Transcranial Stimulation Techniques Research Articles

Mechanisms and Effects of Transcranial Direct Current Stimulation.

The US Air Force Office of Scientific Research convened a meeting of researchers in the fields of neuroscience, psychology, engineering, and medicine to discuss most pressing issues facing ongoing research in the field of transcranial direct current stimulation (tDCS) and related techniques. In this study, we present opinions prepared by participants of the meeting, focusing on the most promising areas of research, immediate and future goals for the field, and the potential for hormesis theory to inform tDCS research. Scientific, medical, and ethical considerations support the ongoing testing of tDCS in healthy and clinical populations, provided best protocols are used to maximize safety. Notwithstanding the need for ongoing research, promising applications include enhancing vigilance/attention in healthy volunteers, which can accelerate training and support learning. Commonly, tDCS is used as an adjunct to training/rehabilitation tasks with the goal of leftward shift in the learning/treatment effect curves. Although trials are encouraging, elucidating the basic mechanisms of tDCS will accelerate validation and adoption. To this end, biomarkers (eg, clinical neuroimaging and findings from animal models) can support hypotheses linking neurobiological mechanisms and behavioral effects. Dosage can be optimized using computational models of current flow and understanding dose–response. Both biomarkers and dosimetry should guide individualized interventions with the goal of reducing variability. Insights from other applied energy domains, including ionizing radiation, transcranial magnetic stimulation, and low-level laser (light) therapy, can be prudently leveraged.

Arm rehabilitation : Current concepts and therapeutic options

Arm paralysis after a stroke is a major cause of impairment. Presentation of therapeutic options and the efficacy in arm rehabilitation after stroke. Based on a systematic critical appraisal of randomized controlled trials (RCT) the therapeutic procedures for arm paralysis after stroke in the context of their effectiveness are introduced, including robotic therapy, mirror therapy, constraint-induced movement therapy (CIMT), arm basis training, arm ability training, neuromuscular electrical stimulation, bilateral and task-specific training, mental training and transcranial stimulation techniques, such as repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS). Several therapeutic procedures with proven efficacy are currently available for arm rehabilitation after stroke. Their differential indications are presented and associated with conclusions for clinical practice.

Transcranial Electrical Stimulation

In recent years, there has been remarkable progress in the understanding and practical use of transcranial electrical stimulation (tES) techniques. Nevertheless, to date, this experimental effort has not been accompanied by substantial reflections on the models and mechanisms that could explain the stimulation effects. Given these premises, the aim of this article is to provide an updated picture of what we know about the theoretical models of tES that have been proposed to date, contextualized in a more specific and unitary framework. We demonstrate that these models can explain the tES behavioral effects as distributed along a continuum from stimulation dependent to network activity dependent. In this framework, we also propose that stochastic resonance is a useful mechanism to explain the general online neuromodulation effects of tES. Moreover, we highlight the aspects that should be considered in future research. We emphasize that tES is not an “easy-to-use” technique; however, it may represent a very fruitful approach if applied within rigorous protocols, with deep knowledge of both the behavioral and cognitive aspects and the more recent advances in the application of stimulation.

Brain Plasticity and the Concept of Metaplasticity in Skilled Musicians.

Early and extensive musical training provides plastic adaptations of the nervous system and enhanced sensory, motor, and cognitive functions. Over decades, neuronal mechanism underlying the plastic adaptation through musical training has been investigated using neuroimaging and transcranial stimulation techniques. Recently, plastic changes in neuroplastic functions through musical training have gradually gained some interest, so-called metaplasticity. Metaplasticity enables faster and more stable skill acquisition for individuals with a history of prior musical training. This mechanism may also serve for prevention of developing maladaptive changes in the nervous system, being pathophysiology of focal dystonia in musicians. The present chapter introduces neurophysiological mechanisms and functional significances of brain plasticity and metaplasticity of the sensory and motor systems of musicians.

