Modulatory effects of anodal transcranial direct current stimulation on perception and pain thresholds in healthy volunteers

Neuromodulation of conditioned placebo/nocebo in heat pain: anodal vs cathodal transcranial direct current stimulation to the right dorsolateral prefrontal cortex

Placebo and nocebo play an important role in clinical practice and medical research. Modulating placebo/nocebo responses using noninvasive brain stimulation methods, such as transcranial direct current stimulation (tDCS), has the potential to harness these effects to therapeutic benefit in a clinical setting. In this study, we assessed the effect of anodal and cathodal tDCS over the right dorsolateral prefrontal cortex (rDLPFC) on conditioned placebo/nocebo cue response to heat pain. Two matched groups of healthy volunteers were subjected to an identical session of conditioning, during which low and high cues (abstract images) were associated with low and high pain levels, respectively. Twenty-minute 2-mA tDCS (either anodal or cathodal) over the rDLPFC was applied. The influence of tDCS current polarity (anodal vs cathodal) on placebo and nocebo was assessed, using subjects' pain ratings in response to identical pain preceded by the conditioned high or low cues. The duration of cue presentation varied to allow either fully conscious or subliminal processing. Significant placebo and nocebo effects in the anodal but not the cathodal group were elicited with the conditioning paradigm. This study provides evidence of a possibility to modulate the conditioned placebo and nocebo effect by changing the excitability of the rDLPFC using tDCS.

Prefrontal tDCS Decreases Pain in Patients with Multiple Sclerosis

Background: In the last few years, transcranial direct current stimulation (tDCS) has emerged as an appealing therapeutic option to improve brain functions. Promising data support the role of prefrontal tDCS in augmenting cognitive performance and ameliorating several neuropsychiatric symptoms, namely pain, fatigue, mood disturbances, and attentional impairment. Such symptoms are commonly encountered in patients with multiple sclerosis (MS).

Objective: The main objective of the current work was to evaluate the tDCS effects over the left dorsolateral prefrontal cortex (DLPFC) on pain in MS patients.Our secondary outcomes were to study its influence on attention, fatigue, and mood.

Materials and Methods: Sixteen MS patients with chronic neuropathic pain were enrolled in a randomized, sham-controlled, and cross-over study.Patients randomly received two anodal tDCS blocks (active or sham), each consisting of three consecutive daily tDCS sessions, and held apart by 3 weeks. Evaluations took place before and after each block. To evaluate pain, we used the Brief Pain Inventory (BPI) and the Visual Analog Scale (VAS). Attention was assessed using neurophysiological parameters and the Attention Network Test (ANT). Changes in mood and fatigue were measured using various scales.

Results: Compared to sham, active tDCS yielded significant analgesic effects according to VAS and BPI global scales.There were no effects of any block on mood, fatigue, or attention.

Conclusion: Based on our results, anodal tDCS over the left DLPFC appears to act in a selective manner and would ameliorate specific symptoms, particularly neuropathic pain. Analgesia might have occurred through the modulation of the emotional pain network. Attention, mood, and fatigue were not improved in this work. This could be partly attributed to the short protocol duration, the small sample size, and the heterogeneity of our MS cohort. Future large-scale studies can benefit from comparing the tDCS effects over different cortical sites, changing the stimulation montage, prolonging the duration of protocol, and coupling tDCS with neuroimaging techniques for a better understanding of its possible mechanism of action.

Transcranial Direct Current Stimulation Over the Primary and Secondary Somatosensory Cortices Transiently Improves Tactile Spatial Discrimination in Stroke Patients

In healthy subjects, dual hemisphere transcranial direct current stimulation (tDCS) over the primary (S1) and secondary somatosensory cortices (S2) has been found to transiently enhance tactile performance. However, the effect of dual hemisphere tDCS on tactile performance in stroke patients with sensory deficits remains unknown. The purpose of this study was to investigate whether dual hemisphere tDCS over S1 and S2 could enhance tactile discrimination in stroke patients. We employed a double-blind, crossover, sham-controlled experimental design. Eight chronic stroke patients with sensory deficits participated in this study. We used a grating orientation task (GOT) to measure the tactile discriminative threshold of the affected and non-affected index fingers before, during, and 10 min after four tDCS conditions. For both the S1 and S2 conditions, we placed an anodal electrode over the lesioned hemisphere and a cathodal electrode over the opposite hemisphere. We applied tDCS at an intensity of 2 mA for 15 min in both S1 and S2 conditions. We included two sham conditions in which the positions of the electrodes and the current intensity were identical to that in the S1 and S2 conditions except that current was delivered for the initial 15 s only. We found that GOT thresholds for the affected index finger during and 10 min after the S1 and S2 conditions were significantly lower compared with each sham condition. GOT thresholds were not significantly different between the S1 and S2 conditions at any time point. We concluded that dual-hemisphere tDCS over S1 and S2 can transiently enhance tactile discriminative task performance in chronic stroke patients with sensory dysfunction.

Transcranial direct current stimulation as a tool in the study of sensory-perceptual processing

Transcranial direct current stimulation (tDCS) is a non-invasive neuromodulatory technique with increasing popularity in the fields of basic research and rehabilitation. It is an affordable and safe procedure that is beginning to be used in the clinic, and is a tool with potential to contribute to the understanding of neural mechanisms in the fields of psychology, neuroscience, and medical research. This review presents examples of investigations in the fields of perception, basic sensory processes, and sensory rehabilitation that employed tDCS. We highlight some of the most relevant efforts in this area and discuss possible limitations and gaps in contemporary tDCS research. Topics include the five senses, pain, and multimodal integration. The present work aims to present the state of the art of this field of research and to inspire future investigations of perception using tDCS.

