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Beta-frequency EEG activity increased during transcranial direct current stimulation
... Only the online method can be defined as a true multimodal approach (e.g. [7,[21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39]), although the offline method can also provide important information. When designing an experiment, it is crucial to specify whether an online or an offline method is going to be adopted because these two approaches require completely different technical procedures and provide different information about the mechanisms of action of tES. ...
... In the following section, after reporting a gross description of the main studies in this field (both online and offline approaches), we will briefly describe only some recent advances (for an overview of the seminal works, see the review paper by Miniussi and coworkers [20]). The majority of the studies have recorded EEG activity in the resting state, such as by analysing neural oscillations associated with tDCS by frequency changes [22,24,26,28,41,43,[89][90][91][92][93][94] or by recording the effects of tDCS on functional connectivity [19,30,31]. In some instances, TMS was also incorporated to probe changes in excitability or connectivity before and after tDCS [25,69,91,[95][96][97] and even during tDCS stimulation [35]. ...
In the field of neuromodulation, we have observed an increase in the popularity of approaches that combine transcranial electrical stimulation (tES) with additional methods to establish, in vivo, the neurophysiological consequences of a given experimental or therapeutic manipulation. Research in the development of multimodal approaches has provided new methods that can be combined with tES to study brain functions. This chapter aims to introduce the reader to some basic principles of this multimodal approach. We begin with a brief definition of multimodal association and a description of its advantages. Afterwards, we provide a more specific description of how we can combine tES with electroencephalography (EEG). We show that EEG is a feasible and reliable way to track electrophysiological changes induced by tES, deepening our understanding of the mechanisms of action of this tool and revealing the key role of several stimulation features. In neuropsychiatric diseases, a combined tES-EEG approach may allow the prediction of clinical responses to tES, the discrimination of responders from non-responders, allowing improvements in the efficacy of tES and the tracking of tES-induced neuroplastic changes associated with recovery.
... All recordings were band-pass-filtered between 0.7 and 45 Hz, with 5 bands of interest chosen: delta (1-4 Hz), theta (4-8 Hz), alpha (8-12 Hz), beta1 (12-18 Hz) and beta2 (18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30). Both sham and active stimulation pre-and post-recordings were visually inspected, and noisy epochs were discarded. ...
... In addition, these patients demonstrated an increase in connectivity after the active stimulation in beta1 between the frontal, prefrontal and frontopolar areas. Previous studies found similar increased beta power after a single stimulation session over the prefrontal cortex [24] or primary motor cortex [25]. The authors concluded that tDCS could prime brain activity to a ''ready state'' to perform cognitive tasks (prefrontal tDCS) or motor-related tasks (M1 tDCS). ...
Background:
Spasticity management in severely brain-injured patients with disorders of consciousness (DOC) is a major challenge because it leads to complications and severe pain that can seriously affect quality of life.
Objectives:
We aimed to determine the feasibility of a single session of transcranial direct current stimulations (tDCS) to reduce spasticity in chronic patients with DOC.
Methods:
We enrolled 14 patients in this double-blind, sham-controlled randomized crossover pilot study. Two cathodes were placed over the left and right primary motor cortex and 2 anodes over the left and right prefrontal cortex. Hypertonia of the upper limbs and level of consciousness were assessed by the Modified Ashworth Scale (MAS) and the Coma Recovery Scale-Revised (CRS-R). Resting state electroencephalography was also performed.
Results:
At the group level, spasticity was reduced in only finger flexors. Four responders (29%) showed reduced hypertonicity in at least 2 joints after active but not sham stimulation. We found no behavioural changes by the CRS-R total score. At the group level, connectivity values in beta2 were higher with active versus sham stimulation. Relative power in the theta band and connectivity in the beta band were higher for responders than non-responders after the active stimulation.
Conclusion:
This pilot study highlights the potential benefit of using tDCS for reducing upper-limb hypertonia in patients with chronic DOC. Large-sample clinical trials are needed to optimize and validate the technique.
... Chronic pain is a multidimensional issue, accompanied by a wide variety of neuronal and psychological factors altering the communication between different brain regions. In this study, all eight patients experienced chronic pain with medium scores of 35.5 (25.5-40) on the PCS and CSI scores of 53 (46)(47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57)(58)(59)(60)(61)(62)(63), respectively meaning a clinically relevant degree of catastrophizing (cutoff scores ≥30/52) (25) and increased risk for the presence of symptoms of central sensitization (cut-off scores ≥40/100) (29). The latter is suggestive for the presence of central sensitization, defined as an abnormal amplification of information in the central nervous system, particularly in response to afferent activity (39,40). ...
... HD SCS: 32[15.5-35]), χ2 (2) = 1.93, p = 0.38, nor in CSI score (no SCS: 53[46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63], CON SCS: 48, HD SCS: 53[45.7-59]), χ2 (2) = 0.54, p = 0.76, between the three conditions. ...
Objectives
Spinal cord stimulation (SCS) is considered an effective pain‐relieving treatment for patients with Failed Back Surgery Syndrome (FBSS). Despite the clinical effectiveness, it is unknown whether the altered functional connectivity in such patients, as compared to healthy persons, can be influenced by SCS. Therefore, the goal of this study is to evaluate whether brain connectivity assessed by EEG differs between baseline and SCS in patients with FBSS.
Materials and Methods
Eight patients with FBSS underwent a resting‐state EEG protocol before SCS, 1.5 months and 2.5 months after receiving SCS. At each frequency band, power spectrums were compared for no SCS, conventional (CON) SCS and High Dose (HD) SCS. Functional connectivity, with the aid of eConnectome was also calculated.
Results
Significant differences in the average power density spectrum over the whole scalp were observed between no SCS, CON SCS and HD SCS in delta, theta and beta frequency bands (p < 0.01). The average power spectrum for CON SCS was significantly lower than the average power spectrum for HD SCS. Marked increases in strength of the information flow between electrode pair FC3‐TP9 in the beta frequency band (p = 0.006) were found in favor of HD SCS.
Conclusions
The differences in power spectrum and connectivity between the three conditions lead to the hypothesis that HD SCS differs from CON SCS on average power spectrum, suggesting that HD SCS may have a higher contribution on the excitatory bottom‐up pathway.
... To better understand the underlying effects that tDCS has on the brain several studies have been conducted using tDCS in conjunction with non-invasive brain recording such as electroencephalography EEG [23][24][25][26][27][28], magnetoencephalography MEG [29][30][31], functional near infrared spectroscopy fNIRS [32], and functional magnetic resonance imaging fMRI [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50]. These studies have shown considerable variability in the effects of tDCS on brain activity and connectivity dependent on presence or absence of a task, stimulation site, polarity of stimulation, amplitude of stimulation, timing of stimulation, and nature of the task under investigation. ...
... For the target-error feedback contrast no significant differences (T = -1. 28 ...
Transcranial direct current stimulation (tDCS) has been shown to enhance cognitive performance on a variety of tasks. It is hypothesized that tDCS enhances performance by affecting task related cortical excitability changes in networks underlying or connected to the site of stimulation facilitating long term potentiation. However, many recent studies have called into question the reliability and efficacy of tDCS to induce modulatory changes in brain activity. In this study, our goal is to investigate the individual differences in tDCS induced modulatory effects on brain activity related to the degree of enhancement in performance, providing insight into this lack of reliability. In accomplishing this goal, we used functional magnetic resonance imaging (fMRI) concurrently with tDCS stimulation (1 mA, 30 minutes duration) using a visual search task simulating real world conditions. The experiment consisted of three fMRI sessions: pre-training (no performance feedback), training (performance feedback which included response accuracy and target location and either real tDCS or sham stimulation given), and post-training (no performance feedback). The right posterior parietal cortex was selected as the site of anodal tDCS based on its known role in visual search and spatial attention processing. Our results identified a region in the right precentral gyrus, known to be involved with visual spatial attention and orienting, that showed tDCS induced task related changes in cortical excitability that were associated with individual differences in improved performance. This same region showed greater activity during the training session for target feedback of incorrect (target-error feedback) over correct trials for the tDCS stim over sham group indicating greater attention to target features during training feedback when trials were incorrect. These results give important insight into the nature of neural excitability induced by tDCS as it relates to variability in individual differences in improved performance shedding some light the apparent lack of reliability found in tDCS research.
... These clinical outcomes failed to provide proof that drugs used for treating MCI can precisely target the neurophysiological objectives. Recently, transcranial direct current stimulation (tDCS), a method used to noninvasively stimulate specific cortical regions of the brain with a mild (<2 mA) and persistent current [13][14][15], has shown a clinically significant effect on various neuropsychiatric diseases [16]. In patients with depression, 1-2 weeks of treatment with tDCS improved both the symptoms and psychological scale of patients on the Montgomery-Asberg Depression Scale (MADRS) [17,18] even more than conventional psychiatric drugs that selectively block the serotonin transporter [19]. ...
... The experimenter was not informed whether the current trial is the real or the sham condition. The patients were stimulated with a DC stimulator developed by Yun and colleagues [15]. The anodal electrode was placed on the left dorsolateral prefrontal cortex (DLPFC) (F3; 10-20 EEG system), and the cathode electrode was placed on the right DLPFC (F4; 10-20 EEG system). ...
Background
Mild cognitive impairment (MCI) is a syndrome that disrupts an individual’s cognitive function but preserves activities of daily living. MCI is thought to be a prodromal stage of dementia, which disrupts patients’ daily lives and causes severe cognitive dysfunction. Although extensive clinical trials have attempted to slow or stop the MCI to dementia conversion, the results have been largely unsuccessful. The purpose of this study was to determine whether noninvasive electrical stimulation of MCI changes glucose metabolism. Methods
Sixteen MCI patients participated in this study. We used transcranial direct current stimulation (tDCS) (2 mA/day, three times per week for 3 weeks) and assessed positron emission tomography (18 F-FDG) before and after 3 weeks of stimulation. ResultsWe showed that regular and relatively long-term use of tDCS significantly increased regional cerebral metabolism in MCI patients. Furthermore, subjective memory satisfaction and improvement of the memory strategies of participants were observed only in the real tDCS group after 3 weeks of stimulation. Conclusion
Our findings suggest that neurophysiological intervention of MCI could improve glucose metabolism and transient memory function in MCI patients.