Application of Transcranial Electric Stimulation (tDCS, tACS, tRNS)

Abstract. Low-intensity transcranial electrical stimulation (tES) techniques are a group of noninvasive brain stimulation approaches, where currents are applied with intensities ranging between 0.4 and 2 mA through the human scalp. The most frequently used tES methods are transcranial direct current (tDCS), alternating current (tACS), and random noise stimulation (tRNS). These methods have been shown to induce changes in cortical excitability and activity during and after the stimulation in a reversible manner. It was observed that while anodal and cathodal tDCS acts on the membrane potentials by depolarizing or hyperpolarizing them, tACS probably modifies cortical oscillations. tRNS, that is a special form of tACS, might act through affecting the signal-to-noise ratio in the brain. Currently, an exponentially increasing number of studies have been published regarding the effects of tES on physiological processes and cognition. The aim of this review is to summarize the basic aspects of tES methods.

Transcranial direct current stimulation (tDCS) neuromodulatory effects on mechanical hyperalgesia and cortical BDNF levels in ovariectomized rats

Epidemiological studies show that painful disorders are more prevalent in women than in men, and the transcranial direct current stimulation (tDCS) technique has been tested in chronic pain states. We explored the effect of tDCS on pain behavior and brain-derived neurotrophic factor (BDNF) levels in ovariectomized rats. Forty-five female Wistar adult rats were distributed into five groups: control (CT), ovariectomy + tDCS (OT), ovariectomy + sham tDCS (OS), sham ovariectomy + tDCS (ST), and sham ovariectomy+shamtDCS (SS). The rats were subjected to cathodal tDCS. The vaginal cytology and the estradiol levels confirmed the hormonal status. In addition, nociceptive behavior was evaluated using the tail-flick, von Frey, and hot-plate tests, as well as the BDNF levels in the serum, hypothalamus, hippocampus, spinal cord, and cerebral cortex. One-way analysis of variance (ANOVA) or two-way ANOVA was used for statistical analysis, followed by the Bonferroni, and P-value b 0.05 was considered significant. The ovariectomized animals presented a hypersensitivity response in the hot-plate (P b 0.01) and von Frey (P b 0.05) tests, as well as increased serum BDNF (P b 0.05) and decreased hypothalamic BDNF (P b 0.01) levels. The OT, OS, ST, and SS groups showed decreased hippocampal BDNF levels as compared with the control group (P b 0.001). The interaction between tDCS and ovariectomy on the cortical BDNF levels (P b 0.01) was observed. The ovariectomy induced nociceptive hypersensitivity and altered serum and hypothalamic BDNF levels. The cathodal tDCS partially reversed nociceptive hypersensitivity.

Effects of the Transcranial Direct Current Stimulation on Prevention of Postoperative Cognitive Dysfunction after Cardiac Surgery: Prospective, Randomized, Double-Blind Study

Introduction: Postoperative cognitive dysfunction (POCD) is a contrary event observed between 20 to 83%, especially in elderly and after cardiac surgery. Prevention and rehabilitation on cases of POCD may improve the quality of life. The neuromodulator effect of the noninvasive cerebral stimulation has been used in the treatment of brain injuries, depression, and also in the cognitive rehabilitation. The hypothesis is that the use of the transcranial direct current stimulation (tDCS) technique can decrease the occurrence of POCD and cognitively rehabilitate patients submitted to cardiac surgeries. The objective of this study will be to evaluate the tDCS effect over the occurrence of POCD in patients on cardiac surgeries. Methods: After approval the institutional ethics committee, will be included in the study 138 adult submitted a cardiac surgery. After assigned the consent form patients will be randomly allocated in two groups. tDCS GROUP: Submitted to 2 daily sessions of cerebral stimulation, starting from the first day after surgery during 4 consecutive days, with each session having 20 minutes. Will be applied a direct current stimulus of 2mA in the right anode and in the left cathode on the prefrontal right region. SHAM GROUP: The same equipment used in tDCS as simulated stimulus similar to the active one. Will also be summited to neuropsychological tests to evaluate memory, attention, and executive functions as well as data relative of surgery, cognitive evolution and quality of life in the postoperative period. The neuropsychological test will be describes according groups and the moments of application, with mean and standard deviation (SD) and compared to results of normative tables with Z-score (±1,96). The data will be expressed in means, medians, confidence intervals (CI-95%) and SD and analyzed by Generalized Estimating Equation (GEE), to comparison of the results between the two groups. P<0,05 will be considered significant.

