an experimental subsample of adults (n = 155). Finally, in an independent sample of male twins (n = 1240, age 51-50 years), learning slope showed significant heritability. Within-session learning slope may be a useful marker beyond performance per se, being heritable and having unique predictive value for long-term memory function, hippocampal volume and training benefit across the human lifespan.

Cognitive training and brain stimulation in prodromal Alzheimer's disease (AD-Stim)-study protocol for a double-blind randomized controlled phase IIb (monocenter) trial

BACKGROUND

Given the growing older population worldwide, and the associated increase in age-related diseases, such as Alzheimer's disease (AD), investigating non-invasive methods to ameliorate or even prevent cognitive decline in prodromal AD is highly relevant. Previous studies suggest transcranial direct current stimulation (tDCS) to be an effective method to boost cognitive performance, especially when applied in combination with cognitive training in healthy older adults. So far, no studies combining tDCS concurrent with an intense multi-session cognitive training in prodromal AD populations have been conducted.

METHODS

The AD-Stim trial is a monocentric, randomized, double-blind, placebo-controlled study, including a 3-week tDCS-assisted cognitive training with anodal tDCS over left DLPFC (target intervention), compared to cognitive training plus sham (control intervention). The cognitive training encompasses a letter updating task and a three-stage Markov decision-making task. Forty-six participants with subjective cognitive decline (SCD) or mild cognitive impairment (MCI) will be randomized block-wise to either target or control intervention group and participate in nine interventional visits with additional pre- and post-intervention assessments. Performance in the letter updating task after training and anodal tDCS compared to sham stimulation will be analyzed as primary outcome. Further, performance on the second training task and transfer tasks will be investigated. Two follow-up visits (at 1 and 7 months post-training) will be performed to assess possible maintenance effects. Structural and functional magnetic resonance imaging (MRI) will be applied before the intervention and at the 7-month follow-up to identify possible neural predictors for successful intervention.

SIGNIFICANCE

With this trial, we aim to provide evidence for tDCS-induced improvements of multi-session cognitive training in participants with SCD and MCI. An improved understanding of tDCS effects on cognitive training performance and neural predictors may help to develop novel approaches to counteract cognitive decline in participants with prodromal AD.

TRIAL REGISTRATION

ClinicalTrials.gov , NCT04265378 . Registered on 07 February 2020. Retrospectively registered. Protocol version: Based on BB 004/18 version 1.2 (May 17, 2019).

SPONSOR

University Medicine Greifswald.

Can genetic polymorphisms predict response variability to anodal transcranial direct current stimulation of the primary motor cortex?

Genetic mediation of cortical plasticity and the role genetic variants play in previously observed response variability to transcranial direct current stimulation (tDCS) have become important issues in the tDCS literature in recent years. This study investigated whether inter-individual variability to tDCS was in-part genetically mediated. In 61 healthy males, anodal-tDCS (a-tDCS) and sham-tDCS were administered to the primary motor cortex at 1 mA for 10-min via 6 × 4 cm active and 7 × 5 cm return electrodes. Twenty-five single-pulse transcranial magnetic stimulation (TMS) motor evoked potentials (MEP) were recorded to represent corticospinal excitability (CSE). Twenty-five paired-pulse MEPs were recorded with 3 ms inter-stimulus interval (ISI) to assess intracortical inhibition (ICI) via short-interval intracranial inhibition (SICI) and 10 ms ISI for intracortical facilitation (ICF). Saliva samples were tested for specific genetic polymorphisms in genes encoding for excitatory and inhibitory neuroreceptors. Individuals were sub-grouped based on a pre-determined threshold and via statistical cluster analysis. Two distinct subgroups were identified, increases in CSE following a-tDCS (i.e. Responders) and no increase or even reductions in CSE (i.e. Non-responders). No changes in ICI or ICF were reported. No relationships were reported between genetic polymorphisms in excitatory receptor genes and a-tDCS responders. An association was reported between a-tDCS responders and GABRA3 gene polymorphisms encoding for GABA-A receptors suggesting potential relationships between GABA-A receptor variations and capacity to undergo tDCS-induced cortical plasticity. In the largest tDCS study of its kind, this study presents an important step forward in determining the contribution genetic factors play in previously observed inter-individual variability to tDCS.

Brain-Derived Neurotrophic Factor Polymorphism Influences Response to Single-Pulse Transcranial Magnetic Stimulation at Rest

OBJECTIVES

The ability of noninvasive brain stimulation to modulate corticospinal excitability and plasticity is influenced by genetic predilections such as the coding for brain-derived neurotrophic factor (BDNF). Otherwise healthy individuals presenting with BDNF Val66Met (Val/Met) polymorphism are less susceptible to changes in excitability in response to repetitive transcranial magnetic stimulation (TMS) and paired associative stimulation paradigms, reflecting reduced neuroplasticity, compared to Val homozygotes (Val/Val). In the current study, we investigated whether BDNF polymorphism influences "baseline" excitability under TMS conditions that are not repetitive or plasticity-inducing. Cross-sectional BDNF levels could predict TMS response more generally because of the ongoing plasticity processes.

