Stimulation Of Left Dorsolateral Prefrontal Cortex Research Articles

Dose-dependent target engagement of a clinical iTBS protocol: An interleaved TMS-fMRI study in healthy subjects

BackgroundIntermittent theta burst stimulation (iTBS) of the dorsolateral prefrontal cortex (DLPFC) is widely applied as therapeutic intervention in mental health, however understanding of its mechanisms is still incomplete. Prior MRI studies have mainly used offline iTBS or short sequences in concurrent TMS-fMRI. This study investigated a full 600 stimuli iTBS protocol using interleaved TMS-fMRI in comparison with two control conditions in healthy subjects. MethodsIn a crossover design, 18 participants underwent three sessions of interleaved iTBS-fMRI: 1) left DLPFC at 40% resting motor threshold (rMT) intensity, 2) left DLPFC at 80% rMT intensity, and 3) left primary motor cortex (M1) at 80% rMT intensity. We compared immediate blood-oxygen-level-dependent (BOLD) responses during interleaved iTBS-fMRI across these conditions including correlations between individual fMRI BOLD activation and iTBS induced electric field (E-field) strength at the target sites. ResultsWhole-brain analysis showed increased activation in several regions following iTBS. Specifically, left DLPFC, as well as bilateral M1, anterior cingulate cortex, and insula showed increased activation during 80% rMT left DLPFC stimulation. Increased BOLD activity in the left DLPFC was not observed with 40% rMT left DLPFC stimulation nor left M1 80% rMT iTBS, whereas activation in other regions was found to overlap between conditions. Of note, BOLD activation and E-field intensities were only correlated for M1 stimulation, but not for the DLPFC conditions. ConclusionsThe study showed dosage and target specific BOLD activation during interleaved TMS-fMRI with 600 stimuli iTBS in healthy subjects. Future studies may use our approach for demonstrating target engagement.

Effectiveness and tolerability of adjunctive transcranial direct current stimulation (tDCS) in management of treatment-resistant depression: A retrospective chart review.

There is a limited number of studies from India investigating the role of transcranial direct current stimulation (tDCS) in treatment-resistant depression (TRD). This clinic-based study reports on the effectiveness of tDCS as an add-on treatment in individuals suffering from TRD. Twenty-six right-handed individuals suffering from major depressive disorder who failed to respond to adequate trials of at least two antidepressant drugs in the current episode received tDCS as an augmenting treatment. Twice daily sessions of conventional tDCS were given providing anodal stimulation at the left dorsolateral prefrontal cortex (DLPFC) and cathodal placement at the right DLPFC. A total of 20 sessions were given over 2 weeks. The outcome was assessed based on changes in scores of the Hamilton Rating Scale for Depression (HAMD) and Montgomery-Asberg Depression Rating Scale (MADRS). There was a significant reduction in outcome assessment after tDCS intervention as compared to baseline, with more than 50% of the participants showing response in both scales, which increased further to approximately 77% by the end of 1 month of the follow-up period. Twice daily tDCS sessions with anodal stimulation of left DLPFC and cathodal stimulation of right DLPFC is an effective add-on treatment strategy in individuals with TRD.

Modulating risk-taking behavior with theta-band tACS

Although risk is prevalent in decision-making, the specific neural processes underlying risk-taking behavior remain unclear. Previous studies have suggested that frontal theta-band activity plays a crucial role in modulating risk-taking behavior. The functional relevance of theta in risk-taking behavior is yet to be clearly established and studies using noninvasive brain stimulation have yielded inconsistent findings. We aimed to investigate this relevance using transcranial alternating current stimulation (tACS) over right or left dorsolateral prefrontal cortex (DLPFC). We also studied the influence of stimulation intensity on risk-taking behavior and electrophysiological effects.We applied theta-band (6.5 Hz) tACS over the left (F3) and right (F4) DLPFC with lower (1.5 mA) and higher (3 mA) tACS intensities. We employed a single-blinded, sham-controlled, within-subject design and combined tACS with electroencephalography (EEG) measurements and the Maastricht Gambling Task (MGT) to elicit and evaluate risk-taking behavior.Our results show an increase in risk-taking behavior after left DLPFC stimulation at both intensities and a reduction of risk-taking behavior after 3 mA (and not 1.5 mA) right DLPFC stimulation compared to sham. Further analyses showed a negative correlation between resting-state frontal theta-power and risk-taking behavior. Overall, frontal theta-power was increased after left, but not right, theta-band tACS independent of stimulation intensity.Our findings confirm the functional relevance of frontal theta-band activity in decision-making under risk and the differential role of left and right DLPFC. We also were able to show that stimulation intensity did have an effect on behavioral responses, namely risk-taking behavior. Significant right hemisphere stimulation effects were observed only after high-intensity stimulation. Nevertheless, electrophysiological effects were only significant after left DLPFC stimulation, regardless of tACS intensity. Furthermore, the results indicate the role of the baseline frontal theta-power in the direction of behavioral effects after theta-band tACS.

