Noninvasive human brain stimulation

Technical aspects of neurostimulation: Focus on equipment, electric field modeling, and stimulation protocols

Neuromodulation is a field of science, medicine, and bioengineering that encompasses implantable and non-implantable technologies for the purpose of improving quality of life and functioning of humans. Brain neuromodulation involves different neurostimulation techniques: transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), vagus nerve stimulation (VNS), and deep brain stimulation (DBS), which are being used both to study their effects on cognitive brain functions and to treat neuropsychiatric disorders. The mechanisms of action of neurostimulation remain incompletely understood. Insight into the technical basis of neurostimulation might be a first step towards a more profound understanding of these mechanisms, which might lead to improved clinical outcome and therapeutic potential. This review provides an overview of the technical basis of neurostimulation focusing on the equipment, the present understanding of induced electric fields, and the stimulation protocols. The review is written from a technical perspective aimed at supporting the use of neurostimulation in clinical practice.

A systematic review of the clinical efficacy of transcranial direct current stimulation (tDCS) in psychiatric disorders

Transcranial direct current stimulation (tDCS) is a non-invasive neuromodulation technique, which can be used to selectively disrupt patterns of neural activity that are associated with symptoms of mental illness. tDCS has been implemented in numerous therapeutic trials across a range of patient populations, with a rapidly increasing number of studies being published each year. This systematic review aimed to evaluate the efficacy of tDCS in the treatment of psychiatric disorders. Four electronic databases were searched from inception until December 2015 by two independent reviewers, and 66 eligible studies were identified. Depression was the most extensively researched condition, followed by schizophrenia and substance use disorders. Data on obsessive compulsive disorder, generalised anxiety disorder, and anorexia nervosa were also obtained. The quality of included studies was appraised using a standardised assessment framework, which yielded a median score corresponding to "weak" on the three-point scale. This improved to "moderate" when case reports/series were excluded from the analysis. Overall, data suggested that tDCS interventions comprising multiple sessions can ameliorate symptoms of several major psychiatric disorders, both acutely and in the long-term. Nevertheless, the tDCS field is still in its infancy, and several methodological and ethical issues must be addressed before clinical efficacy can truly be determined. Studies probing the mechanisms of action of tDCS and those facilitating the definition of optimised stimulation protocols are warranted. Furthermore, evidence from large-scale, multi-centre randomised controlled trials is required if the transition of this therapy from the laboratory to the clinic is to be considered.

Therapeutic Efficacy of Neurostimulation for Depression: Techniques, Current Modalities, and Future Challenges

Depression is the most prevalent debilitating mental illness; it is characterized as a disorder of mood, cognitive function, and neurovegetative function. About one in ten individuals experience depression at some stage of their lives. Antidepressant drugs are used to reduce the symptoms but relapse occurs in ~20% of patients. However, alternate therapies like brain stimulation techniques have shown promising results in this regard. This review covers the brain stimulation techniques electroconvulsive therapy, transcranial direct current stimulation, repetitive transcranial magnetic stimulation, vagus nerve stimulation, and deep brain stimulation, which are used as alternatives to antidepressant drugs, and elucidates their research and clinical outcomes.

Neuroplastic Effects of Transcranial Direct Current Stimulation on Painful Symptoms Reduction in Chronic Hepatitis C: A Phase II Randomized, Double Blind, Sham Controlled Trial

Introduction: Pegylated Interferon Alpha (Peg-IFN) in combination with other drugs is the standard treatment for chronic hepatitis C infection (HCV) and is related to severe painful symptoms. The aim of this study was access the efficacy of transcranial direct current stimulation (tDCS) in controlling the painful symptoms related to Peg-IFN side effects.

Materials and Methods: In this phase II double-blind trial, twenty eight (n = 28) HCV subjects were randomized to receive either 5 consecutive days of active tDCS (n = 14) or sham (n = 14) during 5 consecutive days with anodal stimulation over the primary motor cortex region using 2 mA for 20 min. The primary outcomes were visual analogue scale (VAS) pain and brain-derived neurotrophic factor (BDNF) serum levels. Secondary outcomes were the pressure-pain threshold (PPT), the Brazilian Profile of Chronic Pain: Screen (B-PCP:S), and drug analgesics use.

Results: tDCS reduced the VAS scores (P < 0.003), with a mean pain drop of 56% (p < 0.001). Furthermore, tDCS was able to enhance BDNF levels (p < 0.01). The mean increase was 37.48% in the active group. Finally, tDCS raised PPT (p < 0.001) and reduced the B-PCP:S scores and analgesic use (p < 0.05).

Conclusions: Five sessions of tDCS were effective in reducing the painful symptoms in HCV patients undergoing Peg-IFN treatment. These findings support the efficacy of tDCS as a promising therapeutic tool to improve the tolerance of the side effects related to the use of Peg-IFN. Future larger studies (phase III and IV trials) are needed to confirm the clinical use of the therapeutic effects of tDCS in such condition.

Trial registration: Brazilian Human Health Regulator for Research with the approval number CAAE 07802012.0.0000.5327.

A theoretical framework for studying the electromagnetic stimulation of nervous tissue

In this paper we present a model for calculating the electric field, and its spatial derivatives, produced by arbitrarily shaped, oriented and placed coils carrying time-varying currents. The model has been validated by comparing its results with those obtained using FEM simulations. The model provides a simple and fast computation framework to investigate the electromagnetic stimulation of neural tissues. Some example applications are also provided.

Using fMRI to study reward processing in humans: past, present, and future

Functional magnetic resonance imaging (fMRI) is a noninvasive tool used to probe cognitive and affective processes. Although fMRI provides indirect measures of neural activity, the advent of fMRI has allowed for1) the corroboration of significant animal findings in the human brain, and2) the expansion of models to include more common human attributes that inform behavior. In this review, we briefly consider the neural basis of the blood oxygenation level dependent signal to set up a discussion of how fMRI studies have applied it in examining cognitive models in humans and the promise of using fMRI to advance such models. Specifically, we illustrate the contribution that fMRI has made to the study of reward processing, focusing on the role of the striatum in encoding reward-related learning signals that drive anticipatory and consummatory behaviors. For instance, we discuss how fMRI can be used to link neural signals (e.g., striatal responses to rewards) to individual differences in behavior and traits. While this functional segregation approach has been constructive to our understanding of reward-related functions, many fMRI studies have also benefitted from a functional integration approach that takes into account how interconnected regions (e.g., corticostriatal circuits) contribute to reward processing. We contend that future work using fMRI will profit from using a multimodal approach, such as combining fMRI with noninvasive brain stimulation tools (e.g., transcranial electrical stimulation), that can identify causal mechanisms underlying reward processing. Consequently, advancements in implementing fMRI will promise new translational opportunities to inform our understanding of psychopathologies.

tES Stimulation as a Tool to Investigate Cognitive Processes in Healthy Individuals

Abstract. This paper is aimed at providing an introduction to up-to-date noninvasive brain stimulation tools that have been successful in modulating higher-level cognitive functions in healthy individuals. The current review focuses on transcranial electrical stimulation (tES) studies aiming to explore cognitive models from an experimental rather than clinical viewpoint. It focuses primarily on major advances in language, working memory, learning, response inhibition, and other executive functions in healthy individuals, and the use of different methods of electrical brain stimulation such as transcranial direct current stimulation (tDCS), transcranial alternating current stimulation (tACS), and transcranial random noise stimulation (tRNS). The final section summarizes the scientific novelty of the reviewed papers and discusses the possible roles of brain stimulation in future experimental research and clinical applications.