Optimising repetitive transcranial magnetic stimulation for neural circuit repair following traumatic brain injury.

While it is well-known that neuronal activity promotes plasticity and connectivity, the success of activity-based neural rehabilitation programs remains extremely limited in human clinical experience because they cannot adequately control neuronal excitability and activity within the injured brain in order to induce repair. However, it is possible to non-invasively modulate brain plasticity using brain stimulation techniques such as repetitive transcranial (rTMS) and transcranial direct current stimulation (tDCS) techniques, which show promise for repairing injured neural circuits (Henrich-Noack et al., 2013; Lefaucher et al., 2014). Yet we are far from having full control of these techniques to repair the brain following neurotrauma and need more fundamental research (Ellaway et al., 2014; Lefaucher et al., 2014). In this perspective we discuss the mechanisms by which rTMS may facilitate neurorehabilitation and propose experimental techniques with which magnetic stimulation may be investigated in order to optimise its treatment potential.

Transcranial brain stimulation: potential and limitations

The brain adapts to new requirements in response to activity, learning or reactions to environmental stimuli by continuous reorganization. These reorganization processes can be facilitated and augmented, or also inhibited and prevented, by transcranial neurostimulation. The most common methods are electrical or magnetic stimulation. However, few studies have dealt with the newer methods using near infrared or ultrasound stimulation.Transcranial magnetic stimulation (TMS) allows the pain-free transfer of very short bursts of high intensity electrical energy through the skull and can induce action potentials. By varying the number and intensity of the stimuli, and the stimulus sequence, repetitive TMS (rTMS) can induce either inhibitory or facilitatory effects in the brain. A differentiation is made between short-lived interference with ongoing brain activity, and plastic changes that persist for a longer period beyond the end of the stimulation.Weaker electric fields in the 1 mA range can be applied painlessly through the skull. These probably exert their effects by modulating neuronal membranes and influencing the spontaneous firing rate of cortical neurons. They encompass the range from transcranial direct current stimulation (tDCS) to high frequency alternating current stimulation (tACS) in the kilohertz range. In view of the multitude of physically possible stimulation algorithms, hypothesis-driven protocols based on cellular or neuronal network characteristics are particularly popular, in the effort to narrow the choices in a meaningful manner. Examples are theta burst stimulation or tACS in the so-called “ripple” frequency range. It is, of course, not possible to selectively stimulate individual neurons using transcranial stimulation techniques; however selective after-effects can be achieved when used in combination with neuropharmacologically active drugs. The use of these methods for neuroenhancement is now a topic of intense discussion.

Transcranial brain stimulation: potential and limitations

Abstract The brain adapts to new requirements in response to activity, learning or reactions to environmental stimuli by continuous reorgani­zation. These reorganization processes can be facilitated and augmented, or also inhibit­ed and prevented, by transcranial neurostim­ulation. The most common methods are electrical or magnetic stimulation. However, few studies have dealt with the newer methods using near infrared or ultrasound stimulation. Transcranial magnetic stimulation (TMS) allows the pain-free transfer of very short bursts of high intensity electrical energy through the skull and can induce action po­tentials. By varying the number and intensity of the stimuli, and the stimulus sequence, repetitive TMS (rTMS) can induce either inhib­itory or facilitatory effects in the brain. A differentiation is made between short-lived interference with ongoing brain activity, and plastic changes that persist for a longer period beyond the end of the stimulation. Weaker electric fields in the 1 mA range can be applied painlessly through the skull. These probably exert their effects by modulating neuronal membranes and influencing the spontaneous firing rate of cortical neu­rons. They encompass the range from tran­scranial direct current stimulation (tDCS) to high frequency alternating current stimulation (tACS) in the kilohertz range. In view of the multitude of physically possible stimulation algorithms, hypothesis-driven protocols based on cellular or neuronal network characteristics are particularly popular, in the effort to narrow the choices in a meaningful manner. Examples are theta burst stimulation or tACS in the so-called “ripple” frequen­cy range. It is, of course, not possible to selectively stimulate individual neurons using transcranial stimulation techniques; however selective after-effects can be achieved when used in combination with neuropharmacologically active drugs. The use of these methods for neuroenhancement is now a topic of intense discussion.