Differential effects of remotely supervised transcranial direct current stimulation on recognition memory depending on task order.

Prior work has shown positive effects of High Definition transcranial direct current stimulation (HD-tDCS) over the dorsolateral prefrontal cortex (DLPFC) on semantic memory performance and metamemory monitoring accuracy. However, HD-tDCS requires setup by a trained researcher, which is not always feasible. Few studies have used remotely supervised (rs) tDCS in healthy populations, and remote supervision has strong practical benefits. The goal of the current study was to test if previously shown effects of HD-tDCS over the left DLPFC on semantic memory performance and metamemory monitoring accuracy extended to conventional rs-tDCS, which is less focal than HD-tDCS, and to episodic memory and metamemory tasks. A total of 36 healthy participants completed 6 weeks of rs-tDCS sessions, with either active left or right anodal DLPFC stimulation, or sham. Participants completed semantic and episodic memory and metamemory tasks, which each lasted for three consecutive sessions, and session order was counterbalanced across participants. Overall, there were no main effects of rs-tDCS on metamemory monitoring accuracy or memory performance for either the semantic or the episodic tasks. However, there were effects of rs-tDCS that depended on the order of completing the episodic and semantic task sessions. When participants completed the semantic task sessions after the episodic task sessions, semantic recognition was greater in the left anodal DLPFC condition. In a parallel effect, when participants completed the episodic task sessions after the semantic task sessions, episodic recognition was greater in the right anodal DLPFC condition. Prior experience with tDCS is a factor for effects of rs-tDCS on cognition. Additionally, the current experiment provides evidence for the feasibility of fully remotely supervised tDCS in healthy participants.

Transcranial direct current stimulation (tDCS) in depression induces structural plasticity

Transcranial direct current stimulation (tDCS) is a non-invasive neuromodulation technique involving administration of well-tolerated electrical current to the brain through scalp electrodes. TDCS may improve symptoms in neuropsychiatric disorders, but mixed results from recent clinical trials underscore the need to demonstrate that tDCS can modulate clinically relevant brain systems over time in patients. Here, we analyzed longitudinal structural MRI data from a randomized, double-blind, parallel-design clinical trial in depression (NCT03556124, N = 59) to investigate whether serial tDCS individually targeted to the left dorso-lateral prefrontal cortex (DLPFC) can induce neurostructural changes. Significant (FWEc p < 0.05) treatment-related gray matter changes were observed with active high-definition (HD) tDCS relative to sham tDCS within the left DLPFC stimulation target. No changes were observed with active conventional tDCS. A follow-up analysis within individual treatment groups revealed significant gray matter increases with active HD-tDCS in brain regions functionally connected with the stimulation target, including the bilateral DLPFC, bilateral posterior cingulate cortex, subgenual anterior cingulate cortex, and the right hippocampus, thalamus and left caudate brain regions. Integrity of blinding was verified, no significant differences in stimulation-related discomfort were observed between treatment groups, and tDCS treatments were not augmented by any other adjunct treatments. Overall, these results demonstrate that serial HD-tDCS leads to neurostructural changes at a predetermined brain target in depression and suggest that such plasticity effects may propagate over brain networks.

The Neurobase of ambiguity loss aversion about decision making.