Transcranial direct current stimulation for the treatment of post-stroke depression in aphasic patients: a case series

Aphasia is a common consequence of stroke; it is estimated that about two-thirds of aphasic patients will develop depression in the first year after the stroke. Treatment of post-stroke depression (PSD) is challenging due to the adverse effects of pharmacotherapy and difficulties in evaluating clinical outcomes, including aphasia. Transcranial direct current stimulation (tDCS) is a novel treatment that may improve clinical outcomes in the traditionally pharmacotherapy-refractory PSD. Our aim was to evaluate the safety and efficacy of tDCS for patients with PSD and with aphasia. The Stroke Aphasic Depression Questionnaire (SADQ) and the Aphasic Depression Rating Scale (ADRS) were used to evaluate the severity of PSD. The diagnoses of PSD and aphasia were confirmed by a psychiatrist and a speech-language pathologist, respectively. In this open case series, patients (n = 4) received 10 sessions (once a day) of bilateral tDCS to the dorsolateral prefrontal cortex (DLPFC) and two additional sessions after two and four weeks, for a total of 12 sessions. All patients exhibited improvement in depression after tDCS, as indicated by a decrease in SADQ (47.5%) and in ADRS (65.7%). This improvement was maintained four weeks after the treatment. In this preliminary, open-label study conducted in four PSD patients with aphasia, bilateral tDCS over the DLPFC was shown to induce a substantial mood improvement; tDCS was safe and well tolerated by every patient. Stroke patients with aphasia can be safely treated for PSD with tDCS. Sham-controlled studies are necessary to evaluate this technique further.

Effects of non-invasive brain stimulation on post-stroke dysphagia: A systematic review and meta-analysis of randomized controlled trials

OBJECTIVE

The primary aim of this review is to evaluate the effects of non-invasive brain stimulation on post-stroke dysphagia.

METHODS

Thirteen databases were systematically searched through July 2014. Studies had to meet pre-specified inclusion and exclusion criteria. Each study's methodological quality was examined. Effect sizes were calculated from extracted data and combined for an overall summary statistic.

RESULTS

Eight randomized controlled trials were included. These trials revealed a significant, moderate pooled effect size (0.55; 95% CI=0.17, 0.93; p=0.004). Studies stimulating the affected hemisphere had a combined effect size of 0.46 (95% CI=-0.18, 1.11; p=0.16); studies stimulating the unaffected hemisphere had a combined effect size of 0.65 (95% CI=0.14, 1.16; p=0.01). At long-term follow up, three studies demonstrated a large but non-significant pooled effect size (0.81, p=0.11).

CONCLUSIONS

This review found evidence for the efficacy of non-invasive brain stimulation on post-stroke dysphagia. A significant effect size resulted when stimulating the unaffected rather than the affected hemisphere. This finding is in agreement with previous studies implicating the plasticity of cortical neurons in the unaffected hemisphere.

SIGNIFICANCE

Non-invasive brain stimulation appears to assist cortical reorganization in post-stroke dysphagia but emerging factors highlight the need for more data.

Transcranial magnetic stimulation in autism spectrum disorder: Challenges, promise, and roadmap for future research

Autism Spectrum Disorder (ASD) is a behaviorally defined complex neurodevelopmental syndrome characterized by impairments in social communication, by the presence of restricted and repetitive behaviors, interests and activities, and by abnormalities in sensory reactivity. Transcranial magnetic stimulation (TMS) is a promising, emerging tool for the study and potential treatment of ASD. Recent studies suggest that TMS measures provide rapid and noninvasive pathophysiological ASD biomarkers. Furthermore, repetitive TMS (rTMS) may represent a novel treatment strategy for reducing some of the core and associated ASD symptoms. However, the available literature on the TMS use in ASD is preliminary, composed of studies with methodological limitations. Thus, off-label clinical rTMS use for therapeutic interventions in ASD without an investigational device exemption and outside of an IRB approved research trial is premature pending further, adequately powered and controlled trials. Leaders in this field have gathered annually for a two-day conference (prior to the 2014 and 2015 International Meeting for Autism Research, IMFAR) to share recent progress, promote collaboration across laboratories, and establish consensus on protocols. Here we review the literature in the use of TMS in ASD in the context of the unique challenges required for the study and exploration of treatment strategies in this population. We also suggest future directions for this field of investigations. While its true potential in ASD has yet to be delineated, TMS represents an innovative research tool and a novel, possibly transformative approach to the treatment of neurodevelopmental disorders.

Systems Neuroengineering: Understanding and Interacting with the Brain

In this paper, we review the current state-of-the-art techniques used for understanding the inner workings of the brain at a systems level. The neural activity that governs our everyday lives involves an intricate coordination of many processes that can be attributed to a variety of brain regions. On the surface, many of these functions can appear to be controlled by specific anatomical structures; however, in reality, numerous dynamic networks within the brain contribute to its function through an interconnected web of neuronal and synaptic pathways. The brain, in its healthy or pathological state, can therefore be best understood by taking a systems-level approach. While numerous neuroengineering technologies exist, we focus here on three major thrusts in the field of systems neuroengineering: neuroimaging, neural interfacing, and neuromodulation. Neuroimaging enables us to delineate the structural and functional organization of the brain, which is key in understanding how the neural system functions in both normal and disease states. Based on such knowledge, devices can be used either to communicate with the neural system, as in neural interface systems, or to modulate brain activity, as in neuromodulation systems. The consideration of these three fields is key to the development and application of neuro-devices. Feedback-based neuro-devices require the ability to sense neural activity (via a neuroimaging modality) through a neural interface (invasive or noninvasive) and ultimately to select a set of stimulation parameters in order to alter neural function via a neuromodulation modality. Systems neuroengineering refers to the use of engineering tools and technologies to image, decode, and modulate the brain in order to comprehend its functions and to repair its dysfunction. Interactions between these fields will help to shape the future of systems neuroengineering-to develop neurotechniques for enhancing the understanding of whole-brain function and dysfunction, and the management of neurological and mental disorders.

