Effects of transcranial direct current stimulation coupled with repetitive electrical stimulation on cortical spreading depression

The Efficacy of Repetitive Transcranial Magnetic Stimulation (rTMS) versus Transcranial Direct-Current Stimulation (tDCS) on Migraine Headaches: A Randomized Clinical Trial

Background

Non-pharmacologic prophylactic methods for chronic migraine have been developed, including the promising non-invasive techniques of repetitive transcranial magnetic stimulation (rTMS) and transcranial direct-current stimulation (tDCS). This study aimed to compare the efficacy of rTMS and tDCS on pain intensity, the impact of headaches on daily life, anxiety, and depression in migraine headaches patients.

Materials and Methods

This randomized clinical trial was conducted on 72 patients with migraine headaches, randomly allocated to the rTMS and tDCS groups. Participants received 3 and 12 sessions of stimulation over the left dorsolateral prefrontal cortex (DLPFC), respectively. Follow-up measurements, including pain intensity, anxiety, depression, and impact on daily life, were performed one month after the last sessions. Analyses were done by IBM SPSS statistics version 26 software.

Results

Of 72 patients enrolled in the study, 19 were male (8 in the rTMS group and 11 in the tDCS group). There was no significant difference in baseline characteristics between groups. During the follow-up visit, both groups showed a decrease in anxiety levels (P values = 0.005 and 0.015), while only the rTMS group displayed a significant improvement in depression (P value = 0.01). However, no statistically significant difference was found among the groups regarding changes in pain intensity, anxiety, and the impact of headaches on daily life (P values >0.05).

Conclusion

Our findings suggest that both rTMS and tDCS may be effective in reducing pain intensity and improving the impact of headaches on daily life and anxiety in patients with chronic migraine. However, significant improvement in depression was only observed in the rTMS group patients.

Trigeminal nerve stimulation: a current state-of-the-art review

Nearly 5 decades ago, the effect of trigeminal nerve stimulation (TNS) on cerebral blood flow was observed for the first time. This implication directly led to further investigations and TNS' success as a therapeutic intervention. Possessing unique connections with key brain and brainstem regions, TNS has been observed to modulate cerebral vasodilation, brain metabolism, cerebral autoregulation, cerebral and systemic inflammation, and the autonomic nervous system. The unique range of effects make it a prime therapeutic modality and have led to its clinical usage in chronic conditions such as migraine, prolonged disorders of consciousness, and depression. This review aims to present a comprehensive overview of TNS research and its broader therapeutic potentialities. For the purpose of this review, PubMed and Google Scholar were searched from inception to August 28, 2023 to identify a total of 89 relevant studies, both clinical and pre-clinical. TNS harnesses the release of vasoactive neuropeptides, modulation of neurotransmission, and direct action upon the autonomic nervous system to generate a suite of powerful multitarget therapeutic effects. While TNS has been applied clinically to chronic pathological conditions, these powerful effects have recently shown great potential in a number of acute/traumatic pathologies. However, there are still key mechanistic and methodologic knowledge gaps to be solved to make TNS a viable therapeutic option in wider clinical settings. These include bimodal or paradoxical effects and mechanisms, questions regarding its safety in acute/traumatic conditions, the development of more selective stimulation methods to avoid potential maladaptive effects, and its connection to the diving reflex, a trigeminally-mediated protective endogenous reflex. The address of these questions could overcome the current limitations and allow TNS to be applied therapeutically to an innumerable number of pathologies, such that it now stands at the precipice of becoming a ground-breaking therapeutic modality.

Nonpharmacological modulation of cortical spreading depolarization

AIMS

Cortical spreading depolarization (CSD) is a wave of pathologic neuronal dysfunction that spreads through cerebral gray matter, causing neurologic disturbance in migraine and promoting lesion development in acute brain injury. Pharmacologic interventions have been found to be effective in migraine with aura, but their efficacy in acutely injured brains may be limited. This necessitates the assessment of possible adjunctive treatments, such as nonpharmacologic methods. This review aims to summarize currently available nonpharmacological techniques for modulating CSDs, present their mechanisms of action, and provide insight and future directions for CSD treatment.

MAIN METHODS

A systematic literature review was performed, generating 22 articles across 3 decades. Relevant data is broken down according to method of treatment.

KEY FINDINGS

Both pharmacologic and nonpharmacologic interventions can mitigate the pathological impact of CSDs via shared molecular mechanisms, including modulating K⁺/Ca²⁺/Na⁺/Cl^- ion channels and NMDA, GABA_A, serotonin, and CGRP ligand-based receptors and decreasing microglial activation. Preclinical evidence suggests that nonpharmacologic interventions, including neuromodulation, physical exercise, therapeutic hypothermia, and lifestyle changes can also target unique mechanisms, such as increasing adrenergic tone and myelination and modulating membrane fluidity, which may lend broader modulatory effects. Collectively, these mechanisms increase the electrical initiation threshold, increase CSD latency, slow CSD velocity, and decrease CSD amplitude and duration.

SIGNIFICANCE

Given the harmful consequences of CSDs, limitations of current pharmacological interventions to inhibit CSDs in acutely injured brains, and translational potentials of nonpharmacologic interventions to modulate CSDs, further assessment of nonpharmacologic modalities and their mechanisms to mitigate CSD-related neurologic dysfunction is warranted.

Nebivolol elicits a neuroprotective effect in the cuprizone model of multiple sclerosis in mice: emphasis on M1/M2 polarization and inhibition of NLRP3 inflammasome activation

BACKGROUND AND AIM

Multiple sclerosis (MS) is a demyelinating neurodegenerative inflammatory disease affecting mainly young adults. Microgliosis-derived neuroinflammation represents a key hallmark in MS pathology and progression. Nebivolol (Neb) demonstrated antioxidant, anti-inflammatory and neuroprotective properties in several brain pathologies. This study was conducted to investigate the potential neuroprotective effect of Neb in the cuprizone (Cup) model of MS.

METHODS

C57Bl/6 mice were fed 0.2% Cup mixed into rodent chow for 5 weeks. Neb (5 and 10 mg/kg/day) was administered by oral gavage during the last 2 weeks.