MATERIALS AND METHODS

Forty-five healthy individuals (23 females; age: 25.3 ± 7.0 years) participated in the study, comprising two groups. Motor evoked potentials (MEP) were collected using single-pulse TMS paradigms at fixed stimulation intensities at 110% of the resting motor threshold in one group, and individually-derived intensities based on MEP sizes of 1 mV in the second group. Functional variant Val66Met (rs6265) was genotyped from saliva samples by a technician blinded to the identity of DNA samples.

RESULTS

Twenty-seven participants (60.0%) were identified with Val/Val, sixteen (35.5%) with Val/Met genotype, and two with Met/Met genotype. MEP amplitudes were significantly diminished in the Val/Met than Val/Val individuals. These results held independent of the single-pulse TMS paradigm of choice (p = 0.017110% group; p = 0.035 1 mV group), age, and scalp-to-coil distances.

CONCLUSIONS

The findings should be further substantiated in larger-scale studies. If validated, intrinsic differences by BDNF polymorphism status could index response to TMS prior to implementing plasticity-inducing protocols.

The effect of breaking up prolonged sitting on paired associative stimulation-induced plasticity

Paired associative stimulation (PAS) can induce plasticity in the motor cortex, as measured by changes in corticospinal excitability (CSE). This effect is attenuated in older and less active individuals. Although a single bout of exercise enhances PAS-induced plasticity in young, physically inactive adults, it is not yet known if physical activity interventions affect PAS-induced neuroplasticity in middle-aged inactive individuals. Sixteen inactive middle-aged office workers participated in a randomized cross-over design investigating how CSE and short-interval intracortical inhibition (SICI) were affected by PAS preceded by 3 h of sitting (SIT), 3 h of sitting interrupted every 30 min by 3 min of frequent short bouts of physical activity (FPA) and 2.5 h of sitting followed by 25 min of moderate-intensity exercise (EXE). Transcranial magnetic stimulation was applied over the primary motor cortex (M1) of the dominant abductor pollicis brevis to induce recruitment curves before and 5 min and 30 min post-PAS. Linear mixed models were used to compare changes in CSE using time and condition as fixed effects and subjects as random effects. There was a main effect of time on CSE and planned within-condition comparisons showed that CSE was significantly increased from baseline to 5 min and 30 min post-PAS, in the FPA condition, with no significant changes in the SIT or EXE conditions. SICI decreased from baseline to 5 min post-PAS, but this was not related to changes in CSE. Our findings suggest that in middle-aged inactive adults, FPAs may promote corticospinal neuroplasticity. Possible mechanisms are discussed.

Effects of COMT rs4680 and BDNF rs6265 polymorphisms on brain degree centrality in Han Chinese adults who lost their only child

Losing one's only child is a major traumatic life event that may lead to posttraumatic stress disorder (PTSD); however, not all parents who experience this trauma develop PTSD. Genetic variants are associated with the risk of developing PTSD. Catechol-O-methyltransferase (COMT) rs4680 and brain-derived neurotrophic factor (BDNF) rs6265 are two most well-described single-nucleotide polymorphisms that relate to stress response; however, the neural mechanism underlying their effects on adults who lost an only child remains poorly understood. Two hundred and ten Han Chinese adults who had lost their only child (55 with PTSD and 155 without PTSD) were included in this imaging genetics study. Participants were divided into subgroups according to their COMT rs4680 and BDNF rs6265 genotypes. Degree Centrality (DC)-a resting-state fMRI index reflecting the brain network communication-was compared with a three-way (PTSD diagnosis, COMT, and BDNF polymorphisms) analysis of covariance. Diagnosis state had a significant effect on DC in bilateral inferior parietal lobules and right middle frontal gyrus (MFG), where PTSD adults showed weaker DC. BDNF × diagnosis interaction effect was found in the right MFG and hippocampus, and these two regions were reversely modulated. Also, there was a significant COMT × BDNF interaction effect in left cuneus, middle temporal gyrus, right inferior occipital gyrus, and bilateral putamen, independent of PTSD diagnosis. These findings suggest that the modulatory effect of BDNF polymorphism on the MFG and hippocampus may contribute to PTSD development in bereaved adults. Interactions of COMT × BDNF polymorphisms modulate some cortices and basal ganglia, irrespective of PTSD development.

Motor learning and COMT Val158met polymorphism: Analyses of oculomotor behavior and corticocortical communication

Differences in motor learning can be partially explained by differences in genotype. The catechol-O-methyltransferase (COMT) Val158Met polymorphism regulates the dopamine (DA) availability in the prefrontal cortex modulating motor learning and performance. Given the differences in tonic and phasic DA transmission, this study aimed to investigate whether the greater cognitive flexibility associated with the Val allele would favor the learning of movement parametrization, while the greater cognitive stability associated with the Met allele favors the acquisition of the movement pattern. Furthermore, we investigated if the genotypic characteristics impact visual scanning of information related to parametrization and to the movement pattern, and the level of cortical connectivity associated with motor planning and control. Performance and learning of a sequential motor task were compared among three genotypes (Val/Val, Val/Met, and Met/Met), as well as their oculomotor behavior and level of cortical coherence. The findings show that the cognitive flexibility promoted by the Val allele is associated with a better parametrization. The search for information through visual scanning was specific to each genotype. Also, a greater cortical connectivity associated with the Val allele was found. The combined study of behavioral, electrophysiological and molecular levels of analysis showed that the cognitive stability and flexibility associated with the COMT alleles, influence specific aspects of motor learning.