MRI Guided Brain Stimulation without the Use of a Neuronavigation System

A key issue in the field of noninvasive brain stimulation (NIBS) is the accurate localization of scalp positions that correspond to targeted cortical areas. The current gold standard is to combine structural and functional brain imaging with a commercially available "neuronavigation" system. However, neuronavigation systems are not commonplace outside of specialized research environments. Here we describe a technique that allows for the use of participant-specific functional and structural MRI data to guide NIBS without a neuronavigation system. Surface mesh representations of the head were generated using Brain Voyager and vectors linking key anatomical landmarks were drawn on the mesh. Our technique was then used to calculate the precise distances on the scalp corresponding to these vectors. These calculations were verified using actual measurements of the head and the technique was used to identify a scalp position corresponding to a brain area localized using functional MRI.

Combined exercise and transcranial direct current stimulation intervention for knee osteoarthritis: protocol for a pilot randomised controlled trial

INTRODUCTION

Osteoarthritis (OA) is a major health problem and a leading cause of disability. The knee joint is commonly affected, resulting in pain and physical dysfunction. Exercise is considered the cornerstone of conservative management, yet meta-analyses indicate, at best, moderate effect sizes. Treatments that bolster the effects of exercise, such as transcranial direct current stimulation (tDCS), may improve outcomes in knee OA. The aims of this pilot study are to (1) determine the feasibility, safety and perceived patient response to a combined tDCS and exercise intervention in knee OA, and (2) provide data to support a sample size calculation for a fully-powered trial should trends of effectiveness be present.

METHODS AND ANALYSIS

A pilot randomised, assessor-blind and participant-blind, sham-controlled trial. 20 individuals with knee OA who report a pain score of 40 or more on a 100 mm visual analogue scale on walking, and meet a priori selection criteria will be randomly allocated to receive either: (1) active tDCS plus exercise, or (2) sham tDCS plus exercise. All participants will receive 20 min of either active or sham tDCS immediately prior to 30 min of supervised muscle strengthening exercise twice a week for 8 weeks. Participants in both groups will also complete unsupervised home exercises twice per week. Outcome measures of feasibility, safety, pain, disability and pain system function will be assessed immediately before and after the 8-week intervention. Analyses of feasibility and safety will be performed using descriptive statistics. Statistical analyses will be used to determine trends of effectiveness and will be based on intention-to-treat as well as per protocol.

ETHICS AND DISSEMINATION

This study was approved by the institutional ethics committee (H10184). Written informed consent will be obtained from all participants. The results of this study will be submitted for peer-reviewed publication.

TRIAL REGISTRATION NUMBER

ANZCTR365331.

Use of transcranial magnetic stimulation in autism spectrum disorders

The clinical, social and financial burden of autism spectrum disorder (ASD) is staggering. We urgently need valid and reliable biomarkers for diagnosis and effective treatments targeting the often debilitating symptoms. Transcranial magnetic stimulation (TMS) is beginning to be used by a number of centers worldwide and may represent a novel technique with both diagnostic and therapeutic potential. Here we critically review the current scientific evidence for the use of TMS in ASD. Though preliminary data suggests promise, there is simply not enough evidence yet to conclusively support the clinical widespread use of TMS in ASD, neither diagnostically nor therapeutically. Carefully designed and properly controlled clinical trials are warranted to evaluate the true potential of TMS in ASD.

Full-wave acoustic and thermal modeling of transcranial ultrasound propagation and investigation of skull-induced aberration correction techniques: a feasibility study

Background

Transcranial focused ultrasound (tcFUS) is an attractive noninvasive modality for neurosurgical interventions. The presence of the skull, however, compromises the efficiency of tcFUS therapy, as its heterogeneous nature and acoustic characteristics induce significant distortion of the acoustic energy deposition, focal shifts, and thermal gain decrease. Phased-array transducers allow for partial compensation of skull-induced aberrations by application of precalculated phase and amplitude corrections.

Methods

An integrated numerical framework allowing for 3D full-wave, nonlinear acoustic and thermal simulations has been developed and applied to tcFUS. Simulations were performed to investigate the impact of skull aberrations, the possibility of extending the treatment envelope, and adverse secondary effects. The simulated setup comprised an idealized model of the ExAblate Neuro and a detailed MR-based anatomical head model. Four different approaches were employed to calculate aberration corrections (analytical calculation of the aberration corrections disregarding tissue heterogeneities; a semi-analytical ray-tracing approach compensating for the presence of the skull; two simulation-based time-reversal approaches with and without pressure amplitude corrections which account for the entire anatomy). These impact of these approaches on the pressure and temperature distributions were evaluated for 22 brain-targets

Results

While (semi-)analytical approaches failed to induced high pressure or ablative temperatures in any but the targets in the close vicinity of the geometric focus, simulation-based approaches indicate the possibility of considerably extending the treatment envelope (including targets below the transducer level and locations several centimeters off the geometric focus), generation of sharper foci, and increased targeting accuracy. While the prediction of achievable aberration correction appears to be unaffected by the detailed bone-structure, proper consideration of inhomogeneity is required to predict the pressure distribution for given steering parameters

Conclusions

Simulation-based approaches to calculate aberration corrections may aid in the extension of the tcFUS treatment envelope as well as predict and avoid secondary effects (standing waves, skull heating). Due to their superior performance, simulationbased techniques may prove invaluable in the amelioration of skull-induced aberration effects in tcFUS therapy. The next steps are to investigate shear-wave-induced effects in order to reliably exclude secondary hot-spots, and to develop comprehensive uncertainty assessment and validation procedures.

The combined effects of neurostimulation and priming on creative thinking. A preliminary tDCS study on dorsolateral prefrontal cortex

The role of prefrontal cortex (PFC) in influencing creative thinking has been investigated by many researchers who, while succeeding in proving an effective involvement of PFC, reported suggestive but sometimes conflicting results. In order to better understand the relationships between creative thinking and brain activation in a more specific area of the PFC, we explored the role of dorsolateral PFC (DLPFC). We devised an experimental protocol using transcranial direct-current stimulation (tDCS). The study was based on a 3 (kind of stimulation: anodal vs. cathodal vs. sham) × 2 (priming: divergent vs. convergent) design. Forty-five healthy adults were randomly assigned to one stimulation condition. Participants' creativity skills were assessed using the Product Improvement subtest from the Torrance Tests of Creative Thinking (TTCT). After 20 min of tDCS stimulation, participants were presented with visual images of common objects. Half of the participants were instructed to visualize themselves using the object in an unusual way (divergent priming), whereas the other half were asked to visualize themselves while using the object in a common way (convergent priming). Priming was aimed at inducing participants to adopt different attitudes toward the creative task. Afterwards, participants were asked to describe all of the possible uses of the objects that were presented. Participants' physiological activation was recorded using a biofeedback equipment. Results showed a significant effect of anodal stimulation that enhanced creative performance, but only after divergent priming. Participants showed lower skin temperature values after cathodal stimulation, a finding which is coherent with studies reporting that, when a task is not creative or creative thinking is not prompted, people show lower levels of arousal. Differences in individual levels of creativity as assessed by the Product Improvement test were not influential. The involvement of DLPFC in creativity has been supported, presumably in association to shift of attention modulated by priming.