... One study found that anodal tDCS over the left DLPFC resulted in an overall increase in the average frequency of brain activity, with a reduction in power at lower frequencies and/or an increase at higher frequencies (Accornero et al., 2014). In contrast, an increase in low frequency beta activity was reported during anodal stimulation of the left DLPFC using a bi-frontal (F3-F4) montage (Song et al., 2014). Similarly, Wirth et al. (2011) incorporated a language task during stimulation and EEG recording and found a significant reduction in delta power after anodal tDCS over the left DLPFC. ...
... Using a similar bi-frontal montage and experimental paradigm, Accornero et al. (2014) noted a significant increase in mean frequency following active tDCS, and no change from baseline subsequent to sham stimulation. Similarly, other studies examining the EEG outcomes of tDCS to the prefrontal cortex report an increase in beta (Song et al., 2014), decrease in theta (Jacobson et al., 2012a), or a reduction in delta activity (Keeser et al., 2011b;Wirth et al., 2011). Although not explicitly analyzed, these findings would likely manifest in an increased mean frequency. ...
Transcranial direct current stimulation (tDCS) is proposed as a tool to investigate cognitive functioning in healthy people and as a treatment for various neuropathological disorders. However, the underlying cortical mechanisms remain poorly understood. We aim to investigate whether resting-state electroencephalography (EEG) can be used to monitor the effects of tDCS on cortical activity. To end we tested whether the spectral content of ongoing EEG activity is significantly different after a single session of active tDCS compared to sham stimulation. Twenty participants were tested in a sham-controlled, randomized, crossover design. Resting-state EEG was acquired before, during and after active tDCS to the left dorsolateral prefrontal cortex (15 min of 2mA tDCS) and sham stimulation. Electrodes with a diameter of 3.14 cm2 were used for EEG and tDCS. Partial least squares (PLS) analysis was used to examine differences in power spectral density and the EEG mean frequency to quantify the slowing of EEG activity after stimulation. PLS revealed a significant increase in spectral power at frequencies below 15 Hz and a decrease at frequencies above 15 Hz after active tDCS (P=0.001). The EEG mean frequency was significantly reduced after both active tDCS (P
... Indeed, clinically effective (FDA-approved) neuromodulation technology typically requires patient-specific setup for success, including neuronavigated TMS and DBS [28][29][30][31]; clinical adoption of tES may ultimately be supported through EEGguidance. EEG-informed tES can be implemented under openloop, where EEG is imaged before stimulation [32], or as closed-loop regimes given that scalp EEG patterns vary in time, and tES has been shown to modulate EEG activity [33][34][35][36][37]. EEG-guided tES is supported by increased sophistication in EEG and stimulation hardware [14,15,38]. ...
... In addition to reduced hardware complexity, whereas a few non-ideal EEG electrodes do not necessarily compromise an entire recording, for tES even one poor electrode contact can compromise tolerability [40,77,100]. In contrast to EEG, where broad coverage and high density enhances imaging [36,83], for tES low-electrode deployments can approach optimality if the target is known (model-based approaches in figure 2; [5,62,101]). Whereas approaches based on uniform tES electrode configuration quickly degrade in performance with reduced number of electrodes (figure 3), we show that Ad-Hoc approaches achieve reasonable results targeting with just two and five electrodes for tangential and radial modeled source directions, respectively ( figure 5). ...
Objective:
There is longstanding interest in using EEG measurements to inform transcranial Electrical Stimulation (tES) but adoption is lacking because users need a simple and adaptable recipe. The conventional approach is to use anatomical head-models for both source localization (the EEG inverse problem) and current flow modeling (the tES forward model), but this approach is computationally demanding, requires an anatomical MRI, and strict assumptions about the target brain regions. We evaluate techniques whereby tES dose is derived from EEG without the need for an anatomical head model, target assumptions, difficult case-by-case conjecture, or many stimulation electrodes.
Approach:
We developed a simple two-step approach to EEG-guided tES that based on the topography of the EEG: (1) selects locations to be used for stimulation; (2) determines current applied to each electrode. Each step is performed based solely on the EEG with no need for head models or source localization. Cortical dipoles represent idealized brain targets. EEG-guided tES strategies are verified using a finite element method simulation of the EEG generated by a dipole, oriented either tangential or radial to the scalp surface, and then simulating the tES-generated electric field produced by each model-free technique. These model-free approaches are compared to a 'gold standard' numerically optimized dose of tES that assumes perfect understanding of the dipole location and head anatomy. We vary the number of electrodes from a few to over three hundred, with focality or intensity as optimization criterion.
Main results:
Model-free approaches evaluated include (1) voltage-to-voltage, (2) voltage-to-current; (3) Laplacian; and two Ad-Hoc techniques (4) dipole sink-to-sink; and (5) sink to concentric. Our results demonstrate that simple ad hoc approaches can achieve reasonable targeting for the case of a cortical dipole, remarkably with only 2-8 electrodes and no need for a model of the head.
Significance:
Our approach is verified directly only for a theoretically localized source, but may be potentially applied to an arbitrary EEG topography. For its simplicity and linearity, our recipe for model-free EEG guided tES lends itself to broad adoption and can be applied to static (tDCS), time-variant (e.g., tACS, tRNS, tPCS), or closed-loop tES.
... Similar post-hoc studies have been performed using fMRI in works such as (Keeser et al., 2011) where the network connectivity before and after tES are studied. With respect to the simultaneous analysis of response and stimulation, EEG-based monitoring has been leveraged in a large fraction of works (Schestatsky et al., 2013;Song et al., 2014). Also, a notable pattern in recent works is an increase in the studies of closed-loop tES control design via EEG-based feedback (Boyle and Fröhlich, 2013;Leite et al., 2017;Frohlich and Townsend, 2021). ...
Neurostimulation technologies have seen a recent surge in interest from the neuroscience and controls communities alike due to their proven potential to treat conditions such as epilepsy, Parkinson’s Disease, and depression. The provided stimulation can be of different types, such as electric, magnetic, and optogenetic, and is generally applied to a specific region of the brain in order to drive the local and/or global neural dynamics to a desired state of (in)activity. For most neurostimulation techniques, however, an underlying theoretical understanding of their efficacy is still lacking. From a control-theoretic perspective, it is important to understand how each stimulus modality interacts with the inherent complex network dynamics of the brain in order to assess the controllability of the system and develop neurophysiologically relevant computational models that can be used to design the stimulation profile systematically and in closed loop. In this paper, we review the computational modeling studies of 1) deep brain stimulation, 2) transcranial magnetic stimulation, 3) direct current stimulation, 4) transcranial electrical stimulation, and 5) optogenetics as five of the most popular and commonly used neurostimulation technologies in research and clinical settings. For each technology, we split the reviewed studies into 1) theory-driven biophysical models capturing the low-level physics of the interactions between the stimulation source and neuronal tissue, 2) data-driven stimulus-response models which capture the end-to-end effects of stimulation on various biomarkers of interest, and 3) data-driven dynamical system models that extract the precise dynamics of the brain’s response to neurostimulation from neural data. While our focus is particularly on the latter category due to their greater utility in control design, we review key works in the former two categories as the basis and context in which dynamical system models have been and will be developed. In all cases, we highlight the strength and weaknesses of the reviewed works and conclude the review with discussions on outstanding challenges and critical avenues for future work.
... Similar post-hoc studies have been performed using fMRI in works such as (Keeser et al., 2011) where the network connectivity before and after tES are studied. With respect to the simultaneous analysis of response and stimulation, EEG-based monitoring has been leveraged in a large fraction of works (Song et al., 2014;Schestatsky et al., 2013). Also, a notable pattern in recent works is an increase in the studies of closed-loop tES control design via EEG-based feedback (Boyle and Fröhlich, 2013;Frohlich and Townsend, 2021;Leite et al., 2017). ...
Neurostimulation technologies have seen a recent surge in interest from the neuroscience and controls communities alike due to their proven potential to treat conditions such as Parkinson's Disease, and depression. The provided stimulation can be of different types, such as electric, and optogenetic, and is generally applied to a specific region of the brain in order to drive the local and/or global dynamics to a desired state of (in)activity. However, an underlying theoretical understanding of the efficacy of neurostimulation is still lacking. From a control-theoretic perspective, it is important to understand how each stimulus modality interacts with the complex brain network in order to assess the controllability of the system and develop neurophysiologically relevant computational models that can be used to design the stimulation profile in a closed-loop manner. In this paper, we review the computational modeling studies of (i) deep brain stimulation, (ii) transcranial magnetic stimulation, (iii) direct current stimulation, (iv) transcranial electrical stimulation, and (v) optogenetics as five of the most popular neurostimulation technologies in research and clinical settings. For each technology, we split the reviewed studies into (a)theory-driven biophysical models capturing the low-level physics of the interactions between the stimulation source and neuronal tissue, (b) data-driven stimulus-response models which capture the end-to-end effects of stimulation on various biomarkers of interest and (c) data-driven dynamical system models that extract the precise dynamics of the brain's response to neurostimulation from neural data. While our focus is particularly on the latter category due to their greater utility in control design, we review key works in the former two categories as the basis and context in which dynamical system models have been and will be developed.
