Cumulative benefits of frontal transcranial direct current stimulation on visuospatial working memory training and skill learning in rats

EFMouse: a Matlab toolbox to model electric fields in the mouse brain

Compared to the rapidly growing literature on transcranial electrical stimulation (tES) in humans, research into the mechanisms underlying neuromodulation by tES using in-vivo animal models is growing but still relatively rare. Such research, however, is key to overcoming experimental limitations in humans and essential to build a detailed understanding of the in-vivo consequences of tES that can ultimately lead to development of targeted and effective therapeutic applications of noninvasive brain stimulation. The sheer difference in scale and geometry between animal models and the human brain contributes to the complexity of designing and interpreting animal studies. Here we extend previous approaches to model intracranial electric fields to generate predictions that can be tested with in-vivo intracranial recordings. Although the toolbox has general applicability and could be used to predict intracranial fields for any tES study using mice, we illustrate its usage by comparing fields in a high-density multi-electrode montage with a more traditional two electrode montage. Our simulations show that both montages can produce strong focal homogeneous electric fields in targeted areas. However, the high-density montage produces a field that is more perpendicular to the visual cortical surface, which is expected to result in larger changes in neuronal excitability.

Highlights

EFMouse is a novel, open-source, Matlab-based electric field simulator for the mouse brain.EFMouse quantifies field focality and homogeneity in regions of the Allen Mouse Brain Atlas.Focal and strong stimulation can be produced with two or five electrode montages.A high-density montage with a lumbar return generates fields perpendicular to the cortical surface.

Evidence and sources of placebo effects in transcranial direct current stimulation during a single session of visuospatial working memory practice

Transcranial direct current stimulation (tDCS) can be used to non-invasively augment cognitive training. However, the benefits of tDCS may be due in part to placebo effects, which have not been well-characterized. The purpose of this study was to determine whether tDCS can have a measurable placebo effect on cognitive training and to identify potential sources of this effect. Eighty-three right-handed adults were randomly assigned to one of three groups: control (no exposure to tDCS), sham tDCS, or active tDCS. The sham and active tDCS groups were double-blinded. Each group performed 20 min of an adapted Corsi Block Tapping Task (CBTT), a visuospatial working memory task. Anodal or sham tDCS was applied during CBTT training in a right parietal-left supraorbital montage. After training, active and sham tDCS groups were surveyed on expectations about tDCS efficacy. Linear mixed effects models showed that the tDCS groups (active and sham combined) improved more on the CBTT with training than the control group, suggesting a placebo effect of tDCS. Participants' tDCS expectations were significantly related to the placebo effect, as was the belief of receiving active stimulation. This placebo effect shows that the benefits of tDCS on cognitive training can occur even in absence of active stimulation. Future tDCS studies should consider how treatment expectations may be a source of the placebo effect in tDCS research, and identify ways to potentially leverage them to maximize treatment benefit.

Neural Mechanism Underlying Task-Specific Enhancement of Motor Learning by Concurrent Transcranial Direct Current Stimulation

The optimal protocol for neuromodulation by transcranial direct current stimulation (tDCS) remains unclear. Using the rotarod paradigm, we found that mouse motor learning was enhanced by anodal tDCS (3.2 mA/cm2) during but not before or after the performance of a task. Dual-task experiments showed that motor learning enhancement was specific to the task accompanied by anodal tDCS. Studies using a mouse model of stroke induced by middle cerebral artery occlusion showed that concurrent anodal tDCS restored motor learning capability in a task-specific manner. Transcranial in vivo Ca2+ imaging further showed that anodal tDCS elevated and cathodal tDCS suppressed neuronal activity in the primary motor cortex (M1). Anodal tDCS specifically promoted the activity of task-related M1 neurons during task performance, suggesting that elevated Hebbian synaptic potentiation in task-activated circuits accounts for the motor learning enhancement. Thus, application of tDCS concurrent with the targeted behavioral dysfunction could be an effective approach to treating brain disorders.

Effectiveness of Anodal otDCS Following with Anodal tDCS Rather than tDCS Alone for Increasing of Relative Power of Intrinsic Matched EEG Bands in Rat Brains

BACKGROUND

This study sought to determine whether (1) evidence is available of interactions between anodal tDCS and oscillated tDCS stimulation patterns to increase the power of endogenous brain oscillations and (2) the frequency matching the applied anodal otDCS's frequency and the brain's dominant intrinsic frequency influence power shifting during stimulation pattern sessions by both anodal DCS and anodal oscillated DCS.

METHOD

Rats received different anodal tDCS and otDCS stimulation patterns using 8.5 Hz and 13 Hz state-related dominant intrinsic frequencies of anodal otDCS. The rats were divided into groups with specific stimulation patterns: group A: tDCS-otDCS (8.5 Hz)-otDCS (13 Hz); group B: otDCS (8.5 Hz)-tDCS-otDCS (13 Hz); group C: otDCS (13 Hz)-tDCS-otDCS (8.5 Hz). Acute relative power changes (i.e., following 10 min stimulation sessions) in six frequency bands-delta (1.5-4 Hz), theta (4-7 Hz), alpha-1 (7-10 Hz), alpha-2 (10-12 Hz), beta-1 (12-15 Hz) and beta-2 (15-20 Hz)-were compared using three factors and repeated ANOVA measurement.

RESULTS

For each stimulation, tDCS increased theta power band and, above bands alpha and beta, a drop in delta power was observed. Anodal otDCS had a mild increasing power effect in both matched intrinsic and delta bands. In group pattern stimulations, increased power of endogenous frequencies matched exogenous otDCS frequencies-8.5 Hz or 13 Hz-with more potent effects in upper bands. The power was markedly more potent with the otDCS-tDCS stimulation pattern than the tDCS-otDCS pattern.

SIGNIFICANCE

The findings suggest that the otDCS-tDCS pattern stimulation increased the power in matched intrinsic oscillations and, significantly, in the above bands in an ascending order. We provide evidence for the successful corporation between otDCS (as frequency-matched guidance) and tDCS (as a power generator) rather than tDCS alone when stimulating a desired brain intrinsic band (herein, tES specificity).