Organisation of the motor cortex differs between people with and without knee osteoarthritis

Introduction

The aim of this study was to investigate possible differences in the organisation of the motor cortex in people with knee osteoarthritis (OA) and whether there is an association between cortical organisation and accuracy of a motor task.

Methods

fMRI data were collected while 11 participants with moderate/severe right knee OA (6 male, 69 ± 6 (mean ± SD) years) and seven asymptomatic controls (5 male, 64 ± 6 years) performed three visually guided, variable force, force matching motor tasks involving isolated isometric muscle contractions of: 1) quadriceps (knee), 2) tibialis anterior (ankle) and, 3) finger/thumb flexor (hand) muscles. fMRI data were used to map the loci of peak activation in the motor cortex during the three tasks and to assess whether there were differences in the organisation of the motor cortex between the groups for the three motor tasks. Root mean square of the difference between target and generated forces during muscle contraction quantified task accuracy.

Results

A 4.1 mm anterior shift in the representation of the knee (p = 0.03) and swap of the relative position of the knee and ankle representations in the motor cortex (p = 0.003) were found in people with knee OA. Poorer performance of the knee task was associated with more anterior placement of motor cortex loci in people with (p = 0.05) and without (p = 0.02) knee OA.

Conclusions

Differences in the organisation of the motor cortex in knee OA was demonstrated in relation to performance of knee and ankle motor tasks and was related to quality of performance of the knee motor task. These results highlight the possible mechanistic link between cortical changes and modified motor behavior in people with knee OA.

The surprising temporal specificity of direct-current stimulation

As studies increasingly use transcranial direct-current stimulation (tDCS) to manipulate brain activity, surprising results are emerging. Specifically, research combining tDCS with electrophysiology is showing that the long-lasting effects of tDCS can counter-intuitively influence specific neural mechanisms active for as little as 100 ms during the flow of human information processing.

Increase in PAS-induced neuroplasticity after a treatment course of transcranial direct current stimulation for depression

BACKGROUND

Several lines of evidence suggest that neuroplasticity is impaired in depression and improves with effective treatment. However until now, this evidence has largely involved measures such as learning and memory which can be influenced by subject effort and motivation. This pilot study aimed to objectively measure neuroplasticity in the motor cortex using paired associative stimulation (PAS), which induces short term neuroplastic changes. It is hypothesized that neuroplasticity would improve after effective treatment for depression.

METHODS

Neuroplasticity was measured in 18 depressed subjects before and after a course of anodal transcranial direct current stimulation (tDCS), given as treatment for depression. The relationships between PAS results, mood state and brain-derived neurotrophic factor (BDNF) serum levels were examined.

RESULTS

Neuroplasticity (PAS-induced change) was increased after a course of tDCS (t(17)=-2.651, p=0.017). Treatment with tDCS also led to significant mood improvement, but this did not correlate with improved neuroplasticity. Serum BDNF levels did not change after tDCS, or correlate with change in neuroplasticity after tDCS treatment.

LIMITATIONS

While this study showed evidence of improved neuroplasticity in the motor cortex after effective treatment, we are unable to present evidence that this change is generalized in the depressed brain. Also, the presence of antidepressant medications and the small sample of patients (n=18) meant the study could not definitively resolve the relationship between neuroplasticity, mood and BDNF.

CONCLUSION

This novel preliminary study provides evidence that a treatment course of tDCS can improve neuroplasticity in depressed patients.

Spike-frequency adaptation of a two-compartment neuron modulated by extracellular electric fields

Spike-frequency adaptation has been shown to play an important role in neural coding. Based on a reduced two-compartment model, here we investigate how two common adaptation currents, i.e., voltage-sensitive potassium current (I(M)) and calcium-sensitive potassium current (I(AHP)), modulate neuronal responses to extracellular electric fields. It is shown that two adaptation mechanisms lead to distinct effects on the dynamical behavior of the neuron to electric fields. These effects depend on a neuronal morphological parameter that characterizes the ratio of soma area to total membrane area and internal coupling conductance. In the case of I(AHP) current, changing the morphological parameter switches spike initiation dynamics between saddle-node on invariant cycle bifurcation and supercritical Hopf bifurcation, whereas it only switches between subcritical and supercritical Hopf bifurcations for I(M) current. Unlike the morphological parameter, internal coupling conductance is unable to alter the bifurcation scenario for both adaptation currents. We also find that the electric field threshold for triggering neuronal steady-state firing is determined by two parameters, especially by the morphological parameter. Furthermore, the neuron with I(AHP) current generates mixed-mode oscillations through the canard phenomenon for some small values of the morphological parameter. All these results suggest that morphological properties play a critical role in field-induced effects on neuronal dynamics, which could qualitatively alter the outcome of adaptation by modulating internal current between soma and dendrite. The findings are readily testable in experiments, which could help to reveal the mechanisms underlying how the neuron responds to electric field stimulus.

The appropriate use of neurostimulation: stimulation of the intracranial and extracranial space and head for chronic pain. Neuromodulation Appropriateness Consensus Committee

INTRODUCTION

The International Neuromodulation Society (INS) has identified a need for evaluation and analysis of the practice of neurostimulation of the brain and extracranial nerves of the head to treat chronic pain.

METHODS

The INS board of directors chose an expert panel, the Neuromodulation Appropriateness Consensus Committee (NACC), to evaluate the peer-reviewed literature, current research, and clinical experience and to give guidance for the appropriate use of these methods. The literature searches involved key word searches in PubMed, EMBASE, and Google Scholar dated 1970-2013, which were graded and evaluated by the authors.

RESULTS

The NACC found that evidence supports extracranial stimulation for facial pain, migraine, and scalp pain but is limited for intracranial neuromodulation. High cervical spinal cord stimulation is an evolving option for facial pain. Intracranial neurostimulation may be an excellent option to treat diseases of the nervous system, such as tremor and Parkinson's disease, and in the future, potentially Alzheimer's disease and traumatic brain injury, but current use of intracranial stimulation for pain should be seen as investigational.

CONCLUSIONS

The NACC concludes that extracranial nerve stimulation should be considered in the algorithmic treatment of migraine and other disorders of the head. We should strive to perfect targets outside the cranium when treating pain, if at all possible.

Is effect of transcranial direct current stimulation on visuomotor coordination dependent on task difficulty?