... Other studies have reported effects of tDCS on astrocytes and microglia (Mishima et al., 2019) and shown that it upregulates growth factors including GDF5 and PDGFA, which are associated with increased recovery after stroke (Ahn Sung et al., 2020). tACS is another transcranial electrical stimulation technique that applies oscillatory electrical stimulation which overrides endogenous rhythmic cortical activities during cognitive processes (Antal and Paulus, 2013;Herrmann et al., 2013;Song et al., 2014). Studies using tACS have already shown increases in cerebral blood flow in both hemispheres and lowered resistance in the intracranial vascular bed in patients during the acute phase to 3 months after stroke (Salinet et al., 2014;Wu et al., 2016). ...
Stroke is a leading cause of death and disability worldwide, with limited treatments being available. However, advances in optic methods in neuroscience are providing new insights into the damaged brain and potential avenues for recovery. Direct brain stimulation has revealed close associations between mental states and neuroprotective processes in health and disease, and activity-dependent calcium indicators are being used to decode brain dynamics to understand the mechanisms underlying these associations. Evoked neural oscillations have recently shown the ability to restore and maintain intrinsic homeostatic processes in the brain and could be rapidly deployed during emergency care or shortly after admission into the clinic, making them a promising, non-invasive therapeutic option. We present an overview of the most relevant descriptions of brain injury after stroke, with a focus on disruptions to neural oscillations. We discuss the optical technologies that are currently used and lay out a roadmap for future studies needed to inform the next generation of strategies to promote functional recovery after stroke.
... This explains the observation of less mu rhythm suppression in patients than in healthy controls. Several studies have shown that the post-stimulation effects of GVS and tDCS increase the EEG power of theta, alpha, and beta bands in the frontal, temporal, posterior, parietal, and occipital lobes in normal subjects [18,46,[49][50][51][52], in agreement with our findings in healthy subjects. By using ICA with dipole source localization for EEG analysis, our method goes beyond those used in previous studies, resulting in cleaner EEG signals; thus, a more precise spatial temporal resolution in the vestibular cortex could be determined. ...
Patients with bilateral vestibular hypofunction (BVH) often suffer from imbalance, gait problems, and oscillopsia. Noisy galvanic vestibular stimulation (GVS), a technique that non-invasively stimulates the vestibular afferents, has been shown to enhance postural and walking stability. However, no study has investigated how it affects stability and neural activities while standing and walking with a 2 Hz head yaw turning. Herein, we investigated this issue by comparing differences in neural activities during standing and walking with a 2 Hz head turning, before and after noisy GVS. We applied zero-mean gaussian white noise signal stimulations in the mastoid processes of 10 healthy individuals and seven patients with BVH, and simultaneously recorded electroencephalography (EEG) signals with 32 channels. We analyzed the root mean square (RMS) of the center of pressure (COP) sway during 30 s of standing, utilizing AMTI force plates (Advanced Mechanical Technology Inc., Watertown, MA, USA). Head rotation quality when walking with a 2 Hz head yaw, with and without GVS, was analyzed using a VICON system (Vicon Motion Systems Ltd., Oxford, UK) to evaluate GVS effects on static and dynamic postural control. The RMS of COP sway was significantly reduced during GVS while standing, for both patients and healthy subjects. During walking, 2 Hz head yaw movements was significantly improved by noisy GVS in both groups. Accordingly, the EEG power of theta, alpha, beta, and gamma bands significantly increased in the left parietal lobe after noisy GVS during walking and standing in both groups. GVS post-stimulation effect changed EEG activities in the left and right precentral gyrus, and the right parietal lobe. After stimulation, EEG activity changes were greater in healthy subjects than in patients. Our findings reveal noisy GVS as a non-invasive therapeutic alternative to improve postural stability in patients with BVH. This novel approach provides insight to clinicians and researchers on brain activities during noisy GVS in standing and walking conditions in both healthy and BVH patients.
... Individuals with FM have changes in different brain waves, analyzed by EEG at rest. Given the ability of tDCS to promote modulation of neuronal activity (Cruccu et al., 2016), it is expected that this technique will be able to modulate cortical electrical activity and increase the synchronization of this activity, reflecting in greater spectral power in the alpha frequency range (Boonstra et al., 2016, Song, Shin, & Yun, 2014. Considering that alpha frequency range activity is related to the state of relaxation, the increase in its average spectral power is expected to be associated with clinical improvement in FM (Bell et al., 2004). ...
The objective of the present research is to present a protocol for a randomized, placebo-controlled triple-blind clinical trial, which will evaluate the effects of neuromodulation with transcranial direct current stimulation (tDCS) associated with physiotherapy treatment in fibromyalgia and its electroencephalographic correlates. The volunteers will be women diagnosed with fibromyalgia for at least three months, aged between 40 and 55 years. Participants will be randomly assigned to three groups: Group 1, with anodic stimulation in the left motor cortex and cathodic stimulation in the right supraorbital region; Group 2, with anodic stimulation in the left dorsolateral prefrontal cortex and cathodic stimulation in the right supraorbital region; and Group 3, with simulated type stimulation (sham). All groups will be accompanied by physiotherapy treatment. The primary outcomes will be the variations in pain, anxiety and depression levels, resulting from neuromodulation, as assessed by the Visual Analogue Scale and Beck's Anxiety and Depression Inventories, respectively. The secondary outcome will be the evaluation of the cortical electrical activity as registered by a 32-channel electroencephalogram. In data analysis, a mixed ANOVA will be used, with 3 groups of participants versus 2 moments of evaluation, with a level of significance of p<0.05. For pair comparisons, post hoc test with Bonferroni-Sidak correction will be used. Considering that fibromyalgia is a multifactorial disease, not very responsive to drugs and other conventional treatments, it is important to analyze the potential therapeutic effect of neuromodulation, in addition to the physiotherapeutic treatment, in individuals with fibromyalgia.
... The trivial eye opening during resting state causes an enhancement of beta waves, and this seems to be related to mental and physical state changes, rather than a simple result of eye movements. Therefore, a perturbation induced by tDCS could change the brain to a ready state for efficient cognitive functioning and integration of long-range connections, as reported by other studies (Song et al., 2014). ...
Objectives:
Left dorsolateral prefrontal cortex anodal transcranial direct current stimulation (tDCS) was applied in a group of patients with disorders of consciousness to determine the effects of modulation of spontaneous oscillatory brain activity.
Methods:
12 patients in an unresponsive wakefulness syndrome (UWS) and 12 in a minimally conscious state (MCS) underwent 2-weeks active and 2-weeks sham tDCS. Neurophysiological assessment was performed with EEG power spectra and coherence analysis directly before and after each session.
Results:
An increase of power and coherence of the frontal and parietal alpha and beta frequency bands and significant clinical improvements were seen after the active tDCS in MCS patients. In contrast, UWS patients showed some local frontal changes in the slow frequencies. No treatment effect was observed after sham.
Conclusions:
tDCS could induce changes in cortical EEG oscillations, modulating the travel of alpha and beta waves between anterior and posterior brain areas when some cognitive functions were preserved. This plays an important role in consciousness by integrating cognitive-emotional processing with the state of arousal. In unresponsive people, brain integration seems to be lost.
Significance:
Our results further support the critical role of long-range fronto-parietal connections in consciousness and show the potential therapeutic utility of tDCS.
... This is consistent with a more recent time-frequency analysis study that shows greater association between the left frontal and parietal areas during incongruent tasks than in congruent tasks within a time interval of 100-400 ms in the beta frequency band. Changes in the beta frequency band have previously been found after 20 minutes of anodal tDCS targeting the prefrontal and motor cortices, suggesting that anodal tDCS changes the "ready state" to perform cognitive or motor tasks 106,107 . Taken together, these findings support our data, which show that anodal stimulation modulates the beta frequency band. ...
The dorsal anterior cingulate cortex (dACC) has been identified as a core region affected by many disorders, representing a promising target for neuromodulation. High Definition-transcranial Direct Current Stimulation (HD-tDCS) is a non-invasive neuromodulation technique that has already shown promising outcomes and has been tested to engage deeper structures. This study investigates whether it is possible to modulate dACC activity using anodal and cathodal HD-tDCS. Furthermore, it examines what effects anodal and cathodal HD-tDCS targeting dACC have on cognitive and emotional processing. Forty-five healthy subjects were randomly assigned to 1 of 3 groups: anodal, cathodal, and sham. Resting-state electroencephalography (rsEEG) and a cognitive and emotional Counting Stroop task were administered before and after HD-tDCS. RsEEG showed changes: anodal HD-tDCS showed significant increase in beta frequency band activity in dACC, while cathodal HD-tDCS led to significant increase in activity at dorsal and rostral ACC in the theta frequency band. Behavioral changes were also found after anodal HD-tDCS in the cognitive Counting Stroop for incongruent trials and after cathodal HD-tDCS in the emotional Counting Stroop for emotional trials. This study demonstrated that HD-tDCS is able to modulate dACC activity, suggesting that it has the potential to be used as a treatment tool.
... By contrast, with tDCS, the current describes a monophasic, distinctly non-oscillating baseline voltage. Endogenous activity is modulated by depolarization (anode) or hyperpolarization (cathode) in the global flow of current, which supplies electrons to the anodal electrode (promoting endogenous oscillations) and retracts electrons from the cathodal electrode (suppressing endogenous oscillations; Song et al., 2014). ...
Perception, cognition and consciousness can be modulated as a function of oscillating neural activity, while ongoing neuronal dynamics are influenced by synaptic activity and membrane potential. Consequently, transcranial alternating current stimulation (tACS) may be used for neurological intervention. The advantageous features of tACS include the biphasic and sinusoidal tACS currents, the ability to entrain large neuronal populations, and subtle control over somatic effects. Through neuromodulation of phasic, neural activity, tACS is a powerful tool to investigate the neural correlates of cognition. The rapid development in this area requires clarity about best practices. Here we briefly introduce tACS and review the most compelling findings in the literature to provide a starting point for using tACS. We suggest that tACS protocols be based onfunctional brain mechanisms and appropriate control experiments, including active sham and condition blinding.