Direct Current Stimulation in Cell Culture Systems and Brain Slices-New Approaches for Mechanistic Evaluation of Neuronal Plasticity and Neuromodulation: State of the Art

Non-invasive direct current stimulation (DCS) of the human brain induces neuronal plasticity and alters plasticity-related cognition and behavior. Numerous basic animal research studies focusing on molecular and cellular targets of DCS have been published. In vivo, ex vivo, and in vitro models enhanced knowledge about mechanistic foundations of DCS effects. Our review identified 451 papers using a PRISMA-based search strategy. Only a minority of these papers used cell culture or brain slice experiments with DCS paradigms comparable to those applied in humans. Most of the studies were performed in brain slices (9 papers), whereas cell culture experiments (2 papers) were only rarely conducted. These ex vivo and in vitro approaches underline the importance of cell and electric field orientation, cell morphology, cell location within populations, stimulation duration (acute, prolonged, chronic), and molecular changes, such as Ca2+-dependent intracellular signaling pathways, for the effects of DC stimulation. The reviewed studies help to clarify and confirm basic mechanisms of this intervention. However, the potential of in vitro studies has not been fully exploited and a more systematic combination of rodent models, ex vivo, and cellular approaches might provide a better insight into the neurophysiological changes caused by tDCS.

Neuromodulation in the Treatment of Alzheimer's Disease: Current and Emerging Approaches

Neuromodulation as a treatment strategy for psychiatric and neurological diseases has grown in popularity in recent years, with the approval of repetitive transcranial magnetic stimulation (rTMS) for the treatment of depression being one such example. These approaches offer new hope in the treatment of diseases that have proven largely intractable to traditional pharmacological approaches. For this reason, neuromodulation is increasingly being explored for the treatment of Alzheimer's disease. However, such approaches have variable, and, in many cases, very limited evidence for safety and efficacy, with most human evidence obtained in small clinical trials. Here we review work in animal models and humans with Alzheimer's disease exploring emerging neuromodulation modalities. Approaches reviewed include deep brain stimulation, transcranial magnetic stimulation, transcranial electrical stimulation, ultrasound stimulation, photobiomodulation, and visual or auditory stimulation. In doing so, we clarify the current evidence for these approaches in treating Alzheimer's disease and identify specific areas where additional work is needed to facilitate their clinical translation.

Spatial working memory in rats: Crucial role of the hippocampus in the allothetic place avoidance alternation task demanding stimuli segregation

Working memory is a construct that contains goal maintenance, interference control and memory capacity domains. Spatial working memory in presence of conflicting stimuli requires segregation and maintenance of the relevant information about a goal over a short period of time. Besides the prefrontal cortex, the hippocampus is an anatomical substrate for the working memory. We hypothesized that in a highly challenging task, where spatial stimuli are in a conflict and only some of them describe the goal location, the spatial working memory will be strongly dependant on the hippocampus. To verify this, we used an allothetic place avoidance alternation task (APAAT). Performance of this task demands a small number of entries and a long maximum time avoided between consecutive entries to the shock sector. These parameters reflected both domains of working memory. The experiment was conducted on hippocampal lesioned (HIPP n = 12) and sham-operated (CTRL n = 8) rats trained in four APAAT days, each consisting of four 5-minute stages: habituation, stage1 (st1) and stage2 (st2) of memory training, a 5-minute break followed by a retrieval test. The position of the shock sector was changed each day. The HIPP rats were impaired on both stages of memory training, whereas CTRL rats presented significant memory improvement on stage2. In HIPP rats the cognitive skill learning measured as shock per entrance ratio was compromised. Hippocampal lesions did not impair locomotor activity. In summary, even slight bilateral damage to the hippocampus is blocking working memory formation in a difficult task.

Combined transcranial direct current stimulation and psychological interventions: State of the art and promising perspectives for clinical psychology

Recent literature shows great heterogeneity in the reported efficacy of transcranial direct current stimulation (tDCS) as a stand-alone psychiatric treatment. Aiming to increase its efficacy, tDCS has been combined with psychological interventions. Our state-of-the-art overview of such combined treatment trials indicates, however, that these usually do not elicit synergistic clinical effects. We therefore explored more basic mechanisms related to the brain state-dependency of tDCS. Importantly, based on our overview, the efficacy of combined interventions may depend on whether individual patients present with endophenotypes that are implicated in the development and maintenance of psychopathology, such as prefrontal-mediated cognitive dysfunction. We discuss how future studies may contribute to the development of personally-tailored dual active treatments by adhering to the Research Domain Criteria (RDoC) framework. RDoC-based mechanistic research may reveal alternative neural circuits that should be functionally targeted by both tDCS and psychological interventions, with promising avenues for clinical psychological science and practice.

Transcranial direct current stimulation (tDCS) affects neuroinflammation parameters and behavioral seizure activity in pentylenetetrazole-induced kindling in rats

Despite the introduction of new antiepileptic drugs, about 30 % of patients with epilepsy are refractory to drug therapy. Thus, the search for non-pharmacological interventions such as transcranial direct current stimulation (tDCS) may be an alternative, either alone or in combination with low doses of anticonvulsants. This study evaluated the effect of anodal (a-tDCS) and cathodal tDCS (c-tDCS) on seizure behavior and neuroinflammation parameters. Rats were submitted to the kindling model induced by pentylenetetrazole (PTZ) using diazepam (DZP) as anticonvulsant standard. tDCS groups were submitted to 10 sessions of a-tDCS or c-tDCS or SHAM-tDCS. Every 3 days they received saline (SAL), low dose of DZP (alone or in combination with tDCS) or effective dose of DZP 30 min before administration of PTZ, totaling 16 days of protocol. Neither a-tDCS nor c-tDCS reduced the occurrence of clonic forelimb seizures (convulsive motor seizures - stage 3 by the adapted Racine scale we based on). Associated with DZP, c-tDCS (c-tDCS/DZP0.15) increased the latency to first clonic forelimb seizure on the 10th and 16th days. Hippocampal IL-1β levels were reduced by c-tDCS and c-tDCS/DZP0.15. In contrast, these treatments induced an increase in cortical IL-1β levels. Hippocampal TNF-α levels were not altered by c-tDCS or a-tDCS, but c-tDCS and c-tDCS/DZP0.15 increased those levels in cerebral cortex. Cortical NGF levels were increased by c-tDCS and c-tDCS/DZP0.15. a-tDCS/DZP0.15 reduced hippocampal BDNF levels and c-tDCS/DZP0.15 increased these levels in cerebral cortex. In conclusion, c-tDCS alone or in combination with a low dose of DZP showed to affect neuroinflammation, improving central neurotrophin levels and decreasing hippocampal IL-1β levels after PTZ-induced kindling without statistically significant effect on seizure behavior.

