Left Anodal Stimulation Research Articles

Transcranial Direct Current Stimulation over the Right Inferior Parietal Cortex Reduces Transposition Errors in a Syllabic Reordering Task

Evidence derived from functional imaging and brain-lesion studies has shown a strong left lateralization for language, and a complementary right hemisphere dominance for visuospatial abilities. Nevertheless, the symmetrical functional division of the two hemispheres gives no reason for the complexity of the cognitive operations involved in carrying out a linguistic task. In fact, a growing number of neuroimaging and neurostimulation studies suggest a possible right hemisphere involvement in language processing. The objective of this work was to verify the contribution of the left and right parietal areas in a phonological task. We applied anodal transcranial direct current stimulation (tDCS) to the right or left inferior parietal lobe, during a syllabic reordering task. After having learnt a combination of images of real objects and trisyllabic pseudowords with a simple consonant–vowel (CV) syllabic structure (e.g., tu-ru-cu), participants were shown the same images paired to two different pseudowords: one correct but with transposed syllables, and one alternative, never before seen. The participant’s task was to orally produce the chosen pseudoword, after having rearranged the order of its syllables. Two types of error were considered: transposition (correct pseudoword but incorrectly reordered) and identity (incorrect pseudoword). The results showed that right anodal stimulation significantly reduced the number of transposition errors, whereas left anodal stimulation significantly reduced the number of identity errors. These results suggested that both left and right inferior parietal areas were differentially involved in a syllabic reordering task, and, crucially, they demonstrated that visuospatial processes served by the right inferior parietal area could be competent for establishing the correct syllabic order within a word.

Cortical modulation of nociception by galvanic vestibular stimulation: A potential clinical tool?

ObjectiveVestibular afferents converge with nociceptive ones within the posterior insula, and can therefore modulate nociception. Consistent with this hypothesis, caloric vestibular stimulation (CVS) has been shown to reduce experimental and clinical pain. Since CVS can induce undesirable effects in a proportion of patients, here we explored an alternative means to activate non-invasively the vestibular pathways using innocuous bi-mastoid galvanic stimulation (GVS), and assessed its effects on experimental pain. MethodsSixteen healthy volunteers participated in this study. Experimental pain was induced by noxious laser-heat stimuli to the left hand while recording pain ratings and related brain potentials (LEPs). We evaluated changes of these indices during left- or right-anodal GVS (cathode on contralateral mastoid), and contrasted them with those during sham GVS, optokinetic vestibular stimulation (OKS) using virtual reality, and attentional distraction to ascertain the vestibular-specific analgesic effects of GVS. ResultsGVS elicited brief sensations of head/trunk deviation, inoffensive to all participants. Both active GVS conditions showed analgesic effects, greater for the right anodal stimulation. OKS was helpful to attain significant LEP reductions during the left-anodal stimulation. Neither sham-GVS nor the distraction task were able to modulate significantly pain ratings or LEPs. ConclusionsGVS appeared as a well-tolerated and powerful procedure for the relief of experimental pain, probably through physiological interaction within insular nociceptive networks. Either isolated or in combination with other types of vestibular activation (e.g., optokinetic stimuli), GVS deserves being tested in clinical settings.

Beyond the Vestibulo-Ocular Reflex: Vestibular Input is Processed Centrally to Achieve Visual Stability.

The current study presents a re-analysis of data from Zink et al. (1998, Electroencephalography and Clinical Neurophysiology, 107), who administered galvanic vestibular stimulation through unipolar direct current. They placed electrodes on each mastoid, and applied both right and left anodal stimulation. Ocular torsion and visual tilt were measured under different stimulation intensities. New modelling introduced here demonstrates that directly proportional linear models fit reasonably well to the relationship between vestibular input and visual tilt, but not to that between vestibular input and ocular torsion. Instead, an exponential model characterised by a decreasing slope and an asymptote fitted best. These results demonstrate that in the results presented by Zink et al., ocular torsion could not completely account for visual tilt. This suggests that vestibular input is processed centrally to stabilise vision when ocular torsion is insufficient. Potential mechanisms and seemingly conflicting literature are discussed.