In our daily decision-making, there are two confusing problems: risk and ambiguity. Many psychological studies and neuroscience studies have shown that the prefrontal cortex (PFC) is an important neural mechanism for modulating the human brain in risk and ambiguity decision-making, especially the dorsolateral prefrontal cortex (DLPFC). We used transcranial direct current stimulation (tDCS) to reveal the causal relationship between the DLPFC and ambiguity decision-making. We design two experimental tasks involving ambiguity to gain and ambiguity to loss. The results of our study show that there is a significant effect on left DLPFC stimulation about ambiguity to loss, there is an insignificant effect on left DLPFC stimulation about ambiguity to gain, and there is an insignificant effect on right DLPFC stimulation about ambiguity to gain and ambiguity to loss. This result indicates that people are more sensitive to ambiguity loss than ambiguity gain. Further analysis found that the degree of participants' attitudes toward ambiguity loss who received anodal simulation was lower than that who received sham stimulation across the left DLPFC, which means that the subjects had a strong ambiguity loss aversion after the participants received the anodal simulation of the left DLPFC.

Prefrontal reactivity to TMS perturbation as a toy model of mental health outcomes during the COVID-19 pandemic

Psychosocial hardships associated with the COVID-19 pandemic led many individuals to suffer adverse mental health consequences, however, others show no negative effects. We hypothesized that the electroencephalographic (EEG) response to transcranial magnetic stimulation (TMS) could serve as a toy-model of an individual's capacity to resist psychological stress, in this case linked to the COVID-19 pandemic. We analyzed data from 74 participants who underwent mental health monitoring and concurrent electroencephalography with transcranial magnetic stimulation of the left dorsolateral prefrontal cortex (L-DLPFC) and left inferior parietal lobule (L-IPL). Within the following 19 months, mental health was reassessed at three timepoints during lock-down confinement and different phases of de-escalation in Spain. Compared with participants who remained stable, those who experienced increased mental distress showed, months earlier, significantly larger late EEG responses locally after L-DLPFC stimulation (but not globally nor after L-IPL stimulation). This response, together with years of formal education, was significantly predictive of mental health status during the pandemic. These findings reveal that the effect of TMS perturbation offers a predictive toy model of psychosocial stress response, as exemplified by the COVID-19 pandemic.

Individual interregional perfusion between the left dorsolateral prefrontal cortex stimulation targets and the subgenual anterior cortex predicts response and remission to aiTBS treatment in medication-resistant depression: The influence of behavioral inhibition

BackgroundAccelerated intermittent Theta Burst Stimulation (aiTBS) has been put forward as an effective treatment to alleviate depressive symptoms. Baseline functional connectivity (FC) patterns between the left dorsolateral prefrontal cortex (DLPFC) and the subgenual anterior cortex (sgACC) have gained a lot of attention as a potential biomarker for response. However, arterial spin labeling (ASL) - measuring regional cerebral blood flow - may allow a more straightforward physiological interpretation of such interregional functional connections. ObjectivesWe investigated whether baseline covariance perfusion connectivity between the individually stimulated left DLPFC targets and sgACC could predict meaningful clinical outcome. Considering that individual characteristics may influence efficacy prediction, all patients were also assessed with the Behavioral Inhibition System/Behavioral Activation System (BIS/BAS) scale. MethodsAfter baseline ASL scanning, forty-one medication-resistant depressed patients received twenty sessions of neuronavigated left DLPFC aiTBS in an accelerated sham-controlled crossover fashion, where all stimulation sessions were spread over four days (Trial registration: http://clinicaltrials.gov/show/NCT01832805). ResultsStronger individual baseline interregional covariance perfusion connectivity patterns predicted response and/or remission. Furthermore, responders and remitters with higher BIS scores displayed stronger baseline interregional perfusion connections. ConclusionsTargeting the left DLPFC with aiTBS based on personal structural imaging data only may not be the most optimal method to enhance meaningful antidepressant responses. Individual baseline interregional perfusion connectivity could be an important added brain imaging method for individual optimization of more valid stimulation targets within the left DLPFC. Additional therapies dealing with behavioral inhibition may be warranted.