High-Definition Transcranial Direct Current Stimulation Enhances Conditioned Pain Modulation in Healthy Volunteers: A Randomized Trial

Transcranial direct current stimulation (tDCS) is a form of brain stimulation that allows for the selective increase or decrease in the cortical excitability of a targeted region. When applied over the motor cortex it has been shown to induce changes in cortical and subcortical brain regions involved in descending pain inhibition or conditioned pain modulation (CPM). The aim of the current study was to assess whether activation of pain inhibitory pathways via tDCS of the motor cortex facilitates the CPM response. Elevated CPM after active tDCS of the motor cortex was hypothesized. Thirty healthy male volunteers attended 2 experimental sessions separated by 7 days. Both sessions consisted of CPM assessment after 20 minutes of either active or sham (placebo) tDCS over the motor cortex. CPM capacity was assessed via the pain-inhibits-pain protocol; CPM responses were shown to be elevated after active compared with sham tDCS. This report concludes that tDCS of the motor cortex enhances the CPM response in healthy men. This finding supports the potential utility of tDCS interventions in clinical pain treatment.

PERSPECTIVE

The use of noninvasive brain stimulation over the motor cortex was shown to enhance the CPM effect. This finding supports the use of tDCS in the treatment of chronic pain, particularly in sufferers exhibiting maladaptive CPM.

Social Psychology and Noninvasive Electrical Stimulation

Abstract. Social neuroscience and psychology have made substantial advances in the last few decades. Nonetheless, the field has relied mostly on behavioral, imaging, and other correlational research methods. Here we argue that transcranial direct current stimulation (tDCS) is an effective and relevant technique to be used in this field of research, allowing for the establishment of more causal brain-behavior relationships than can be achieved with most of the techniques used in this field. We review relevant brain stimulation-aided research in the fields of social pain, social interaction, prejudice, and social decision-making, with a special focus on tDCS. Despite the fact that the use of tDCS in Social Neuroscience and Psychology studies is still in its early days, results are promising. As better understanding of the processes behind social cognition becomes increasingly necessary due to political, clinical, and even philosophical demands, the fact that tDCS is arguably rare in Social Neuroscience research is very noteworthy. This review aims at inspiring researchers to employ tDCS in the investigation of issues within Social Neuroscience. We present substantial evidence that tDCS is indeed an appropriate tool for this purpose.

Transcranial Direct Current Stimulation (tDCS) Targeting Left Dorsolateral Prefrontal Cortex Modulates Task-Induced Acute Pain in Healthy Volunteers

OBJECTIVE

Current chronic pain treatments target nociception rather than affective "suffering" and its associated functional and psychiatric comorbidities. The left dorsolateral prefrontal cortex (DLPFC) has been implicated in affective, cognitive, and attentional aspects of pain and is a primary target of neuromodulation for affective disorders. Transcranial direct current stimulation (tDCS) can non-invasively modulate cortical activity. The present study tests whether anodal tDCS targeting the left DLPFC will increase tolerability of acute painful stimuli vs cathodal tDCS.

METHODS

Forty tDCS-naive healthy volunteers received anodal and cathodal stimulation targeting the left DLPFC in two randomized and counterbalanced sessions. During stimulation, each participant performed cold pressor (CP) and breath holding (BH) tasks. We measured pain intensity with the Defense and Veterans Pain Rating Scale (DVPRS) before and after each task.

RESULTS

Mixed ANOVA revealed no main effect of stimulation polarity for mean CP threshold, tolerance, or endurance, or mean BH time (allP > 0.27). However, DVPRS rise associated with CP was significantly smaller with anodal vs cathodal tDCS (P = 0.024). We further observed a significant tDCS polarity × stimulation order interaction (P = 0.042) on CP threshold, suggesting task sensitization.

CONCLUSIONS

Although our results do not suggest that polarity of tDCS targeting the left DLPFC differentially modulates the tolerability of CP- and BH-related pain distress in healthy volunteers, there was a significant effect on DVPRS pain ratings. This contrasts with our previous findings that tDCS targeting the left dorsal anterior cingulate cortex showed a trend toward higher mean CP tolerance with cathodal vs anodal stimulation. The present results may suggest tDCS-related effects on nociception or DLPFC-mediated attention, or preferential modulation of the affective valence of pain as captured by the DVPRS. Sham-controlled clinical studies are needed.

The effect of transcranial direct current stimulation of the motor cortex on exercise-induced pain

PURPOSE

Transcranial direct current stimulation (tDCS) provides a new exciting means to investigate the role of the brain during exercise. However, this technique is not widely used in exercise science, with little known regarding effective electrode montages. This study investigated whether tDCS of the motor cortex (M1) would elicit an analgesic response to exercise-induced pain (EIP).

METHODS

Nine participants completed a VO2max test and three time to exhaustion (TTE) tasks on separate days following either 10 min 2 mA tDCS of the M1, a sham or a control. Additionally, seven participants completed 3 cold pressor tests (CPT) following the same experimental conditions (tDCS, SHAM, CON). Using a well-established tDCS protocol, tDCS was delivered by placing the anodal electrode above the left M1 with the cathodal electrode above dorsolateral right prefrontal cortex. Gas exchange, blood lactate, EIP and ratings of perceived exertion (RPE) were monitored during the TTE test. Perceived pain was recorded during the CPT.

RESULTS

During the TTE, no significant differences in time to exhaustion, RPE or EIP were found between conditions. However, during the CPT, perceived pain was significantly (P < 0.05) reduced in the tDCS condition (7.4 ± 1.2) compared with both the CON (8.6 ± 1.0) and SHAM (8.4 ± 1.3) conditions.