... We showed that tDCS over the left primary motor cortex (M1) induces a beta-power enhancement after 20 min of stimulation. A previous study demonstrated similar results after a single stimulation session over the prefrontal cortex [32]. The authors concluded that tDCS could change the brain to a "ready state" to perform cognitive (if the prefrontal area was stimulated) or motor (if the primary motor area was stimulated) tasks. ...
... [12][13][14][15] Also, EEG power is a reliable measure to detect specific cognitive and motor features across sessions, 16,17 as well as the effects of tDCS. 18,19 Invasive closed-loop systems incorporating EEG and brain stimulation techniques have been demonstrated in both animal and human studies. 20,21 To our knowledge, the only study testing a noninvasive closed-loop system in humans is a recent feasibility study showing that motor-imagery induced desynchronization detected by surface EEG can trigger transcranial magnetic stimulation (TMS) leading to increased excitability of the motor cortex. ...
Conventional transcranial direct current stimulation (tDCS) protocols rely on applying electrical current at a fixed intensity and duration without using surrogate markers to direct the interventions. This has led to some mixed results; especially because tDCS induced effects may vary depending on the ongoing level of brain activity. Therefore, the objective of this preliminary study was to assess the feasibility of an EEG-triggered tDCS system based on EEG online analysis of its frequency bands. Six healthy volunteers were randomized to participate in a double-blind sham-controlled crossover design to receive a single session of 10[Formula: see text]min 2[Formula: see text]mA cathodal and sham tDCS. tDCS trigger controller was based upon an algorithm designed to detect an increase in the relative beta power of more than 200%, accompanied by a decrease of 50% or more in the relative alpha power, based on baseline EEG recordings. EEG-tDCS closed-loop-system was able to detect the predefined EEG magnitude deviation and successfully triggered the stimulation in all participants. This preliminary study represents a proof-of-concept for the development of an EEG-tDCS closed-loop system in humans. We discuss and review here different methods of closed loop system that can be considered and potential clinical applications of such system.
... Somewhat in line with our present findings, a recent study by Boonstra et al. (2016) which delivered anodal tDCS (2 mA, 15 min) over the left DLPFC also reported a reduction in fast oscillatory activity ( > 20 Hz), following stimulation, recorded across all EEG channels. Other authors have, however, also reported changes in slower θ and α bands (Boonstra et al., 2016;Miller et al., 2015), which we did not observe in the present study using TMS-EEG, while β power increases have also been reported during, but not following, anodal tDCS over the left DLPFC (Song et al., 2014). Given the mixed results observed in the tDCS literature regarding resting-state EEG activity, further research is clearly needed to better delineate any specific tDCS-related effects on neural oscillations. ...
Transcranial direct current stimulation (tDCS) is a well-recognised neuromodulatory technology which has been shown to induce short-lasting changes in motor-cortical excitability. The recent and rapid expansion of tDCS into the cognitive domain, however, necessitates deeper mechanistic understanding of its neurophysiological effects over non-motor brain regions. The present study utilised transcranial magnetic stimulation combined with electroencephalography (TMS-EEG) to probe the immediate and longer-term effects of both a bipolar (BP-tDCS) and more focal 4 × 1 High-Definition tDCS (HD-tDCS) montage applied over the left DLPFC on TMS-evoked potentials (TEPs) and oscillations in 19 healthy adult participants. 2-back working memory (WM) performance was also assessed as a marker of cognitive function. Region of interest (ROI) analyses taken from the F1 electrode directly adjacent to the stimulation site revealed increased P60 TEP amplitudes at this location 5 minutes following BP-tDCS and 30 minutes following HD-tDCS. Further global cluster based analyses of all scalp electrodes revealed widespread neuromodulatory changes following HD-tDCS, but not BP-tDCS, both five and 30 minutes after stimulation, with reductions also detected in both beta and gamma oscillatory power over parieto-occipital channels 30 minutes after stimulation. No significant changes in WM performance were observed following either HD-tDCS or BP-tDCS. This study highlights the capacity for single-session prefrontal anodal tDCS montages to modulate neurophysiological processes, as assessed with TMS-EEG.
... We showed that tDCS over the left primary motor cortex (M1) induces a beta-power enhancement after 20 min of stimulation. A previous study demonstrated similar results after a single stimulation session over the prefrontal cortex [32]. The authors concluded that tDCS could change the brain to a "ready state" to perform cognitive (if the prefrontal area was stimulated) or motor (if the primary motor area was stimulated) tasks. ...
Transcranial pulsed current stimulation (tPCS) and transcranial direct current stimulation (tDCS) are two noninvasive neuromodulatory brain stimulation techniques whose effects on human brain and behavior have been studied individually. In the present study we aimed to quantify the effects of tDCS and tPCS, individually and in combination, on cortical activity, sensitivity and pain-related assessments in healthy individuals in order to understand their neurophysiological mechanisms and potential applications in clinical populations. A total of 48 healthy individuals participated in this randomized double blind sham controlled study. Participants were randomized to receive a single stimulation session of either: active or sham tPCS and active or sham tDCS. Quantitative electroencephalography (qEEG), sensitivity and pain assessments were used before and after each stimulation session. We observed that tPCS had a higher effect on power, as compared to tDCS, in several bandwidths on various cortical regions: the theta band in the parietal region (p = 0.021), the alpha band in the temporal (p = 0.009), parietal (p = 0.0063), and occipital (p < 0.0001) regions. We found that the combination of tPCS and tDCS significantly decreased power in the low beta bandwidth of the frontal (p = 0.0006), central (p = 0.0001), and occipital (p = 0.0003) regions, when compared to sham stimulation. Additionally, tDCS significantly increased power in high beta over the temporal (p = 0.0015) and parietal (p = 0.0007) regions, as compared to sham. We found no effect on sensitivity or pain-related assessments. We concluded that tPCS and tDCS have different neurophysiological mechanisms, elicit distinct signatures, and that the combination of the two leads to no effect or a decrease on qEEG power. Further studies are required to examine the effects of these techniques on clinical populations in which EEG signatures have been found altered.
... To try to explain these alterations and to gain new insight into these mechanisms, tDCS and electroencephalograpic (EEG) recordings have been used in sequential offline (Miniussi et al., 2012), and online tDCS-EEG approaches (e.g., Accornero et al., 2014;Baxter et al., 2014;Mangia et al., 2014), or in combination with other techniques (Hunter et al., 2013), such as transcranial magnetic stimulation (TMS) (Pellicciari et al., 2013;Romero et al. 2014), magnetoencephalography (e.g., Garcia-Cossio et al., 2015) and electromyography (EMG) (Dutta et al., 2014). Until now, studies using EEG have shown how the tDCS induces polarity-specific on brain activity oscillations in different frequency bands (Kirov et al., 2009;Miller et al., 2015;Notturno et al. 2014;Song et al., 2014;Spitoni et al., 2013;Ulam et al. 2014). However, a network approach could be used to obtain a better understanding of the ongoing effects induced by neuromodulation (Bortoletto et al., 2015;Luft et al., 2014) and to capture brain functions in a multi-dimensional manner (i.e., from a network A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT 4 prospective). ...
... Recent studies have highlighted that different EEG measures (e.g., evoked potentials, event-related desynchronization/synchronization, and functional connectivity) can be used to probe the state of the cortical area stimulated by tDCS by adopting a multimodal approach that combines tDCS with EEG, both off-and online (e.g., Matsumoto et al., 2010;Polania et al., 2010;Pellicciari et al., 2013; for a review, see Miniussi et al., 2012). Specifically, tDCS has enabled the modulation, in a polarity-dependent manner, of local neural activity, altering ongoing brain activity in the frequency domain-with topographic dependency as a function of the stimulated sites (Antal et al., 2004;Spitoni et al., 2013;Mangia et al., 2014;Song et al., 2014). ...
Transcranial direct current stimulation (tDCS) is an emerging therapeutic tool for treating posttraumatic stress disorder (PTSD). Prior studies have shown that tDCS responses are highly individualized, thus necessitating the individualized optimization of treatment configurations. To date, an effective tool for predicting tDCS treatment outcomes in patients with PTSD has not yet been proposed. Therefore, we aimed to build and validate a tool for predicting tDCS treatment outcomes in patients with PTSD. Forty-eight patients with PTSD received 20 min of 2 mA tDCS stimulation in position of the anode over the F3 and cathode over the F4 region. Non-responders were defined as those with less than 50% improvement after reviewing clinical symptoms based on the Clinician-Administered DSM-5 PTSD Scale (before and after stimulation). Resting-state electroencephalograms were recorded for 3 min before and after stimulation. We extracted power spectral densities (PSDs) for five frequency bands. A support vector machine (SVM) model was used to predict responders and non-responders using PSDs obtained before stimulation. We investigated statistical differences in PSDs before and after stimulation and found statistically significant differences in the F8 channel in the theta band (p = 0.01). The SVM model had an area under the ROC curve (AUC) of 0.93 for predicting responders and non-responders using PSDs. To our knowledge, this study provides the first empirical evidence that PSDs can be useful biomarkers for predicting the tDCS treatment response, and that a machine learning model can provide robust prediction performance. Machine learning models based on PSDs can be useful for informing treatment decisions in tDCS treatment for patients with PTSD.
Background
Transcranial direct current stimulation (tDCS) provides a noninvasive polarity-specific constant current to treat epilepsy, through a mechanism possibly involving excitability modulation and neural oscillation.
Objective
To determine whether EEG oscillations underlie the interictal spike changes after tDCS in rats with chronic spontaneous seizures.
Methods
Rats with kainic acid-induced spontaneous seizures were subjected to cathodal tDCS or sham stimulation for 5 consecutive days. Video-EEG recordings were collected immediately pre- and post-stimulation and for the subsequent 2 weeks following stimulation. The acute pre-post stimulation and subacute follow-up changes of interictal spikes and EEG oscillations in tDCS-treated rats were compared with sham. Ictal EEG with seizure behaviors, hippocampal brain-derived neurotrophic factor (BDNF) protein expression, and mossy fiber sprouting were compared between tDCS and sham rats.