RESULTS

Neb prevented Cup-induced weight loss and motor deficits as evidenced by increased latency to fall in the rotarod test and enhanced locomotor activity as compared to Cup-intoxicated mice. Neb reversed Cup-induced demyelination as confirmed by Luxol fast blue staining and myelin basic protein western blotting. Administration of Neb modulated microglial activation status by suppressing M1 markers (Iba-1, CD86, iNOS, NO and TNF-α) and increasing M2 markers (Arg-1 and IL-10) as compared to Cup-fed mice. Furthermore, Neb hindered NLRP3/caspase-1/IL-18 inflammatory cascade and alleviated oxidative stress by reducing lipid peroxidation, as well as increasing catalase and superoxide dismutase activities.

CONCLUSION

These findings suggest the potential neuroprotective effect of Neb in the Cup-induced model of MS in mice, at least partially by virtue of shifting microglia towards M2 phenotype, mitigation of NLRP3 inflammasome activation and alleviation of oxidative stress.

Low-Intensity Pulsed Ultrasound Stimulation Inhibits Cortical Spreading Depression

Cortical spreading depression (CSD), which is closely correlated with migraine aura, cerebral ischemia, seizure, and brain injury, is a spreading wave of neuronal and glial depolarization. The purpose of this study is to investigate whether low-intensity pulsed ultrasound stimulation (PUS) inhibits CSD by modulating neural activity and hemodynamics. Behavioral test, intrinsic signal optical imaging and western blot analysis were used for evaluating the inhibition effect of PUS on CSD in rat. We found that: 1) 30 min of PUS can significantly improve motor activity of rat with CSD. 2) Both 30 s and 30 min of PUS can significantly reduce count and propagation speed of CSD in rat and the inhibitory effect was enhanced with increase of ultrasound intensity. 3) 30 min of PUS significantly enhanced levels of brain-derived neurotrophic factor protein in brain tissue with CSD. These results suggest that PUS has the potential to treat brain disorders associated with CSD.

Non-invasive Brain Stimulation for Gambling Disorder: A Systematic Review

Background: Gambling disorder (GD) is the most common behavioral addiction and shares pathophysiological and clinical features with substance use disorders (SUDs). Effective therapeutic interventions for GD are lacking. Non-invasive brain stimulation (NIBS) may represent a promising treatment option for GD.

Objective: This systematic review aimed to provide a comprehensive and structured overview of studies applying NIBS techniques to GD and problem gambling.

Methods: A literature search using Pubmed, Web of Science, and Science Direct was conducted from databases inception to December 19, 2019, for studies assessing the effects of repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (t-DCS) on subjects with GD or problem gambling. Studies using NIBS techniques on healthy subjects and those without therapeutic goals but only aiming to assess basic neurophysiology measures were excluded.

Results: A total of 269 articles were title and abstract screened, 13 full texts were assessed, and 11 were included, of which six were controlled and five were uncontrolled. Most studies showed a reduction of gambling behavior, craving for gambling, and gambling-related symptoms. NIBS effects on psychiatric symptoms were less consistent. A decrease of the behavioral activation related to gambling was also reported. Some studies reported modulation of behavioral measures (i.e., impulsivity, cognitive and attentional control, decision making, cognitive flexibility). Studies were not consistent in terms of NIBS protocol, site of stimulation, clinical and surrogate outcome measures, and duration of treatment and follow-up. Sample size was small in most studies.

Conclusions: The clinical and methodological heterogeneity of the included studies prevented us from drawing any firm conclusion on the efficacy of NIBS interventions for GD. Further methodologically sound, robust, and well-powered studies are needed.

Therapeutic implications of cortical spreading depression models in migraine

Migraine is among the most common and disabling neurological diseases in the world. Cortical spreading depression (CSD) is a wave of near-complete depolarization of neurons and glial cells that slowly propagates along the cortex creating the perception of aura. Evidence suggests that CSD can trigger migraine headache. Experimental models of CSD have been considered highly translational as they recapitulate migraine-related phenomena and have been validated for screening migraine therapeutics. Here we outline the essential components of validated experimental models of CSD and provide a comprehensive review of potential modulators and targets against CSD. We further focus on novel interventions that have been recently shown to suppress CSD susceptibility that may lead to therapeutic targets in migraine.

Effects of network topologies on stochastic resonance in feedforward neural network

The effects of network topologies on signal propagation are studied in noisy feedforward neural network in detail, where the network topologies are modulated by changing both the in-degree and out-degree distributions of FFNs as identical, uniform and exponential respectively. Stochastic resonance appeared in three FFNs when the same external stimuli and noise are applied to the three different network topologies. It is found that optimal noise intensity decreases with the increase of network's layer index. Meanwhile, the Q index of FFN with identical distribution is higher than that of the other two FFNs, indicating that the synchronization between the neuronal firing activities and the external stimuli is more obvious in FFN with identical distribution. The optimal parameter regions for the time cycle of external stimuli and the noise intensity are found for three FFNs, in which the resonance is more easily induced when the parameters of stimuli are set in this region. Furthermore, the relationship between the in-degree, the average membrane potential and the resonance performance is studied at the neuronal level, where it is found that both the average membrane potentials and the Q indexes of neurons in FFN with identical degree distribution is more consistent with each other than that of the other two FFNs due to their network topologies. In summary, the simulations here indicate that the network topologies play essential roles in affecting the signal propagation of FFNs.

Neuromodulatory Effects of Transcranial Direct Current Stimulation on Motor Excitability in Rats

Transcranial direct current stimulation (tDCS) is a noninvasive technique for modulating neural plasticity and is considered to have therapeutic potential in neurological disorders. For the purpose of translational neuroscience research, a suitable animal model can be ideal for providing a stable condition for identifying mechanisms that can help to explore therapeutic strategies. Here, we developed a tDCS protocol for modulating motor excitability in anesthetized rats. To examine the responses of tDCS-elicited plasticity, the motor evoked potential (MEP) and MEP input-output (IO) curve elicited by epidural motor cortical electrical stimulus were evaluated at baseline and after 30 min of anodal tDCS or cathodal tDCS. Furthermore, a paired-pulse cortical electrical stimulus was applied to assess changes in the inhibitory network by measuring long-interval intracortical inhibition (LICI) before and after tDCS. In the results, analogous to those observed in humans, the present study demonstrates long-term potentiation- (LTP-) and long-term depression- (LTD-) like plasticity can be induced by tDCS protocol in anesthetized rats. We found that the MEPs were significantly enhanced immediately after anodal tDCS at 0.1 mA and 0.8 mA and remained enhanced for 30 min. Similarly, MEPs were suppressed immediately after cathodal tDCS at 0.8 mA and lasted for 30 min. No effect was noted on the MEP magnitude under sham tDCS stimulation. Furthermore, the IO curve slope was elevated following anodal tDCS and presented a trend toward diminished slope after cathodal tDCS. No significant differences in the LICI ratio of pre- to post-tDCS were observed. These results indicated that developed tDCS schemes can produce consistent, rapid, and controllable electrophysiological changes in corticomotor excitability in rats. This newly developed tDCS animal model could be useful to further explore mechanical insights and may serve as a translational platform bridging human and animal studies, establishing new therapeutic strategies for neurological disorders.