Effects of a Multi-Session Cognitive Training Combined With Brain Stimulation (TrainStim-Cog) on Age-Associated Cognitive Decline - Study Protocol for a Randomized Controlled Phase IIb (Monocenter) Trial

Background

With increasing aging populations worldwide, developing interventions against age-associated cognitive decline is particularly important. Evidence suggests that combination of brain stimulation with cognitive training intervention may enhance training effects in terms of performance gain or transfer to untrained domains. This protocol describes a Phase IIb clinical trial that investigates the intervention effects of training combined with brain stimulation in older adults.

Methods

The TrainStim-Cog study is a monocentric, randomized, single-blind, placebo-controlled intervention. The study will investigate cognitive training with concurrent anodal transcranial direct current stimulation (tDCS) over the left dorsolateral prefrontal cortex (target intervention) compared to cognitive training with sham stimulation (control intervention) over nine sessions in 3 weeks, consisting of a letter updating task, and a three-stage Markov decision-making task. Fifty-six older adults will be recruited from the general population. Baseline assessment will be performed including neuropsychological screening and performance on training tasks. Participants will be allocated to one of the two study arms using block-wise randomization stratified by age and baseline performance with a 1:1 allocation ratio. Primary outcome is performance in the letter updating task after training under anodal tDCS compared to sham stimulation. Secondary outcomes include performance changes in the decision-making task and transfer tasks, as well as brain structure and functional networks assessed by structural, and functional magnetic resonance imaging (MRI) that are acquired pre- and post-intervention.

Significance

The main aim of the TrainStim-Cog study is to provide evidence for behavioral and neuronal effects of tDCS-accompanied cognitive training and to elucidate the underlying mechanisms in older adults. Our findings will contribute toward developing efficient interventions for age-associated cognitive decline.

Trial registration

This trial was retrospectively registered at Clinicaltrials.gov Identifier: NCT03838211 at February 12, 2019, https://clinicaltrials.gov/ct2/show/NCT03838211.

Protocol version

Based on BB 004/18 version 1.2 (May 17, 2019).

Paired Associative Stimulation as a Tool to Assess Plasticity Enhancers in Chronic Stroke

Background and Purpose

The potential for adaptive plasticity in the post-stroke brain is difficult to estimate, as is the demonstration of central nervous system (CNS) target engagement of drugs that show promise in facilitating stroke recovery. We set out to determine if paired associative stimulation (PAS) can be used (a) as an assay of CNS plasticity in patients with chronic stroke, and (b) to demonstrate CNS engagement by memantine, a drug which has potential plasticity-modulating effects for use in motor recovery following stroke.

Methods

We examined the effect of PAS in fourteen participants with chronic hemiparetic stroke at five time-points in a within-subjects repeated measures design study: baseline off-drug, and following a week of orally administered memantine at doses of 5, 10, 15, and 20 mg, comprising a total of seventy sessions. Each week, MEP amplitude pre and post-PAS was assessed in the contralesional hemisphere as a marker of enhanced or diminished plasticity. Strength and dexterity were recorded each week to monitor motor-specific clinical status across the study period.

Results

We found that MEP amplitude was significantly larger after PAS in baseline sessions off-drug, and responsiveness to PAS in these sessions was associated with increased clinical severity. There was no observed increase in MEP amplitude after PAS with memantine at any dose. Motor threshold (MT), strength, and dexterity remained unchanged during the study.

Conclusion

Paired associative stimulation successfully induced corticospinal excitability enhancement in chronic stroke subjects at the group level. However, this response did not occur in all participants, and was associated with increased clinical severity. This could be an important way to stratify patients for future PAS-drug studies. PAS was suppressed by memantine at all doses, regardless of responsiveness to PAS off-drug, indicating CNS engagement.

Genetic influences on the variability of response to repetitive transcranial magnetic stimulation in human pharyngeal motor cortex

BACKGROUND

Recent studies have reported substantial variability in response to repetitive transcranial magnetic stimulation (rTMS). We hypothesized that an individual's genetic predisposition may contribute to such variability in the pharyngeal motor cortex. This study aimed to investigate the response to 1 and 5 Hz rTMS paradigms on pharyngeal motor cortex in healthy participants and its relationship with genetic predisposition.

METHODS

Forty-one healthy participants (25.4 ± 4.6 years old) received either or both 1 Hz (n = 39) and 5 Hz rTMS (n = 40) over pharyngeal motor cortex. Pharyngeal and thenar motor-evoked potentials were recorded at baseline and for 1 hour post-rTMS. The participants were then classified according to their response. The associations between rTMS response and gender, time of day of the stimulation, and eight prespecified single nucleotide polymorphisms (SNPs) were analyzed.

KEY RESULTS

There was no direction-specific response to either paradigm (1 Hz: F[3.69, 129.21] = 0.78, P = 0.56; 5 Hz: F[4.08, 146.85] = 1.38, P = 0.25). Only 13% of participants showed the expected bidirectional response (inhibition for 1 Hz and excitation for 5 Hz). Significant associations were found between response and COMT (1 Hz: P = 0.03) and DRD2 (1 Hz: P = 0.02; 5 Hz: P = 0.04) polymorphisms. Carriers of minor allele G from SNP rs6269 (COMT) were more likely to show inhibitory or excitatory outcomes after 1 Hz rTMS. By contrast, carriers of minor allele A from SNP rs1800497 (DRD2) were more likely to show no response to 1 Hz rTMS and inhibition after 5 Hz rTMS.