Visualizing simulated electrical fields from electroencephalography and transcranial electric brain stimulation: A comparative evaluation

Electrical activity of neuronal populations is a crucial aspect of brain activity. This activity is not measured directly but recorded as electrical potential changes using head surface electrodes (electroencephalogram - EEG). Head surface electrodes can also be deployed to inject electrical currents in order to modulate brain activity (transcranial electric stimulation techniques) for therapeutic and neuroscientific purposes. In electroencephalography and noninvasive electric brain stimulation, electrical fields mediate between electrical signal sources and regions of interest (ROI). These fields can be very complicated in structure, and are influenced in a complex way by the conductivity profile of the human head. Visualization techniques play a central role to grasp the nature of those fields because such techniques allow for an effective conveyance of complex data and enable quick qualitative and quantitative assessments. The examination of volume conduction effects of particular head model parameterizations (e.g., skull thickness and layering), of brain anomalies (e.g., holes in the skull, tumors), location and extent of active brain areas (e.g., high concentrations of current densities) and around current injecting electrodes can be investigated using visualization. Here, we evaluate a number of widely used visualization techniques, based on either the potential distribution or on the current-flow. In particular, we focus on the extractability of quantitative and qualitative information from the obtained images, their effective integration of anatomical context information, and their interaction. We present illustrative examples from clinically and neuroscientifically relevant cases and discuss the pros and cons of the various visualization techniques.

Augmentation of motor evoked potentials using multi-train transcranial electrical stimulation in intraoperative neurophysiologic monitoring during spinal surgery

Transcranial motor evoked potentials (TcMEPs) are widely used to monitor motor function during spinal surgery. Improvements in transcranial stimulation techniques and general anesthesia have made it possible to record reliable and reproducible potentials. However, TcMEPs are much smaller in amplitude compared with compound muscle action potentials (CMAPs) evoked by maximal peripheral nerve stimulation. In this study, multi-train transcranial electrical stimulation (mt-TES) was introduced to enhance TcMEPs, and the optimal setting of mt-TES was investigated. In 30 patients undergoing surgical correction of spinal deformities (4 males and 26 females with normal motor status; age range 11-75years), TcMEPs from the abductor hallucis (AH) and quadriceps femoris (QF) were analyzed. A multipulse (train) stimulus with an individual pulse width of 0.5ms and an inter-pulse interval of 2ms was delivered repeatedly (2-7 times) at different rates (2, 5, and 10Hz). TcMEP amplitudes increased with the number of train stimuli for AH, with the strongest facilitation observed at 5Hz. The response amplitude increased 6.1 times on average compared with single-train transcranial electrical stimulation (st-TES). This trend was also observed in the QF. No adverse events (e.g., seizures, cardiac arrhythmias, scalp burns, accidental injury resulting from patient movement) were observed in any patients. Although several facilitative techniques using central or peripheral stimuli, preceding transcranial electrical stimulation, have been recently employed to augment TcMEPs during surgery, responses are still much smaller than CMAPs. Changing from conventional st-TES to mt-TES has potential to greatly enhance TcMEP responses.