Beyond the Vestibulo-Ocular Reflex: Vestibular Input is Processed Centrally to Achieve Visual Stability

The current study presents a re-analysis of data from Zink et al. (1998, Electroencephalography and Clinical Neurophysiology, 107), who administered galvanic vestibular stimulation through unipolar direct current. They placed electrodes on each mastoid and applied either right or left anodal stimulation. Ocular torsion and visual tilt were measured under different stimulation intensities. New modelling introduced here demonstrates that directly proportional linear models fit reasonably well with the relationship between vestibular input and visual tilt, but not to that between vestibular input and ocular torsion. Instead, an exponential model characterised by a decreasing slope and an asymptote fitted best. These results demonstrate that in the results presented by Zink et al. (1998), ocular torsion could not completely account for visual tilt. This suggests that vestibular input is processed centrally to stabilise vision when ocular torsion is insufficient. Potential mechanisms and seemingly conflicting literature are discussed.

Balanced bifrontal transcranial direct current stimulation enhances working memory in adults with high-functioning autism: a sham-controlled crossover study

BackgroundWorking memory (WM) often is impaired in autism spectrum disorder (ASD). Such impairment may underlie core deficits in cognition and social functioning. Transcranial direct current stimulation (tDCS) has been shown to enhance WM in both healthy adults and clinical populations, but its efficacy in ASD is unknown. We predicted that bifrontal tDCS would improve WM performances of adults with high-functioning autism during active stimulation compared to sham stimulation and that such enhancement would generalize to an untrained task.MethodsTwelve adults with high-functioning ASD engaged in a battery of WM tasks that included backward spatial span, backward digit span, spatial n-back and letter n-back. While engaged, 40 min of 1.5 mA bifrontal stimulation was applied over the left and the right dorsolateral prefrontal cortices (DLPFC). Using a single-blind crossover design, each participant received left anodal/right cathodal stimulation, right anodal/left cathodal stimulation, or sham stimulation, in randomized counterbalanced order on three separate days. Following tDCS, participants again engaged in letter and spatial n-back tasks before taking the Brief Test of Attention (BTA). We used repeated-measures ANOVA to compare overall performance on the WM battery as measured by a composite of z-scores for all five measures. Post hoc ANOVAs, t tests, Friedman’s tests, and Wilcoxon signed-rank tests were used to measure the online and offline effects of tDCS and to assess performances on individual measures.ResultsCompared to sham stimulation, both left DLPFC anodal stimulation (t11 = 5.4, p = 0.0002) and right DLPFC anodal stimulation (t11 = 3.57, p = 0.004) improved overall WM performance. Left anodal stimulation (t11 = 3.9, p = 0.003) and right anodal stimulation (t11 = 2.7, p = 0.019) enhanced performances during stimulation. Enhancement transferred to an untrained task 50 min after right anodal stimulation (z11 = 2.263, p = 0.024). The tasks that showed the largest effects of active stimulation were spatial span backward (z11 = 2.39, p = 0.017) and BTA (z11 = 2.263, p = 0.024).ConclusionsIn adults with high-functioning ASD, active bifrontal tDCS given during WM tasks appears to improve performance. TDCS benefits also transferred to an untrained task completed shortly after stimulation. These results suggest that tDCS can improve WM task performance and could reduce some core deficits of autism.Trial registrationNCT01602263

P195 On the effect of tdcs on risk taking behaviour: A study using the balloons analogue risk task

Introduction and Objectives Fecteau et al. (2007) used the Balloon Analogue Risk Task (BART) in a transcranial direct current stimulation (tDCS) study to assess the extent to which the modulation of the activity of the dorsolateral prefrontal cortex (DLPFC) affects risk taking behaviour. Three separate bilaterally stimulated groups (right anodal/left cathodal; left anodal/right cathodal and sham) were tested under double-blind conditions with the electrodes placed over the DLPFC. They found that in both active stimulation groups (right anodal/left cathodal; left anodal/right cathodal), compared to sham, upregulating the DLPFC diminished risk-taking behaviour. In a second experiment using unilateral stimulation conditions where only right or left anodal stimulation was administered (referent electrode over the contralateral supraorbital region), no significant effect. They concluded that increasing activity in the DLPFC led participants to become more risk-averse. There are some potential caveats regarding their findings: primarily the study lacked in statistical power (total n = 35). Methods To address the above issue we tried to replicate Fecteau et al. results closely mimicking their procedure while increasing the number of people tested (over 200 participants in 2 experiments). Results and conclusions Overall, we could not replicate Fecteau et al.’s results. In one neuromodulation condition (right anodal/left cathodal), contrary to Fecteau et al. results, risk taking increased, however a closer look to the data suggests that this increase is more apparent than real.