The effects of transcranial direct current stimulation to left DLPFC on attention, inhibition and working memory for people with dementia

AbstractBackgroundThe left dorsolateral prefrontal cortex (DLPFC) is a brain region that has been associated with executive function. In functional perspective, it involves the ability to organize, plan and carry out activities of daily living in an efficient manner.MethodA double‐blinded, randomized case‐control, single session interventional study was conducted to a match group of 24 older adults with dementia and 24 healthy control. Participants were then randomized to either anodal left DLPFC stimulation or sham stimulation . Those recruited subjects were equally randomized to 4 groups of single intervention, namely experimental verum stimulation, experimental sham stimulation, healthy control verum stimulation and health control sham stimulation. The outcome measures included pre‐and‐post stimulation performance‐based measure of executive function (The Home‐based Evaluation of Executive Function; The Home ‐MET), and three well established experimental paradigms of cognitive psychology such as Trail Making Task (TMT), N‐back Task (NBT) and Stroop Test (ST) under different modes of cognitive stimulation.ResultWith age and gender as covariates, the repeated measure ANOVAs of the MET results showed a significant group effect within subjects with F(1, 3) = 5.56, p &lt; .01, with small to medium effect size of partial eta square = .28 with observed power = .92 , p &lt; .05. In univariate general linear model analyses, NBT demonstrated there is significant interaction effect between group and types of stimulation, the univariate F(1, 44) = 8.77 with p = .001, small to medium effect size with partial eta square = .37 with observed power = .99. By multi‐variate general linear model, NBT and TMT together demonstrated there is significant interaction effect between groups, for NBT, the multivariate F(1, 42) = 9.03, p = .001 with partial eta square = .39 with observed power = .99.ConclusionIn this paper we investigate the effect single‐session tDCS may have on impact on performance‐based measure and cognition enhancement by using three well established experimental paradigms of cognitive psychology. Significant difference noted between experimental and health control in verum tDCS stimulation. Interesting, the sham tDCS also demonstrated its effect on executive function enhancement in healthy control but not the dementia subjects.

High-definition transcranial direct current stimulation modulates performance and alpha/beta parieto-frontal connectivity serving fluid intelligence.

Fluid intelligence (Gƒ) includes logical reasoning abilities and is an essential component of normative cognition. Despite the broad consensus that parieto-prefrontal connectivity is critical for Gƒ (e.g. the parieto-frontal integration theory of intelligence, P-FIT), the dynamics of such functional connectivity during logical reasoning remains poorly understood. Further, given the known importance of these brain regions for Gƒ, numerous studies have targeted one or both of these areas with non-invasive stimulation with the goal of improving Gƒ, but to date there remains little consensus on the overall stimulation-related effects. To examine this, we applied high-definition direct current anodal stimulation to the left and right dorsolateral prefrontal cortex (DLPFC) of 24 healthy adults for 20min in three separate sessions (sham, left, and right active). Following stimulation, participants completed a logical reasoning task during magnetoencephalography (MEG). Significant neural responses at the sensor-level were imaged using a beamformer, and peak task-induced activity was subjected to dynamic functional connectivity analyses to evaluate the impact of distinct stimulation montages on network activity. We found that participants responded faster following right DLPFC stimulation vs. sham. Moreover, our neural findings followed a similar trajectory of effects such that left parieto-frontal connectivity decreased following right and left DLPFC stimulation compared to sham, with connectivity following right stimulation being significantly correlated with the faster reaction times. Importantly, our findings are consistent with P-FIT, as well as the neural efficiency hypothesis (NEH) of intelligence. In sum, this study provides evidence for beneficial effects of right DLPFC stimulation on logical reasoning. KEY POINTS: Logical reasoning is an indispensable component of fluid intelligence and involves multispectral oscillatory activity in parietal and frontal regions. Parieto-frontal integration is well characterized in logical reasoning; however, its direct neural quantification and neuromodulation by brain stimulation remain poorly understood. High-definition transcranial direct current stimulation of dorsolateral prefrontal cortex (DLPFC) had modulatory effects on task performance and neural interactions serving logical reasoning, with right stimulation showing beneficial effects. Right DLPFC stimulation led to a decrease in the response time (i.e. better task performance) and left parieto-frontal connectivity with a marginal positive association between behavioural and neural metrics. Other modes of targeted stimulation of DLPFC (e.g. frequency-specific) can be employed in future studies.

Stimulation of the left dorsolateral prefrontal cortex with slow rTMS enhances verbal memory formation.