IS 32. Impaired cortical plasticity in schizophrenia

Questions Neural plasticity involves reorganization of synaptic connections and represents the brain’s capacity to reorganize its function in response to a challenge or to a stimulus. Plasticity implies changing synaptic activity and connectivity and the underlying mechanisms are long-term potentiation (LTP) and long-term depression (LTD). Methods In four studies, using excitability-enhancing anodal and excitability-diminishing cathodal transcranial direct current stimulation (tDCS) and transcranial theta-burst stimulation (TBS), we performed an in vivo assessment of glutamatedependent LTP-like and LTD-like cortical plasticity in schizophrenia patients, their relatives and healthy controls with no family history of schizophrenia. To determine the physiological basis of possible plasticity changes, different inhibitory and facilitatory networks were investigated. Furthermore, the impact of the brain-derived-neurotrophic factor on cortical plasticity was analysed. Results Multi-episode schizophrenia patients showed significantly reduced LTP-like plasticity compared to recent-onset schizophrenia patients and healthy controls. All schizophrenia patients presented abolished LTD-like plasticity and schizophrenia patients showed a dysfunctional plasticity spread (LTD) across hemispheres. First-degree relatives showed an inversed plasticity reaction compared to healthy controls and schizophrenia patients on the non-stimulated hemisphere. Conclusions The pattern of our results provides evidence for a specific plasticity deficit in schizophrenia patients which might be associated with a hyperglutamatergicstate, dysfunctional N -methyl- d -aspartate-receptors and dysfunctional intracortical inhibitory networks across hemispheres. These results indicate that the available transcranial stimulation techniques might be not optimal for the treatment of schizophrenia. New treatment tools need to be developed and the effects of the disease state, medication and the genetic background need to be taken into consideration.

High-Frequency TRNS Reduces BOLD Activity during Visuomotor Learning

Transcranial direct current stimulation (tDCS) and transcranial random noise stimulation (tRNS) consist in the application of electrical current of small intensity through the scalp, able to modulate perceptual and motor learning, probably by changing brain excitability. We investigated the effects of these transcranial electrical stimulation techniques in the early and later stages of visuomotor learning, as well as associated brain activity changes using functional magnetic resonance imaging (fMRI). We applied anodal and cathodal tDCS, low-frequency and high-frequency tRNS (lf-tRNS, 0.1–100 Hz; hf-tRNS 101–640 Hz, respectively) and sham stimulation over the primary motor cortex (M1) during the first 10 minutes of a visuomotor learning paradigm and measured performance changes for 20 minutes after stimulation ceased. Functional imaging scans were acquired throughout the whole experiment. Cathodal tDCS and hf-tRNS showed a tendency to improve and lf-tRNS to hinder early learning during stimulation, an effect that remained for 20 minutes after cessation of stimulation in the late learning phase. Motor learning-related activity decreased in several regions as reported previously, however, there was no significant modulation of brain activity by tDCS. In opposition to this, hf-tRNS was associated with reduced motor task-related-activity bilaterally in the frontal cortex and precuneous, probably due to interaction with ongoing neuronal oscillations. This result highlights the potential of lf-tRNS and hf-tRNS to differentially modulate visuomotor learning and advances our knowledge on neuroplasticity induction approaches combined with functional imaging methods.

Head-to-Head Comparison of Transcranial Random Noise Stimulation, Transcranial AC Stimulation, and Transcranial DC Stimulation for Tinnitus

Tinnitus is the perception of a sound in the absence of an external sound stimulus. This phantom sound has been related to plastic changes and hyperactivity in the auditory cortex. Different neuromodulation techniques such as transcranial magnetic stimulation and transcranial direct current stimulation (tDCS) have been used in an attempt to modify local and distant neuroplasticity as to reduce tinnitus symptoms. Recently, two techniques of pulsed electrical stimulation using weak electrical currents – transcranial alternating current stimulation (tACS) and transcranial random noise stimulation (tRNS) – have also shown significant neuromodulatory effects. In the present study we conducted the first head-to-head comparison of three different transcranial electrical stimulation (tES) techniques, namely tDCS, tACS, and tRNS in 111 tinnitus patients by placing the electrodes overlying the auditory cortex bilaterally. The results demonstrated that tRNS induced the larger transient suppressive effect on the tinnitus loudness and the tinnitus related distress as compared to tDCS and tACS. Both tDCS and tACS induced small and non-significant effects on tinnitus symptoms, supporting the superior effects of tRNS as a method for tinnitus suppression.