CONCLUSION

These findings demonstrate that stimulation of the M1 using tDCS does not induce analgesia during exercise, suggesting that the processing of pain produced via classic measures of experimental pain (i.e., a CPT) is different to that of EIP. These results provide important methodological advancement in developing the use of tDCS in exercise.

Evaluation of a home-based transcranial direct current stimulation (tDCS) treatment device for chronic pain: study protocol for a randomised controlled trial

Background

Stimulation of the primary motor cortex (M1) has been shown to reduce the pain of neuropathy in multiple studies. There are several methods of stimulation both invasive and non-invasive. Recent work by this laboratory has seen that 40% of a sample of chronic neuropathic pain patients responded positively to non-invasive repetitive transcranial magnetic stimulation (rTMS) to the motor cortex with a reduction in pain levels by at least 20%. The effect however is short lived and multiple return visits are necessary to maintain this response. Transcranial direct current stimulation (tDCS) offers a more mobile method of motor cortex stimulation and is similarly non-invasive. The protocol described is designed to assess the analgesic effect of a home-based tDCS treatment device on chronic neuropathic pain in both responders and non-responders to previous TMS treatment.

Methods/design

This article reports the protocol for a randomised, sham-controlled, double-blinded crossover study in which patients with chronic neuropathic pain (n = 24) will receive anodal, cathodal and sham tDCS over M1. All patients will have previously completed a study of rTMS of the motor cortex and have been designated as responders or non-responders to this modality.

Patients receive all three tDCS stimulation types by self-administration. We assess the effect on pain scores [numerical rating scale (NRS)], self reported health status (Short Form-36 Health Survey) and anxiety/depression (Hospital Anxiety and Depression Scale). A linear mixed model with fixed effects will analyse changes in pain scores from pre- to post- interventions. Analysis will be carried out on an intention-to-treat basis. A proportion analysis will also be carried out with patients separated into either responders or non-responders to previous TMS.

Safety will be assessed throughout the study by monitoring of adverse events.

Discussion

The result of this trial will assess the efficacy of self-administered tDCS of the motor cortex in the treatment of chronic neuropathic pain and also provide insight into whether a potential differential effect is seen in patients that have previously been shown to be either responsive or non-responsive to rTMS over the same area.

Trial registration

ISRCTN56839387 date 27 January 2014. First patient randomised to trial 30 October 2012.

Effectiveness of transcranial direct current stimulation preceding cognitive behavioural management for chronic low back pain: sham controlled double blinded randomised controlled trial

OBJECTIVE

To evaluate the effectiveness of transcranial direct current stimulation alone and in combination with cognitive behavioural management in patients with non-specific chronic low back pain.

DESIGN

Double blind parallel group randomised controlled trial with six months' follow-up conducted May 2011-March 2013. Participants, physiotherapists, assessors, and analyses were blinded to group allocation.

SETTING

Interdisciplinary chronic pain centre.

PARTICIPANTS

135 participants with non-specific chronic low back pain >12 weeks were recruited from 225 patients assessed for eligibility.

INTERVENTION

Participants were randomised to receive anodal (20 minutes to motor cortex at 2 mA) or sham transcranial direct current stimulation (identical electrode position, stimulator switched off after 30 seconds) for five consecutive days immediately before cognitive behavioural management (four week multidisciplinary programme of 80 hours).

MAIN OUTCOMES MEASURES

Two primary outcome measures of pain intensity (0-100 visual analogue scale) and disability (Oswestry disability index) were evaluated at two primary endpoints after stimulation and after cognitive behavioural management.

RESULTS

Analyses of covariance with baseline values (pain or disability) as covariates showed that transcranial direct current stimulation was ineffective for the reduction of pain (difference between groups on visual analogue scale 1 mm (99% confidence interval -8.69 mm to 6.3 mm; P=0.68)) and disability (difference between groups 1 point (-1.73 to 1.98; P=0.86)) and did not influence the outcome of cognitive behavioural management (difference between group 3 mm (-10.32 mm to 6.73 mm); P=0.58; difference between groups on Oswestry disability index 0 point (-2.45 to 2.62); P=0.92). The stimulation was well tolerated with minimal transitory side effects.

CONCLUSIONS

This results of this trial on the effectiveness of transcranial direct current stimulation for the reduction of pain and disability do not support its clinical use for managing non-specific chronic low back pain.Trial registration Current controlled trials ISRCTN89874874.

Hemispheric dorsolateral prefrontal cortex lateralization in the regulation of empathy for pain

The dorsolateral prefrontal cortex (DLPFC) is involved in the cognitive appraisal and modulation of the pain experience. In this sham-controlled study, with healthy volunteers, we used bi-hemispheric transcranial direct current stimulation (tDCS) over the DLPFC to assess emotional reactions elicited by pain observation. Left-cathodal/right-anodal tDCS decreased valence and arousal evaluations compared to other tDCS conditions. Compared to sham condition, both left-cathodal/right-anodal and left-anodal/right-cathodal tDCS decreased hostility, sadness and self-pain perception. These decreased sensations after both active tDCS suggest a common role for left and right DLPFC in personal distress modulation. However, the differences in arousal and valence evaluations point to distinct roles of lateralized DLPFC in cognitive empathy, probably through distinct emotion regulation mechanisms.

How does anodal transcranial direct current stimulation of the pain neuromatrix affect brain excitability and pain perception? A randomised, double-blind, sham-control study

Background

Integration of information between multiple cortical regions of the pain neuromatrix is thought to underpin pain modulation. Although altered processing in the primary motor (M1) and sensory (S1) cortices is implicated in separate studies, the simultaneous changes in and the relationship between these regions are unknown yet. The primary aim was to assess the effects of anodal transcranial direct current stimulation (a-tDCS) over superficial regions of the pain neuromatrix on M1 and S1 excitability. The secondary aim was to investigate how M1 and S1 excitability changes affect sensory (STh) and pain thresholds (PTh).