Encoding of episodic memories relies on stimulus-specific information processing and involves the left prefrontal cortex. We here present an incidental finding from a simultaneous EEG-TMS experiment as well as a replication of this unexpected effect. Our results reveal that stimulating the left dorsolateral prefrontal cortex (DLPFC) with slow repetitive transcranial magnetic stimulation (rTMS) leads to enhanced word memory performance. A total of 40 healthy human participants engaged in a list learning paradigm. Half of the participants (N = 20) received 1 Hz rTMS to the left DLPFC, while the other half (N = 20) received 1 Hz rTMS to the vertex and served as a control group. Participants receiving left DLPFC stimulation demonstrated enhanced memory performance compared to the control group. This effect was replicated in a within-subjects experiment where 24 participants received 1 Hz rTMS to the left DLPFC and vertex. In this second experiment, DLPFC stimulation also induced better memory performance compared to vertex stimulation. In addition to these behavioural effects, we found that 1 Hz rTMS to DLPFC induced stronger beta power modulation in posterior areas, a state that is known to be beneficial for memory encoding. Further analysis indicated that beta modulations did not have an oscillatory origin. Instead, the observed beta modulations were a result of a spectral tilt, suggesting inhibition of these parietal regions. These results show that applying 1 Hz rTMS to DLPFC, an area involved in episodic memory formation, improves memory performance via modulating neural activity in parietal regions.

Prefrontal transcranial direct current stimulation (tDCS) has a domain-specific impact on bilingual language control.

Researchers debate whether domain-general cognitive control supports bilingual language control through brain regions such as the dorsolateral prefrontal cortex (DLPFC). Transcranial direct current stimulation (tDCS) is a method to alter brain activity, which can lead to causal attribution of task performance to regional brain activity. The current study examined whether the DLPFC enables domain-general control for between-language switching and nonlinguistic switching and whether the control enabled by DLPFC differs between bilinguals and monolinguals. tDCS was applied to the DLPFC of bilingual and monolingual young adults before they performed linguistic and nonlinguistic switching measures. For bilinguals, left DLPFC stimulation selectively worsened nonlinguistic switching, but not within-language switching. Left DLPFC stimulation also resulted in higher overall accuracy on bilingual picture-naming. These findings suggest that language control and cognitive control are distinct processes in relation to the left DLPFC. The left DLPFC may aid bilingual language control, but stimulating it does not benefit nonlinguistic control. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

The effect of high-frequency rTMS of the left dorsolateral prefrontal cortex on the resolution of response, semantic and task conflict in the colour-word Stroop task

Previous work investigating the effect of rTMS of left Dorso-Lateral Prefrontal Cortex (DLPFC) on Stroop task performance reports no changes to the Stroop effect but reduced reaction times on both congruent and incongruent trials relative to sham stimulation; an effect attributed to an enhanced attentional (or task) set for colour classification. The present study tested this account by investigating whether, relative to vertex stimulation, rTMS of the left DLPFC modifies task conflict, a form of conflict that arises when task sets for colour classification and word reading compete, given that this particular type of conflict would be reduced by an enhanced task set for colour classification. Furthermore, the present study included measures of other forms of conflict present in the Stroop task (response and semantic conflict), the potential effects on which would have been hidden in previous studies employing only incongruent and congruent stimuli. Our data showed that left DLPFC stimulation had no effect on the magnitude of task conflict, nor did it affect response, semantic or overall conflict (where the null is supported by sensitive Bayes Factors in most cases). However, consistent with previous research left DLPFC stimulation had the general effect of reducing reaction times. We, therefore, show for the first time that relative to real vertex stimulation left DLPFC stimulation does not modify Stroop interference. Alternative accounts of the role of the left DLPFC in Stroop task performance in which it either modifies response thresholds or facilitates responding by keeping the correct response keys active in working memory are discussed.

A Causal Role for the Right Dorsolateral Prefrontal Cortex in Avoidance of Risky Choices and Making Advantageous Selections

In everyday life, risky decision-making relies on multiple cognitive processes including sensitivity to reinforcers, exploration, learning, and forgetting. Neuroimaging evidence suggests that the dorsolateral prefrontal cortex (DLPFC) is involved in exploration and risky decision-making, but the nature of its computations and its causal role remain uncertain. We provide evidence for the role of the DLPFC in value-independent, directed exploration on the Iowa Gambling Task (IGT) and we describe a new computational model to account for the competition of directed exploration and exploitation in guiding decisions. Forty-two healthy human participants were included in a right DLPFC, left DLPFC or sham stimulation groups using continuous theta-burst stimulation (cTBS). Immediately after cTBS, the IGT was completed. Computational modelling was used to account for exploration and exploitation with different combinations with value-based and sensitivity to reinforcers for each group. Applying cTBS to the left and right DLPFC selectively decreased directed exploration on the IGT compared to sham stimulation. Model-based analyses further indicated that the right (but not the left) DLPFC stimulation increased sensitivity to reinforcers, leading to avoidance of risky choices and promoting advantageous choices during the task. Although these findings are based on small sample sizes per group, they nevertheless elucidate the causal role of the right DLPFC in governing the exploration–exploitation tradeoff during decision-making in uncertain and ambiguous contexts.