Transcranial direct current stimulation (tDCS), an emerging technique for non-invasive brain stimulation, is increasingly used to induce changes in cortical excitability and modulate motor behavior, especially for upper limbs. The purpose of this study was to investigate the effects of tDCS of the primary motor cortex on visuomotor coordination based on three levels of task difficulty in healthy subjects. Thirty-eight healthy participants underwent real tDCS or sham tDCS. Using a single-blind, sham-controlled crossover design, tDCS was applied to the primary motor cortex. For real tDCS conditions, tDCS intensity was 1 mA while stimulation was applied for 15 minutes. For the sham tDCS, electrodes were placed in the same position, but the stimulator was turned off after 5 seconds. Visuomotor tracking task, consisting of three levels (levels 1, 2, 3) of difficulty with higher level indicating greater difficulty, was performed before and after tDCS application. At level 2, real tDCS of the primary motor cortex improved the accurate index compared to the sham tDCS. However, at levels 1 and 3, the accurate index was not significantly increased after real tDCS compared to the sham tDCS. These findings suggest that tasks of moderate difficulty may improve visuomotor coordination in healthy subjects when tDCS is applied compared with easier or more difficult tasks.

Electrical stimuli in the central nervous system microenvironment

Electrical stimulation to manipulate the central nervous system (CNS) has been applied as early as the 1750s to produce visual sensations of light. Deep brain stimulation (DBS), cochlear implants, visual prosthetics, and functional electrical stimulation (FES) are being applied in the clinic to treat a wide array of neurological diseases, disorders, and injuries. This review describes the history of electrical stimulation of the CNS microenvironment; recent advances in electrical stimulation of the CNS, including DBS to treat essential tremor, Parkinson's disease, and depression; FES for the treatment of spinal cord injuries; and alternative electrical devices to restore vision and hearing via neuroprosthetics (retinal and cochlear implants). It also discusses the role of electrical cues during development and following injury and, importantly, manipulation of these endogenous cues to support regeneration of neural tissue.

TMS-induced motor evoked potentials in Wilson's disease: a systematic literature review

Wilson's disease (WD) is a metabolic brain disease resulting from improper copper metabolism. Although pyramidal symptoms are rarely observed, subclinical injury is highly possible as copper accumulates in all brain structures. The usefulness of motor evoked potentials (MEPs) in pyramidal tracts damage evaluation still appears to be somehow equivocal. We searched for original papers assessing the value of transcranial magnetic stimulation elicited MEPs with respect to motor function of upper and lower extremity in WD. We searched PubMed for original papers evaluating use of MEPs in WD using key words: "motor evoked potentials Wilson's disease" and "transcranial magnetic stimulation Wilson's disease." We found six articles using the above key words. One additional article and one case report were found while viewing the references lists. Therefore, we included eight studies. Number of patients in studies was low and their clinical characteristic was variable. There were also differences in methodology. Abnormal MEPs were confirmed in 20-70% of study participants. MEPs were not recorded in 7.6-66.7% of patients. Four studies reported significantly increased cortical excitability (up to 70% of patients). Prolonged central motor conduction time was observed in four studies (30-100% of patients). One study reported absent or prolonged central motor latency in 66.7% of patients. Although MEPs may be abnormal in WD, this has not been thoroughly assessed. Hence, further studies are indispensable to evaluate MEPs' usefulness in assessing pyramidal tract damage in WD.

Transcranial direct current stimulation in psychiatric disorders

The interest in non-invasive brain stimulation techniques is increasing in recent years. Among these techniques, transcranial direct current stimulation (tDCS) has been the subject of great interest among researchers because of its easiness to use, low cost, benign profile of side effects and encouraging results of research in the field. This interest has generated several studies and randomized clinical trials, particularly in psychiatry. In this review, we provide a summary of the development of the technique and its mechanism of action as well as a review of the methodological aspects of randomized clinical trials in psychiatry, including studies in affective disorders, schizophrenia, obsessive compulsive disorder, child psychiatry and substance use disorder. Finally, we provide an overview of tDCS use in cognitive enhancement as well as a discussion regarding its clinical use and regulatory and ethical issues. Although many promising results regarding tDCS efficacy were described, the total number of studies is still low, highlighting the need of further studies aiming to replicate these findings in larger samples as to provide a definite picture regarding tDCS efficacy in psychiatry.

Image-guided transcranial focused ultrasound stimulates human primary somatosensory cortex

Focused ultrasound (FUS) has recently been investigated as a new mode of non-invasive brain stimulation, which offers exquisite spatial resolution and depth control. We report on the elicitation of explicit somatosensory sensations as well as accompanying evoked electroencephalographic (EEG) potentials induced by FUS stimulation of the human somatosensory cortex. As guided by individual-specific neuroimage data, FUS was transcranially delivered to the hand somatosensory cortex among healthy volunteers. The sonication elicited transient tactile sensations on the hand area contralateral to the sonicated hemisphere, with anatomical specificity of up to a finger, while EEG recordings revealed the elicitation of sonication-specific evoked potentials. Retrospective numerical simulation of the acoustic propagation through the skull showed that a threshold of acoustic intensity may exist for successful cortical stimulation. The neurological and neuroradiological assessment before and after the sonication, along with strict safety considerations through the individual-specific estimation of effective acoustic intensity in situ and thermal effects, showed promising initial safety profile; however, equal/more rigorous precautionary procedures are advised for future studies. The transient and localized stimulation of the brain using image-guided transcranial FUS may serve as a novel tool for the non-invasive assessment and modification of region-specific brain function.

Regulatory Considerations for the Clinical and Research Use of Transcranial Direct Current Stimulation (tDCS): review and recommendations from an expert panel

The field of transcranial electrical stimulation (tES) has experienced significant growth in the past 15 years. One of the tES techniques leading this increased interest is transcranial direct current stimulation (tDCS). Significant research efforts have been devoted to determining the clinical potential of tDCS in humans. Despite the promising results obtained with tDCS in basic and clinical neuroscience, further progress has been impeded by a lack of clarity on international regulatory pathways. We therefore convened a group of research and clinician experts on tDCS to review the research and clinical use of tDCS. In this report, we review the regulatory status of tDCS, and we summarize the results according to research, off-label and compassionate use of tDCS in the following countries: Australia, Brazil, France, Germany, India, Iran, Italy, Portugal, South Korea, Taiwan and United States. Research use, off label treatment and compassionate use of tDCS are employed in most of the countries reviewed in this study. It is critical that a global or local effort is organized to pursue definite evidence to either approve and regulate or restrict the use of tDCS in clinical practice on the basis of adequate randomized controlled treatment trials.