Results
Interictal spike counts were reduced immediately following tDCS with augmented delta and diminished beta and gamma oscillations compared with sham. Cathodal tDCS also enhanced delta oscillations in normal rats. However, increased numbers of interictal spikes with a decrease of delta and theta oscillations were observed in tDCS-treated rats compared with sham during the following 2 weeks after stimulation. Resuming tDCS suppressed the increase of interictal spike activity. In tDCS rats, hippocampal BDNF protein expression was decreased while mossy fiber sprouting did not change compared with sham.
Conclusions
The inverse relationship between the changes of delta oscillation and interictal spikes during tDCS on and off stimulation periods indicates that an enhanced endogenous delta oscillation underlies the tDCS inhibitory effect on epileptic excitability.
Transcranial alternating current stimulation (tACS) is a unique form of non-invasive brain stimulation. Sinusoidal alternating electric currents are delivered to the scalp to affect mostly cortical neurons. tACS is supposed to modulate brain function and, in turn, cognitive processes by entraining brain oscillations and inducing long-term synaptic plasticity. Therefore, tACS has been investigated in cognitive neuroscience, but only recently, it has been also introduced in psychiatric clinical trials. This review describes current concepts and first findings of applying tACS as a potential therapeutic tool in the field of psychiatry. The current understanding of its mechanisms of action is explained, bridging cellular neuronal activity and the brain network mechanism. Revisiting the relevance of altered brain oscillations found in six major psychiatric disorders, putative targets for the management of mental disorders using tACS are discussed. A systematic literature search on PubMed was conducted to report findings of the clinical studies applying tACS in patients with psychiatric conditions. In conclusion, the initial results may support the feasibility of tACS in clinical psychiatric populations without serious adverse events. Moreover, these results showed the ability of tACS to reset disturbed brain oscillations, and thus to improve behavioural outcomes. In addition to its potential therapeutic role, the reactivity of the brain circuits to tACS could serve as a possible tool to determine the diagnosis, classification or prognosis of psychiatric disorders. Future double-blind randomised controlled trials are necessary to answer currently unresolved questions. They may aim to detect response predictors and control for various confounding factors.
The main goal of this study was to assess the changes in brain activities of patients with severe depression by applying transcranial direct current stimulation (tDCS) using event related potentials (ERPs). Seven patients (four males, with the mean age 34.85 ± 4.25) were asked to fill out Beck’s depression questionnaires. EEG signals of subjects were recorded during Stroop test. This test entailed 360 stimulations, which included 120 congruent, 120 incongruent, and 120 neutral stimulations lasting for 12 min. Subsequently, the dorso lateral prefrontal cortex in patients’ left hemisphere was stimulated for six sessions using tDCS. At the end of tDCS treatment period, subjects filled out Beck’s depression questionnaires again and EEG signal recordings were repeated simultaneously with Stroop test. Wavelet coefficients of EEG frequency bands in every stimulation type were extracted from ERP components. The changes in Beck score before and after tDCS were estimated using neural network model. The ERP results showed that the latency period of N400 component after applying tDCS decreased significantly. Moreover, a significant correlation was observed between percentage changes of congruent and incongruent accuracy and the increase in the average energy of wavelet coefficients in alpha band in Pz electrode with p = 0.0128, r = 0.9060 and p = 0.0037, r = 0.95, respectively. Additionally, the results of neural network model revealed that the changes in Beck score were estimated with an average error of 0.0519. Consequently, the improvement of depressed patients treated with tDCS could be estimated with good accuracy using average energy of wavelet coefficients in alpha band.
In the last decade, in the field of neuromodulation, we have observed an increase in the popularity of approaches that combine transcranial electrical stimulation (tES) with additional methods to establish, in vivo, the neurophysiological consequences of a given experimental or therapeutic manipulation. We are at the beginning of the development of multimodal approaches, and several methods are available that can be combined with tES to study brain functions. This chapter aims to introduce the reader to some basic principles of this multimodal approach. We begin with a brief definition of multimodal association and a description of the advantages of such an approach. Afterwards, we provide a more specific description of how we can combine tES with electroencephalography (EEG). We show that EEG is a feasible and reliable way to track electrophysiological changes induced by tES, deepening our understanding of the mechanisms of action of this tool and revealing the key role of several stimulation features. In neuropsychiatric diseases, a combined tES-EEG approach may allow the prediction of clinical responses to tES, the discrimination of responders from non-responders, improvement in the efficacy of tES, and the tracking of tES-induced neuroplastic changes associated with recovery.
Although EEG signals are highly complex, there are still some neural mass models that describe its systematic dynamics. In this paper, we presented an empirical exploration to the theoretical prediction of such a model by fitting the actual EEG signal to the model, with a particular
concern on the influence of the extrinsic input p(t) to EEG signal. The results suggest that the neural mass model can produce good approximation to the actual EEG signal, and the mean of estimated input signal fell well within the interval for the simulate study recommended
by previous reports. However, it is also found that the variance of the input signal commonly accepted for simulating EEG rhythmic activity is far higher than the value in real data, thus may lead to the generation of unreliable synthetic data, and bias the analysis result.
Conform to the Norm
Human societies have always enforced compliance with norms of acceptable behavior among their members by threatening punishment. It has been proposed that the human brain may have developed neural processes that support norm enforcement behavior and generate appropriate behavioral responses to social punishment threats. However, evidence for the neural circuitry underlying sanction-induced norm compliance in humans is limited. Using noninvasive brain stimulation, Ruff et al. (p. 482 , published online 10 October) observed that alteration of the activity and excitability of the right lateral prefrontal cortex affected norm compliance, without affecting awareness of the content of the respective norms, or the expected sanctions. These alterations were much larger in a social, as compared to a nonsocial, context.
The midbrain lies deep within the brain and has an important role in reward, motivation, movement and the pathophysiology of
various neuropsychiatric disorders such as Parkinson’s disease, schizophrenia, depression and addiction. To date, the primary
means of acting on this region has been with pharmacological interventions or implanted electrodes. Here we introduce a new
noninvasive brain stimulation technique that exploits the highly interconnected nature of the midbrain and prefrontal cortex to
stimulate deep brain regions. Using transcranial direct current stimulation (tDCS) of the prefrontal cortex, we were able to
remotely activate the interconnected midbrain and cause increases in participants’ appraisals of facial attractiveness.
Participants with more enhanced prefrontal/midbrain connectivity following stimulation exhibited greater increases in
attractiveness ratings. These results illustrate that noninvasive direct stimulation of prefrontal cortex can induce neural activity
in the distally connected midbrain, which directly effects behavior. Furthermore, these results suggest that this tDCS protocol
could provide a promising approach to modulate midbrain functions that are disrupted in neuropsychiatric disorders.
One may have experienced his or her footsteps unconsciously synchronize with the footsteps of a friend while walking together, or heard an audience's clapping hands naturally synchronize into a steady rhythm. However, the mechanisms of body movement synchrony and the role of this phenomenon in implicit interpersonal interactions remain unclear. We aimed to evaluate unconscious body movement synchrony changes as an index of implicit interpersonal interaction between the participants, and also to assess the underlying neural correlates and functional connectivity among and within the brain regions. We found that synchrony of both fingertip movement and neural activity between the two participants increased after cooperative interaction. These results suggest that the increase of interpersonal body movement synchrony via interpersonal interaction can be a measurable basis of implicit social interaction. The paradigm provides a tool for identifying the behavioral and the neural correlates of implicit social interaction.
This study aimed to investigate if methamphetamine (MA) abusers exhibit alterations in complexity of the electroencephalogram (EEG) and to determine if these possible alterations are associated with their abuse patterns. EEGs were recorded from 48 former MA-dependent males and 20 age- and sex-matched healthy subjects. Approximate Entropy (ApEn), an information-theoretical measure of irregularity, of the EEGs was estimated to quantify the degree of cortical complexity. The ApEn values in MA abusers were significantly lower than those of healthy subjects in most of the cortical regions, indicating decreased cortical complexity of MA abusers, which may be associated with impairment in specialization and integration of cortical activities owing to MA abuse. Moreover, ApEn values exhibited significant correlations with the clinical factors including abuse patterns, symptoms of psychoses, and their concurrent drinking and smoking habits. These findings provide insights into abnormal information processing in MA abusers and suggest that ApEn of EEG recordings may be used as a potential supplementary tool for quantitative diagnosis of MA abuse. This is the first investigation to assess the "severity-dependent dynamical complexity" of EEG patterns in former MA abusers and their associations with the subjects' abuse patterns and other clinical measures.
Transcranial direct current stimulation (tDCS) has been proposed for experimental and therapeutic modulation of regional brain function. Specifically, anodal tDCS of the dorsolateral prefrontal cortex (DLPFC) together with cathodal tDCS of the supraorbital region have been associated with improvement of cognition and mood, and have been suggested for the treatment of several neurological and psychiatric disorders. Although modeled mathematically, the distribution, direction, and extent of tDCS-mediated effects on brain physiology are not well understood. The current study investigates whether tDCS of the human prefrontal cortex modulates resting-state network (RSN) connectivity measured by functional magnetic resonance imaging (fMRI). Thirteen healthy subjects underwent real and sham tDCS in random order on separate days. tDCS was applied for 20 min at 2 mA with the anode positioned over the left DLPFC and the cathode over the right supraorbital region. Patterns of resting-state brain connectivity were assessed before and after tDCS with 3 T fMRI, and changes were analyzed for relevant networks related to the stimulation-electrode localizations. At baseline, four RSNs were detected, corresponding to the default mode network (DMN), the left and right frontal-parietal networks (FPNs) and the self-referential network. After real tDCS and compared with sham tDCS, significant changes of regional brain connectivity were found for the DMN and the FPNs both close to the primary stimulation site and in connected brain regions. These findings show that prefrontal tDCS modulates resting-state functional connectivity in distinct functional networks of the human brain.
