Mechanisms of action underlying the effect of repetitive transcranial magnetic stimulation on mood: behavioral and brain imaging studies

Association between Mood and Sensation Seeking Following rTMS

Previous studies investigating mood changes in healthy subjects after prefrontal repetitive transcranial magnetic stimulation (rTMS) have shown largely inconsistent results. This may be due to methodological issues, considerable inter-individual variation in prefrontal connectivity or other factors, e.g., personality traits. This pilot study investigates whether mood changes after rTMS are affected by personality parameters. In a randomized cross-over design, 17 healthy volunteers received three sessions of 1 Hz rTMS to Fz, F3 and T3 (10/20 system). The T3 electrode site served as the control condition with the coil angled 45° to the scalp. Subjective mood was rated at baseline and after each condition. Personality traits were assessed using the NEO Five-Factor Inventory (NEO-FFI) and the Sensation Seeking Scale (SSS). For all conditions, a significant association between mood changes towards a deterioration in mood and SSS scores was observed. There were no differences between conditions and no correlations between mood changes and NEO-FFI. The data show that sensation-seeking personality has an impact on subjective mood changes following prefrontal rTMS in all conditions. Future studies investigating the effects of rTMS on emotional paradigms should include individual measures of sensation-seeking personality. The pre-selection of subjects according to personality criteria may reduce the variability in results.

Functional MRI Lateralization [M1] of dlPFC and Implications for Transcranial Magnetic Stimulation (TMS) Targeting

The present study investigates a potential method of optimizing effective strategies for the functional lateralization of the dorsolateral prefrontal cortex (dlPFC) while in a scanner. Effective hemisphere lateralization of the dlPFC is crucial for lowering the functional risks connected to specific interventions (such as neurosurgery and transcranial magnetic stimulation (TMS), as well as increasing the effectiveness of a given intervention by figuring out the optimal location. This task combines elements of creative problem solving, executive decision making based on an internal rule set, and working memory. A retrospective analysis was performed on a total of 58 unique participants (34 males, 24 females, Mage = 42.93 years, SDage = 16.38). Of these participants, 47 were classified as right-handed, 7 were classified as left-handed, and 4 were classified as ambidextrous, according to the Edinburgh Handedness Inventory. The imaging data were qualitatively judged by two trained, blinded investigators (neurologist and neuropsychologist) for dominant handedness (primary motor cortex) and dominant dorsolateral prefrontal cortex (dlPFC). The results demonstrated that 21.4% of right-handed individuals showed a dominant dlPFC localized to the right hemisphere rather than the assumed left, and 16.7% of left-handers were dominant in their left hemisphere. The task completed in the scanner might be an efficient method for localizing a potential dlPFC target for the purpose of brain stimulation (e.g., TMS), though further study replications are needed to extend and validate these findings.

The Static and dynamic functional connectivity characteristics of the left temporoparietal junction region in schizophrenia patients with auditory verbal hallucinations during low-frequency rTMS treatment

BACKGROUND

Auditory verbal hallucinations (AVH) are a core symptom of schizophrenia. Low-frequency (e.g., 1 Hz) repetitive transcranial magnetic stimulation (rTMS) targeting language processing regions (e.g., left TPJ) has been evident as a potential treatment for AVH. However, the underlying neural mechanisms of the rTMS treatment effect remain unclear. The present study aimed to investigate the effects of 1 Hz rTMS on functional connectivity (FC) of the temporoparietal junction area (TPJ) seed with the whole brain in schizophrenia patients with AVH.

METHODS

Using a single-blind placebo-controlled randomized clinical trial, 55 patients with AVH were randomly divided into active treatment group (n = 30) or placebo group (n = 25). The active treatment group receive 15-day 1 Hz rTMS stimulation to the left TPJ, whereas the placebo group received sham rTMS stimulation to the same site. Resting-state fMRI scans and clinical measures were acquired for all patients before and after treatment. The seed-based (left TPJ) static and DFC was used to assess the connectivity characteristics during rTMS treatment in patients with AVH.

RESULTS

Overall, symptom improvement following 1 Hz rTMS treatment was found in the active treatment group, whereas no change occurred in the placebo group. Moreover, decreased static FC (SFC) of the left TPJ with the right temporal lobes, as well as increased SFC with the prefrontal cortex and subcortical structure were observed in active rTMS group. Increased dynamic FC (DFC) of the left TPJ with frontoparietal areas was also found in the active rTMS group. However, seed-based SFC and DFC were reduced to a great extent in the placebo group. In addition, these changed FC (SFC) strengths in the active rTMS group were associated with reduced severity of clinical outcomes (e.g., positive symptoms).