Neurostimulation in Alzheimer's disease: from basic research to clinical applications

The development of different methods of brain stimulation provides a promising therapeutic tool with potentially beneficial effects on subjects with impaired cognitive functions. We performed a systematic review of the studies published in the field of neurostimulation in Alzheimer's disease (AD), from basic research to clinical applications. The main methods of non-invasive brain stimulation are repetitive transcranial magnetic stimulation and transcranial direct current stimulation. Preliminary findings have suggested that both techniques can enhance performances on several cognitive functions impaired in AD. Another non-invasive emerging neuromodulatory approach, the transcranial electromagnetic treatment, was found to reverse cognitive impairment in AD transgenic mice and even improves cognitive performance in normal mice. Experimental studies suggest that high-frequency electromagnetic fields may be critically important in AD prevention and treatment through their action at mitochondrial level. Finally, the application of a widely known invasive technique, the deep brain stimulation (DBS), has increasingly been considered as a therapeutic option also for patients with AD; it has been demonstrated that DBS of fornix/hypothalamus and nucleus basalis of Meynert might improve or at least stabilize cognitive functioning in AD. Initial encouraging results provide support for continuing to investigate non-invasive and invasive brain stimulation approaches as an adjuvant treatment for AD patients.

Differential cerebral response to somatosensory stimulation of an acupuncture point vs. two non-acupuncture points measured with EEG and fMRI

Acupuncture can be regarded as a complex somatosensory stimulation. Here, we evaluate whether the point locations chosen for a somatosensory stimulation with acupuncture needles differently change the brain activity in healthy volunteers. We used EEG, event-related fMRI, and resting-state functional connectivity fMRI to assess neural responses to standardized needle stimulation of the acupuncture point ST36 (lower leg) and two control point locations (CP1 same dermatome, CP2 different dermatome). Cerebral responses were expected to differ for stimulation in two different dermatomes (CP2 different from ST36 and CP1), or stimulation at the acupuncture point vs. the control points. For EEG, mu rhythm power increased for ST36 compared to CP1 or CP2, but not when comparing the two control points. The fMRI analysis found more pronounced insula and S2 (secondary somatosensory cortex) activation, as well as precuneus deactivation during ST36 stimulation. The S2 seed-based functional connectivity analysis revealed increased connectivity to right precuneus for both comparisons, ST36 vs. CP1 and ST36 vs. CP2, however in different regions. Our results suggest that stimulation at acupuncture points may modulate somatosensory and saliency processing regions more readily than stimulation at non-acupuncture point locations. Also, our findings suggest potential modulation of pain perception due to acupuncture stimulation.

Non-invasive electrical and magnetic stimulation of the brain, spinal cord, roots and peripheral nerves: Basic principles and procedures for routine clinical and research application. An updated report from an I.F.C.N. Committee

These guidelines provide an up-date of previous IFCN report on “Non-invasive electrical and magnetic stimulation of the brain, spinal cord and roots: basic principles and procedures for routine clinical application” (Rossini et al., 1994). A new Committee, composed of international experts, some of whom were in the panel of the 1994 “Report”, was selected to produce a current state-of-the-art review of non-invasive stimulation both for clinical application and research in neuroscience.

Since 1994, the international scientific community has seen a rapid increase in non-invasive brain stimulation in studying cognition, brain–behavior relationship and pathophysiology of various neurologic and psychiatric disorders. New paradigms of stimulation and new techniques have been developed. Furthermore, a large number of studies and clinical trials have demonstrated potential therapeutic applications of non-invasive brain stimulation, especially for TMS. Recent guidelines can be found in the literature covering specific aspects of non-invasive brain stimulation, such as safety (Rossi et al., 2009), methodology (Groppa et al., 2012) and therapeutic applications (Lefaucheur et al., 2014).

This up-dated review covers theoretical, physiological and practical aspects of non-invasive stimulation of brain, spinal cord, nerve roots and peripheral nerves in the light of more updated knowledge, and include some recent extensions and developments.

Transcranial direct current stimulation promotes the mobility of engrafted NSCs in the rat brain

Transcranial direct current stimulation (tDCS) is used in numerous clinical studies and considered an effective and versatile add-on therapy in neurorehabilitation. To date, however, the underlying neurobiological mechanisms remain elusive. In a rat model of tDCS, we recently observed a polarity-dependent accumulation of endogenous neural stem cells (NSCs) in the stimulated cortex. Based upon these findings, we hypothesized that tDCS may exert a direct migratory effect on endogenous NSCs towards the stimulated cortex. Using noninvasive imaging, we here investigated whether tDCS may also cause a directed migration of engrafted NSCs. Murine NSCs were labeled with superparamagnetic particles of iron oxide (SPIOs) and implanted into rat striatum and corpus callosum. MRI was performed (i) immediately after implantation and (ii) after 10 tDCS sessions of anodal or cathodal polarity. Sham-stimulated rats served as control. Imaging results were validated ex vivo using immunohistochemistry. Overall migratory activity of NSCs almost doubled after anodal tDCS. However, no directed migration within the electric field (i.e. towards or away from the electrode) could be observed. Rather, an undirected outward migration from the center of the graft was detected. Xenograft transplantation induced a neuroinflammatory response that was significantly enhanced following cathodal tDCS. This inflammatory response did not impact negatively on the survival of implanted NSCs. Data suggest that anodal tDCS increases the undirected migratory activity of implanted NSCs. Since the electric field did not guide implanted NSCs over large distances, previously observed polarity-dependent accumulation of endogenous NSCs in the cortex might have originated from local proliferation. Results enhance our understanding of the neurobiological mechanisms underlying tDCS, and may thereby help to develop a targeted and sustainable application of tDCS in clinical practice.

Far Space Remapping by Tool Use: A rTMS Study Over the Right Posterior Parietal Cortex

BACKGROUND

In previous studies, rTMS has been successfully employed to interfere with the right posterior parietal cortex (rPPC) inducing neglect-like behavior in healthy subjects. Several studies have shown that the use of tools can modulate the boundaries between near and far space: indeed when far space is reached by the stick, far space can be remapped as near.

OBJECTIVE

The aim of the present study was to investigate whether once that rTMS on the rPPC has selectively induced neglect-like bias in the near space (but not in the far space), neglect can appears also in the far space when the subjects used a tool to perform the task.

METHODS

Fifteen right-handed healthy subjects executed a line length judgment task in two different spatial positions (60 cm: near space and 120 cm: far space), with or without rPPC on-line rTMS. In the far space condition, subjects performed the perceptual task while holding or not a tool.

RESULTS

During rTMS, visuospatial performance significantly shifted toward right when the task was performed in the near space and in the far space when the tool was used. No significant effect was found when rTMS was delivered in the far space condition without tool use.

CONCLUSIONS

Our results demonstrate that the application of rTMS on rPPC, specifically affect the representation of near space because it caused neglect both when the subjects acted in the near space and when they acted in a far space that was remapped as near by the use of a tool.

Modeling TMS-induced I-waves in human motor cortex

Despite many years of research, it is still unknown how exactly transcranial magnetic stimulation activates cortical circuits. A recent computational model by Rusu et al. (2014) has attempted to shed light on potential underlying mechanisms and has successfully explained key experimental findings on I-wave physiology. Here, we critically discuss this model, point out some of its shortcomings, and suggest a number of extensions that may be necessary for it to capture additional existing and emerging data on the physiology of I-waves.