Methods

Twelve healthy participants received 20 min a-tDCS under five different conditions including a-tDCS of M1, a-tDCS of S1, a-tDCS of DLPFC, sham a-tDCS, and no-tDCS. Excitability of dominant M1 and S1 were measured before, immediately, and 30 minutes after intervention respectively. Moreover, STh and PTh to peripheral electrical and mechanical stimulation were evaluated. All outcome measures were assessed at three time-points of measurement by a blind rater.

Results

A-tDCS of M1 and dorsolateral prefrontal cortex (DLPFC) significantly increased brain excitability in M1 (p < 0.05) for at least 30 min. Following application of a-tDCS over the S1, the amplitude of the N20-P25 component of SEPs increased immediately after the stimulation (p < 0.05), whilst M1 stimulation decreased it. Compared to baseline values, significant STh and PTh increase was observed after a-tDCS of all three stimulated areas. Except in M1 stimulation, there was significant PTh difference between a-tDCS and sham tDCS.

Conclusion

a-tDCS of M1 is the best spots to enhance brain excitability than a-tDCS of S1 and DLPFC. Surprisingly, a-tDCS of M1 and S1 has diverse effects on S1 and M1 excitability. A-tDCS of M1, S1, and DLPFC increased STh and PTh levels. Given the placebo effects of a-tDCS of M1 in pain perception, our results should be interpreted with caution, particularly with respect to the behavioural aspects of pain modulation.

Trial Registration

Australian New Zealand Clinical Trials, ACTRN12614000817640, http://www.anzctr.org.au/.

Rapid treatment-induced brain changes in pediatric CRPS

To date, brain structure and function changes in children with complex regional pain syndrome (CRPS) as a result of disease and treatment remain unknown. Here, we investigated (a) gray matter (GM) differences between patients with CRPS and healthy controls and (b) GM and functional connectivity (FC) changes in patients following intensive interdisciplinary psychophysical pain treatment. Twenty-three patients (13 females, 9 males; average age ± SD = 13.3 ± 2.5 years) and 21 healthy sex- and age-matched controls underwent magnetic resonance imaging. Compared to controls, patients had reduced GM in the primary motor cortex, premotor cortex, supplementary motor area, midcingulate cortex, orbitofrontal cortex, dorsolateral prefrontal cortex (dlPFC), posterior cingulate cortex, precuneus, basal ganglia, thalamus, and hippocampus. Following treatment, patients had increased GM in the dlPFC, thalamus, basal ganglia, amygdala, and hippocampus, and enhanced FC between the dlPFC and the periaqueductal gray, two regions involved in descending pain modulation. Accordingly, our results provide novel evidence for GM abnormalities in sensory, motor, emotional, cognitive, and pain modulatory regions in children with CRPS. Furthermore, this is the first study to demonstrate rapid treatment-induced GM and FC changes in areas implicated in sensation, emotion, cognition, and pain modulation.

The uncertain outcome of prefrontal tDCS

BACKGROUND

Transcranial direct current stimulation (tDCS) is increasingly used in research and clinical settings, and the dorsolateral prefrontal cortex (DLPFC) is often chosen as a target for stimulation. While numerous studies report modulation of cognitive abilities following DLPFC stimulation, the wide array of cognitive functions that can be modulated makes it difficult to predict its precise outcome.

OBJECTIVE

The present review aims at identifying and characterizing the various cognitive domains affected by tDCS over DLPFC.

METHODS

Articles using tDCS over DLPFC indexed in PubMed and published between January 2000 and January 2014 were included in the present review.

RESULTS

tDCS over DLPFC affects a wide array of cognitive functions, with sometimes apparent conflicting results.

CONCLUSION

Prefrontal tDCS has the potential to modulate numerous cognitive functions simultaneously, but to properly interpret the results, a clear a priori hypothesis is necessary, careful technical consideration are mandatory, further insights into the neurobiological impact of tDCS are needed, and consideration should be given to the possibility that some behavioral effects may be partly explained by parallel modulation of related functions.

Habituation to experimentally induced electrical pain during voluntary-breathing controlled electrical stimulation (BreEStim)

Objective

Painful peripheral electrical stimulation to acupuncture points was found to cause sensitization if delivered randomly (EStim), but induced habituation if triggered by voluntary breathing (BreEStim). The objective was to systematically compare the effectiveness of BreEStim and EStim and to investigate the possible mechanisms mediating the habituation effect of BreEStim.

Methods

Eleven pain-free, healthy subjects (6 males, 5 females) participated in the study. Each subject received the BreEStim and EStim treatments in a random order at least three days apart. Both treatments consisted of 120 painful but tolerable stimuli to the ulnar nerve at the elbow on the dominant arm. BreEStim was triggered by voluntary breathing while EStim was delivered randomly. Electrical sensation threshold (EST) and electrical pain threshold (EPT) were measured from the thenar and hypothenar eminences on both hands at pre-intervention and 10-minutes post-intervention.

Results

There was no difference in the pre-intervention baseline measurement of EST and EPT between BreEStim and EStim. BreEStim increased EPT in all tested sites on both hands, while EStim increased EPT in the dominant hypothenar eminence distal to the stimulating site and had no effect on EPT in other sites. There was no difference in the intensity of electrical stimulation between EStim and BreEStim.

Conclusion

Our findings support the important role human voluntary breathing plays in the systemic habituation effect of BreEStim to peripheral painful electrical stimulation.