CONCLUSIONS & INFERENCES

Two SNPs from COMT and DRD2 genes may partially explain the response variability to rTMS in the pharyngeal motor system. Further research should focus on stratified approaches for neurostimulatory dysphagia treatment using rTMS.

Gene polymorphisms and response to transcranial direct current stimulation for auditory verbal hallucinations in schizophrenia

OBJECTIVE

Recent observations demonstrate a significant ameliorative effect of add-on transcranial direct current stimulation (tDCS) on auditory verbal hallucinations (AVHs) in schizophrenia. Of the many SNPs, NRG1 rs35753505 and catechol-o-methyl transferase (COMT) rs4680 polymorphisms have shown to have a strong association with neuroplasticity effect in schizophrenia.

METHODS

Schizophrenia patients (n=32) with treatment resistant auditory hallucinations were administered with an add-on tDCS. The COMT (rs4680) and NRG1 (rs35753505) genotypes were determined. The COMT genotypes were categorised into Val group (GG; n=15) and Met group (GG/AG; n=17) and NRG1 genotypes were categorised into AA group (n=12) and AG/GG group (n=20).

RESULTS

The reduction in auditory hallucination sub-scale score was significantly affected by COMT-GG genotype [Time×COMT interaction: F(1,28)=10.55, p=0.003, ɳ2=0.27]. Further, COMT-GG effect was epistatically influenced by the co-occurrence of NRG1-AA genotype [Time×COMT×NRG1 interaction: F(1,28)=8.09, p=0.008, ɳ2=0.22]. Irrespective of genotype, females showed better tDCS response than males [Time×Sex interaction: F(1,21)=4.67, p=0.04, ɳ2=0.18].

CONCLUSION

COMT-GG and NRG1-AA genotypes aid the tDCS-induced improvement in AVHs in schizophrenia patients. Our preliminary observations need replication and further systematic research to understand the neuroplastic gene determinants that modulate the effect of tDCS.

The Intersection of Central Dopamine System and Stroke: Potential Avenues Aiming at Enhancement of Motor Recovery

Dopamine, a major neurotransmitter, plays a role in a wide range of brain sensorimotor functions. Parkinson's disease and schizophrenia are two major human neuropsychiatric disorders typically associated with dysfunctional dopamine activity levels, which can be alleviated through the druggability of the dopaminergic systems. Meanwhile, several studies suggest that optimal brain dopamine activity levels are also significantly impacted in other serious neurological conditions, notably stroke, but this has yet to be fully appreciated at both basic and clinical research levels. This is of utmost importance as there is a need for better treatments to improve recovery from stroke. Here, we discuss the state of knowledge regarding the modulation of dopaminergic systems following stroke, and the use of dopamine boosting therapies in animal stroke models to improve stroke recovery. Indeed, studies in animals and humans show stroke leads to changes in dopamine functioning. Moreover, evidence from animal stroke models suggests stimulation of dopamine receptors may be a promising therapeutic approach for enhancing motor recovery from stroke. With respect to the latter, we discuss the evidence for several possible receptor-linked mechanisms by which improved motor recovery may be mediated. One avenue of particular promise is the subtype-selective stimulation of dopamine receptors in conjunction with physical therapy. However, results from clinical trials so far have been more mixed due to a number of potential reasons including, targeting of the wrong patient populations and use of drugs which modulate a wide array of receptors. Notwithstanding these issues, it is hoped that future research endeavors will assist in the development of more refined dopaminergic therapeutic approaches to enhance stroke recovery.

Age-Modulated Associations between KIBRA, Brain Volume, and Verbal Memory among Healthy Older Adults

The resource modulation hypothesis suggests that the influence of genes on cognitive functioning increases with age. The KIBRA single nucleotide polymorphism rs17070145, associated with episodic memory and working memory, has been suggested to follow such a pattern, but few studies have tested this assertion directly. The present study investigated the relationship between KIBRA alleles (T carriers vs. CC homozygotes), cognitive performance, and brain volumes in three groups of cognitively healthy adults-middle aged (ages 52-64, n = 38), young old (ages 65-72, n = 45), and older old (ages 73-92, n = 62)-who were carefully matched on potentially confounding variables including apolipoprotein ε4 status and hypertension. Consistent with our prediction, T carriers maintained verbal memory performance with increasing age while CC homozygotes declined. Voxel-based morphometric analysis of magnetic resonance images showed an advantage for T carriers in frontal white matter volume that increased with age. Focusing on the older old group, this advantage for T carriers was also evident in left lingual gyrus gray matter and several additional frontal white matter regions. Contrary to expectations, neither KIBRA nor the interaction between KIBRA and age predicted hippocampal volumes. None of the brain regions investigated showed a CC homozygote advantage. Taken together, these data suggest that KIBRA results in decreased verbal memory performance and lower brain volumes in CC homozygotes compared to T carriers, particularly among the oldest old, consistent with the resource modulation hypothesis.