Transcranial direct current stimulation (tDCS) is a non-invasive method of brain stimulation that has been intensively investigated in clinical and cognitive neuroscience. Although the general impression is that tDCS is a safe technique with mild and transient adverse effects (AEs), human data on safety and tolerability are largely provided from single-session studies in healthy volunteers. In addition the frequency of AEs and its relationship with clinical variables is unknown. With the aim of assessing tDCS safety in different conditions and study designs, we performed a systematic review and meta-analysis of tDCS clinical trials. We assessed Medline and other databases and reference lists from retrieved articles, searching for articles from 1998 (first trial with contemporary tDCS parameters) to August 2010. Animal studies, review articles and studies assessing other neuromodulatory techniques were excluded. According to our eligibility criteria, 209 studies (from 172 articles) were identified. One hundred and seventeen studies (56%) mentioned AEs in the report. Of these studies, 74 (63%) reported at least one AE and only eight studies quantified AEs systematically. In the subsample reporting AEs, the most common were, for active vs. sham tDCS group, itching (39.3% vs. 32.9%, p>0.05), tingling (22.2% vs. 18.3%, p>0.05), headache (14.8% vs. 16.2%, p>0.05), burning sensation (8.7% vs. 10%, p>0.05) and discomfort (10.4% vs. 13.4%, p>0.05). Meta-analytical techniques could be applied in only eight studies for itching, but no definite results could be obtained due to between-study heterogeneity and low number of studies. Our results suggested that some AEs such as itching and tingling were more frequent in the tDCS active group, although this was not statistically significant. Although results suggest that tDCS is associated with mild AEs only, we identified a selective reporting bias for reporting, assessing and publishing AEs of tDCS that hinders further conclusions. Based on our findings, we propose a revised adverse effects questionnaire to be applied in tDCS studies in order to improve systematic reporting of tDCS-related AEs.
Interest is rapidly developing in transcranial direct current stimulation (tDCS) as an emerging tool in neurology and psychiatry. tDCS involves the application of weak, unidirectional currents through scalp electrodes to alter neuronal excitability, that may outlast the period of stimulation (Arul-Anandam & Loo, 2009). In addition to being a tool for neurophysiological investigations, tDCS has been examined as a treatment for many neuropsychiatric disorders (Nitsche et al. 2008), in particular depression (Boggio et al. 2008; Fregni et al. 2006; Loo et al. 2010).
Clinical application of tDCS in neuropsychiatric disorders often involves repeated stimulation sessions, typically on consecutive days, in an attempt to create robust and lasting changes in neuronal functioning. Stimulation parameters (current intensity, stimulation duration, etc.) have been gradually adjusted to optimize therapeutic effects (Arul-Anandam & Loo, 2009). Skin burns have recently been reported in treatment trials of tDCS in depression involving multiple stimulation sessions given at the upper range of stimulation parameters, and when applied repeatedly to the same scalp sites (Frank et al. 2010; Palm et al. 2008). Other researchers have provided guidance on safety issues in tDCS technique (Nitsche et …
Effects of weak electrical currents on brain and neuronal function were first described decades ago. Recently, DC polarization of the brain was reintroduced as a noninvasive technique to alter cortical activity in humans. Beyond this, transcranial direct current stimulation (tDCS) of different cortical areas has been shown, in various studies, to result in modifications of perceptual, cognitive, and behavioral functions. Moreover, preliminary data suggest that it can induce beneficial effects in brain disorders. Brain stimulation with weak direct currents is a promising tool in human neuroscience and neurobehavioral research. To facilitate and standardize future tDCS studies, we offer this overview of the state of the art for tDCS.
Motor skills can take weeks to months to acquire and can diminish over time in the absence of continued practice. Thus, strategies that enhance skill acquisition or retention are of great scientific and practical interest. Here we investigated the effect of noninvasive cortical stimulation on the extended time course of learning a novel and challenging motor skill task. A skill measure was chosen to reflect shifts in the task's speed-accuracy tradeoff function (SAF), which prevented us from falsely interpreting variations in position along an unchanged SAF as a change in skill. Subjects practiced over 5 consecutive days while receiving transcranial direct current stimulation (tDCS) over the primary motor cortex (M1). Using the skill measure, we assessed the impact of anodal (relative to sham) tDCS on both within-day (online) and between-day (offline) effects and on the rate of forgetting during a 3-month follow-up (long-term retention). There was greater total (online plus offline) skill acquisition with anodal tDCS compared to sham, which was mediated through a selective enhancement of offline effects. Anodal tDCS did not change the rate of forgetting relative to sham across the 3-month follow-up period, and consequently the skill measure remained greater with anodal tDCS at 3 months. This prolonged enhancement may hold promise for the rehabilitation of brain injury. Furthermore, these findings support the existence of a consolidation mechanism, susceptible to anodal tDCS, which contributes to offline effects but not to online effects or long-term retention.
Two experiments were designed to examine the effects of attentional demands on the electroencephalogram during cognitive and
emotional tasks. We found an interaction of task with hemisphere as well as more overall parietal alpha for tasks not requiring
attention to the environment, such as mental arithmetic, than for those requiring such attention. Differential hemispheric
activation for beta was found most strongly in the temporal areas for emotionally positive or negative tasks and in the parietal
areas for cognitive tasks.
In this paper we demonstrate in the intact human the possibility of a non-invasive modulation of motor cortex excitability by the application of weak direct current through the scalp. Excitability changes of up to 40 %, revealed by transcranial magnetic stimulation, were accomplished and lasted for several minutes after the end of current stimulation. Excitation could be achieved selectively by anodal stimulation, and inhibition by cathodal stimulation. By varying the current intensity and duration, the strength and duration of the after-effects could be controlled. The effects were probably induced by modification of membrane polarisation. Functional alterations related to post-tetanic potentiation, short-term potentiation and processes similar to postexcitatory central inhibition are the likely candidates for the excitability changes after the end of stimulation. Transcranial electrical stimulation using weak current may thus be a promising tool to modulate cerebral excitability in a non-invasive, painless, reversible, selective and focal way.
Weak transcranial direct current stimulation (tDCS) induces persisting excitability changes in the human motor cortex. These plastic excitability changes are selectively controlled by the polarity, duration and current strength of stimulation. To reveal the underlying mechanisms of direct current (DC)-induced neuroplasticity, we combined tDCS of the motor cortex with the application of Na(+)-channel-blocking carbamazepine (CBZ) and the N-methyl-D-aspartate (NMDA)-receptor antagonist dextromethorphan (DMO). Monitored by transcranial magnetic stimulation (TMS), motor cortical excitability changes of up to 40% were achieved in the drug-free condition. Increase of cortical excitability could be selected by anodal stimulation, and decrease by cathodal stimulation. Both types of excitability change lasted several minutes after cessation of current stimulation. DMO suppressed the post-stimulation effects of both anodal and cathodal DC stimulation, strongly suggesting the involvement of NMDA receptors in both types of DC-induced neuroplasticity. In contrast, CBZ selectively eliminated anodal effects. Since CBZ stabilizes the membrane potential voltage-dependently, the results reveal that after-effects of anodal tDCS require a depolarization of membrane potentials. Similar to the induction of established types of short- or long-term neuroplasticity, a combination of glutamatergic and membrane mechanisms is necessary to induce the after-effects of tDCS. On the basis of these results, we suggest that polarity-driven alterations of resting membrane potentials represent the crucial mechanisms of the DC-induced after-effects, leading to both an alteration of spontaneous discharge rates and to a change in NMDA-receptor activation.
We assessed the relation between hemodynamic and electrical indices of brain function by performing simultaneous functional MRI (fMRI) and electroencephalography (EEG) in awake subjects at rest with eyes closed. Spontaneous power fluctuations of electrical rhythms were determined for multiple discrete frequency bands, and associated fMRI signal modulations were mapped on a voxel-by-voxel basis. There was little positive correlation of localized brain activity with alpha power (8-12 Hz), but strong and widespread negative correlation in lateral frontal and parietal cortices that are known to support attentional processes. Power in a 17-23 Hz range of beta activity was positively correlated with activity in retrosplenial, temporo-parietal, and dorsomedial prefrontal cortices. This set of areas has previously been characterized by high but coupled metabolism and blood flow at rest that decrease whenever subjects engage in explicit perception or action. The distributed patterns of fMRI activity that were correlated with power in different EEG bands overlapped strongly with those of functional connectivity, i.e., intrinsic covariations of regional activity at rest. This result indicates that, during resting wakefulness, and hence the absence of a task, these areas constitute separable and dynamic functional networks, and that activity in these networks is associated with distinct EEG signatures. Taken together with studies that have explicitly characterized the response properties of these distributed cortical systems, our findings may suggest that alpha oscillations signal a neural baseline with "inattention" whereas beta rhythms index spontaneous cognitive operations during conscious rest.
The International 10-20 system for EEG electrode placement is increasingly applied for the positioning of transcranial magnetic stimulation (TMS) in cognitive neuroscience and in psychiatric treatment studies. The crucial issue in TMS studies remains the reliable positioning of the coil above the skull for targeting a desired cortex region. In order to asses the precision of the 10-20 system for this purpose, we tested its projections onto the underlying cortex by using neuronavigation.
In 21 subjects, the 10-20 positions F3, F4, T3, TP3, and P3, as determined by a 10-20 positioning cap, were targeted stereotactically. The corresponding individual anatomical sites were identified in the Talairach atlas.