Memory and Cognition-Related Neuroplasticity Enhancement by Transcranial Direct Current Stimulation in Rodents: A Systematic Review

Brain stimulation techniques, including transcranial direct current stimulation (tDCS), were identified as promising therapeutic tools to modulate synaptic plasticity abnormalities and minimize memory and learning deficits in many neuropsychiatric diseases. Here, we revised the effect of tDCS on the modulation of neuroplasticity and cognition in several animal disease models of brain diseases affecting plasticity and cognition. Studies included in this review were searched following the terms (“transcranial direct current stimulation”) AND (mice OR mouse OR animal) and according to the PRISMA statement requirements. Overall, the studies collected suggest that tDCS was able to modulate brain plasticity due to synaptic modifications within the stimulated area. Changes in plasticity-related mechanisms were achieved through induction of long-term potentiation (LTP) and upregulation of neuroplasticity-related proteins, such as c-fos, brain-derived neurotrophic factor (BDNF), or N-methyl-D-aspartate receptors (NMDARs). Taken into account all revised studies, tDCS is a safe, easy, and noninvasive brain stimulation technique, therapeutically reliable, and with promising potential to promote cognitive enhancement and neuroplasticity. Since the use of tDCS has increased as a novel therapeutic approach in humans, animal studies are important to better understand its mechanisms as well as to help improve the stimulation protocols and their potential role in different neuropathologies.

Randomized controlled trial of TDCS on cognition in 201 seniors with mild neurocognitive disorder

OBJECTIVE

To examine the efficacy and safety of combined transcranial direct current stimulation (tDCS) and working memory training (WMT) in enhancing the cognitive functions for individuals with mild neurocognitive disorder due to AD (NCD-AD).

METHODS

In this double-blind, sham-controlled randomized clinical trial (RCT), 201 patients with NCD-AD were randomly assigned for a 4-week intervention of either a combination of tDCS and WMT, sham tDCS and WMT, or tDCS and control cognitive training (CCT). Global cognition and domain-specific cognitive function were assessed before and after the intervention with Alzheimer's disease assessment scale-cognitive subscale (ADAS-Cog), category verbal fluency test, logical memory, digit, and visual span tests.

RESULTS

Study participants did not show intervention group differences in baseline demographics, or cognitive characteristics (ANOVA). Cognitive enhancement was found across three groups after 4 weeks intervention. Combined tDCS-WMT group showed significantly greater improvement compared with single-modality groups in delayed recall (P = 0.043, η²  = 0.036) and working memory capacity (P = 0.04, η²  = 0.038) at 4th week, and logical memory at 12th week (P = 0.042, η²  = 0.037). Adverse events, including skin lesions (2.2%), were similar between groups.

INTERPRETATION

tDCS or WMT could be a safe, feasible, and effective intervention for individuals with NCD-AD. A combination of tDCS and WMT presents greater cognitive enhancement, which may highlight the potential synergistic effects of combined modality intervention on cognition.

Long-term enhancement of visual responses by repeated transcranial electrical stimulation of the mouse visual cortex

BACKGROUND

Transcranial electrical stimulation (tES) is a popular method to modulate brain activity by sending a weak electric current through the head. Despite its popularity, long-term effects are poorly understood.

OBJECTIVE

We wanted to test if anodal tES immediately changes cerebral responses to visual stimuli, and if repeated sessions of tES produce plasticity in these responses.

METHODS

We applied repeated anodal tES, like transcranial direct current stimulation (tDCS), but pulsed (8 s on, 10 s off), to the visual cortex of mice while visually presenting gratings. We measured the responses to these visual stimuli in the visual cortex using the genetically encoded calcium indicator GCaMP3.

RESULTS

We found an increase in the visual response when concurrently applying tES on the bone without skin (epicranially). This increase was only transient when tES was applied through the skin (transcutaneous). There was no immediate after-effect of tES. However, repeated transcutaneous tES for four sessions at two-day intervals increased the visual response in the visual cortex. This increase was not specific to the grating stimulus coupled to tES and also occurred for an orthogonal grating presented in the same sessions but without concurrent tES. No increase was found in mice that received no tES.

CONCLUSION

Our study provides evidence that tES induces long-term changes in the mouse brain. Results in mice do not directly translate to humans, because of differences in stimulation protocols and the way current translates to electric field strength in vastly different heads.

Transcranial direct current stimulation does not improve memory deficits or alter pathological hallmarks in a rodent model of Alzheimer's disease

Alzheimer's disease (AD) is a progressive and debilitating degenerative disorder for which there are currently no effective therapeutic options. Non-invasive neuromodulation, including transcranial direct current stimulation (tDCS), has been investigated for the treatment of cognitive symptoms in AD. Results from clinical and preclinical studies, however, have been somewhat controversial. We investigate whether tDCS delivered to triple transgenic (3xTg) AD mice improves memory deficits and mitigates the development of AD-type neuropathology. 3xTg AD mice and controls were implanted with paddle electrodes over the skull. The cathode was anterior to bregma and the anode anterior to lamda. tDCS was delivered for 20 min/day, 5 days/week over three weeks at 50 μA. Though this amplitude was lower than the one used in the preclinical literature, it generated a high current density compared to the clinical scenario. Memory testing was conducted during treatment weeks 2 and 3. Post-mortem pathological AD markers were studied. Our results show that performance of 3xTg mice in the novel object recognition and Morris water maze tests was significantly impaired compared to that of controls. In addition, AD transgenics had an increased expression of tau, phosphorylated-tau and amyloid precursor protein in the hippocampus. tDCS did not improve behavioural deficits or mitigated the development of AD neuropathology in 3xTg animals. In summary, we found that tDCS at the settings selected in our study was largely ineffective in improving memory performance or altering the expression of AD pathological hallmarks in a validated mouse model.

Delayed effect of bifrontal transcranial direct current stimulation in patients with treatment-resistant depression: a pilot study

BACKGROUND

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique, which has yielded promising results in treating major depressive disorder. However, its effect on treatment-resistant depression remains to be determined. Meanwhile, as an emerging treatment option, patients' acceptability of tDCS is worthy of attention.