Interindividual variability in response to continuous theta-burst stimulation in healthy adults

OBJECTIVE

We used complete-linkage cluster analysis to identify healthy subpopulations with distinct responses to continuous theta-burst stimulation (cTBS).

METHODS

21 healthy adults (age±SD, 36.9±15.2years) underwent cTBS of left motor cortex. Natural log-transformed motor evoked potentials (LnMEPs) at 5-50min post-cTBS (T5-T50) were calculated.

RESULTS

Two clusters were found; Group 1 (n=12) that showed significant MEP facilitation at T15, T20, and T50 (p's<0.006), and Group 2 (n=9) that showed significant suppression at T5-T15 (p's<0.022). LnMEPs at T10 and T40 were best predictors of, and together accounted for 80% of, cluster assignment. In an exploratory analysis, we examined the roles of brain-derived neurotrophic factor (BDNF) and apolipoprotein E (APOE) polymorphisms in the cTBS response. Val66Met participants showed greater facilitation at T10 than Val66Val participants (p=0.025). BDNF and cTBS intensity predicted 59% of interindividual variability in LnMEP at T10. APOE did not significantly affect LnMEPs at any time point (p's>0.32).

CONCLUSIONS

Data-driven cluster analysis can identify healthy subpopulations with distinct cTBS responses. T10 and T40 LnMEPs were best predictors of cluster assignment. T10 LnMEP was influenced by BDNF polymorphism and cTBS intensity.

SIGNIFICANCE

Healthy adults can be sorted into subpopulations with distinct cTBS responses that are influenced by genetics.

Effects of the Brain-Derived Neurotrophic Factor Val66Met polymorphism and resting brain functional connectivity on individual differences in tactile cognitive performance in healthy young adults

Cognitive processes involve input from multiple sensory modalities and obvious differences in the level of cognitive function can be observed between individuals. Evidence to date understanding the biological basis of tactile cognitive variability, however, is limited compared with other forms of sensory cognition. Data from auditory and visual cognition research suggest that variations in both genetics and intrinsic brain function might contribute to individual differences in tactile cognitive performance. In the present study, by using the tactual performance test (TPT), a widely used neuropsychological assessment tool, we investigated the effects of the brain-derived neurotrophic factor (BDNF) Val66Met polymorphism and resting-state brain functional connectivity (FC) on interindividual variability in TPT performance in healthy, young Chinese adults. Our results showed that the BDNF genotypes and resting-state FC had significant effects on the variability in TPT performance, together accounting for 32.5% and 19.1% of the variance on TPT total score and Memory subitem score respectively. Having fewer Met alleles, stronger anticorrelations between left posterior superior temporal gyrus and somatosensory areas (right postcentral gyrus and right parietal operculum cortex), and greater positive correlation between left parietal operculum cortex and left central opercular cortex, all correspond with better performance of TPT task. And FC between left parietal operculum cortex and left central opercular cortex might be a mediator of the relationship between BDNF genotypes and Memory subitem score. These data demonstrate a novel contribution of intrinsic brain function to tactile cognitive capacity, and further confirm the genetic basis of tactile cognition. Our findings might also explain the interindividual differences in cognitive ability observed in those who are blind and/or deaf from a new perspective.

Genetic Variation and Neuroplasticity: Role in Rehabilitation After Stroke

BACKGROUND AND PURPOSE

In many neurologic diagnoses, significant interindividual variability exists in the outcomes of rehabilitation. One factor that may impact response to rehabilitation interventions is genetic variation. Genetic variation refers to the presence of differences in the DNA sequence among individuals in a population. Genetic polymorphisms are variations that occur relatively commonly and, while not disease-causing, can impact the function of biological systems. The purpose of this article is to describe genetic polymorphisms that may impact neuroplasticity, motor learning, and recovery after stroke.

SUMMARY OF KEY POINTS

Genetic polymorphisms for brain-derived neurotrophic factor (BDNF), dopamine, and apolipoprotein E have been shown to impact neuroplasticity and motor learning. Rehabilitation interventions that rely on the molecular and cellular pathways of these factors may be impacted by the presence of the polymorphism. For example, it has been hypothesized that individuals with the BDNF polymorphism may show a decreased response to neuroplasticity-based interventions, decreased rate of learning, and overall less recovery after stroke. However, research to date has been limited and additional work is needed to fully understand the role of genetic variation in learning and recovery.

RECOMMENDATIONS FOR CLINICAL PRACTICE

Genetic polymorphisms should be considered as possible predictors or covariates in studies that investigate neuroplasticity, motor learning, or motor recovery after stroke. Future predictive models of stroke recovery will likely include a combination of genetic factors and other traditional factors (eg, age, lesion type, corticospinal tract integrity) to determine an individual's expected response to a specific rehabilitation intervention.