Additional effects of transcranial direct-current stimulation and trigger-point injection for treatment of myofascial pain syndrome: a pilot study with randomized, single-blinded trial

BACKGROUND

Chronic pain caused by myofascial pain syndrome (MPS) results in generalized and debilitating conditions. Trigger-point injection (TPI) is the mainstay of MPS management to reduce acute and localized pain. Other adjunctive intervention to modulate the central pain pathway might be helpful if they are combined with TPI. Transcranial direct-current stimulation (tDCS), which is a form of neurostimulation, has been reported to be safe and effective in treating chronic pain by changing cortical excitability.

OBJECTIVES

To determine whether there is an additional effect of tDCS and TPI to reduce pain in patients with MPS.

PATIENTS

Twenty-one patients with newly diagnosed MPS of shoulder girdle muscles.

INTERVENTIONS

Patients were randomly assigned into 1 of 3 groups (2 active and 1 sham stimulation groups) and received TPI. Immediately after TPI, tDCS (2 mA for 20 minutes on 5 consecutive days) was administered. For the active stimulation groups, tDCS was applied over 2 different locations (primary motor cortex and dorsolateral prefrontal cortex [DLPFC]).

OUTCOME MEASURES

Visual analogue scale (VAS), Pain Threshold Test, and short form of the McGill Pain Questionnaire were measured before and immediately after stimulation for 5 consecutive days.

RESULTS

The mean VAS values were decreased in all three groups after 5 days. There was a significant change between before and after stimulation only in the DLPFC group. The significant change in the mean VAS value was shown from after the second stimulation session (p=0.031), and this remained significant until the last stimulation session (p=0.027).

CONCLUSION

This study suggests that tDCS over DLPFC may have additional effects with TPI to reduce pain in patients with MPS. tDCS over DLPFC can be used to reverse central pain pathway by modulating cortical plasticity.

Orders to shoot (a camera): effects of ostracism on obedience

Research suggests that ostracism increases susceptibility to indirect forms of social influence (e.g., conformity). Yet, no study to date has explored whether the effects of ostracism extend to the most direct form of social influence--obedience. We investigated whether ostracized individuals would be more likely to obey a direct command to do something effortful in uncomfortable conditions. Participants (N = 62) were randomly assigned to be included or ostracized in Cyberball, or assigned to a control condition. They were then approached by the experimenter and commanded to go outside when temperatures were below 30 degrees F and take 39 unique and creative photographs in the cold of winter. Ostracized participants were more likely to obey the experimenter's command to be creative when taking photographs. No differences in obedience emerged between the inclusion and the control condition. We provided evidence completing the social influence "trifecta": ostracism increases susceptibility to conformity, compliance, and now, obedience.

Motor cortex-induced plasticity by noninvasive brain stimulation: a comparison between transcranial direct current stimulation and transcranial magnetic stimulation

The aim of this study was to test and compare the effects of a within-subject design of repetitive transcranial magnetic stimulation (rTMS) [coupled with sham transcranial direct current stimulation (tDCS)] and tDCS (coupled with sham rTMS) on the motor cortex excitability and also compare the results against sham tDCS/sham rTMS. We conducted a double-blinded, randomized, sham-controlled, cross-over trial. Eleven right-handed, healthy individuals (five women, mean age: 39.8 years, SD 13.4) received the three interventions (cross-over design) in a randomized order: (a) high-frequency (HF) rTMS (+sham tDCS), (b) anodal tDCS (+sham rTMS), and (c) sham stimulation (sham rTMS+sham tDCS). Cortical excitability measurements [motor threshold, motor evoked potential (MEP), intracortical facilitation and inhibition, and transcallosal inhibition] and motor behavioral assessments were used as outcome measures. Between-group analysis of variance showed that MEP amplitude after HF rTMS was significantly higher than MEP amplitude after anodal tDCS (P=0.001). Post-hoc analysis showed a significant increase in MEP amplitude after HF rTMS (25.3%, P=0.036) and a significant decrease in MEP amplitude after anodal tDCS (-32.7%, P=0.001). There was a similar increase in motor function as indexed by Jebsen-Taylor Hand Function Test in the two active groups compared with sham stimulation. In conclusion, here, we showed that although both techniques induced similar motor gains, they induce opposing results in cortical excitability. HF rTMS is associated with an increase in corticospinal excitability, whereas 20 min of tDCS induces the opposite effect. We discuss potential implications of these results to future clinical experiments using rTMS or tDCS for motor function enhancement.

Therapeutic time window of noninvasive brain stimulation for pain treatment: inhibition of maladaptive plasticity with early intervention

Neuromodulatory effects of noninvasive brain stimulation (NIBS) have been extensively studied in chronic disorders such as major depression, chronic pain and stroke. However, few studies have explored the use of these techniques in acute conditions. A possible use of NIBS in acute disorders is to prevent or reverse ongoing maladaptive plastic alterations, seemingly responsible for treatment refractoriness and detrimental behavioral changes. In this review, the authors discuss the potential role of NIBS in blocking maladaptive plasticity using the transition of acute to chronic pain in conditions such as postsurgical pain, central poststroke pain, pain after spinal cord injury and pain after traumatic brain injury as a model. The authors also present suggestions for clinical trial design using NIBS in the acute stage of illnesses.

Randomized, sham controlled trial of transcranial direct current stimulation for painful diabetic polyneuropathy

Objective

To investigate the analgesic effect of transcranial direct current stimulation (tDCS) over the primary motor (M1), dorsolateral prefrontal cortex (DLPFC), and sham tDCS in patients with painful diabetic polyneuropathy (PDPN).