The Effect of Anodal Transcranial Direct Current Stimulation Over Left and Right Temporal Cortex on the Cardiovascular Response: A Comparative Study

Background: Stimulation of the right and left anterior insular cortex, increases and decreases the cardiovascular response respectively, thus indicating the brain’s lateralization of the neural control of circulation. Previous experiments have demonstrated that transcranial direct current stimulation (tDCS) modulates the autonomic cardiovascular control when applied over the temporal cortex. Given the importance of neural control for a normal hemodynamic response, and the potential for the use of tDCS in the treatment of cardiovascular diseases, this study investigated whether tDCS was capable of modulating autonomic regulation.

Methods: Cardiovascular response was monitored during a post-exercise muscle ischemia (PEMI) test, which is well-documented to increase sympathetic drive. A group of 12 healthy participants performed a PEMI test in a control (Control), sham (Sham) and two different experimental sessions where the anodal electrode was applied over the left temporal cortex and right temporal cortex with the cathodal electrode placed over the contralateral supraorbital area. Stimulation lasted 20 min at 2 mA. The hemodynamic profile was measured during a PEMI test. The cardiovascular parameters were continuously measured with a transthoracic bio-impedance device both during the PEMI test and during tDCS.

Results: None of the subjects presented any side effects during or after tDCS stimulation. A consistent cardiovascular response during PEMI test was observed in all conditions. Statistical analysis did not find any significant interaction and any significant main effect of condition on cardiovascular parameters (all ps > 0.316) after tDCS. No statistical differences regarding the hemodynamic responses were found between conditions and time during tDCS stimulation (p > 0.05).

Discussion: This is the first study comparing the cardiovascular response after tDCS stimulation of left and right TC both during exercise and at rest. The results of the current study suggest that anodal tDCS of the left and right TC does not affect functional cardiovascular response during exercise PEMI test and during tDCS. In light of the present and previous findings, the effect of tDCS on the cardiovascular response remains inconclusive.

Transcranial Electrical Brain Stimulation in Alert Rodents

Transcranial electrical brain stimulation can modulate cortical excitability and plasticity in humans and rodents. The most common form of stimulation in humans is transcranial direct current stimulation (tDCS). Less frequently, transcranial alternating current stimulation (tACS) or transcranial random noise stimulation (tRNS), a specific form of tACS using an electrical current applied randomly within a pre-defined frequency range, is used. The increase of noninvasive electrical brain stimulation research in humans, both for experimental and clinical purposes, has yielded an increased need for basic, mechanistic, safety studies in animals. This article describes a model for transcranial electrical brain stimulation (tES) through the intact skull targeting the motor system in alert rodents. The protocol provides step-by-step instructions for the surgical set-up of a permanent epicranial electrode socket combined with an implanted counter electrode on the chest. By placing a stimulation electrode into the epicranial socket, different electrical stimulation types, comparable to tDCS, tACS, and tRNS in humans, can be delivered. Moreover, the practical steps for tES in alert rodents are introduced. The applied current density, stimulation duration, and stimulation type may be chosen depending on the experimental needs. The caveats, advantages, and disadvantages of this set-up are discussed, as well as safety and tolerability aspects.

Novel Therapeutic Targets Against Spreading Depression

Migraine is among the most prevalent and disabling neurological diseases in the world. Cortical spreading depression (SD) is an intense wave of neuronal and glial depolarization underlying migraine aura, and a headache trigger, which has been used as an experimental platform for drug screening in migraine. Here, we provide an overview of novel therapeutic targets that show promise to suppress SD, such as acid-sensing ion channels, casein kinase Iδ, P2X7-pannexin 1 complex, and neuromodulation, and outline the experimental models and essential quality measures for rigorous and reproducible efficacy testing.

Neuromodulation interventions for addictive disorders: challenges, promise, and roadmap for future research

Addictive disorders are a major public health concern, associated with high relapse rates, significant disability and substantial mortality. Unfortunately, current interventions are only modestly effective. Preclinical studies as well as human neuroimaging studies have provided strong evidence that the observable behaviours that characterize the addiction phenotype, such as compulsive drug consumption, impaired self-control, and behavioural inflexibility, reflect underlying dysregulation and malfunction in specific neural circuits. These developments have been accompanied by advances in neuromodulation interventions, both invasive as deep brain stimulation, and non-invasive such as repetitive transcranial magnetic stimulation and transcranial direct current stimulation. These interventions appear particularly promising as they may not only allow us to probe affected brain circuits in addictive disorders, but also seem to have unique therapeutic applications to directly target and remodel impaired circuits. However, the available literature is still relatively small and sparse, and the long-term safety and efficacy of these interventions need to be confirmed. Here we review the literature on the use of neuromodulation in addictive disorders to highlight progress limitations with the aim to suggest future directions for this field.