Better modulation for risk decision-making after optimized magnetic stimulation.

Traditional repetitive transcranial magnetic stimulation can only produce a significant but weak effect on the cortex while theta burst stimulation (TBS), a patterned accelerated form of stimulation, can produce a stronger poststimulation effect, which may improve decision-making abilities. We designed a comparative assessment of the effect of intermittent TBS (iTBS), 20Hz, in two risk decision-making tasks on healthy controls. Participants were randomized and assigned to the iTBS (n=29), 20Hz (n=29), or sham (n=29) groups. The effects of the different methods of left dorsolateral prefrontal cortex stimulation on risk decision-making functions were compared based on subjects' performance in the Game of Dice Task (GDT) and Risky Gains Task (RGT). The main indicators were positive and negative feedback utilization rates of GDT and RGT. Both iTBS and 20 Hz stimulation resulted in significant improvements upon negative feedback in the GDT, with increases in safe options and reductions in risky options; iTBS stimulation increased subjects' use of positive feedback in the GDT and RGT (all p<0.05). Furthermore, the iTBS group had a stronger feedback risk reduction effect than the 20Hz or sham group following RGT negative feedback (p<0.05). Individuals would integrate positive and negative information more efficiently, leading to them making rational choices after excitatory transcranial magnetic stimulation. Moreover, iTBS has a stronger risk reduction effect following negative feedback than the 20Hz stimulation did. In summary, iTBS might have clinical value in decision promotion.

Prefrontal Cortical Abnormalities in Schizophrenia: A Validation via a CausalNeuromodulation Method

Neuroimaging studies have reliably detected prefrontal cortical abnormalities in schizophrenia. In a recent study, we built on these correlative findings using interleaved transcranial magnetic stimulation and functional magnetic resonance imaging (TMS fMRI), a tool that enables simultaneous interrogation and imaging of discrete neural circuits and their connections. Compared to controls subjects with schizophrenia showed increased activation at the left dorsolateral prefrontal cortex stimulation site (BA9 and adjacent BA46) and decreased activation in contralateral right BA9 putatively indicative of impaired interhemispheric functional connectivity. In this minireview, we discuss the implications of these findings and offer recommendations for how future studies can build on our results to shed novel light on the pathophysiology of schizophrenia.

Transcranial direct current stimulation of dorsolateral prefrontal cortex improves dual-task gait performance in patients with Parkinson’s disease: A double blind, sham-controlled study

BackgroundDespite advances in pharmacological treatments and surgical processes, the problem of impaired dual-tasking persists in people with Parkinson’s disease (PD). Recently, transcranial direct current stimulation (tDCS) applied to the dorsolateral prefrontal cortex (DLPFC) has shown the potential to improve dual-task walking. Research QuestionCan combining left DLPFC stimulation using tDCS with dual-task performance reduce the cost of dual-tasking in individuals with PD? MethodsWe conducted a sham-controlled, cross-over, and double-blind study to investigate the effect of combining tDCS with the dual-task walk and its sustained effects among people with PD. Twenty participants with PD completed two sessions (anodal or sham tDCS) with at least a 1-week gap. Stimulation involved transferring 2 mA current through the left DLPFC for 30 min. Single- and dual-task gait was assessed before, during, immediately after, 15, and 30 min after stimulation ceased. Phoneme verbal fluency task was given as the cognitive distractor during dual task. Results and ConclusionThe results of this study show that in the dual-task condition, participants walked faster at fifteen minutes (p = 0.017) and thirty minutes (p < 0.01) after anodal tDCS ceased compared to sham. Similarly, participants generated a higher number of words per minute at fifteen minutes (p = 0.017), and thirty minutes (p < 0.01) after anodal tDCS ceased compared to sham. Furthermore, the dual-task cost (DTC) associated with gait speed was significantly lower (p = 0.022) at fifteen minutes after anodal tDCS compared to sham tDCS. However, no significant effect of tDCS was observed on gait and cognitive performance under the single-task condition. In conclusion, left DLPFC stimulation can improve dual-tasking in participants with PD and the peaking of the tDCS effect was observed at fifteen minutes after stimulation ceased.