METHODS

This pilot study enrolled 18 patients (women = 13) with treatment-resistant unipolar (n = 13) or bipolar (n = 5) depression. Twelve sessions of tDCS were administered with anode over F3 and cathode over F4. Each session delivered a current of 2 mA for 30 min per ten working days, and at the 4th and 6th week. Severity of depression was determined by Montgomery-Åsberg Depression Rating Scale (MADRS); cognitive performance was assessed by a computerized battery.

RESULTS

Scores of MADRS at baseline (29.6, SD = 9.7) decreased significantly to 22.9 (11.7) (p = 0.03) at 6 weeks and 21.5 (10.3) (p = 0.01) at 8 weeks. Six (33.3%) participants were therapeutically responsive to tDCS. MADRS scores of responders were significantly lower than those of non-responders at the 6th and 8th week. Regarding change of cognitive performance, improved accuracy of paired association (p = 0.017) and social cognition (p = 0.047) was observed at the 8th week. Overall, tDCS was perceived as safe and tolerable. For the majority of patients, it is preferred than pharmacotherapy and psychotherapy.

CONCLUSIONS

TDCS can be a desirable option for treatment-resistant depression, however, its efficacy may be delayed; identifying predictors of therapeutic response may achieve a more targeted application. Larger controlled studies with optimized montages and sufficient periods of observation are warranted.

TRIAL REGISTRATION

This trial has been registered at the Chinese Clinical Trial Registry ( ChiCTR-INR-16008179 ).

The Effects of Transcranial Direct Current Stimulation (tDCS) on Working Memory Training in Healthy Young Adults

Working memory (WM) is a fundamental cognitive ability to support complex thought, but it is limited in capacity. WM training has shown the potential benefit for those in need of a higher WM ability. Many studies have shown the potential of transcranial direct current stimulation (tDCS) to transiently enhance WM performance by delivering a low current to the brain cortex of interest, via electrodes on the scalp. tDCS has also been revealed as a promising intervention to augment WM training in a few studies. However, those few tDCS-paired WM training studies, focused more on the effect of tDCS on WM enhancement and its transferability after training and paid less attention to the variation of cognitive performance during the training procedure. The current study attempted to explore the effect of tDCS on the variation of performance, during WM training, in healthy young adults. All the participants received WM training with the load-adaptive verbal N-back task, for 5 days. During the training procedure, active/sham anodal high-definition tDCS (HD-tDCS) was used to stimulate the left dorsolateral prefrontal cortex (DLPFC). To examine the training effect, pre- and post-tests were performed, respectively, 1 day before and after the training sessions. At the beginning of each training session, stable-load WM tasks were performed, to examine the performance variation during training. Compared to the sham stimulation, higher learning rates of performance metrics during the training procedure were found when WM training was combined with active anodal HD-tDCS. The performance improvements (post–pre) of the active group, were also found to be higher than those of the sham group and were transferred to a similar untrained WM task. Further analysis revealed a negative relationship between the training improvements and the baseline performance. These findings show the potential that tDCS may be leveraged as an intervention to facilitate WM training, for those in need of a higher WM ability.

Electrical fields induced inside the rat brain with skin, skull, and dural placements of the current injection electrode

Transcranial electrical stimulation (tES) is rapidly becoming an indispensable clinical tool with its different forms. Animal data are crucially needed for better understanding of the underlying mechanisms of tES. For reproducibility of results in animal experiments, the electric fields (E-Fields) inside the brain parenchyma induced by the injected currents need to be predicted accurately. In this study, we measured the electrical fields in the rat brain perpendicular to the brain surface, i.e. vertical electric field (VE-field), when the stimulation electrode was placed over the skin, skull, or dura mater through a craniotomy hole. The E-field attenuation through the skin was a few times larger than that of the skull and the presence of skin substantially reduced the VE-field peak at the cortical surface near the electrode. The VE-field declined much quicker in the gray matter underneath the pial surface than it did in the white matter, and thus the large VE-fields were contained mostly in the gray matter. The transition at the gray/white matter border caused a significant peak in the VE-field, as well as at other local inhomogeneties. A conductivity value of 0.57 S/m is predicted as a global value for the whole brain by matching our VE-field measurements to the field profile given by analytical equations for volume conductors. Finally, insertion of the current return electrode into the shoulder, submandibular, and hind leg muscles had virtually no effects on the measured E-field amplitudes in the cortex underneath the epidural electrodes.

Exploring new transcranial electrical stimulation strategies to modulate brain function in animal models

Transcranial electrical stimulation (tES) refers to a group of non-invasive brain stimulation techniques to induce changes in the excitability of cortical neurons in humans. In recent years, studies in animal models have been shown to be essential for disentangling the neuromodulatory effects of tES, defining safety limits, and exploring potential therapeutic applications in neurological and neuropsychiatric disorders. Testing in animal models is valuable for the development of new unconventional protocols intended to improve tES administration and optimize the desired effects by increasing its focality and enabling deep-brain stimulation. Successful and controlled application of tES in humans relies on the knowledge acquired from studies meticulously performed in animal models.

Using animal models to improve the design and application of transcranial electrical stimulation in humans

Purpose of Review

Transcranial electrical stimulation (tES) is a non-invasive stimulation technique used for modulating brain function in humans. To help tES reach its full therapeutic potential, it is necessary to address a number of critical gaps in our knowledge. Here, we review studies that have taken advantage of animal models to provide invaluable insight about the basic science behind tES.

Recent Findings

Animal studies are playing a key role in elucidating the mechanisms implicated in tES, defining safety limits, validating computational models, inspiring new stimulation protocols, enhancing brain function and exploring new therapeutic applications.

Summary

Animal models provide a wealth of information that can facilitate the successful utilization of tES for clinical interventions in human subjects. To this end, tES experiments in animals should be carefully designed to maximize opportunities for applying discoveries to the treatment of human disease.