BDNF and LTP-/LTD-like plasticity of the primary motor cortex in Gilles de la Tourette syndrome

Gilles de la Tourette syndrome (GTS) is characterized by motor and vocal tics and often associated with obsessive-compulsive disorder (OCD). Responses to intermittent/continuous theta-burst stimulation (iTBS/cTBS), which probe long-term potentiation (LTP)-/depression (LTD)-like plasticity in the primary motor cortex (M1), are reduced in GTS. ITBS-/cTBS-induced M1 plasticity can be affected by brain-derived neurotrophic factor (BDNF) polymorphism. We investigated whether the BDNF polymorphism influences iTBS-/cTBS-induced LTP-/LTD-like M1 plasticity in 50 GTS patients and in 50 age- and sex-matched healthy subjects. In GTS patients, motor and psychiatric (OCD) symptom severity was rated using the Yale Global Tic Severity Scale (YGTSS) and the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS). We compared M1 iTBS-/cTBS-induced plasticity in healthy subjects and in patients with GTS. We also compared responses to TBS according to BDNF polymorphism (Val/Val vs Met carriers) in patients and controls. Fourteen healthy subjects and 13 GTS patients were Met carriers. When considering the whole group of controls, as expected, iTBS increased whereas cTBS decreased MEPs. Differently, iTBS/cTBS failed to induce LTP-/LTD-like plasticity in patients with GTS. When comparing responses to TBS according to BDNF polymorphism, in healthy subjects, Met carriers showed reduced MEP changes compared with Val/Val individuals. Conversely, in patients with GTS, responses to iTBS/cTBS were comparable in Val/Val individuals and Met carriers. YGTSS and Y-BOCS scores were comparable in Met carriers and in Val/Val subjects. We conclude that iTBS and cTBS failed to induce LTP-/LTD-like plasticity in patients with GTS, and this was not affected by BDNF genotype.

Variations in COMT and NTRK2 Influence Symptom Burden in Women Undergoing Breast Cancer Treatment

Women with breast cancer frequently report distressing symptoms during and after treatment that can significantly erode quality of life (QOL). Symptom burden among women with breast cancer is of complex etiology and is likely influenced by disease, treatment, and environmental factors as well as individual genetic differences. The purpose of the present study was to examine the relationships between genetic polymorphisms within Neurotrophic tyrosine kinase receptor 1 (NTRK1), Neurotrophic tyrosine kinase receptor 2 (NTRK2), and catechol-O-methyltransferase ( COMT) and patient symptom burden of QOL, pain, fatigue, anxiety, depression, and sleep disturbance before, during, and after treatment for breast cancer in a subset of participants ( N = 51) in a randomized clinical trial of a novel symptom-management modality for women with breast cancer undergoing chemotherapy. Patients were recruited at the time of initial breast cancer diagnosis and completed all survey measures at the time of recruitment, after the initiation of treatment (surgery and/or chemotherapy), and then following treatment conclusion. Multiple linear regression analyses revealed significant associations between NTRK2 and COMT single nucleotide polymorphism (SNP) genotype and symptom burden. Two COMT variants were associated with the specific symptoms of anxiety and QOL measures prior to the initiation of chemotherapy as well as pain interference and severity during and after treatment. Genotype at the NTRK2 SNP rs1212171 was associated with both sleep disturbance and fatigue. These findings, while exploratory, indicate that the genotypes of NTRK2 and COMT may contribute to relative risk for symptom burden during and shortly after the period of chemotherapy in women with early stage breast cancer.

High-Intensity Locomotor Exercise Increases Brain-Derived Neurotrophic Factor in Individuals with Incomplete Spinal Cord Injury

High-intensity locomotor exercise is suggested to contribute to improved recovery of locomotor function after neurological injury. This may be secondary to exercise-intensity-dependent increases in neurotrophin expression demonstrated previously in control subjects. However, rigorous examination of intensity-dependent changes in neurotrophin levels is lacking in individuals with motor incomplete spinal cord injury (SCI). Therefore, the primary aim of this study was to evaluate the effect of locomotor exercise intensity on peripheral levels of brain-derived neurotrophic factor (BDNF) in individuals with incomplete SCI. We also explored the impact of the Val66Met single-nucleotide polymorphism (SNP) on the BDNF gene on intensity-dependent changes. Serum concentrations of BDNF and insulin-like growth factor-1 (IGF-1), as well as measures of cardiorespiratory dynamics, were evaluated across different levels of exercise intensity achieved during a graded-intensity, locomotor exercise paradigm in 11 individuals with incomplete SCI. Our results demonstrate a significant increase in serum BDNF at high, as compared to moderate, exercise intensities (p = 0.01) and 15 and 30 min post-exercise (p < 0.01 for both), with comparison to changes at low intensity approaching significance (p = 0.05). Serum IGF-1 demonstrated no intensity-dependent changes. Significant correlations were observed between changes in BDNF and specific indicators of exercise intensity (e.g., rating of perceived exertion; R = 0.43; p = 0.02). Additionally, the data suggest that Val66Met SNP carriers may not exhibit intensity-dependent changes in serum BDNF concentration. Given the known role of BDNF in experience-dependent neuroplasticity, these preliminary results suggest that exercise intensity modulates serum BDNF concentrations and may be an important parameter of physical rehabilitation interventions after neurological injury.