Animal models of transcranial direct current stimulation: Methods and mechanisms

The objective of this review is to summarize the contribution of animal research using direct current stimulation (DCS) to our understanding of the physiological effects of transcranial direct current stimulation (tDCS). We comprehensively address experimental methodology in animal studies, broadly classified as: (1) transcranial stimulation; (2) direct cortical stimulation in vivo and (3) in vitro models. In each case advantages and disadvantages for translational research are discussed including dose translation and the overarching "quasi-uniform" assumption, which underpins translational relevance in all animal models of tDCS. Terminology such as anode, cathode, inward current, outward current, current density, electric field, and uniform are defined. Though we put key animal experiments spanning decades in perspective, our goal is not simply an exhaustive cataloging of relevant animal studies, but rather to put them in context of ongoing efforts to improve tDCS. Cellular targets, including excitatory neuronal somas, dendrites, axons, interneurons, glial cells, and endothelial cells are considered. We emphasize neurons are always depolarized and hyperpolarized such that effects of DCS on neuronal excitability can only be evaluated within subcellular regions of the neuron. Findings from animal studies on the effects of DCS on plasticity (LTP/LTD) and network oscillations are reviewed extensively. Any endogenous phenomena dependent on membrane potential changes are, in theory, susceptible to modulation by DCS. The relevance of morphological changes (galvanotropy) to tDCS is also considered, as we suggest microscopic migration of axon terminals or dendritic spines may be relevant during tDCS. A majority of clinical studies using tDCS employ a simplistic dose strategy where excitability is singularly increased or decreased under the anode and cathode, respectively. We discuss how this strategy, itself based on classic animal studies, cannot account for the complexity of normal and pathological brain function, and how recent studies have already indicated more sophisticated approaches are necessary. One tDCS theory regarding "functional targeting" suggests the specificity of tDCS effects are possible by modulating ongoing function (plasticity). Use of animal models of disease are summarized including pain, movement disorders, stroke, and epilepsy.

The in vivo reduction of afferent facilitation induced by low frequency electrical stimulation of the motor cortex is antagonized by cathodal direct current stimulation of the cerebellum

Background

Low-frequency electrical stimulation to the motor cortex (LFSMC) depresses the excitability of motor circuits by long-term depression (LTD)-like effects. The interactions between LFSMC and cathodal direct current stimulation (cDCS) over the cerebellum are unknown.

Methods

We assessed the corticomotor responses and the afferent facilitation of corticomotor responses during a conditioning paradigm in anaesthetized rats. We applied LFSMC at a frequency of 1 Hz and a combination of LFSMC with cDCS.

Results

LFSMC significantly depressed both the corticomotor responses and the afferent facilitation of corticomotor responses. Simultaneous application of cDCS over the cerebellum antagonized the depression of corticomotor responses and cancelled the depression of the afferent facilitation.

Conclusion

Our results demonstrate that cDCS of the cerebellum is a potent modulator the inhibition of the motor circuits induced by LFSMC applied in vivo. These results expand our understanding of the effects of cerebellar DCS on motor commands and open novel applications for a cerebellar remote control of LFSMC-induced neuroplasticity. We suggest that the cerebellum acts as a neuronal machine supervising not only long-term potentiation (LTP)-like effects, but also LTD-like effects in the motor cortex, two mechanisms which underlie cerebello-cerebral interactions and the cerebellar control of remote plasticity. Implications for clinical ataxiology are discussed.

Pathophysiological targets for non-pharmacological treatment of migraine

Background Migraine is the most prevalent neurological disorder worldwide and ranked sixth among all diseases in years lived with disability. Overall preventive anti-migraine therapies have an effect in one patient out of two at the most, many of them being endowed with disabling adverse effects. No new disease-modifying drugs have come into clinical practice since the application to migraine of topiramate and botulinum toxin, the latter for its chronic form. There is thus clearly a need for more effective treatments that are devoid of, or have acceptable side effects. In recent years, scientific progress in migraine research has led to substantial changes in our understanding of the pathophysiology of migraine and paved the way for novel non-drug pathophysiological-targeted treatment strategies. Overview Several such non-drug therapies have been tested in migraine, such as oxidative phosphorylation enhancers, diets and non-invasive central or peripheral neurostimulation. All of them are promising for preventive migraine treatment and are quasi-devoid of side effects. Their advantage is that they can in theory be selected for individual patients according to their pathophysiological profile and they can (and probably should) be combined with the classical pharmacological armamentarium. Conclusion We will review here how knowledge of the functional anatomy and physiology of migraine mechanisms holds the key for more specific and effective non-pharmacological treatments.

Transcranial magnetic stimulation and potential cortical and trigeminothalamic mechanisms in migraine

A single pulse of transcranial magnetic stimulation has been shown to be effective for the acute treatment of migraine with and without aura. Here we aimed to investigate the potential mechanisms of action of transcranial magnetic stimulation, using a transcortical approach, in preclinical migraine models. We tested the susceptibility of cortical spreading depression, the experimental correlate of migraine aura, and further evaluated the response of spontaneous and evoked trigeminovascular activity of second order trigemontothalamic and third order thalamocortical neurons in rats. Single pulse transcranial magnetic stimulation significantly inhibited both mechanical and chemically-induced cortical spreading depression when administered immediately post-induction in rats, but not when administered preinduction, and when controlled by a sham stimulation. Additionally transcranial magnetic stimulation significantly inhibited the spontaneous and evoked firing rate of third order thalamocortical projection neurons, but not second order neurons in the trigeminocervical complex, suggesting a potential modulatory effect that may underlie its utility in migraine. In gyrencephalic cat cortices, when administered post-cortical spreading depression, transcranial magnetic stimulation blocked the propagation of cortical spreading depression in two of eight animals. These results are the first to demonstrate that cortical spreading depression can be blocked in vivo using single pulse transcranial magnetic stimulation and further highlight a novel thalamocortical modulatory capacity that may explain the efficacy of magnetic stimulation in the treatment of migraine with and without aura.

Computational modeling of neurostimulation in brain diseases

Neurostimulation as a therapeutic tool has been developed and used for a range of different diseases such as Parkinson's disease, epilepsy, and migraine. However, it is not known why the efficacy of the stimulation varies dramatically across patients or why some patients suffer from severe side effects. This is largely due to the lack of mechanistic understanding of neurostimulation. Hence, theoretical computational approaches to address this issue are in demand. This chapter provides a review of mechanistic computational modeling of brain stimulation. In particular, we will focus on brain diseases, where mechanistic models (e.g., neural population models or detailed neuronal models) have been used to bridge the gap between cellular-level processes of affected neural circuits and the symptomatic expression of disease dynamics. We show how such models have been, and can be, used to investigate the effects of neurostimulation in the diseased brain. We argue that these models are crucial for the mechanistic understanding of the effect of stimulation, allowing for a rational design of stimulation protocols. Based on mechanistic models, we argue that the development of closed-loop stimulation is essential in order to avoid inference with healthy ongoing brain activity. Furthermore, patient-specific data, such as neuroanatomic information and connectivity profiles obtainable from neuroimaging, can be readily incorporated to address the clinical issue of variability in efficacy between subjects. We conclude that mechanistic computational models can and should play a key role in the rational design of effective, fully integrated, patient-specific therapeutic brain stimulation.