Non-invasive modulation reduces repetitive behavior in a rat model through the sensorimotor cortico-striatal circuit

Involuntary movements as seen in repetitive disorders such as Tourette Syndrome (TS) results from cortical hyperexcitability that arise due to striato-thalamo-cortical circuit (STC) imbalance. Transcranial direct current stimulation (tDCS) is a stimulation procedure that changes cortical excitability, yet its relevance in repetitive disorders such as TS remains largely unexplored. Here, we employed the dopamine transporter-overexpressing (DAT-tg) rat model to investigate behavioral and neurobiological effects of frontal tDCS. The outcome of tDCS was pathology dependent, as anodal tDCS decreased repetitive behavior in the DAT-tg rats yet increased it in wild-type (wt) rats. Extensive deep brain stimulation (DBS) application and computational modeling assigned the response in DAT-tg rats to the sensorimotor pathway. Neurobiological assessment revealed cortical activity changes and increase in striatal inhibitory properties in the DAT-tg rats. Our findings show that tDCS reduces repetitive behavior in the DAT-tg rat through modulation of the sensorimotor STC circuit. This sets the stage for further investigating the usage of tDCS in repetitive disorders such as TS.

Repeated anodal transcranial direct current stimulation induces neural plasticity-associated gene expression in the rat cortex and hippocampus

BACKGROUND

Anodal transcranial direct current stimulation (A-tDCS) induces a long-lasting increase in cortical excitability that can increase gene transcription in the brain.

OBJECTIVE

The purpose of this study was to evaluate the expression of genes related to activity-dependent neuronal plasticity in the sensorimotor cortex and hippocampus of young Sprague-Dawley rats following A-tDCS.

METHODS

We applied A-tDCS over the right sensorimotor cortex epicranially with a circular electrode (3 mm diameter) at 250 μA for 20 min per day for 7 consecutive days. Levels of mRNA for brain-derived neurotrophic factor (BDNF), cAMP response element-binding protein (CREB), synapsin I, Ca2+/calmodulin-dependent protein kinase II (CaMKII), activity-regulated cytoskeleton-associated protein (Arc), and c-Fos were analyzed using SYBR Green quantitative real-time polymerase chain reaction (PCR).

RESULTS

We found that 7 days of unilateral A-tDCS resulted in significant increases in transcription of all plasticity-related genes tested in the ipsilateral cortex. Daily A-tDCS also resulted in a significant increase in c-Fos mRNA in the ipsilateral hippocampus.

CONCLUSION

These results indicate that altered expression of plasticity-associated genes in the cortex and hippocampus is a molecular substrate of A-tDCS-induced neural plasticity.

Transcranial Electrical Brain Stimulation in Alert Rodents

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

Repeated transcranial direct current stimulation improves cognitive dysfunction and synaptic plasticity deficit in the prefrontal cortex of streptozotocin-induced diabetic rats

BACKGROUND

Cognitive dysfunction is commonly observed in diabetic patients. We have previously reported that anodal transcranial direct current stimulation (tDCS) over the dorsolateral prefrontal cortex can facilitate visuospatial working memory in diabetic patients with concomitant diabetic peripheral neuropathy and mild cognitive impairment, but the underlying mechanisms remain unclear.

OBJECTIVE

We investigated the cellular mechanisms underlying the effect of tDCS on cognitive decline in streptozotocin (STZ)-induced diabetic rats.

METHODS

STZ-induced diabetic rats were subjected to either repeated anodal tDCS or sham stimulation over the medial prefrontal cortex (mPFC). Spatial working memory performance in delayed nonmatch-to-place T maze task (DNMT), the induction of long-term potentiation (LTP) in the mPFC, and dendritic morphology of Golgi-stained pyramidal neurons in the mPFC were assessed.

RESULTS

Repeated applications of prefrontal anodal tDCS improved spatial working memory performance in DNMT and restored the impaired mPFC LTP of diabetic rats. The mPFC of tDCS-treated diabetic rats exhibited higher levels of brain-derived neurotrophic factor (BDNF) protein and N-Methyl-d-aspartate receptor (NMDAR) subunit mRNA and protein compared to sham stimulation group. Furthermore, anodal tDCS significantly increased dendritic spine density on the apical dendrites of mPFC layer V pyramidal cells in diabetic rats, whereas the complexity of basal and apical dendritic trees was unaltered.

CONCLUSIONS

Our findings suggest that repeated anodal tDCS may improve spatial working memory performance in streptozotocin-induced diabetic rats through augmentation of synaptic plasticity that requires BDNF secretion and transcription/translation of NMDARs in the mPFC, and support the therapeutic potential of tDCS for cognitive decline in diabetes mellitus patients.

Non-ketogenic combination of nutritional strategies provides robust protection against seizures

Epilepsy is a neurological condition that affects 1% of the world population. Conventional treatments of epilepsy use drugs targeting neuronal excitability, inhibitory or excitatory transmission. Yet, one third of patients presents an intractable form of epilepsy and fails to respond to pharmacological anti-epileptic strategies. The ketogenic diet is a well-established non-pharmacological treatment that has been proven to be effective in reducing seizure frequency in the pharmaco-resistant patients. This dietary solution is however extremely restrictive and can be associated with complications caused by the high [fat]:[carbohydrate + protein] ratio. Recent advances suggest that the traditional 4:1 ratio of the ketogenic diet is not a requisite for its therapeutic effect. We show here that combining nutritional strategies targeting specific amino-acids, carbohydrates and fatty acids with a low [fat]:[proteins + carbohydrates] ratio also reduces excitatory drive and protects against seizures to the same extent as the ketogenic diet. Similarly, the morphological and molecular correlates of temporal lobe seizures were reduced in animals fed with the combined diet. These results provide evidence that low-fat dietary strategies more palatable than the ketogenic diet could be useful in epilepsy.

Augmentation of working memory training by transcranial direct current stimulation (tDCS)

Transcranial direct current stimulation (tDCS) to the dorsolateral prefrontal cortex (dlPFC) can modulate working memory (WM) performance. However, evidence regarding the enhancement of WM training, its sustainability and transferability is ambiguous. Since WM functioning appears to be lateralized in respect to stimulus characteristics, this study examined the difference between task-congruent (spatial-right, verbal-left), task-incongruent (spatial-left, verbal-right) and sham tDCS in regards to the efficacy of WM training. In a randomized, sham-controlled experiment, 71 healthy adults trained on a spatial or verbal adaptive n-back task. After a baseline session, anodal or sham tDCS (1 mA) to the right or left dlPFC was applied during the next three training sessions. Sustainability of training gains and near-transfer (verbal or spatial 3-back task) were tested in a fourth training and a follow-up session. Compared to sham stimulation, we found a steeper learning curve when WM training was combined with task-congruent tDCS. This advantage was also present compared to task-incongruent tDCS. Moreover, these effects lasted for up to nine months and transferred to the respective untrained task. These long-lasting, transferable, task-specific effects demonstrate a behaviorally relevant and sustainable facilitation of neuroplastic processes by tDCS that could be harnessed for the treatment of disorders associated with deficient WM.