Methods

Patients with PDPN (n=60) were divided randomly into the three groups (n=20 per group). Each group received anodal tDCS with the anode centered over the left M1, DLPFC, or sham stimulation for 20 minutes at intensity of 2 mA for 5 consecutive days. A blinded physician rated the patients' pain using a visual analog scale (VAS), Clinical Global Impression (CGI) score, anxiety score, sleep quality, Beck Depression Inventory (BDI), and the pain threshold (PT) to pressure.

Results

After the tDCS sessions, the M1 group showed a significantly greater reduction in VAS for pain and PT versus the sham and DLPFC groups (p<0.001). The reduction in VAS for pain was sustained after 2 and 4 weeks of follow-up in the M1 group compared with the sham group (p<0.001, p=0.007). Significant differences were observed among the three groups over time in VAS for pain (p<0.001), CGI score (p=0.01), and PT (p<0.001). No significant difference was observed among the groups in sleep quality, anxiety score, or BDI score immediately after tDCS.

Conclusion

Five daily sessions of tDCS over the M1 can produce immediate pain relief, and relief 2- and 4-week in duration in patients with PDPN. Our findings provide the first evidence of a beneficial effect of tDCS on PDPN.

Transcranial Direct Current Stimulation to Lessen Neuropathic Pain After Spinal Cord Injury

Background. It is suggested that transcranial direct current stimulation (tDCS) can produce lasting changes in corticospinal excitability and can potentially be used for the treatment of neuropathic pain. However, the detailed mechanisms underlying the effects of tDCS are unknown. Objective. We investigated the underlying neural mechanisms of tDCS for chronic pain relief using [18F]-fluorodeoxyglucose positron emission tomography ([18F]FDG-PET). Methods. Sixteen patients with neuropathic pain (mean age 44.1 ± 8.6 years, 4 females) due to traumatic spinal cord injury received sham or active anodal stimulation of the motor cortex using tDCS for 10 days (20 minutes, 2 mA, twice a day). The effect of tDCS on regional cerebral glucose metabolism was evaluated by [18F]FDG-PET before and after tDCS sessions. Results. There was a significant decrease in the numeric rating scale scores for pain, from 7.6 ± 0.5 at baseline to 5.9 ± 1.8 after active tDCS ( P = .016). We found increased metabolism in the medulla and decreased metabolism in the left dorsolateral prefrontal cortex after active tDCS treatment compared with the changes induced by sham tDCS. Additionally, an increase in metabolism after active tDCS was observed in the subgenual anterior cingulate cortex and insula. Conclusion. The results of this study suggest that anodal stimulation of the motor cortex using tDCS can modulate emotional and cognitive components of pain and normalize excessive attention to pain and pain-related information.

Putative physiological mechanisms underlying tDCS analgesic effects

Transcranial direct current stimulation (tDCS) is a non-invasive neuromodulation technique that induces changes in excitability, and activation of brain neurons and neuronal circuits. It has been observed that beyond regional effects under the electrodes, tDCS also alters activity of remote interconnected cortical and subcortical areas. This makes the tDCS stimulation technique potentially promising for modulation of pain syndromes. Indeed, utilizing specific montages, tDCS resulted in analgesic effects in experimental settings, as well as in post-operative acute pain and chronic pain syndromes. The promising evidence of tDCS-induced analgesic effects raises the challenging and complex question of potential physiologic mechanisms that underlie/mediate the accomplished pain relief. Here we present hypotheses on how the specific montages and targets for stimulation may affect the pain processing network.

Widespread modulation of cerebral perfusion induced during and after transcranial direct current stimulation applied to the left dorsolateral prefrontal cortex

Noninvasive neuromodulatory techniques such as transcranial direct current stimulation (tDCS) are attracting increasing interest as potential therapies for a wide range of neurological and psychiatric conditions. When targeted to the dorsolateral prefrontal cortex (DLPFC), anodal, facilitatory tDCS has been shown to improve symptoms in a range of domains including working memory, mood, and pain perception (Boggio et al., 2008a; Dockery et al., 2009; Kalu et al., 2012). However, the mechanisms underlying these promising behavioral effects are not well understood. Here, we investigated brain perfusion changes, as assessed using whole-brain arterial spin labeling (ASL), during tDCS applied to the left DLPFC in healthy humans. We demonstrated increased perfusion in regions closely anatomically connected to the DLPFC during anodal tDCS in conjunction with a decreased functional coupling between the left DLPFC and the thalami bilaterally. Despite highly similar effects on cortical excitability during and after stimulation (Nitsche and Paulus, 2000, 2001), cortical perfusion changes were markedly different during these two time periods, with widespread decreases in cortical perfusion being demonstrated after both anodal and cathodal tDCS compared to the period during stimulation. These findings may at least partially explain the different effects on behavior in these time periods described previously in the motor system (Stagg et al., 2011). In addition, the data presented here provide mechanistic explanations for the behavioral effects of anodal tDCS applied to the left DLPFC in terms of modulating functional connectivity between the DLPFC and thalami, as has been hypothesized previously (Lorenz et al., 2003).

Direct electrical stimulation of the somatosensory cortex in humans using electrocorticography electrodes: a qualitative and quantitative report

OBJECTIVE

Recently, electrocorticography-based brain-computer interfaces have been successfully used to translate cortical activity into control signals for external devices. However, the utility of such devices would be greatly enhanced by somatosensory feedback. Direct stimulation of somatosensory cortex evokes sensory perceptions, and is thus a promising option for closing the loop. Before this can be implemented in humans it is necessary to evaluate how changes in stimulus parameters are perceived and the extent to which they can be discriminated.

APPROACH

Electrical stimulation was delivered to the somatosensory cortex of human subjects implanted with electrocorticography grids. Subjects were asked to discriminate between stimuli of different frequency and amplitude as well as to report the qualitative sensations elicited by the stimulation.