CONCLUSION

The application of 1 Hz rTMS over the left TPJ may affect connectivity characteristics of the targeted region and contribute to clinical improvement, which shed light on the therapeutic effect of rTMS on schizophrenia with AVH.

Changing Cerebral Blood Flow, Glucose Metabolism, and Dopamine Binding Through Transcranial Magnetic Stimulation: A Systematic Review of Transcranial Magnetic Stimulation-Positron Emission Tomography Literature

Transcranial magnetic stimulation (TMS) is a noninvasive neuromodulation tool currently used as a treatment in multiple psychiatric and neurologic disorders. Despite its widespread use, we have an incomplete understanding of the way in which acute and chronic sessions of TMS affect various neural and vascular systems. This systematic review summarizes the state of our knowledge regarding the effects TMS may be having on cerebral blood flow, glucose metabolism, and neurotransmitter release. Forty-five studies were identified. Several key themes emerged: 1) TMS transiently increases cerebral blood flow in the area under the coil; 2) TMS to the prefrontal cortex increases glucose metabolism in the anterior cingulate cortex of patients with depression; and 3) TMS to the motor cortex and prefrontal cortex decreases dopamine receptor availability in the ipsilateral putamen and caudate respectively. There is, however, a paucity of literature regarding the effects TMS may have on other neurotransmitter and neuropeptide systems of interest, all of which may shed vital light on existing biologic mechanisms and future therapeutic development. SIGNIFICANCE STATEMENT: Transcranial magnetic stimulation (TMS) is a noninvasive neuromodulation tool currently used as a treatment in multiple psychiatric and neurologic disorders. This systematic review summarizes the state of our knowledge regarding the effects TMS on cerebral blood flow, glucose metabolism, and neurotransmitter release.

Repetitive Transcranial Magnetic Stimulation for Neuropathic Pain and Neuropsychiatric Symptoms in Traumatic Brain Injury: A Systematic Review and Meta-Analysis

Neuropathic pain and neuropsychiatric symptoms are common complications reported by the traumatic brain injury (TBI) population. Although a growing body of research has indicated the effectiveness of repetitive transcranial magnetic stimulation (rTMS) for the management of neurological and psychiatric disorders, little evidence has been presented to support the effects of rTMS on neuropathic pain and neuropsychiatric symptoms in patients with TBI in all age groups. In addition, a better understanding of the potential factors that might influence the therapeutic effect of rTMS is necessary. The objective of this preregistered systematic review and meta-analysis was to quantify the effects of rTMS on physical and psychological symptoms in individuals with TBI. We systematically searched six databases for randomized controlled trials (RCTs) of rTMS in TBI patients reporting pain and neuropsychiatric outcomes published until March 20, 2022. The mean difference (MD) with 95% confidence intervals (CIs) was estimated separately for outcomes to understand the mean effect size. Twelve RCTs with 276 TBI patients were ultimately selected from 1605 records for systematic review, and 11 of the studies were included in the meta-analysis. Overall, five of the included studies showed a low risk of bias. The effects of rTMS on neuropathic pain were statistically significant ( $\text{MD}=-1.00$ , 95% CI -1.76 to -0.25, $P=0.009$ ), with high heterogeneity ( $I^2=76\%$ ). A significant advantage of 1 Hz rTMS over the right dorsolateral prefrontal cortex (DLPFC) in improving depression ( $\text{MD}=-6.52$ , 95% CI -11.58 to -1.46, $P=0.01$ ) was shown, and a significant improvement was noted in the Rivermead Post-Concussion Symptoms Questionnaire-13 (RPQ-13) scores of mild TBI patients after rTMS ( $\text{MD}=-5.87$ , 95% CI -10.63 to -1.11, $P=0.02$ ). However, no significance was found in cognition measurement. No major adverse events related to rTMS were reported. Moderate evidence suggests that rTMS can effectively and safely improve neuropathic pain, while its effectiveness on depression, postconcussion symptoms, and cognition is limited. More trials with a larger number of participants are needed to draw firm conclusions. This trial is registered with PROSPERO (PROSPERO registration number: CRD42021242364.

Effect of Intermittent Theta Burst Stimulation on the Neural Processing of Emotional Stimuli in Healthy Volunteers

BACKGROUND

Intermittent theta burst stimulation (iTBS) is a form of repetitive transcranial magnetic stimulation that has shown to be effective in treatment-resistant depression. Through studying the effect of iTBS on healthy subjects, we wished to attain a greater understanding of its impact on the brain. Our objective was to assess whether 10 iTBS sessions altered the neural processing of emotional stimuli, mood and brain anatomy in healthy subjects.