The main targeted regions were: for F3 Brodmann areas (BA) 8/9 within the dorsolateral prefrontal cortex, for T3 BA 22/42 on the superior temporal gyrus, for TP3 BA 40/39 in thearea of the supramarginal and angular gyrus, and for P3 BA 7/40 on the inferior parietal lobe. However, in about 10% of the measurements adjacent and possibly functionally distinct BAs were reached. The ranges were mainly below 20 mm.
Using the 10-20 system for TMS positioning is applicable at low cost and may reach desired cortex regions reliably on a larger scale level. For finer grained positioning, possible interindividual differences, and therefore the application of neuroimaging based methods, are to be considered.
Previous studies have claimed that weak transcranial direct current stimulation (tDCS) induces persisting excitability changes in the human motor cortex that can be more pronounced than cortical modulation induced by transcranial magnetic stimulation, but there are no studies that have evaluated the effects of tDCS on working memory. Our aim was to determine whether anodal transcranial direct current stimulation, which enhances brain cortical excitability and activity, would modify performance in a sequential-letter working memory task when administered to the dorsolateral prefrontal cortex (DLPFC). Fifteen subjects underwent a three-back working memory task based on letters. This task was performed during sham and anodal stimulation applied over the left DLPFC. Moreover seven of these subjects performed the same task, but with inverse polarity (cathodal stimulation of the left DLPFC) and anodal stimulation of the primary motor cortex (M1). Our results indicate that only anodal stimulation of the left prefrontal cortex, but not cathodal stimulation of left DLPFC or anodal stimulation of M1, increases the accuracy of the task performance when compared to sham stimulation of the same area. This accuracy enhancement during active stimulation cannot be accounted for by slowed responses, as response times were not changed by stimulation. Our results indicate that left prefrontal anodal stimulation leads to an enhancement of working memory performance. Furthermore, this effect depends on the stimulation polarity and is specific to the site of stimulation. This result may be helpful to develop future interventions aiming at clinical benefits.
The electrophysiological inhibitory mechanism of cognitive control for alcohol remains largely unknown. The purpose of the study was to compare electroencephalogram (EEG) power spectra and cross-frequency phase-amplitude coupling (CFPAC) at rest and during a simple subtraction task after acute alcohol ingestion.
Twenty-one healthy subjects participated in this study. Two experiments were performed 1 week apart, and the order of the experiments was randomly assigned to each subject. During the experiments, each subject was provided with orange juice containing alcohol or orange juice only. We recorded EEG activity and analyzed power spectra and CFPAC data.
The results showed prominent theta-phase gamma-amplitude coupling at the frontal and parietal electrodes at rest. This effect was significantly reduced after alcohol ingestion.
Our findings suggest that theta-phase gamma-amplitude coupling is deficiently synchronized at rest after alcohol ingestion. Therefore, cross-frequency coupling could be a useful tool for studying the effects of alcohol on the brain and investigating alcohol addiction.
Modulation of cortico-cortical connectivity in speci®c neural circuits might underlie some of the behavioural effects observed following repetitive transcranial magnetic stimulation (rTMS) of the human frontal cortex. This possibility was tested by applying rTMS to the left mid-dorsolateral frontal cortex (MDL-FC) and subsequently measuring functional connectivity of this region with positron emission tomography (PET) and TMS. The results showed a strong rTMS-related modulation of brain activity in the fronto-cingulate circuit. These results were con®rmed in a parallel experiment in the rat using electrical stimulation and ®eld-potential recordings. Future studies are needed to provide a direct link between the rTMS-induced modulation of cortical connectivity and its effects on speci®c behaviours.
Background. When the physiological activity of the brain (e.g., electroencephalogram, functional magnetic resonance imaging, etc.) is monitored in real-time, feedback can be returned to the subject and he/she can try to exercise some control over it. This idea is at the base of research on neurofeedback and brain-computer interfaces. Current advances in the speed of microprocessors, graphics cards and digital signal processing algorithms allow significant improvements in these methods. More meaningful features from the continuous flow of brain activation can be extracted and feedback can be more informative.Methods. Borrowing technology so far employed only in virtual reality, we have created Open-ViBE (Open Platform for Virtual Brain Environments). Open-ViBE is a general purpose platform for the development of three dimensional real-time virtual representations of brain physiological and anatomical data. Open-ViBE is a flexible and modular platform that integrates modules for brain physiological data acquisition, processing, and volumetric rendering.Results. When input data is the electroencephalogram, Open-ViBE uses the estimation of intra-cranial current density to represent brain activation as a regular grid of three dimensional graphical objects. The color and size of these objects co-vary with the amplitude and/or direction of the electrical current. This representation can be superimposed onto a volumetric rendering of the subject's MRI data to form the anatomical background of the scene. The user can navigate in this virtual brain and visualize it as a whole or only some of its parts. This allows the user to experience the sense of presence (being there) in the scene and to observe the dynamics of brain current activity in its original spatio-temporal relations.Conclusions. The platform is based on publicly available frameworks such as OpenMASK and OpenSG and is open source itself. In this way we aim to enhance the cooperation of researchers and to promote the use of the platform on a large scale.
We aimed to investigate the feasibility of an experimental system for simultaneous transcranial DC stimulation (tDCS) and EEG recording in human epilepsy. We report tolerability of this system in a cross-over controlled trial with 15 healthy subjects and preliminary effects of its use, testing repeated tDCS sessions, in two patients with drug-refractory Continuous Spike-Wave Discharges During Slow Sleep (CSWS). Our system combining continuous recording of the EEG with tDCS allows detailed evaluation of the interictal activity during the entire process. Stimulation with 1mA was well-tolerated in both healthy volunteers and patients with refractory epilepsy. The large reduction in interictal epileptiform EEG discharges in the two subjects with epilepsy supports further investigation of tDCS using this combined method of stimulation and monitoring in epilepsy. Continuous monitoring of epileptic activity throughout tDCS improves safety and allows detailed evaluation of epileptic activity changes induced by tDCS in patients.
Major depressive disorder (MDD) is a common psychiatric illness, with 6-12% lifetime prevalence. It is also among the five most disabling diseases worldwide. Current pharmacological treatments, although relatively effective, present important side effects that lead to treatment discontinuation. Therefore, novel treatment options for MDD are needed. Here, we discuss the recent advancements of one new neuromodulatory technique--transcranial direct current stimulation (tDCS)--that has undergone intensive research over the past decade with promising results. tDCS is based on the application of weak, direct electric current over the scalp, leading to cortical hypo- or hyper-polarization according to the specified parameters. Recent studies have shown that tDCS is able to induce potent changes in cortical excitability as well as to elicit long-lasting changes in brain activity. Moreover, tDCS is a technique with a low rate of reported side effects, relatively easy to apply and less expensive than other neuromodulatory techniques--appealing characteristics for clinical use. In the past years, 4 of 6 phase II clinical trials and one recent meta-analysis have shown positive results in ameliorating depression symptoms. tDCS has some interesting, unique aspects such as noninvasiveness and low rate of adverse effects, being a putative substitutive/augmentative agent for antidepressant drugs, and low-cost and portability, making it suitable for use in clinical practice. Still, further phase II and phase III trials are needed as to better clarify tDCS role in the therapeutic arsenal of MDD.
Studies have mainly documented behavioral changes induced by transcranial direct current stimulation (tDCS), but recently cortical modulations of tDCS have also been investigated. Our previous work revealed behavioral inhibition modulation by anodal tDCS over the right inferior frontal gyrus (rIFG); however, the electrophysiological correlates underlying this stimulation montage have yet to be established. The current work aimed to evaluate the distribution of neuronal oscillations changes following anodal tDCS over rIFG coupled with cathodal tDCS over left orbitofrontal cortex (lOFC) using spectral power analysis.
Healthy subjects underwent sham and real tDCS (15 min, 1.5 mA, anodal rIFG; cathodal lOFC) stimulation conditions in a single-blind, placebo-controlled cross-over trial. Following tDCS session, resting EEG recordings were collected during 15 min.
Analysis showed a significant and selective diminution of the power of theta band. The theta diminution was observed in the rIFG area (represented the anode electrode), and was not found in the lOFC area (represented the cathode electrode). A significant effect was observed only in the theta but not in other bands.
These results are the first demonstration of modulating oscillatory activity as measured by EEG with tDCS over rIFG in general, and documenting theta band reduction with this montage in particular.
Our results may explain the improvement in behavioral inhibition reported in our previous work, and although this study was conducted with healthy subjects, the findings suggest that tDCS may also modulate electrophysiological changes among ADHD patients, where decreasing theta activity is the target of neuro-feedback methods aimed to improve cognitive control.
Immediately after patients with Alzheimer's disease (AD) receive a single anodal transcranial direct current stimulation (tDCS) session their memory performance improves. Whether multiple tDCS sessions improve memory performance in the longer term remains unclear.
In this study we aimed to assess memory changes after five consecutive sessions of anodal tDCS applied over the temporal cortex in patients with AD.
A total of 15 patients were enrolled in two centers. Cognitive functions were evaluated before and after therapeutic tDCS. tDCS was delivered bilaterally through two scalp anodal electrodes placed over the temporal regions and a reference electrode over the right deltoid muscle. The stimulating current was set at 2 mA intensity and was delivered for 30 minutes per day for 5 consecutive days.
After patients received tDCS, their performance in a visual recognition memory test significantly improved. We found a main effect of tDCS on memory performance, i.e., anodal stimulation improved it by 8.99% from baseline, whereas sham stimulation decreased it by 2.62%. tDCS failed to influence differentially general cognitive performance measures or a visual attention measure.
Our findings show that after patients with AD receive anodal tDCS over the temporal cerebral cortex in five consecutive daily sessions their visual recognition memory improves and the improvement persists for at least 4 weeks after therapy. These encouraging results provide additional support for continuing to investigate anodal tDCS as an adjuvant treatment for patients with AD.