Mechanisms and Effects of Transcranial Direct Current Stimulation

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

Animal models of transcranial direct current stimulation: Methods and mechanisms

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

Working memory capacity differentially influences responses to tDCS and HD-tDCS in a retro-cue task

There is growing interest in non-invasive brain stimulation techniques. A drawback is that the relationship between stimulation and cognitive outcomes for various tasks are unknown. Transcranial direct current stimulation (tDCS) provides diffuse current spread, whereas high-definition tDCS (HD-tDCS) provides more targeted current. The direction of behavioral effects after tDCS can be difficult to predict in cognitive realms such as attention and working memory (WM). Previously, we showed that in low and high WM capacity groups tDCS modulates performance in nearly equal and opposite directions on a change detection task, with improvement for the high capacity participants alone. Here, we used the retro-cue paradigm to test attentional shifting among items in WM to investigate whether WM capacity (WMC) predicted different behavioral consequences during anodal tDCS or HD-tDCS to posterior parietal cortex (PPC). In two experiments, with 24 participants each, we used different stimulus categories (colored circles, letters) and stimulation sites (right, left PPC). The results showed a significant (Experiment 1) or trending (Experiment 2) WMC x stimulation interaction. Compared to tDCS, after HD-tDCS the retro-cueing benefit was significantly greater for the low WMC group but numerically worse for the high WMC group. These data highlight the importance of considering group differences when using non-invasive neurostimulation techniques.

Calcium imaging reveals glial involvement in transcranial direct current stimulation-induced plasticity in mouse brain

Transcranical direct current stimulation (tDCS) is a treatment known to ameliorate various neurological conditions and enhance memory and cognition in humans. tDCS has gained traction for its potential therapeutic value; however, little is known about its mechanism of action. Using a transgenic mouse expressing G-CaMP7 in astrocytes and a subpopulation of excitatory neurons, we find that tDCS induces large-amplitude astrocytic Ca²⁺ surges across the entire cortex with no obvious changes in the local field potential. Moreover, sensory evoked cortical responses are enhanced after tDCS. These enhancements are dependent on the alpha-1 adrenergic receptor and are not observed in IP₃R2 (inositol trisphosphate receptor type 2) knockout mice, in which astrocytic Ca²⁺ surges are absent. Together, we propose that tDCS changes the metaplasticity of the cortex through astrocytic Ca²⁺/IP₃ signalling.

While transcranical direct current stimulation (tDCS) is used in clinical setting, its cellular mechanism of action is unclear. Here, Hajime Hirase and colleagues visualize cellular response in mouse brain to tDCS and show robust astrocyte activation that coincide with plasticity changes.

Transcranial direct current stimulation improves short-term memory in an animal model of attention-deficit/hyperactivity disorder

Attention deficit hyperactivity disorder (ADHD) is characterized by impairing levels of hyperactivity, impulsivity and inattention. However, different meta-analyses have reported disruptions in short and long-term memory in ADHD patients. Previous studies indicate that mnemonic dysfunctions might be the result of deficits in attentional circuits, probably due to ineffective dopaminergic modulation of hippocampal synaptic plasticity. In this study we aimed to evaluate the potential therapeutic effects of a neuromodulatory technique, transcranial direct current stimulation (tDCS), in short-term memory (STM) deficits presented by the spontaneous hypertensive rats (SHR), the most widely used animal model of ADHD. Adult male SHR and Wistar Kyoto rats (WKY) were subjected to a constant electrical current of 0.5 mA intensity applied on the frontal cortex for 20 min/day during 8 days. STM was evaluated with an object recognition test conducted in an open field. Exploration time and locomotion were recorded, and brain regions were dissected to determine dopamine and BDNF levels. SHR spent less time exploring the new object when compared to WKY, and tDCS improved object recognition deficits in SHR without affecting WKY performance. Locomotor activity was higher in SHR and it was not affected by tDCS. After stimulation, dopamine levels were increased in the hippocampus and striatum of both strains, while BDNF levels were increased only in the striatum of WKY. These findings suggest that tDCS on the frontal cortex might be able to improve STM deficits present in SHR, which is potentially related to dopaminergic neurotransmission in the hippocampus and striatum of those animals.

Transcranial direct current stimulation (tDCS) reverts behavioral alterations and brainstem BDNF level increase induced by neuropathic pain model: Long-lasting effect

INTRODUCTION

Neuropathic pain (NP) is a chronic pain modality that usually results of damage in the somatosensory system. NP often shows insufficient response to classic analgesics and remains a challenge to medical treatment. The transcranial direct current stimulation (tDCS) is a non-invasive technique, which induces neuroplastic changes in central nervous system of animals and humans. The brain derived neurotrophic factor plays an important role in synaptic plasticity process. Behavior changes such as decreased locomotor and exploratory activities and anxiety disorders are common comorbidities associated with NP.

OBJECTIVE

Evaluate the effect of tDCS treatment on locomotor and exploratory activities, and anxiety-like behavior, and peripheral and central BDNF levels in rats submitted to neuropathic pain model.

METHODS

Rats were randomly divided: Ss, SsS, SsT, NP, NpS, and NpT. The neuropathic pain model was induced by partial sciatic nerve compression at 14 days after surgery; the tDCS treatment was initiated. The animals of treated groups were subjected to a 20 minute session of tDCS, for eight days. The Open Field and Elevated Pluz Maze tests were applied 24 h (phase I) and 7 days (phase II) after the end of tDCS treatment. The serum, spinal cord, brainstem and cerebral cortex BDNF levels were determined 48 h (phase I) and 8 days (phase II) after tDCS treatment by ELISA.