Improvements in Attention and Decision-Making Following Combined Behavioral Training and Brain Stimulation.

In recent years there has been a significant commercial interest in 'brain training' - massed or spaced practice on a small set of tasks to boost cognitive performance. Recently, researchers have combined cognitive training regimes with brain stimulation to try and maximize training benefits, leading to task-specific cognitive enhancement. It remains unclear, however, whether the performance gains afforded by such regimes can transfer to untrained tasks, or how training and stimulation affect the brain's latent information processing dynamics. To examine these issues, we applied transcranial direct current stimulation (tDCS) over the prefrontal cortex while participants undertook decision-making training over several days. Anodal, relative to cathodal/sham tDCS, increased performance gains from training. Critically, these gains were reliable for both trained and untrained tasks. The benefit of anodal tDCS occurred for left, but not right, prefrontal stimulation, and was absent for stimulation delivered without concurrent training. Modeling revealed left anodal stimulation combined with training caused an increase in the brain's rate of evidence accumulation for both tasks. Thus tDCS applied during training has the potential to modulate training gains and give rise to transferable performance benefits for distinct cognitive operations through an increase in the rate at which the brain acquires information.

Exploring the impact of laterality and polarity of tDCS on therapy for chronic post-stroke anomia

Event Abstract Back to Event Exploring the impact of laterality and polarity of tDCS on therapy for chronic post-stroke anomia Margaret Sandars1*, Lauren L. Cloutman1 and Anna M. Woollams1 1 University of Manchester, School of Psychological Sciences, United Kingdom Introduction: Anomia is a frequent and persistent symptom of post-stroke aphasia. Transcranial Direct Current Stimulation (tDCS) is a non-invasive neurostimulation technique that can be used to enhance the effects of behavioural speech and language therapy. Previous studies have suggested that applying anodal (excitatory) tDCS to perilesional areas in the damaged left hemisphere and/or cathodal (inhibitory) tDCS to homologous areas in the intact right hemisphere may be particularly beneficial (e.g. Baker et al., 2010; Rosso et al., 2014). However, the effects of varying both polarity and laterality of tDCS have yet to be systematically investigated within participants. The aim of the current study was to determine the optimal tDCS parameters to increase naming ability in two stroke survivors with chronic anomia: JSc, with Broca’s aphasia, and JSo, with Anomic aphasia. Methods: Six individualised 20-item treated sets were created from a pool of those incorrectly named prior to therapy. Participants completed six therapy cycles, each involving a different stimulation condition: left perilesional anodal, cathodal and sham and right contralesional anodal, cathodal and sham. Perilesional sites were determined on the basis of MRI structural scans: JSc=inferior frontal gryus (IFG), JSo=posterior superior temporal gyrus (STG). In each cycle, participants received 20 minutes of 1mA tDCS (electrodes 5cm x 7cm) on three consecutive days alongside computerised naming therapy. In the sham conditions, anodal stimulation was applied for one minute before being slowly turned off. Results: For JSc, there were significant immediate gains following left anodal, left cathodal and right sham stimulation, one week after left cathodal stimulation, and three weeks after left anodal and left cathodal stimulation. The effect of left anodal stimulation was significantly greater than that for sham immediately post-therapy (χ2=4.57, p<0.05), and three weeks later (χ2=6.99, p<0.01). JSo named significantly more items correctly immediately in all conditions, one week after left cathodal, right anodal, right cathodal and right sham stimulation, and three weeks after left cathodal, right cathodal and right sham stimulation. None of the active stimulation conditions resulted in significantly greater item gains than sham. Conclusion: Although there were clear therapeutic gains across the majority of conditions for both patients, the additional benefits for neurostimulation were more selective. For JSc, the beneficial effect of behavioural therapy for anomia was enhanced by anodal tDCS applied to left frontal perilesional regions, consistent with Baker et al. (2010) and Vestito et al. (2014), and neuroimaging of recovery and therapeutic gains in patients with chronic anomia (e.g. Fridriksson, 2010; Fridriksson et al., 2012; Meinzer et al., 2008). There was no benefit associated with cathodal stimulation of right contralesional sites, inconsistent with Rosso et al. (2014). In contrast, active tDCS did not increase JSo’s therapy gains above those observed for sham, irrespective of laterality and polarity. Overall, our results highlight variability of chronic stroke aphasic patients with differing behavioural and lesion profiles in their response to tDCS. Figure 1 Acknowledgements This research was funded by a Stroke Association Junior Research Training Fellowship awarded to the lead author (Award number TSA JRTF 2013/01) References