MAIN RESULTS

In this study we show that in humans implanted with electrocorticography grids, variations in the amplitude or frequency of cortical electrical stimulation produce graded variations in percepts. Subjects were able to reliably distinguish between different stimuli.

SIGNIFICANCE

These results indicate that direct cortical stimulation is a feasible option for sensory feedback with brain-computer interface devices.

Impact of acoustic coordinated reset neuromodulation on effective connectivity in a neural network of phantom sound

Chronic subjective tinnitus is an auditory phantom phenomenon characterized by abnormal neuronal synchrony in the central auditory system. As recently shown in a proof of concept clinical trial, acoustic coordinated reset (CR) neuromodulation causes a significant relief of tinnitus symptoms combined with a significant decrease of pathological oscillatory activity in a network comprising auditory and non-auditory brain areas. The objective of the present study was to analyze whether CR therapy caused an alteration of the effective connectivity in a tinnitus related network of localized EEG brain sources. To determine which connections matter, in a first step, we considered a larger network of brain sources previously associated with tinnitus. To that network we applied a data-driven approach, combining empirical mode decomposition and partial directed coherence analysis, in patients with bilateral tinnitus before and after 12 weeks of CR therapy as well as in healthy controls. To increase the signal-to-noise ratio, we focused on the good responders, classified by a reliable-change-index (RCI). Prior to CR therapy and compared to the healthy controls, the good responders showed a significantly increased connectivity between the left primary cortex auditory cortex and the posterior cingulate cortex in the gamma and delta bands together with a significantly decreased effective connectivity between the right primary auditory cortex and the dorsolateral prefrontal cortex in the alpha band. Intriguingly, after 12 weeks of CR therapy most of the pathological interactions were gone, so that the connectivity patterns of good responders and healthy controls became statistically indistinguishable. In addition, we used dynamic causal modeling (DCM) to examine the types of interactions which were altered by CR therapy. Our DCM results show that CR therapy specifically counteracted the imbalance of excitation and inhibition. CR significantly weakened the excitatory connection between posterior cingulate cortex and primary auditory cortex and significantly strengthened inhibitory connections between auditory cortices and the dorsolateral prefrontal cortex. The overall impact of CR therapy on the entire tinnitus-related network showed up as a qualitative transformation of its spectral response, in terms of a drastic change of the shape of its averaged transfer function. Based on our findings we hypothesize that CR therapy restores a silence based cognitive auditory comparator function of the posterior cingulate cortex.

Effect of transcranial direct current stimulation on elbow flexor maximal voluntary isometric strength and endurance

The effects of transcranial direct current stimulation (tDCS) on maximal voluntary isometric contraction (MVC) strength and the time to failure (TTF) in an isometric (30% MVC) muscle endurance test of the elbow flexors were investigated. Fifteen men (mean age, 27.7 ± 8.4 years) were tested for MVC strength and TTF 2 times, separated by a 60-min rest. During the last 10 min of the rest period, 1 of 2 tDCS treatments or 1 sham intervention session was administered, in a randomized order, with 1 week between sessions. In the tDCS intervention, a 2 mA direct current was delivered for 10 min through an anode placed on the scalp, overlying the right motor cortical representation of the left arm; a cathode was secured over the right shoulder. In the sham intervention, the current was delivered for the first 30 s only. No significant differences between the first and second tDCS sessions were evident for MVC strength or TTF. For MVC strength (baseline, 66.0 ± 11.4 Nm), postintervention measures decreased by 5.9% ± 4.2% (p < 0.05), but no significant difference in the changes was evident between tDCS and sham sessions. TTF did not change significantly from preintervention (309.2 ± 91.6 s) to postintervention (327.2 ± 128.5 s), and there was no significant difference between interventions. It was concluded that the tDCS intervention did not affect muscle function, perhaps because of ceiling effects, in which the intervention does not enhance muscle function further when muscle function is already maximal.

tDCS Modulation of Visually Induced Analgesia

Multisensory interactions can produce analgesic effects. In particular, viewing one's own body reduces pain levels, perhaps because of changes in connectivity between visual areas specialized for body representation, and sensory areas underlying pain perception. We tested the causal role of the extrastriate visual cortex in triggering visually induced analgesia by modulating the excitability of this region with transcranial direct current stimulation (tDCS). Anodal, cathodal, or sham tDCS (2 mA, 10 min) was administered to 24 healthy participants over the right occipital or over the centro-parietal areas thought to be involved in the sensory processing of pain. Participants were required to rate the intensity of painful electrical stimuli while viewing either their left hand or an object occluding the left hand, both before and immediately after tDCS. We found that the analgesic effect of viewing the body was enhanced selectively by anodal stimulation of the occipital cortex. The effect was specific for the polarity and the site of stimulation. The present results indicate that visually induced analgesia may depend on neural signals from the extrastriate visual cortex.

No effect of a single session of transcranial direct current stimulation on experimentally induced pain in patients with chronic low back pain--an exploratory study

Transcranial direct current stimulation (tDCS) has been shown to modulate cortical excitability. A small number of studies suggested that tDCS modulates the response to experimental pain paradigms. No trials have been conducted to evaluate the response of patients already suffering from pain, to an additional experimental pain before and after tDCS. The present study investigated the effect of a single session of anodal, cathodal and sham stimulation (15 mins/1 mA) over the primary motor cortex on the perceived intensity of repeated noxious thermal and electrical stimuli and on elements of quantitative sensory testing (thermal pain and perception thresholds) applied to the right hand in 15 patients with chronic low back pain. The study was conducted in a double-blind sham-controlled and cross-over design. No significant alterations of pain ratings were found. Modalities of quantitative sensory testing remained equally unchanged. It is therefore hypothesized that a single 15 mins session of tDCS at 1 mA may not be sufficient to alter the perception of experimental pain and in patients with chronic pain. Further studies applying repetitive tDCS to patients with chronic pain are required to fully answer the question whether experimental pain perception may be influenced by tDCS over the motor cortex.