Genetic Modulation of Transcranial Direct Current Stimulation Effects on Cognition

High inter-individual variability substantially challenges the explanatory power of studies on the modulation of cognitive functions with transcranial direct current stimulation (tDCS). These differences in responsivity have been linked with a critical state-dependency of stimulation effects. In general, genetic diversity is a decisive biological basis of variations in neuronal network functioning. Therefore, it is most likely that inter-individual variability of tDCS-induced changes in cognitive functions is due to specific interactions between genetically determined network properties and the specific type of stimulation. In this context, predominantly the brain-derived neurotrophic factor (BDNF) Val66Met and the catechol-O-methyltransferase (COMT) Val108/158Met polymorphisms have been investigated. The studies on the interaction between the BDNF Val66Met polymorphism and the effect of brain stimulation indicate a critical but yet heterogeneous interaction. But up to now, data on the interplay between this polymorphism and tDCS on cognitive functioning are not available. However, recently, the functional Val(108/158)Met polymorphism in the COMT gene, that is particularly involved in the regulation of executive functions by means of the dopaminergic tone in frontal brain areas, has been demonstrated to specifically predict the effect of tDCS on cognitive control. Following an inverted U-shaped function, the high dopaminergic activity in Met allele homozygous individuals has been shown to be associated with a reduction of executive functioning by anodal tDCS to the prefrontal cortex. Consistently, Val homozygous individuals with lower dopaminergic tone show a clear reduction of response inhibition with cathodal tDCS. These findings exemplify the notion of a complex but neurophysiologically consistent interaction between genetically determined variations of neuronal activity and tDCS, particularly in the cognitive domain. Consequently, a systematic analysis and consideration of genetic modulators of tDCS effects will be helpful to improve the efficacy of brain stimulation and particularly tDCS in the investigation and treatment of cognitive functions.

Fluoxetine Does Not Enhance Visual Perceptual Learning and Triazolam Specifically Impairs Learning Transfer

The selective serotonin reuptake inhibitor fluoxetine significantly enhances adult visual cortex plasticity within the rat. This effect is related to decreased gamma-aminobutyric acid (GABA) mediated inhibition and identifies fluoxetine as a potential agent for enhancing plasticity in the adult human brain. We tested the hypothesis that fluoxetine would enhance visual perceptual learning of a motion direction discrimination (MDD) task in humans. We also investigated (1) the effect of fluoxetine on visual and motor cortex excitability and (2) the impact of increased GABA mediated inhibition following a single dose of triazolam on post-training MDD task performance. Within a double blind, placebo controlled design, 20 healthy adult participants completed a 19-day course of fluoxetine (n = 10, 20 mg per day) or placebo (n = 10). Participants were trained on the MDD task over the final 5 days of fluoxetine administration. Accuracy for the trained MDD stimulus and an untrained MDD stimulus configuration was assessed before and after training, after triazolam and 1 week after triazolam. Motor and visual cortex excitability were measured using transcranial magnetic stimulation. Fluoxetine did not enhance the magnitude or rate of perceptual learning and full transfer of learning to the untrained stimulus was observed for both groups. After training was complete, trazolam had no effect on trained task performance but significantly impaired untrained task performance. No consistent effects of fluoxetine on cortical excitability were observed. The results do not support the hypothesis that fluoxetine can enhance learning in humans. However, the specific effect of triazolam on MDD task performance for the untrained stimulus suggests that learning and learning transfer rely on dissociable neural mechanisms.

Interaction Effects of BDNF and COMT Genes on Resting-State Brain Activity and Working Memory

Catechol-O-methyltransferase (COMT) and brain-derived neurotrophic factor (BDNF) genes have been found to interactively influence working memory (WM) as well as brain activation during WM tasks. However, whether the two genes have interactive effects on resting-state activities of the brain and whether these spontaneous activations correlate with WM are still unknown. This study included behavioral data from WM tasks and genetic data (COMT rs4680 and BDNF Val66Met) from 417 healthy Chinese adults and resting-state fMRI data from 298 of them. Significant interactive effects of BDNF and COMT were found for WM performance as well as for resting-state regional homogeneity (ReHo) in WM-related brain areas, including the left medial frontal gyrus (lMeFG), left superior frontal gyrus (lSFG), right superior and medial frontal gyrus (rSMFG), right medial orbitofrontal gyrus (rMOFG), right middle frontal gyrus (rMFG), precuneus, bilateral superior temporal gyrus, left superior occipital gyrus, right middle occipital gyrus, and right inferior parietal lobule. Simple effects analyses showed that compared to other genotypes, subjects with COMT-VV/BDNF-VV had higher WM and lower ReHo in all five frontal brain areas. The results supported the hypothesis that COMT and BDNF polymorphisms influence WM performance and spontaneous brain activity (i.e., ReHo).

Cellular and System Biology of Memory: Timing, Molecules, and Beyond

The storage of information in the mammalian nervous systems is dependent on a delicate balance between change and stability of neuronal networks. The induction and maintenance of processes that lead to changes in synaptic strength to a multistep process which can lead to long-lasting changes, which starts and ends with a highly choreographed and perfectly timed dance of molecules in different cell types of the central nervous system. This is accompanied by synchronization of specific networks, resulting in the generation of characteristic "macroscopic" rhythmic electrical fields, whose characteristic frequencies correspond to certain activity and information-processing states of the brain. Molecular events and macroscopic fields influence each other reciprocally. We review here cellular processes of synaptic plasticity, particularly functional and structural changes, and focus on timing events that are important for the initial memory acquisition, as well as mechanisms of short- and long-term memory storage. Then, we cover the importance of epigenetic events on the long-time range. Furthermore, we consider how brain rhythms at the network level participate in processes of information storage and by what means they participating in it. Finally, we examine memory consolidation at the system level during processes of sleep.