An innovative intervention for the treatment of cognitive impairment-Emisymmetric bilateral stimulation improves cognitive functions in Alzheimer's disease and mild cognitive impairment: an open-label study

BACKGROUND AND AIMS

In the last decade, the development of different methods of brain stimulation by electromagnetic fields (EMF) provides a promising therapeutic tool for subjects with impaired cognitive functions. Emisymmetric bilateral stimulation (EBS) is a novel and innovative EMF brain stimulation, whose working principle is to introduce very weak noise-like stimuli through EMF to trigger self-arrangements in the cortex of treated subjects, thereby improving cognitive faculties. The aim of this pilot study was to investigate in patients with cognitive impairment the effectiveness of EBS treatment with respect to global cognitive function, episodic memory, and executive functions.

METHODS

Fourteen patients with cognitive decline (six with mild cognitive impairment and eight with Alzheimer's disease) underwent three EBS applications per week to both the cerebral cortex and auricular-specific sites for a total of 5 weeks. At baseline, after 2 weeks and 5 weeks, a neuropsychological assessment was performed through mini-mental state examination, free and cued selective reminding tests, and trail making test. As secondary outcomes, changes in behavior, functionality, and quality of life were also evaluated.

RESULTS

After 5 weeks of standardized EBS therapy, significant improvements were observed in all neurocognitive assessments. Mini-mental state examination score significantly increased from baseline to end treatment (+3.19, P=0.002). Assessment of episodic memory showed an improvement both in immediate and delayed recalls (immediate recall =+7.57, P=0.003; delayed recall =+4.78, P<0.001). Executive functions significantly improved from baseline to end stimulation (trail making test A -53.35 seconds; P=0.001). Of note, behavioral disorders assessed through neuropsychiatric inventory significantly decreased (-28.78, P<0.001). The analysis concerning the Alzheimer's disease and mild cognitive impairment group confirmed a significant improvement of cognitive functions and behavior after EBS treatment.

CONCLUSION

This pilot study has shown EBS to be a promising, effective, and safe tool to treat cognitive impairment, in addition to the drugs presently available. Further investigations and controlled clinical trials are warranted.

Suppression of subthalamic nucleus activity by micromagnetic stimulation

Magnetic stimulation delivered via 0.5-mm diameter coils was recently shown to activate retinal neurons; the small coil size raises the possibility that micromagnetic stimulation ( μMS) could underlie a new generation of implanted neural prosthetics. Such an approach has several inherent advantages over conventional electric stimulation, including the potential for selective activation of neuronal targets as well as less susceptibility to inflammatory responses. The viability of μMS for some applications, e.g., deep brain stimulation (DBS), may require suppression (rather than creation) of neuronal activity, however, and therefore we explore here whether (μMS) could, in fact, suppress activity. While single pulses elicited weak and inconsistent spiking in neurons of the mouse subthalamic nucleus (in vitro), repetitive stimulation effectively suppressed activity in ∼ 70% of targeted neurons. This is the same percentage suppressed by conventional electric stimulation; with both modalities, suppression occurred only after an initial increase in spiking. The latency to the onset of suppression was inversely correlated to the energy of the stimulus waveform: larger amplitudes and lower frequencies had the fastest onset of suppression. These findings continue to support the viability of μMS as a next-generation implantable neural prosthetic.

High frequency rTMS; a more effective treatment for auditory verbal hallucinations?

The great majority of studies on repetitive transcranial magnetic stimulation (rTMS) as a therapeutic tool for auditory verbal hallucinations (AVH) have used 1-Hz stimulation with inconsistent results. Recently, it has been suggested that 20-Hz rTMS has strong therapeutic effects. It is conceivable that this 20-Hz stimulation is more effective than 1-Hz stimulation. The aim of this preliminary study is to investigate the efficacy of 20-Hz rTMS compared with 1-Hz rTMS as a treatment for AVH. Eighteen schizophrenia patients with medication-resistant AVH were randomized over two treatment groups. Each group received either 20 min of 1-Hz rTMS or 13 trains of 20-Hz rTMS daily over 1 week. After week 1, patients received a follow-up treatment once a week for 3 weeks. Stimulation location was based on individual AVH-related activation patterns identified with functional magnetic resonance imaging. Severity of AVH was monitored with the Auditory Hallucination Rating Scale (AHRS). Both groups showed a decrease in AVH after week 1 of rTMS. This decrease was significant for the 20-Hz group and the 1-Hz group. When the two treatment types were compared, no treatment type was superior. Based on these results we cannot conclude whether high frequency rTMS is more effective against AVH than is traditional 1-Hz rTMS. More research is needed to optimize stimulation parameters and to investigate potential target locations for stimulation.

Transcranial direct current stimulation in the prophylactic treatment of migraine based on interictal visual cortex excitability abnormalities: A pilot randomized controlled trial

PURPOSE

The aims of this paper are (i) to compare the excitability of visual cortex in migraine patients with healthy volunteers; and (ii) if an abnormal excitability has been found, to modulate cortical excitability in migraine patients with transcranial direct current stimulation (tDCS) and observe their clinical and neurophysiological effects.

METHODS

The study was divided into two steps. A cross-sectional study (step 1) was conducted to compare the cortical excitability of 23 migraineurs (11 with and 12 without aura) on 11 healthy individuals. On step 2, a randomized, double blinded, controlled pilot trial was carried on with 19 migraineurs, randomly divided into: experimental and control group. During 12 sessions, experimental and group received active tDCS to visual cortex and control group received sham tDCS. The headache diary was applied for a total of 90days (before, during and after tDCS sessions). Phosphene threshold (PT) induced by transcranial magnetic stimulation was recorded to measure the excitability of the visual cortex before and after each session.

RESULTS

Step 1 showed higher level of cortical excitability between migraineurs when compared to healthy volunteers; therefore, cathodal tDCS was applied over visual cortex in step 2. After tDCS application, a significant decrease was observed in a number of migraine attacks, painkiller intake and duration of each attack just in experimental group. The analysis of PT indicated no difference in cortical excitability after tDCS.

CONCLUSIONS

Findings of the study suggested that inhibitory tDCS on visual cortex might be an alternative and non-pharmacological treatment for migraine prophylaxis. However the clinical improvements of patients after tDCS treatment are not correlated with changes in cortical excitability.

Modulating functional and dysfunctional mentalizing by transcranial magnetic stimulation

Mentalizing, the ability to attribute mental states to others and oneself, is a cognitive function with high relevance for social interactions. Recent neuroscientific research has increasingly contributed to attempts to decompose this complex social cognitive function into constituting neurocognitive building blocks. Additionally, clinical research that focuses on social cognition to find links between impaired social functioning and neurophysiological deviations has accumulated evidence that mentalizing is affected in most psychiatric disorders. Recently, both lines of research have started to employ transcranial magnetic stimulation: the first to modulate mentalizing in order to specify its neurocognitive components, the latter to treat impaired mentalizing in clinical conditions. This review integrates findings of these two different approaches to draw a more detailed picture of the neurocognitive basis of mentalizing and its deviations in psychiatric disorders. Moreover, we evaluate the effectiveness of hitherto employed stimulation techniques and protocols, paradigms and outcome measures. Based on this overview we highlight new directions for future research on the neurocognitive basis of functional and dysfunctional social cognition.