Effects of anodal TDCS stimulation of left parietal cortex on visual spatial attention tasks in men and women across menstrual cycle

Sex hormonal variations have been shown to affect functional cerebral asymmetries in cognitive domains, contributing to sex-related differences in functional cerebral organization. The aim of this study was to investigate spatial attention by means of a bisection line test and computer-supported attention task during the menstrual cycle in healthy women compared to men, in basal condition and under Transcranial Direct Current Stimulation (TDCS) of the left parietal cortex. Women were studied during the menses, follicular and luteal phases, ascertained by transvaginal ultrasounds. In basal conditions, women showed a clear deviation toward the right in the bisection line test during the menstrual phase, similarly to men. The midpoint recognition in the computer-supported attention task was not influenced by the menstrual cycle for women, while men showed a significant increase in errors toward the left side. The anodal activation of the left parietal cortex did not affect the line bisection task, while in men it reduced the total amount of errors in midpoint recognition observed in the computer supported attention task. The hand-use effect demonstrated by the bisection-line test could be influenced by estrogen fluctuations, while the right hemisphere prevalence in spatial attention appears to be gender-related and scarcely influenced by the menstrual cycle. The left parietal cortex seems to exert a scarce effect on hand-use effect, while its activation is able to revert sex related right hemisphere supremacy.

Spreading depression features and Iba1 immunoreactivity in the cerebral cortex of developing rats submitted to treadmill exercise after treatment with monosodium glutamate

Physical exercise and excessive consumption of monosodium glutamate (MSG) can affect the morphological and electrophysiological organization of the brain during development. However, the interaction of both factors remains unclear. We analyzed the effect of this interaction on the excitability-related phenomenon known as cortical spreading depression (CSD) and the microglial reaction expressed as Iba1-immunolabeled cells in the rat motor cortex. MSG (2g/kg or 4g/kg) was administered every other day during the first 14 postnatal days. Treadmill exercise started at 21-23 days of life and lasted 3 weeks, 5 days/week, for 30min/day. At 45-60 days, CSD was recorded for 4h at two cortical points and the CSD parameters (velocity, amplitude, and duration of the negative potential change) calculated. Confirming previous observations, exercised rats presented with lower CSD velocities (3.29±0.18mm/min) than the sedentary group (3.80±0.18mm/min; P<0.05). MSG increased CSD velocities in the exercised rats compared to saline-treated and exercised animals in a dose-dependent manner (3.49±0.19, 4.05±0.18, and 3.27±0.26 for 2g/kg MSG, 4g/kg MSG, and saline, respectively; P<0.05). The amplitude (ranging from 14.3±5.9 to 18.7±6.2mV) and duration (46.7±11.1 to 60.5±11.6s) of the negative slow potential shift of the CSD were similar in all groups. Both exercise and MSG treatment increased Iba1 immunolabeling. The results confirm that physical exercise decelerates CSD propagation. However, it does not impede the CSD-accelerating action of MSG. These effects were accompanied by a cortical microglia reaction. Therefore, the data suggest that treadmill exercise early in life can influence the development of cortical electrical activity.

Safety and efficacy of transcranial direct current stimulation in acute experimental ischemic stroke

BACKGROUND AND PURPOSE

Transcranial direct current stimulation is emerging as a promising tool for the treatment of several neurological conditions, including cerebral ischemia. The therapeutic role of this noninvasive treatment is, however, limited to chronic phases of stroke. We thus ought to investigate whether different stimulation protocols could also be beneficial in the acute phase of experimental brain ischemia.

METHODS

The influence of both cathodal and anodal transcranial direct current stimulation in modifying brain metabolism of healthy mice was first tested by nuclear magnetic resonance spectroscopy. Then, mice undergoing transient proximal middle cerebral artery occlusion were randomized and treated acutely with anodal, cathodal, or sham transcranial direct current stimulation. Brain metabolism, functional outcomes, and ischemic lesion volume, as well as the inflammatory reaction and blood brain barrier functionality, were analyzed.

RESULTS

Cathodal stimulation was able, if applied in the acute phase of stroke, to preserve cortical neurons from the ischemic damage, to reduce inflammation, and to promote a better clinical recovery compared with sham and anodal treatments. This finding was attributable to the significant decrease of cortical glutamate, as indicated by nuclear magnetic resonance spectroscopy. Conversely, anodal stimulation induced an increase in the postischemic lesion volume and augmented blood brain barrier derangement.

CONCLUSIONS

Our data indicate that transcranial direct current stimulation exerts a measurable neuroprotective effect in the acute phase of stroke. However, its timing and polarity should be carefully identified on the base of the pathophysiological context to avoid potential harmful side effects.

Cathodal transcranial direct current stimulation induces regional, long-lasting reductions of cortical blood flow in rats

OBJECTIVE

Transcranial direct current stimulation (tDCS) induces polarity-specific changes of cerebral blood flow (CBF). To determine whether these changes are focally limited or if they incorporate large cortical regions and thus have the potential for a therapeutic application, we investigated the effects of cathodal tDCS on CBF in an established tDCS rat model with particular attention to the spatial extension in CBF changes using laser Doppler blood perfusion imaging (LDI).

METHODS

Twenty-one Sprague Dawley rats received a single 15-minute session of cathodal tDCS at current intensities of 200, 400, 600, or 700 μA applied over electrode contact areas (ECA) of 3·5, 7·0, 10·5, or 14·0 mm(2). One animal died prior to the stimulation. Cerebral blood flow was measured prior and after tDCS with LDI in three defined regions of interest (ROI) over the stimulated left hemisphere (region anterior to ECA - ROI 1, ECA - ROI 2, region posterior to ECA - ROI 3).

RESULTS

A regional decrease in CBF was measured after cathodal tDCS, the extent of the decrease depending on the current density applied. The most effective and spatially limited reduction in CBF (up to 50%, lasting as long as 90 minutes) was found after the application of 600 μA over an ECA of 10·5 mm(2). This significant reduction in CBF even lasted up to 90 minutes in distant cortical areas (ROI 1 and 3) that were not directly related to the ECA (ROI 2).

DISCUSSION

Cathodal tDCS induces a regional, long-lasting, reversible decrease in CBF that is not limited to the region to which tDCS is applied.