Genetic polymorphisms and the adequacy of brain stimulation: state of the art

INTRODUCTION

Heterogeneity of therapeutic response to brain stimulation techniques has inspired scientists to uncover the secrets to success or failure of these projects. Genetic polymorphisms are one of the major causes of this heterogeneity.

AREAS COVERED

More than twenty genetic variants within more than ten genes (e.g. BDNF, COMT, DRD2, TRPV1, 5-HT1A, 5-HHT, P2RX7, VEGF, TPH1, TPH2, ACE, APOE, GNB3, NET, NMDA receptors, and RGS4) have been investigated, among which the BDNF gene and its polymorphism, Val66Met, is the best documented variant. We review the genotypic combinations, which are reported to interact with the work of brain stimulation, of which the DRD2 C957T polymorphism is the most prominent type. Finally, implications of transcranial magnetic stimulation in deciphering the interaction between genetic background (e.g. SCN1A and 5-HTT) and drugs (e.g. carbamazepine and citalopram) at the cortical excitability level is explained. Expert commentary: Studies are ongoing to find missing factors responsible for heterogeneity of response to brain stimulation techniques. Further knowledge about genetic factors affecting the therapeutic response to brain stimulation techniques might provide helpful guidelines for choosing ideal candidates for treatment.

BDNF Genotype Interacts with Motor Function to Influence Rehabilitation Responsiveness Poststroke

BACKGROUND

Persistent motor impairment is common but highly heterogeneous poststroke. Genetic polymorphisms, including those identified on the brain-derived neurotrophic factor (BDNF) and apolipoprotein E (APOE) genes, may contribute to this variability by limiting the capacity for use-dependent neuroplasticity, and hence rehabilitation responsiveness.

OBJECTIVE

To determine whether BDNF and APOE genotypes influence motor improvement facilitated by poststroke upper-limb rehabilitation.

METHODS

BDNF-Val66Met and APOE isoform genotypes were determined using leukocyte DNA for 55 community-dwelling patients 2-123 months poststroke. All patients completed a dose-matched upper-limb rehabilitation program of either Wii-based Movement Therapy or Constraint-induced Movement Therapy. Upper-limb motor function was assessed pre- and post-therapy using a suite of functional measures.

RESULTS

Motor function improved for all patients post-therapy, with no difference between therapy groups. In the pooled data, there was no significant effect of BDNF or APOE genotype on motor function at baseline, or following the intervention. However, a significant interaction between the level of residual motor function and BDNF genotype was identified (p = 0.029), whereby post-therapy improvement was significantly less for Met allele carriers with moderate and high, but not low motor function. There was no significant association between APOE genotype and therapy outcomes.

CONCLUSION

This study identified a novel interaction between the BDNF-Val66Met polymorphism, motor-function status, and the magnitude of improvement with rehabilitation in chronic stroke. This polymorphism does not preclude, but may reduce, the magnitude of motor improvement with therapy, particularly for patients with higher, but not lower residual motor function. BDNF genotype should be considered in the design and interpretation of clinical trials.

Interaction of COMT rs4680 and BDNF rs6265 polymorphisms on functional connectivity density of the left frontal eye field in healthy young adults

As modulators of dopamine availability and release in the brain, COMT and BDNF polymorphisms have demonstrated interactions on human cognition; however, the underlying neural mechanisms remain largely unknown. In this study, we aimed to investigate the interactions of COMT rs4680 and BDNF rs6265 on global functional connectivity density (gFCD) of the brain in 265 healthy young subjects. We found a significant COMT × BDNF interaction on the gFCD in the left frontal eye field (FEF), showing an inverted U-shape modulation by the presumed dopamine signaling. This finding was consistently repeated in the gFCD analyses using other four connection thresholds. Our findings reveal a COMT × BDNF interaction on the FCD in the left FEF, which may be helpful for understanding the neural mechanisms of the COMT × BDNF interactions on the FEF-related cognitive functions. Hum Brain Mapp 37:2468-2478, 2016. © 2016 Wiley Periodicals, Inc.

Does transcranial direct current stimulation enhance cognitive and motor functions in the ageing brain? A systematic review and meta- analysis

The use of transcranial direct current stimulation (tDCS) to enhance cognitive and motor functions has enjoyed a massive increase in popularity. Modifying neuroplasticity via non-invasive cortical stimulation has enormous potential to slow or even reverse declines in functions associated with ageing. The current meta-analysis evaluated the effects of tDCS on cognitive and motor performance in healthy older adults. Of the 81 studies identified, 25 qualified for inclusion. A random effects model meta-analysis revealed a significant overall standardized mean difference equal to 0.53 (SE=0.09; medium heterogeneity: I(2)=57.08%; and high fail-safe: N=448). Five analyses on moderator variables indicated significant tDCS beneficial effects: (a) on both cognitive and motor task performances, (b) across a wide-range of cognitive tasks, (c) on specific brain areas, (d) stimulation offline (before) or online (during) the cognitive and motor tasks. Although the meta-analysis revealed robust support for enhancing both cognitive and motor performance, we outline a number of caveats on the use of tDCS.