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

Introduction

Two methods of non-invasive brain stimulation, transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS), have demonstrable positive effects on cognition and can ameliorate neuropsychiatric symptoms such as depression. Less is known about the efficacy of these approaches in common neurodegenerative diseases. In this review, we evaluate the effects of TMS and tDCS upon cognitive and neuropsychiatric symptoms in the major dementias, including Alzheimer’s disease (AD), vascular dementia (VaD), dementia with Lewy bodies (DLB), Parkinson’s disease with dementia (PDD), and frontotemporal dementia (FTD), as well as the potential pre-dementia states of Mild Cognitive Impairment (MCI) and Parkinson’s disease (PD).

Methods

PubMed (until 7 February 2014) and PsycINFO (from 1967 to January Week 3 2014) databases were searched in a semi-systematic manner in order to identify relevant treatment studies. A total of 762 studies were identified and 32 studies (18 in the dementias and 14 in PD populations) were included.

Results

No studies were identified in patients with PDD, FTD or VaD. Of the dementias, 13 studies were conducted in patients with AD, one in DLB, and four in MCI. A total of 16 of the 18 studies showed improvements in at least one cognitive or neuropsychiatric outcome measure. Cognitive or neuropsychiatric improvements were observed in 12 of the 14 studies conducted in patients with PD.

Conclusions

Both TMS and tDCS may have potential as interventions for the treatment of symptoms associated with dementia and PD. These results are promising; however, available data were limited, particularly within VaD, PDD and FTD, and major challenges exist in order to maximise the efficacy and clinical utility of both techniques. In particular, stimulation parameters vary considerably between studies and are likely to subsequently impact upon treatment efficacy.

Preliminary guidelines for safe and effective use of repetitive transcranial magnetic stimulation in moderate to severe traumatic brain injury

Transcranial magnetic stimulation has generated extensive interest within the traumatic brain injury (TBI) rehabilitation community, but little work has been done with repetitive protocols, which can produce prolonged changes in behavior. This is partly because of concerns about the safety of repetitive transcranial magnetic stimulation (rTMS) in subjects with TBI, particularly the risk of seizures. These risks can be minimized by careful selection of the rTMS protocol and exclusion criteria. In this article, we identify guidelines for safe use of rTMS in subjects with TBI based on a review of the literature and illustrate their application with a case study. Our subject is a 48-year-old man who sustained a severe TBI 5 years prior to beginning rTMS for the treatment of post-TBI depression. After a 4-week baseline period, we administered daily sessions of low-frequency stimulation to the right dorsolateral prefrontal cortex for 6 weeks. After stimulation, we performed monthly assessments for 3 months. The Hamilton Depression Rating Scale (HAMD) was our primary outcome measure. The stimulation was well tolerated and the patient reported no side effects. After 6 weeks of stimulation, the patient's depression was slightly improved, and these improvements continued through follow-up. At the end of follow-up, the patient's HAMD score was 49% of the average baseline score.

Impact of 5-Hz rTMS over the primary sensory cortex is related to white matter volume in individuals with chronic stroke

Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive brain stimulation technique that may facilitate mechanisms of motor learning. In a recent single-blind, pseudo-randomized study, we showed that 5-Hz rTMS over ipsilesional primary somatosensory cortex followed by practice of a skilled motor task enhanced motor learning compared with sham rTMS + practice in individuals with chronic stroke. However, the beneficial effect of stimulation was inconsistent. The current study examined how differences in sensorimotor cortex morphology might predict rTMS-related improvements in motor learning in these individuals. High-resolution T1-weighted magnetic resonance images were acquired and processed in FreeSurfer using a newly developed automated, whole brain parcellation technique. Gray matter and white matter volumes of the ipsilesional primary somatosensory and motor cortices were extracted. A significant positive association was observed between the volume of white matter in the primary somatosensory cortex and motor learning-related change, exclusively in the group that received active 5-Hz rTMS. A regression model with age, gray matter and white matter volumes as predictors was significant for predicting motor learning-related change in individuals who received active TMS. White matter volume predicted the greatest amount of variance (47.6%). The same model was non-significant when volumes of the primary motor cortex were considered. We conclude that white matter volume in the cortex underlying the TMS coil may be a novel predictor for behavioral response to 5-Hz rTMS over the ipsilesional primary somatosensory followed by motor practice.

Binocular vision in amblyopia: structure, suppression and plasticity

The amblyopic visual system was once considered to be structurally monocular. However, it now evident that the capacity for binocular vision is present in many observers with amblyopia. This has led to new techniques for quantifying suppression that have provided insights into the relationship between suppression and the monocular and binocular visual deficits experienced by amblyopes. Furthermore, new treatments are emerging that directly target suppressive interactions within the visual cortex and, on the basis of initial data, appear to improve both binocular and monocular visual function, even in adults with amblyopia. The aim of this review is to provide an overview of recent studies that have investigated the structure, measurement and treatment of binocular vision in observers with strabismic, anisometropic and mixed amblyopia.

Enhanced long-term memory encoding after parietal neurostimulation

Neurostimulation, e.g., transcranial direct current stimulation (tDCS), shows promise as an effective cognitive intervention. In spite of low spatial resolution, limited penetration, and temporary influence, evidence highlights tDCS-linked cognitive benefits in a range of cognitive domains. The left posterior parietal cortex (PPC) is an accessible node in frontoparietal networks engaged during long-term memory (LTM). Here, we tested the hypothesis that tDCS can facilitate LTM by pairing LTM encoding and retrieval with PPC stimulation. Healthy young adults performed a verbal LTM task (California Verbal Learning Task) with four different stimulation parameters. In Experiment 1, we applied tDCS to left PPC during LTM encoding. In Experiment 2, we applied tDCS just prior to retrieval to test the temporal specificity of tDCS during a LTM task. In later experiments, we tested hemispheric specificity by replicating Experiment 1 while stimulating the right PPC. Experiment 1 showed that tDCS applied during LTM encoding improved the pace of list learning and enhanced retrieval after a short delay. Experiment 2 indicated anodal left PPC tDCS only improved LTM when applied during encoding, and not during maintenance. Experiments 3 and 4 confirmed that tDCS effects were hemisphere specific and that no effects were found after right PPC stimulation during encoding. These findings indicate that anodal tDCS to the PPC helps verbal LTM in healthy young adults under certain conditions. First, when it is applied to the left, not the right, PPC and second, when it is applied during encoding.