Trains of epidural DC stimulation of the cerebellum tune corticomotor excitability

We assessed the effects of anodal/cathodal direct current stimulation (DCS) applied epidurally over the cerebellum. We studied the excitability of both the motor cortex and the anterior horn of the spinal cord in adult rats under continuous anesthesia. We also investigated the effects on the spatial representation of a couple of agonist/antagonist muscles on primary motor cortex. Moreover, we evaluated the effects on the afferent inhibition in a paradigm of conditioned corticomotor responses. Anodal DCS of the cerebellum (1) decreased the excitability of the motor cortex, (2) reduced the excitability of F waves, as shown by the decrease of both mean F/mean M ratios and persistence of F waves, (3) exerted a “smoothing effect” on corticomotor maps, reshaping the representation of muscles on the motor cortex, and (4) enhanced the afferent inhibition of conditioned motor evoked responses. Cathodal DCS of the cerebellum exerted partially reverse effects. DCS of the cerebellum modulates the excitability of both motor cortex and spinal cord at the level of the anterior horn. This is the first demonstration that cerebellar DCS tunes the shape of corticomotor maps. Our findings provide a novel mechanism by which DCS of the cerebellum exerts a remote neuromodulatory effect upon motor cortex.

Treatments in context: transcranial direct current brain stimulation as a potential treatment in pediatric psychosis

Childhood-onset schizophrenia is a chronic, severe form of schizophrenia, and is typically treatment resistant. Even after optimized pharmacotherapy, a majority (over 70%) of these pediatric patients present lasting psychotic symptoms and impaired cognition, necessitating the need for novel treatment modalities. Recent work in transcranial magnetic stimulation suggests moderate efficacy in symptom reduction in adult patients with schizophrenia; however, the transcranial magnetic stimulation treatment is cumbersome for this severely ill population. Transcranial direct current stimulation may provide a safe and effective adjuvant treatment for continued residual symptoms of schizophrenia.

Transcranial direct current stimulation in stroke rehabilitation: a review of recent advancements

Transcranial direct current stimulation (tDCS) is a promising technique to treat a wide range of neurological conditions including stroke. The pathological processes following stroke may provide an exemplary system to investigate how tDCS promotes neuronal plasticity and functional recovery. Changes in synaptic function after stroke, such as reduced excitability, formation of aberrant connections, and deregulated plastic modifications, have been postulated to impede recovery from stroke. However, if tDCS could counteract these negative changes by influencing the system's neurophysiology, it would contribute to the formation of functionally meaningful connections and the maintenance of existing pathways. This paper is aimed at providing a review of underlying mechanisms of tDCS and its application to stroke. In addition, to maximize the effectiveness of tDCS in stroke rehabilitation, future research needs to determine the optimal stimulation protocols and parameters. We discuss how stimulation parameters could be optimized based on electrophysiological activity. In particular, we propose that cortical synchrony may represent a biomarker of tDCS efficacy to indicate communication between affected areas. Understanding the mechanisms by which tDCS affects the neural substrate after stroke and finding ways to optimize tDCS for each patient are key to effective rehabilitation approaches.

Epidural direct current stimulation over the left medial prefrontal cortex facilitates spatial working memory performance in rats

BACKGROUND

Extensive evidence supports the notion that modulation of PFC excitability using low-intensity electrical stimulation is a promising modality for treating neuropsychiatric diseases and improving cognitive function.

OBJECTIVE

This study examined the effects of epidural direct current stimulation (eDCS), a method providing smaller shunting of current and more focal stimulation, on spatial working memory.

METHODS

Male Wistar rats that were well trained in an 8-arm radial maze and in which 5-mm round electrodes were implanted over the left medial prefrontal cortex (mPFC) received anodal eDCS (400 μA during 11 min) (n = 9) or sham procedure (n = 9) five minutes before delayed tests in the radial maze.

RESULTS

Animals that received eDCS over the left mPFC had significantly fewer errors in the post-delay performance on the 1-h (P < 0.01), 4-h (P < 0.001), and 10-h (P < 0.001) delayed tests compared with sham-treated animals. General locomotor activity was unaffected because time spent in each visited arm did not change significantly by eDCS. There was no evidence of neuronal lesions in the mPFC underneath the eDCS.

CONCLUSIONS

Our results suggest that epidural direct current stimulation over the mPFC facilitates spatial working memory in rats, an effect that persisted over the long term.

Clinical research with transcranial direct current stimulation (tDCS): challenges and future directions

BACKGROUND

Transcranial direct current stimulation (tDCS) is a neuromodulatory technique that delivers low-intensity, direct current to cortical areas facilitating or inhibiting spontaneous neuronal activity. In the past 10 years, tDCS physiologic mechanisms of action have been intensively investigated giving support for the investigation of its applications in clinical neuropsychiatry and rehabilitation. However, new methodologic, ethical, and regulatory issues emerge when translating the findings of preclinical and phase I studies into phase II and III clinical studies. The aim of this comprehensive review is to discuss the key challenges of this process and possible methods to address them.

METHODS

We convened a workgroup of researchers in the field to review, discuss, and provide updates and key challenges of tDCS use in clinical research.

MAIN FINDINGS/DISCUSSION

We reviewed several basic and clinical studies in the field and identified potential limitations, taking into account the particularities of the technique. We review and discuss the findings into four topics: (1) mechanisms of action of tDCS, parameters of use and computer-based human brain modeling investigating electric current fields and magnitude induced by tDCS; (2) methodologic aspects related to the clinical research of tDCS as divided according to study phase (ie, preclinical, phase I, phase II, and phase III studies); (3) ethical and regulatory concerns; and (4) future directions regarding novel approaches, novel devices, and future studies involving tDCS. Finally, we propose some alternative methods to facilitate clinical research on tDCS.

The use of cortical spreading depression for studying the brain actions of antioxidants

OBJECTIVES

We review the main adverse effects of reactive oxygen species (ROS) in the mammalian organism, introducing the reader on the worldwide problem of the ROS neurophysiological impact on the developing and the adult brain, and discussing the neuroprotective action of antioxidant molecules.

METHODS

We briefly present the electrophysiological phenomenon designated as 'cortical spreading depression' (CSD), as a parameter of normal brain functioning. We highlight recent electrophysiological advances obtained in experimental studies from our laboratory and from others, showing how to investigate the ROS effects on the brain by using the CSD phenomenon.