Modulating the brain at work using noninvasive transcranial stimulation

This paper proposes a shift in the way researchers currently view and use transcranial brain stimulation technologies. From a neuroscience perspective, the standard application of both transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) has been mainly to explore the function of various brain regions. These tools allow for noninvasive and painless modulation of cortical tissue. In the course of studying the function of an area, many studies often report enhanced performance of a task during or following the stimulation. However, little follow-up research is typically done to further explore these effects. Approaching this growing pool of cognitive neuroscience literature with a neuroergonomics mindset (i.e., studying the brain at work), the possibilities of using these stimulation techniques for more than simply investigating the function of cortical areas become evident. In this paper, we discuss how cognitive neuroscience brain stimulation studies may complement neuroergonomics research on human performance optimization. And, through this discussion, we hope to shift the mindset of viewing transcranial stimulation techniques as solely investigatory basic science tools or possible clinical therapeutic devices to viewing transcranial stimulation techniques as interventional tools to be incorporated in applied science research and systems for the augmentation and enhancement of human operator performance.

Transcranial stimulation techniques: which genetics is the best for which purpose?

Transcranial stimulation techniques: which genetics is the best for which purpose?

Neuroscience insights improve neurorehabilitation of poststroke aphasia

The treatment of aphasias-acquired language disorders-caused by stroke and other neurological conditions has benefitted from insights from neuroscience and neuropsychology. Hebbian mechanisms suggest that massed practice and exploitation of residual neurological capacities can aid neurorehabilitation of patients with poststroke aphasia, and progress in basic neuroscience research indicates that the language system of the human brain is functionally interwoven with perceptual and motor systems. Intensive speech and language therapies, including constraint-induced aphasia therapy, that activate both the linguistic and concordant motor circuits utilize the knowledge gained from these advances in neuroscience research and can lead to surprisingly rapid improvements in language performance, even in patients with chronic aphasia. Drug-based therapies alone and in conjunction with behavioral language therapies also increase language performance in patients with aphasia. Furthermore, noninvasive transcranial magnetic stimulation and electrical stimulation techniques that target neuronal activity within perilesional areas might help patients with aphasia to regain lost language functions. Intensive language-action therapies that lead to rapid improvements in language skills might provide a new opportunity for investigating fast plastic neuronal changes in the areas of the brain associated with language processing. Here, we review progress in basic neuroscience research and its translational impact on the neurorehabilitation of language disorders after stroke.

Evaluating Aftereffects of Short-Duration Transcranial Random Noise Stimulation on Cortical Excitability

A 10-minute application of highfrequency (100–640 Hz) transcranial random noise stimulation (tRNS) over the primary motor cortex (M1) increases baseline levels of cortical excitability, lasting around 1 hr poststimulation Terney et al. (2008). We have extended previous work demonstrating this effect by decreasing the stimulation duration to 4, 5, and 6 minutes to assess whether a shorter duration of tRNS can also induce a change in cortical excitability. Single-pulse monophasic transcranial magnetic stimulation (TMS) was used to measure baseline levels of cortical excitability before and after tRNS. A 5- and 6-minute tRNS application induced a significant facilitation. 4-minute tRNS produced no significant aftereffects on corticospinal excitability. Plastic after effects after tRNS on corticospinal excitability require a minimal stimulation duration of 5 minutes. However, the duration of the aftereffect of 5-min tRNS is very short compared to previous studies using tRNS. Developing different transcranial stimulation techniques may be fundamental in understanding how excitatory and inhibitory networks in the human brain can be modulated and how each technique can be optimised for a controlled and effective application.

Electrode-distance dependent after-effects of transcranial direct and random noise stimulation with extracephalic reference electrodes

Objective To evaluate the importance of the distance between stimulation electrodes, in various montages, on the ability to induce sustained cortical excitability changes using transcranial direct and random noise stimulation. Methods Twelve healthy subjects participated in four different experimental conditions. The stimulation electrode was always placed over the primary motor cortex; the reference electrode was placed at the contralateral orbit or at the ipsilateral/contralateral arm. MEPs were recorded in order to measure changes in cortical excitability over time. Results The distance between the two electrodes correlates negatively with the duration and magnitude of induced after-effects. Conclusions In particular when using extracephalic reference electrodes with transcranial electric stimulation techniques, the stimulation intensity has to be adapted to account for interelectrode distance. Significance Electrode distance plays a critical role in the induction for stimulation after-effects in tDCS and tRNS studies, and must be taken into account in future studies and also when making comparisons with the published literature.