RESULTS

The chronic constriction injury (CCI) induces decrease in locomotor and exploratory activities, increases in the behavior-like anxiety, and increases in the brainstem BDNF levels, the last, in phase II (one-way ANOVA/SNK, P<0.05 for all). The tDCS treatment already reverted all these effects induced by CCI (one-way ANOVA/SNK, P<0.05 for all). Furthermore, the tDCS treatment decreased serum and cerebral cortex BDNF levels and it increased these levels in the spinal cord in phase II (one-way ANOVA/SNK, P<0.05).

CONCLUSION

tDCS reverts behavioral alterations associated to neuropathic pain, indicating possible analgesic and anxiolytic tDCS effects. tDCS treatment induces changes in the BDNF levels in different regions of the central nervous system (CNS), and this effect can be attributed to different cellular signaling activations.

Modulating Hippocampal Plasticity with In Vivo Brain Stimulation

Investigations into the use of transcranial direct current stimulation (tDCS) in relieving symptoms of neurological disorders and enhancing cognitive or motor performance have exhibited promising results. However, the mechanisms by which tDCS effects brain function remain under scrutiny. We have demonstrated that in vivo tDCS in rats produced a lasting effect on hippocampal synaptic plasticity, as measured using extracellular recordings. Ex vivo preparations of hippocampal slices from rats that have been subjected to tDCS of 0.10 or 0.25 mA for 30 min followed by 30 min of recovery time displayed a robust twofold enhancement in long-term potentiation (LTP) induction accompanied by a 30% increase in paired-pulse facilitation (PPF). The magnitude of the LTP effect was greater with 0.25 mA compared with 0.10 mA stimulations, suggesting a dose-dependent relationship between tDCS intensity and its effect on synaptic plasticity. To test the persistence of these observed effects, animals were stimulated in vivo for 30 min at 0.25 mA and then allowed to return to their home cage for 24 h. Observation of the enhanced LTP induction, but not the enhanced PPF, continued 24 h after completion of 0.25 mA of tDCS. Addition of the NMDA blocker AP-5 abolished LTP in both control and stimulated rats but maintained the PPF enhancement in stimulated rats. The observation of enhanced LTP and PPF after tDCS demonstrates that non-invasive electrical stimulation is capable of modifying synaptic plasticity.

SIGNIFICANCE STATEMENT

Researchers have used brain stimulation such as transcranial direct current stimulation on human subjects to alleviate symptoms of neurological disorders and enhance their performance. Here, using rats, we have investigated the potential mechanisms of how in vivo brain stimulation can produce such effect. We recorded directly on viable brain slices from rats after brain stimulation to detect lasting changes in pattern of neuronal activity. Our results showed that 30 min of brain stimulation in rats induced a robust enhancement in synaptic plasticity, a neuronal process critical for learning and memory. Understanding such molecular effects will lead to a better understanding of the mechanisms by which brain stimulation produces its effects on cognition and performance.

Cellular and molecular mechanisms of action of transcranial direct current stimulation: evidence from in vitro and in vivo models

Transcranial direct current stimulation is a noninvasive technique that has been experimentally tested for a number of psychiatric and neurological conditions. Preliminary observations suggest that this approach can indeed influence a number of cellular and molecular pathways that may be disease relevant. However, the mechanisms of action underlying its beneficial effects are largely unknown and need to be better understood to allow this therapy to be used optimally. In this review, we summarize the physiological responses observed in vitro and in vivo, with a particular emphasis on cellular and molecular cascades associated with inflammation, angiogenesis, neurogenesis, and neuroplasticity recruited by direct current stimulation, a topic that has been largely neglected in the literature. A better understanding of the neural responses to transcranial direct current stimulation is critical if this therapy is to be used in large-scale clinical trials with a view of being routinely offered to patients suffering from various conditions affecting the central nervous system.

Transcranial direct current stimulation for memory enhancement: from clinical research to animal models

There is a growing demand for new brain-enhancing technologies to improve mental performance, both for patients with cognitive disorders and for healthy individuals. Transcranial direct current stimulation (tDCS) is a non-invasive, painless, and easy to use neuromodulatory technique that can improve performance on a variety of cognitive tasks in humans despite its exact mode of action remains unclear. We have conducted a mini-review of the literature to first briefly summarize the growing amount of data from clinical trials assessing the efficacy of tDCS, focusing exclusively on learning and memory performances in healthy human subjects and in patients with depression, schizophrenia, and other neurological disorders. We then discuss these findings in the context of the strikingly few studies resulting from animal research. Finally, we highlight future directions and limitations in this field and emphasize the need to develop translational studies to better understand how tDCS improves memory, a necessary condition before it can be used as a therapeutic tool.

Place avoidance tasks as tools in the behavioral neuroscience of learning and memory

Spatial navigation comprises a widely-studied complex of animal behaviors. Its study offers many methodological advantages over other approaches, enabling assessment of a variety of experimental questions and the possibility to compare the results across different species. Spatial navigation in laboratory animals is often considered a model of higher human cognitive functions including declarative memory. Almost fifteen years ago, a novel dry-arena task for rodents was designed in our laboratory, originally named the place avoidance task, and later a modification of this approach was established and called active place avoidance task. It employs a continuously rotating arena, upon which animals are trained to avoid a stable sector defined according to room-frame coordinates. This review describes the development of the place avoidance tasks, evaluates the cognitive processes associated with performance and explores the application of place avoidance in the testing of spatial learning after neuropharmacological, lesion and other experimental manipulations.

Transcranial slow oscillation stimulation during sleep enhances memory consolidation in rats

BACKGROUND

The importance of slow-wave sleep (SWS), hallmarked by the occurrence of sleep slow oscillations (SO), for the consolidation of hippocampus-dependent memories has been shown in numerous studies. Previously, the application of transcranial direct current stimulation, oscillating at the frequency of endogenous slow oscillations, during SWS enhanced memory consolidation for a hippocampus dependent task in humans suggesting a causal role of slowly oscillating electric fields for sleep dependent memory consolidation.

OBJECTIVE

Here, we aimed to replicate and extend these findings to a rodent model.

METHODS

Slow oscillatory direct transcranial current stimulation (SO-tDCS) was applied over the frontal cortex of rats during non-rapid eye movement (NREM) sleep and its effects on memory consolidation in the one-trial object-place recognition task were examined. A retention interval of 24 h was used to investigate the effects of SO-tDCS on long-term memory.