Individualized theta-burst stimulation modulates hippocampal activity and connectivity in patients with major depressive disorder

BackgroundWhile intermittent theta-burst stimulation (iTBS) has been shown to improve symptoms of major depressive disorder (MDD), research has been largely limited to targeting the dorsolateral prefrontal cortex (DLPFC). New approaches utilize patients’ individual resting state fMRI data in order to identify superficial cortical stimulation targets functionally connected to deeper brain regions, thus enabling the modulation of previously inaccessible targets for antidepressant therapy. ObjectiveTo improve iTBS treatment of MDD by inducing plasticity in the hippocampus through stimulation of an individually mapped, functionally interconnected site in the parietal cortex. MethodsFifty-three MDD patients were randomized to three treatment groups and underwent 15 sessions of iTBS to the left DLPFC. This was augmented by adding a second daily session of (i) stimulation over individualized parietal targets functionally connected to the hippocampus, (ii) left DLPFC stimulation, or (iii) sham stimulation. To evaluate the improvement of treatment, we assessed depression severity, neuropsychological performance, functional connectivity and neural activation during an associative memory paradigm pre- vs. post-treatment. ResultsAugmentation of left DLPFC stimulation by parieto-hippocampal stimulation increased functional connectivity between hippocampus and DLPFC as well as encoding-related hippocampal activation; the latter was associated with better performance during a spatial planning task dependent on prefrontal and hippocampal contributions. Depressive symptoms improved in all groups after treatment, with best clinical outcomes following twice-daily left DLPFC stimulation. ConclusionFunctional connectivity-guided stimulation of the hippocampus may serve as an adjunct to iTBS in order to target the cognitive symptoms of MDD.

The Effect of High-frequency Repetitive Transcranial Magnetic Stimulation on Reducing Depression and Anxiety in Methamphetamine Users.

BackgroundMethamphetamine use has been associated with higher rates of depression and anxiety. The mesocorticolimbic dopaminergic reward system seems to play a crucial role in inducing depression and anxiety in methamphetamine users. High-frequency repetitive transcranial magnetic stimulation (rTMS) has been shown to alter dopaminergic neurotransmission considering the acute rewarding and reinforcing effects in the subcortical structure. The aim of this study was to investigate the efficacy of rTMS in reducing depression and anxiety symptoms in methamphetamine users.MethodsIn a single-subject method with concurrent multiple baseline designs, in 2017, in Iran, eight methamphetamine users were included, which compared 15 days of active versus placebo stimulation and control group. Two subjects received rTMS on the right dorsolateral prefrontal cortex (DLPFC) and two subjects received rTMS on the left DLPFC. We carried out the measurement using the Beck Anxiety Inventory (BAI) and Beck Depression Inventory (BDI) before, during, and after 15 and 30 days of the procedure.FindingsRight and left DLPFC stimulation significantly reduced depression and anxiety, but the reduction of depression and anxiety by the right DLPFC stimulation was noticeable in this study.ConclusionHigh-frequency rTMS is useful for the treatment of depression and anxiety in methamphetamine users.

Transcranial magnetic stimulation over the dorsolateral prefrontal cortex affects emotional processing: accounting for individual differences in antisocial behavior

The study was designed to investigate the effects of transcranial magnetic stimulation (TMS) over the dorsolateral prefrontal cortex (DLPFC) on emotional recognition among individuals differentiated on antisocial personality disorder (APD) symptoms. Participants (N = 93) received continuous theta burst stimulation (cTBS) under four conditions: real or sham cTBS over the left and right DLPFC. After stimulation, participants performed a dynamic face recognition task depicting fearful, happy, sad, and painful expressions. Left and right DLPFC stimulation were followed by improved accuracy of happy and painful emotions compared to sham conditions. Participants receiving left stimulation were also better able to recognize sad expressions compared to the left sham condition. A three-way interaction between type of stimulation, emotion recognition, and APD groups suggested that the identified TMS effects on emotion recognition were only significant for individuals at elevated risk for APD symptoms. Findings suggest that DLPFC stimulation can lead to benefits in emotion recognition among individuals high on APD symptoms.