Prefrontal transcranial direct current stimulation (tDCS) with the anode placed on the left dorsolateral prefrontal cortex (DLPFC) has been reported to enhance working memory in healthy subjects and to improve mood in major depression. However, its putative antidepressant, cognitive and behavior action is not well understood. Here, we evaluated the distribution of neuronal electrical activity changes after anodal tDCS of the left DLPFC and cathodal tDCS of the right supraorbital region using spectral power analysis and standardized low resolution tomography (sLORETA). Ten healthy subjects underwent real and sham tDCS on separate days in a double-blind, placebo-controlled cross-over trial. Anodal tDCS was applied for 20 min at 2 mA intensity over the left DLPFC, while the cathode was positioned over the contralateral supraorbital region. After tDCS, EEG was recorded during an eyes-closed resting state followed by a working memory (n-back) task. Statistical non-parametric mapping showed reduced left frontal delta activity in the real tDCS condition. Specifically, a significant reduction of mean current densities (sLORETA) for the delta band was detected in the left subgenual PFC, the anterior cingulate and in the left medial frontal gyrus. Moreover, the effect was strongest for the first 5 min (p<0.01). The following n-back task revealed a positive impact of prefrontal tDCS on error rate, accuracy and reaction time. This was accompanied by increased P2- and P3- event-related potentials (ERP) component-amplitudes for the 2-back condition at the electrode Fz. A source localization using sLORETA for the time window 250-450 ms showed enhanced activity in the left parahippocampal gyrus for the 2-back condition. These results suggest that anodal tDCS of the left DLPFC and/or cathodal tDCS of the contralateral supraorbital region may modulate regional electrical activity in the prefrontal and anterior cingulate cortex in addition to improving working memory performance.
Cognitive deficits that are reported in heavy marijuana users (attention, memory, affect perception, decision-making) appear to be completely reversible after a prolonged abstinence period of about 28 days. However, it remains unclear whether the reversibility of these cognitive deficits indicates that (1) chronic marijuana use is not associated with long-lasting changes in cortical networks or (2) that such changes occur but the brain adapts to and compensates for the drug-induced changes. Therefore, we examined whether chronic marijuana smokers would demonstrate a differential pattern of response in comparison to healthy volunteers on a decision-making paradigm (Risk Task) while undergoing sham or active transcranial direct current stimulation (tDCS) of the dorsolateral prefrontal cortex (DLPFC). Twenty-five chronic marijuana users who were abstinent for at least 24h were randomly assigned to receive left anodal/right cathodal tDCS of DLPFC (n=8), right anodal/left cathodal tDCS of DLPFC (n=9), or sham stimulation (n=8); results on Risk Task during sham/active tDCS were compared to healthy volunteers from a previously published dataset. Chronic marijuana users demonstrated more conservative (i.e. less risky) decision-making during sham stimulation. While right anodal stimulation of the DLPFC enhanced conservative decision-making in healthy volunteers, both right anodal and left anodal DLPFC stimulation increased the propensity for risk-taking in marijuana users. These findings reveal alterations in the decision-making neural networks among chronic marijuana users. Finally, we also assessed the effects of tDCS on marijuana craving and observed that right anodal/left cathodal tDCS of DLPFC is significantly associated with a diminished craving for marijuana.
Despite its increasing use in experimental and clinical settings, the cellular and molecular mechanisms underlying transcranial direct current stimulation (tDCS) remain unknown. Anodal tDCS applied to the human motor cortex (M1) improves motor skill learning. Here, we demonstrate in mouse M1 slices that DCS induces a long-lasting synaptic potentiation (DCS-LTP), which is polarity specific, NMDA receptor dependent, and requires coupling of DCS with repetitive low-frequency synaptic activation (LFS). Combined DCS and LFS enhance BDNF-secretion and TrkB activation, and DCS-LTP is absent in BDNF and TrkB mutant mice, suggesting that BDNF is a key mediator of this phenomenon. Moreover, the BDNF val66met polymorphism known to partially affect activity-dependent BDNF secretion impairs motor skill acquisition in humans and mice. Motor learning is enhanced by anodal tDCS, as long as activity-dependent BDNF secretion is in place. We propose that tDCS may improve motor skill learning through augmentation of synaptic plasticity that requires BDNF secretion and TrkB activation within M1.
Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation technique that has been investigated for the treatment of many neurological or neuropsychiatric disorders. Its main effect is to modulate the cortical excitability depending on the polarity of the current applied. However, understanding the mechanisms by which these modulations are induced and persist is still an open question. A possible marker indicating a change in cortical activity is the subsequent variation in regional blood flow and metabolism. These variations can be effectively monitored using functional near-infrared spectroscopy (fNIRS), which offers a noninvasive and portable measure of regional blood oxygenation state in cortical tissue. We studied healthy volunteers at rest and evaluated the changes in cortical oxygenation related to tDCS using fNIRS. Subjects were tested after active stimulation (12 subjects) and sham stimulation (10 subjects). Electrodes were applied at two prefrontal locations; stimulation lasted 10 min and fNIRS data were then collected for 20 min. The anodal stimulation induced a significant increase in oxyhemoglobin (HbO(2)) concentration compared to sham stimulation. Additionally, the effect of active 10-min tDCS was localized in time and lasted up to 8-10 min after the end of the stimulation. The cathodal stimulation manifested instead a negligible effect. The changes induced by tDCS on HbO(2), as captured by fNIRS, agreed with the results of previous studies. Taken together, these results help clarify the mechanisms underlying the regional alterations induced by tDCS and validate the use of fNIRS as a possible noninvasive method to monitor the neuromodulation effect of tDCS.
Rapid-presentation event-related functional MRI (ER-fMRI) allows neuroimaging methods based on hemodynamics to employ behavioral task paradigms typical of cognitive settings. However, the sluggishness of the hemodynamic response and its variance provide constraints on how ER-fMRI can be applied. In a series of two studies, estimates of the hemodynamic response in or near the primary visual and motor cortices were compared across various paradigms and sampling procedures to determine the limits of ER-fMRI procedures and, more generally, to describe the behavior of the hemodynamic response. The temporal profile of the hemodynamic response was estimated across overlapping events by solving a set of linear equations within the general linear model. No assumptions about the shape were made in solving the equations. Following estimation of the temporal profile, the amplitude and timing were modeled using a gamma function. Results indicated that (1) within a region, for a given subject, estimation of the hemodynamic response is extremely stable for both amplitude (r(2) = 0.98) and time to peak (r(2) = 0.95), from one series of measurements to the next, and slightly less stable for estimation of time to onset (r(2) = 0.60). (2) As the trial presentation rate changed (from those spaced 20 s apart to temporally overlapping trials), the hemodynamic response amplitude showed a small, but significant, decrease. Trial onsets spaced (on average) 5 s apart showed a 17-25% reduction in amplitude compared to those spaced 20 s apart. Power analysis indicated that the increased number of trials at fast rates outweighs this decrease in amplitude if statistically reliable response detection is the goal. (3) Knowledge of the amplitude and timing of the hemodynamic response in one region failed to predict those properties in another region, even for within-subject comparisons. (4) Across subjects, the amplitude of the response showed no significant correlation with timing of the response, for either time-to-onset or time-to-peak estimates. (5) The within-region stability of the response was sufficient to allow offsets in the timing of the response to be detected that were under a second, placing event-related fMRI methods in a position to answer questions about the change in relative timing between regions.
Modulation of cortico-cortical connectivity in specific neural circuits might underlie some of the behavioural effects observed following repetitive transcranial magnetic stimulation (rTMS) of the human frontal cortex. This possibility was tested by applying rTMS to the left mid-dorsolateral frontal cortex (MDL-FC) and subsequently measuring functional connectivity of this region with positron emission tomography (PET) and TMS. The results showed a strong rTMS-related modulation of brain activity in the fronto-cingulate circuit. These results were confirmed in a parallel experiment in the rat using electrical stimulation and field-potential recordings. Future studies are needed to provide a direct link between the rTMS-induced modulation of cortical connectivity and its effects on specific behaviours.
We examined the hypothesis that cognitive dysfunction in Alzheimer's disease is associated with abnormal spontaneous fluctuations of EEG synchronization levels during an eyes-closed resting state.
EEGs were recorded during an eyes-closed resting state in Alzheimer patients (N=24; 9 males; mean age 76.3 years; SD 7.8; range 59-86) and non-demented subjects with subjective memory complaints (N=19; 9 males; mean age 76.1 years; SD 6.7; range: 67-89). The mean level of synchronization was determined in different frequency bands with the synchronization likelihood and fluctuations of the synchronization level were analysed with detrended fluctuation analysis (DFA).
The mean level of EEG synchronization was lower in Alzheimer patients in the upper alpha (10-13Hz) and beta (13-30Hz) band. Spontaneous fluctuations of synchronization were diminished in Alzheimer patients in the lower alpha (8-10Hz) and beta bands. In patients as well as controls the synchronization fluctuations showed a scale-free pattern.
Alzheimer's disease is characterized both by a lower mean level of functional connectivity as well as by diminished fluctuations in the level of synchronization. The dynamics of these fluctuations in patients and controls was scale-free which might point to self-organized criticality of neural networks in the brain.
Impaired functional connectivity can manifest itself not only in decreased levels of synchronization but also in disturbed fluctuations of synchronization levels.
Transcranial direct current stimulation for the treatment of major depressive disorder: a summary of preclinical, clinical and translational findings
- A R Brunoni
- R Ferrucci
- F Fregni
- P S Boggio
- A Priori
Brunoni AR, Ferrucci R, Fregni F, Boggio PS, Priori A. Transcranial direct
current stimulation for the treatment of major depressive disorder: a summary
of preclinical, clinical and translational findings. Prog Neuropsychopharmacol
Biol Psychiatry 2012; 39:9-16.
Transcranial direct current stimulation for the treatment of major depressive disorder: a summary of preclinical, clinical and translational findings.
- Brunoni