RESULTS

Animals' preference for the displaced object was significantly greater than chance only when animals received SO-tDCS. EEG spectral power indicated a trend toward a transient enhancement of endogenous SO activity in the SO-tDCS condition.

CONCLUSIONS

These results support the hypothesis that slowly oscillating electric fields causal affect sleep dependent memory consolidation, and demonstrate that oscillatory tDCS can be a valuable tool to investigate the function of endogenous cortical network activity.

Spatial Navigation: Implications for Animal Models, Drug Development and Human Studies

Spatial navigation and memory is considered to be a part of the declarative memory system and it is widely used as an animal model of human declarative memory. However, spatial tests typically involve only static settings, despite the dynamic nature of the real world. Animals, as well as people constantly need to interact with moving objects, other subjects or even with entire moving environments (flowing water, running stairway). Therefore, we design novel spatial tests in dynamic environments to study brain mechanisms of spatial processing in more natural settings with an interdisciplinary approach including neuropharmacology. We also translate data from neuropharmacological studies and animal models into development of novel therapeutic approaches to neuropsychiatric disorders and more sensitive screening tests for impairments of memory, thought, and behavior.

Transcranial slow oscillation stimulation during NREM sleep enhances acquisition of the radial maze task and modulates cortical network activity in rats

Slow wave sleep, hallmarked by the occurrence of slow oscillations (SO), plays an important role for the consolidation of hippocampus-dependent memories. Transcranial stimulation by weak electric currents oscillating at the endogenous SO frequency (SO-tDCS) during post-learning sleep was previously shown by us to boost SO activity and improve the consolidation of hippocampus-dependent memory in human subjects. Here, we aimed at replicating and extending these results to a rodent model. Rats were trained for 12 days at the beginning of their inactive phase in the reference memory version of the radial arm maze. In a between subjects design, animals received SO-tDCS over prefrontal cortex (PFC) or sham stimulation within a time frame of 1 h during subsequent non-rapid eye movement (NREM) sleep. Applied over multiple daily sessions SO-tDCS impacted cortical network activity as measured by EEG and behavior: at the EEG level, SO-tDCS enhanced post-stimulation upper delta (2–4 Hz) activity whereby the first stimulations of each day were preferentially affected. Furthermore, commencing on day 8, SO-tDCS acutely decreased theta activity indicating long-term effects on cortical networks. Behaviorally, working memory for baited maze arms was enhanced up to day 4, indicating enhanced consolidation of task-inherent rules, while reference memory errors did not differ between groups. Taken together, we could show here for the first time an effect of SO-tDCS during NREM sleep on cognitive functions and on cortical activity in a rodent model.

In vivo assessment of human brain oscillations during application of transcranial electric currents

Brain oscillations reflect pattern formation of cell assemblies’ activity, which is often disturbed in neurological and psychiatric diseases like depression, schizophrenia and stroke. In the neurobiological analysis and treatment of these conditions, transcranial electric currents applied to the brain proved beneficial. However, the direct effects of these currents on brain oscillations have remained an enigma because of the inability to record them simultaneously. Here we report a novel strategy that resolves this problem. We describe accurate reconstructed localization of dipolar sources and changes of brain oscillatory activity associated with motor actions in primary cortical brain regions undergoing transcranial electric stimulation. This new method allows for the first time direct measurement of the effects of non-invasive electrical brain stimulation on brain oscillatory activity and behavior.

Low-dose memantine-induced working memory improvement in the allothetic place avoidance alternation task (APAAT) in young adult male rats

N-methyl-D-aspartate receptors (NMDAR) are involved in neuronal plasticity. To assess their role simultaneously in spatial working memory and non-cognitive learning, we used NMDAR antagonists and the Allothetic Place Avoidance Alternation Task (APAAT). In this test rats should avoid entering a place where shocks were presented on a rotating arena which requires cognitive coordination for the segregation of stimuli. The experiment took place 30 min after intraperitoneal injection of memantine (5, 10, 20 mg/kg b.w.: MemL, MemM, MemH, respectively) and (+)MK-801 (0.1, 0.2, 0.3 mg/kg b.w.: MK-801L, MK-801M, MK-801H, respectively). Rats from the control group were intact or injected with saline (0.2 ml/kg). Over three consecutive days the rats underwent habituation, two avoidance training intervals with shocks, and a retrieval test. The shock sector was alternated daily. The after-effects of the agents were tested on Day 21. Rats treated with low dose memantine presented a longer maximum time avoided and fewer entrances than the MemH, MK-801M, MK-801H and Control rats. The shocks per entrances ratio, used as an index of cognitive skill learning, showed skill improvement after D1, except for rats treated by high doses of the agents. The activity levels, indicated by the distance walked, were higher for the groups treated with high doses of the agents. On D21 the MK801H rats performed the memory task better than the MemH rats, whereas the rats' activity depended on condition, not on the group factor. These results suggest that in naïve rats mild NMDAR blockade by low-dose memantine improves working memory related to a highly challenging task.

Can transcranial direct current stimulation enhance outcomes from cognitive training? A randomized controlled trial in healthy participants

Computer-administered cognitive training (CT) tasks are a common component of cognitive remediation treatments. There is growing evidence that transcranial direct current stimulation (tDCS), when given during cognitive tasks, improves performance. This randomized, controlled trial explored the potential synergistic effects of CT combined with tDCS in healthy participants. Altogether, 60 healthy participants were randomized to receive either active or sham tDCS administered during training on an adaptive CT task (dual n-back task), or tDCS alone, over 10 daily sessions. Cognitive testing (working memory, processing speed, executive function, reaction time) was conducted at baseline, end of the 10 sessions, and at 4-wk follow-up to examine potential transfer effects to non-trained tasks. Altogether, 54 participants completed the study. Over the 10 'online' sessions, participants in the active tDCS+CT condition performed more accurately on the CT task than participants who received sham tDCS+CT. The performance enhancing effect, however, was present only during tDCS and did not result in greater learning (i.e. improvement over sessions) on the CT task. These results confirm prior reports of enhancement of cognitive function during tDCS stimulation. At follow-up, the active tDCS+CT group, but not the sham tDCS+CT group, showed greater gains on a non-trained test of attention and working memory than the tDCS-only group (p < 0.01). Although this gain can mainly be attributable to training, this result suggests that active tDCS may have a role in further enhancing outcomes.