RESULTS

Under conditions such as aging, ROS production by photo-activation of dye molecules and ethanol consumption, we describe the effects, on CSD, of treating animals with (1) antioxidants and (2) with antioxidant-deficient diets.

DISCUSSION

The current understanding of how ROS affect brain electrophysiological activity and the possible interaction between these ROS effects and those effects of altered nutritional status of the organism are discussed.

Therapeutic effects of peripheral magnetic stimulation on traumatic brachial plexopathy: clinical and neurophysiological study

OBJECTIVE

To evaluate the therapeutic effects of peripheral repetitive magnetic stimulation (rMS) on recovery of traumatic brachial plexopathy.

PATIENTS AND METHODS

Thirty-four patients with traumatic brachial plexopathy were studied. Strength of different muscles of upper limbs was evaluated neurologically. Nerve conduction studies (NCS), upper limb F-waves and visual analogue scales (VAS) for shoulder pain were obtained for all patients. These were randomly assigned into two groups with a ratio of 2:1; each patient received conventional physical therapy modalities and active exercises as well as real or sham rMS applied over the superior trapezius muscle of the affected limb daily for 10 sessions. Patients were reassessed with the same parameters after the 5th and the 10th session, and 1 month after rMS treatment.

RESULTS

No significant between-group differences were recorded at baseline assessment. Significant improvement was observed (time X groups) after real rMS in comparison to the sham group (P=0.0001 for muscle strength and 0.01 for VAS of shoulder pain). These improvements were still present at 1 month after the end of treatment. In accordance with the clinical improvement, a significant improvement was recorded in the neurophysiological parameters in the real vs the sham group.

CONCLUSIONS

We demonstrate that peripheral rMS for 10 sessions may have positive therapeutic effects on motor recovery and pain relief in patients with traumatic brachial plexopathy. Therefore, it is a useful adjuvant in the therapy of these patients.

Differential effects of physical exercise and L-arginine on cortical spreading depression in developing rats

OBJECTIVE

We investigated the effect of early-in-life administration of L-arginine, combined with physical exercise, on cortical spreading depression (CSD) in young and adult rats.

METHODS

L-arginine (300 mg/kg/day, n = 40) or distilled water (vehicle, n = 40) was given to the rats during postnatal days 7-35 by gavage. Physical exercise (treadmill) was carried out during postnatal days 15-35 in half of the animals in each gavage condition described above. The other half (non-exercised) was used for comparison. When the animals reached 35-45 days (young groups) or 90-120 days of age (adult) CSD was recorded on two cortical points during 4 hours and CSD propagation velocity was calculated.

RESULTS

L-arginine-treated + exercised rats had increased body weight, but not brain weight, in adult age compared to L-arginine + non-exercised ones (P < 0.05). In both young and adult animals, L-arginine increased, whereas exercise decreased the CSD propagation velocity. Analysis of variance revealed a significant interaction between gavage treatment and age (P < 0.001), and also between gavage treatment and exercise (P = 0.004), but not between age and exercise. An additional control group of young rats, treated with 300 mg/kg of L-histidine, presented CSD velocities comparable to the corresponding water-treated controls, suggesting that the CSD acceleration seen in the L-arginine group was an L-arginine-specific effect, rather than an effect due to a non-specific amino acid imbalance.

DISCUSSION

L-arginine and exercise affect CSD differentially (L-arginine accelerated, while exercise decelerated CSD), and both effects did interact. Probably, they depend on developmental plasticity changes associated with the treatments.

Dynamic Diffusion Magnetic Resonance Imaging of Infarct Formation and Peri-infarct Spreading Depression after Middle Cerebral Artery Occlusion (MCAO) in macacca fasicularis

Dynamic diffusion MRI was used to visualize hyperacute stroke formation in the brain of a cynomolgus macaque. Under fluoroscopic guidance, a microcatheter was placed into the middle cerebral artery (MCA). The animal was immediately transferred to a 1.5T clinical scanner. Dynamic T2-weighted imaging during bolus injection of Oxygen-17 enriched water through the microcatheter mapped out the territory perfused by the MCA segment. Serial diffusion measurements were made using diffusion-weighted echo-planar imaging, with a temporal resolution of 15 seconds, during injection of a glue embolus into the microcatheter. The apparent diffusion coefficient declined within the lesion core. A wave of transient diffusion decline spread through peripheral uninvolved brain immediately following stroke induction. The propagation speed and pattern is consistent with spreading peri-infarct depolarizations (PID). The detection of PIDs following embolic stroke in a higher nonhuman primate brain supports the hypothesis that spreading depressions may occur following occlusive stroke in humans.

Lack of clinically detectable acute changes on autonomic or thermoregulatory functions in healthy subjects after transcranial direct current stimulation (tDCS)

BACKGROUND

Neuromodulatory techniques, such as transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS), have been increasingly studied as possible treatments for many neurological and psychiatric disorders. tDCS is capable of inducing changes in regional cerebral blood flow in both cortical and subcortical structures, as shown by positron emission tomography studies, and might conceivably affect hypothalamic and autonomic nervous system functions. However, it remains unknown whether acute changes in autonomic or hypothalamic functions may be triggered by conventional tDCS protocols.

OBJECTIVE/HYPOTHESIS

To verify whether tDCS, when performed with a bipolar cephalic montage, is capable of inducing acute changes in autonomic or hypothalamic functions in healthy subjects.

METHODS

Fifty healthy volunteers were studied. tDCS was performed with the anode over the C3 position and the cathode over the right supraorbital region. Subjects received either real or sham tDCS. Parameters assessed before and after a 20-minute session included blood pressure, tympanic thermometry, hand skin temperature, heart rate and ventilatory rate. Plasma concentrations of cortisol were also measured in a sub-set of 10 participants.

RESULTS

A repeated-measures, mixed-design ANOVA showed significant changes in hand skin temperature (P = .005) and cortisol levels (P < .001) after both real and sham stimulation. There were no statistically significant changes in any of the other measurements.

CONCLUSIONS

The changes in hand temperature and cortisol levels, having occurred in both the sham and experimental groups, probably reflect a non-specific stress response to a new procedure. There were no significant changes in autonomic functions, ventilation rate or core body temperature that can be attributed to conventional tDCS applied to healthy volunteers.

Respective implications of glutamate decarboxylase antibodies in stiff person syndrome and cerebellar ataxia

BACKGROUND

To investigate whether Stiff-person syndrome (SPS) and cerebellar ataxia (CA) are associated with distinct GAD65-Ab epitope specificities and neuronal effects.