Transcranial direct current stimulation ameliorates tactile sensory deficit in multiple sclerosis

BACKGROUND

Deficit of tactile sensation in patients with MS is frequent and can be associated with interference with daily life activities. Transcranial direct current stimulation (tDCS) showed to increase tactile discrimination in healthy subjects.

OBJECTIVE

In the present study, we investigated whether tDCS may be effective in ameliorating tactile sensory deficit in MS patients.

METHODS

Patients received sham or real anodal tDCS of the somatosensory cortex for 5 consecutive days in a randomized, double blind, sham-controlled study. Discrimination thresholds of spatial tactile sensation were measured using the grating orientation task (GOT). As secondary outcomes we also measured subjective perception of tactile sensory deficit through a visual analog scale (VAS), quality of life and overall disability to evaluate the impact of the treatment on patients daily life. Evaluations were performed at baseline and during a 4-week follow-up period.

RESULTS

Following anodal but not sham tDCS over the somatosensory cortex, there was a significant improvement of discriminatory thresholds at the GOT and increased VAS for sensation scores. Quality of life, and disability changes were not observed.

CONCLUSION

Our results indicate that a five day course of anodal tDCS is able to ameliorate tactile sensory loss with long-lasting beneficial effects and could thus represent a therapeutic tool for the treatment of tactile sensory deficit in MS patients.

Transcranial direct current stimulation in tinnitus patients: a systemic review and meta-analysis

Although transcranial direct current stimulation (tDCS) has already been used to manage tinnitus patients, paucity of reports and variations in protocols preclude a comprehensive understanding. Hence, we conducted a meta-analysis based on systemic review to assess effectiveness of tDCS in tinnitus management and to compare stimulation parameters. PubMed was searched for tDCS studies in tinnitus. For randomized controlled trials (RCTs), a meta-analysis was performed. A total of 17 studies were identified and 6 of them were included in the systemic review and 2 RCTs were included in the meta-analysis. Overall 39.5% responded to active tDCS with a mean tinnitus intensity reduction of 13.5%. Additionally, left temporal area (LTA) and bifrontal tDCS indicated comparable results. Active tDCS was found to be more effective than sham tDCS for tinnitus intensity reduction (Hedges' g = .77, 95% confidence interval 0.23-1.31). The efficacy of tDCS in tinnitus could not be fully confirmed by the current study because of the limited number of studies, but all studies included in the current systemic review and meta-analysis demonstrated significant tinnitus intensity improvement. Therefore, tDCS may be a promising tool for tinnitus management. Future RCTs in a large series regarding the efficacy as well as the comparison between LTA- and bifrontal tDCS are recommended.

Comparing cortical plasticity induced by conventional and high-definition 4 × 1 ring tDCS: a neurophysiological study

BACKGROUND

Transcranial direct current stimulation (tDCS) induces long-lasting NMDA receptor-dependent cortical plasticity via persistent subthreshold polarization of neuronal membranes. Conventional bipolar tDCS is applied with two large (35 cm(2)) rectangular electrodes, resulting in directional modulation of neuronal excitability. Recently a newly designed 4 × 1 high-definition (HD) tDCS protocol was proposed for more focal stimulation according to the results of computational modeling. HD tDCS utilizes small disc electrodes deployed in 4 × 1 ring configuration whereby the physiological effects of the induced electric field are thought to be grossly constrained to the cortical area circumscribed by the ring.

OBJECTIVE

We aim to compare the physiological effects of both tDCS electrode arrangements on motor cortex excitability.

METHODS

tDCS was applied with 2 mA for 10 min. Fourteen healthy subjects participated, and motor cortex excitability was monitored by transcranial magnetic stimulation (TMS) before and after tDCS.

RESULTS

Excitability enhancement following anodal and a respective reduction after cathodal stimulation occurred in both, conventional and HD tDCS. However, the plastic changes showed a more delayed peak at 30 min and longer lasting after-effects for more than 2 h after HD tDCS for both polarities, as compared to conventional tDCS.

CONCLUSION

The results show that this new electrode arrangement is efficient for the induction of neuroplasticity in the primary motor cortex. The pattern of aftereffects might be compatible with the concept of GABA-mediated surround inhibition, which should be explored in future studies directly.

Direct current brain polarization: a simple, noninvasive technique for human neuromodulation

OBJECTIVES

  It has been known for decades that neurons in vitro and in vivo respond in a polarity-specific manner to changes in their electrical environment. Likewise, investigators have passed direct current (DC) across the human head for decades in attempts to alter brain function and behavior. Recent human data, however, have put this technique on a more solid empirical footing and it has re-emerged from obscurity as a "new," noninvasive means of neuromodulation, called transcranial direct current stimulation (TDCS).

MATERIALS AND METHODS

  Here, we offer a selective literature review together with our own research on the basic mechanisms and human applications of TDCS in neurophysiologic, cognitive, and behavioral research. We discuss a possible role for TDCS in enhancing normal brain function and treating neurologic and behavioral disorders.

RESULTS

  While there are uncertainties about how TDCS produces behavioral effects and how the current is distributed in the human brain, TDCS has safely produced a variety effects on human brain function in small studies.

CONCLUSIONS

  The field is very young and many findings will require replication. Nevertheless, TDCS appears to have the potential to be a simple and safe means of neuromodulation.