The Effects of Transcranial Direct-Current Stimulation on Cognition in Stroke Patients.

Background and PurposeTo investigate whether transcranial direct-current stimulation (tDCS) can improve cognition in stroke patients.MethodsForty-five stroke patients (20 males and 25 females, average age: 62.7 years) with cognitive dysfunction were included in this prospective, double-blinded, randomized case–control study. All patients were right-handed and the mean elapsed time after stroke was 39.3 days. Three different treatments groups were used: (1) anodal stimulation of the left anterior temporal lobe, (2) anodal stimulation of the right anterior temporal lobe, and (3) sham stimulation. tDCS was delivered for 30 minutes at 2 mA with 25 cm2 electrodes, five times/week, for a total of 3 weeks, using a Phoresor II Auto Model PM 850 (IOMED®). The evaluation of cognitive impairment was based on a Computerized Neuropsychological Test (CNT), Korean Mini-Mental State Examination (K-MMSE). The Korean version of the Modified Barthel Index (K-MBI) was used to assess activities of daily living functionality. These evaluations were conducted in all patients before and after treatment.ResultsEach group included 15 patients. Pre-treatment evaluation showed no significant differences between the three groups for any of the parameters. There was significant improvement in the verbal learning test on the CNT in the left anodal stimulation group (P < 0.05). There were, however, no significant differences in the K-MMSE or K-MBI scores among the three groups.ConclusionsThese results demonstrated the beneficial effects of anodal tDCS on memory function. Thus, tDCS can successfully be used as a treatment modality for patients with cognitive dysfunction after stroke.

Transcranial direct current stimulation modulates efficiency of reading processes.

Transcranial direct current stimulation (tDCS) is a neuromodulatory technique that offers promise as an investigative method for understanding complex cognitive operations such as reading. This study explores the ability of a single session of tDCS to modulate reading efficiency and phonological processing performance within a group of healthy adults. Half the group received anodal or cathodal stimulation, on two separate days, of the left temporo-parietal junction while the other half received anodal or cathodal stimulation of the right homologue area. Pre- and post-stimulation assessment of reading efficiency and phonological processing was carried out. A larger pre-post difference in reading efficiency was found for participants who received right anodal stimulation compared to participants who received left anodal stimulation. Further, there was a significant post-stimulation increase in phonological processing speed following right hemisphere anodal stimulation. Implications for models of reading and reading impairment are discussed.

Visual memory improved by non-invasive brain stimulation

Our visual memories are susceptible to errors, but less so in people who have a more literal cognitive style. This inspired us to attempt to improve visual memory with non-invasive brain stimulation. We applied 13 min of bilateral transcranial direct current stimulation (tDCS) to the anterior temporal lobes. Our stimulation protocol included 3 conditions, each with 12 neurotypical participants: (i) left cathodal stimulation together with right anodal stimulation, (ii) left anodal stimulation together with right cathodal stimulation, and (iii) sham (control) stimulation. Only participants who received left cathodal stimulation (decrease in excitability) together with right anodal stimulation (increase in excitability) showed an improvement in visual memory. This 110% improvement in visual memory was similar to the advantage people with autism, who are known to be more literal, show over normal people in the identical visual task. Importantly, participants receiving stimulation of the opposite polarity (left anodal together with right cathodal stimulation) failed to show any change in memory performance. This is the first demonstration that visual memory can be enhanced in healthy people using non-invasive brain stimulation.