METHODS

Purified GAD65-Ab from neurological patients and monoclonal GAD65-Ab with distinct epitope specificities (b78 and b96.11) were administered in vivo to rat cerebellum. Effects of intra-cerebellar administration of GAD65-Ab were determined using neurophysiological and neurochemical methods.

RESULTS

Intra-cerebellar administration of GAD65-Ab from a SPS patient (Ab SPS) impaired the NMDA-mediated turnover of glutamate, but had no effect on NMDA-mediated turnover of glycerol. By contrast, GAD65-Ab from a patient with cerebellar ataxia (Ab CA) markedly decreased the NMDA-mediated turnover of glycerol. Both GAD65-Ab increased the excitability of the spinal cord, as assessed by the F wave/M wave ratios. The administration of BFA, an inhibitor of the recycling of vesicles, followed by high-frequency stimulation of the cerebellum, severely impaired the cerebello-cortical inhibition only when Ab CA was used. Moreover, administration of transcranial direct current stimulation (tDCS) of the motor cortex revealed a strong disinhibition of the motor cortex with Ab CA. Monoclonal antibodies b78 and b96.11 showed distinct effects, with greater effects of b78 in terms of increase of glutamate concentrations, impairment of the adaptation of the motor cortex to repetitive peripheral stimulation, disinhibition of the motor cortex following tDCS, and increase of the F/M ratios. Ab SPS shared antibody characteristics with b78, both in epitope recognition and ability to inhibit enzyme activity, while Ab CA had no effect on GAD65 enzyme activity.

CONCLUSIONS

These results suggest that, in vivo, neurological impairments caused by GAD65-Ab could vary according to epitope specificities. These results could explain the different neurological syndromes observed in patients with GAD65-Ab.

Spreading depression: from serendipity to targeted therapy in migraine prophylaxis

Despite the relatively well-characterized headache mechanisms in migraine, upstream events triggering individual attacks are poorly understood. This lack of mechanistic insight has hampered a rational approach to prophylactic drug discovery. Unlike targeted abortive and analgesic interventions, mainstream migraine prophylaxis has been largely based on serendipitous observations (e.g. propranolol) and presumed class effects (e.g. anticonvulsants). Recent studies suggest that spreading depression is the final common pathophysiological target for several established or investigational migraine prophylactic drugs. Building on these observations, spreading depression can now be explored for its predictive utility as a preclinical drug screening paradigm in migraine prophylaxis.

Propagation of spreading depression inversely correlates with cortical myelin content

OBJECTIVE

Cortical myelin can be severely affected in patients with demyelinating disorders of the central nervous system. However, the functional implication of cortical demyelination remains elusive. In this study, we investigated whether cortical myelin influences cortical spreading depression (CSD).

METHODS

CSD measurements were performed in rodent models of toxic and autoimmune induced cortical demyelination, in neuregulin-1 type I transgenic mice displaying cortical hypermyelination, and in glial fibrillary acidic protein-transgenic mice exhibiting pronounced astrogliosis.

RESULTS

Cortical demyelination, but not astrogliosis or inflammation per se, was associated with accelerated CSD. In contrast, hypermyelinated neuregulin-1 type I transgenic mice displayed a decelerated CSD propagation.

INTERPRETATION

Cortical myelin may be crucially involved in the stabilization and buffering of extracellular ion content that is decisive for CSD propagation velocity and cortical excitability, respectively. Our data thus indicate that cortical involvement in human demyelinating diseases may lead to relevant alterations of cortical function.

Trains of transcranial direct current stimulation antagonize motor cortex hypoexcitability induced by acute hemicerebellectomy

OBJECT

The cerebellum is a key modulator of motor cortex activity, allowing both the maintenance and fine-tuning of motor cortex discharges. One elemental defect associated with acute cerebellar lesions is decreased excitability of the contralateral motor cortex, which is assumed to participate in deficits in skilled movements and considered a major defect in motor cortex properties. In the present study, the authors assessed the effect of trains of anodal transcranial direct current stimulation (tDCS), which elicits polarity-dependent shifts in resting membrane potentials.

METHODS

Transcranial DCS countered the defect in motor cortex excitability contralaterally to the hemicerebellar ablation.

RESULTS

The depression of both the H-reflex and F wave remained unchanged with tDCS, and cutaneomuscular reflexes remained unaffected. Transcranial DCS antagonized motor cortex hypoexcitability induced by high-frequency stimulation of interpositus nucleus.

CONCLUSIONS

The authors' results show that tDCS has the potential to modulate motor cortex excitability after acute cerebellar dysfunction. By putting the motor cortex at the appropriate level of excitability, tDCS might allow the motor cortex to become more reactive to the procedures of training or learning.

Spinal hyperexcitability and bladder hyperreflexia during reversible frontal cortical inactivation induced by low-frequency electrical stimulation in the cat

Spinal hyperexcitability and hyperreflexia gradually develop in the majority of stroke patients. These pathologies develop as a result of reduced cortical modulation of spinal reflexes, mediated largely indirectly via relays in the brainstem and other subcortical structures. Cortical control of spinal reflexes is markedly different in small animals, such as rodents, while in some larger species, such as cats, it is more comparable to that in humans. In this study, we developed a novel model of stroke in the cat, with controllable and reversible inhibition of cortical neuronal activity appearing approximately 1h after initiation of low-frequency electrical stimulation in the frontal cerebral cortex, evidenced by a large increase in the alpha frequency band (7-14 Hz) of the frontal electrocorticographic signal. Hyperreflexia of the urinary bladder developed 3h or more after induction of reversible cortical inactivation with optimized stimulation parameters (frequency of 1-2 Hz, amplitude of 10 mA, applied for 30 min). The bladder hyperreflexia persisted for at least 8h, and disappeared within 24h. At the S2 level of the spinal cord, where neural circuits mediating micturition and other pelvic reflexes reside, we have recorded an increase in neuronal activity correlated with the development of hyperreflexia. The low-frequency stimulation-induced reversible cortical inactivation model of stroke is highly reproducible and allows evaluation of spinal hyperexcitability and hyperreflexia using within-animal comparisons across experimental conditions, which can be of great value in examination of mechanisms of spinal hyperreflexia following stroke or brain trauma, and for developing more effective treatments for these conditions.