METHODS

In this double-blind randomized sham-controlled study, 30 subjects received either active iTBS treatment (10 sessions, two sessions a day) or sham treatment over the left dorsolateral prefrontal cortex. Assessments of mood, structural magnetic resonance imaging (MRI) and functional MRI (fMRI) were performed before and after iTBS sessions. During the fMRI, three different categories of stimuli were presented: positive, negative and neutral photographs.

RESULTS

This study showed that, during the presentation of negative stimuli (compared with neutral stimuli), 10 sessions of iTBS increased activity in the left anterior insula. However, iTBS did not induce any change in mood, regional gray matter volume or cortical thickness.

CONCLUSIONS

iTBS modifies healthy subjects' brain activity in a key region that processes emotional stimuli. (AFSSAPS: ID-RCB 2010A01032-37).

Suppression of neuropathic pain and comorbidities by recurrent cycles of repetitive transcranial direct current motor cortex stimulation in mice

Transcranial, minimally-invasive stimulation of the primary motor cortex (M1) has recently emerged to show promise in treating clinically refractory neuropathic pain. However, there is a major need for improving efficacy, reducing variability and understanding mechanisms. Rodent models hold promise in helping to overcome these obstacles. However, there still remains a major divide between clinical and preclinical studies with respect to stimulation programs, analysis of pain as a multidimensional sensory-affective-motivational state and lack of focus on chronic phases of established pain. Here, we employed direct transcranial M1 stimulation (M1 tDCS) either as a single 5-day block or recurring blocks of repetitive stimulation over early or chronic phases of peripherally-induced neuropathic pain in mice. We report that repeated blocks of stimulation reverse established neuropathic mechanical allodynia more strongly than a single 5-day regime and also suppress cold allodynia, aversive behavior and anxiety without adversely affecting motor function over a long period. Activity mapping revealed highly selective alterations in the posterior insula, periaqueductal gray subdivisions and superficial spinal laminae in reversal of mechanical allodynia. Our preclinical data reveal multimodal analgesia and improvement in quality of life by multiple blocks of M1 tDCS and uncover underlying brain networks, thus helping promote clinical translation.

Neuroimaging of depression with diffuse optical tomography during repetitive transcranial magnetic stimulation

Repetitive transcranial magnetic stimulation (rTMS) is an effective and safe treatment for depression; however, its potential has likely been hindered due to non-optimized targeting, unclear ideal stimulation parameters, and lack of information regarding how the brain is physiologically responding during and after stimulation. While neuroimaging is ideal for obtaining such critical information, existing modalities have been limited due to poor resolutions, along with significant noise interference from the electromagnetic spectrum. In this study, we used a novel diffuse optical tomography (DOT) device in order to advance our understanding of the neurophysiological effects of rTMS in depression. Healthy and depressed subjects aged 18–70 were recruited. Treatment parameters were standardized with targeting of the left dorsolateral prefrontal cortex with a magnetic field intensity of 100% of motor threshold, pulse frequency of 10 per second, a 4 s stimulation time and a 26 s rest time. DOT imaging was simultaneously acquired from the contralateral dorsolateral prefrontal cortex. Six healthy and seven depressed subjects were included for final analysis. Hemoglobin changes and volumetric three-dimensional activation patterns were successfully captured. Depressed subjects were observed to have a delayed and less robust response to rTMS with a decreased volume of activation compared to healthy subjects. In this first-in-human study, we demonstrated the ability of DOT to safely and reliably capture and compare cortical response patterns to rTMS in depressed and healthy subjects. We introduced this emerging optical functional imaging modality as a novel approach to investigating targeting, new treatment parameters, and physiological effects of rTMS in depression.

Natural or Urban Campus Walks and Vitality in University Students: Exploratory Qualitative Findings from a Pilot Randomised Controlled Study

Despite extensive evidence of the restorative effects of nature, the potential vitalizing effects of connecting with nature are yet understudied, particularly in higher education settings. University students face high levels of stress and anxiety, and may benefit from nature-based interventions that enhance positive states such as vitality. Using preliminary data from a pilot randomized controlled study with qualitative interviews, we explored the psychological experiences associated with a brief walk either in nature or an urban environment in a sample of 13 university students. The qualitative thematic analysis revealed that walking in nature was a more energizing and vitalizing experience than the urban walk. The nature walk was also found to have both affective and cognitive enhancing effects on participants. Our study highlights the usefulness of exploring subjective psychological experiences of interacting with nature, as well as supporting its restorative potential. Implications for further research and interventions are discussed.

Interhemispheric compensation: A hypothesis of TMS-induced effects on language-related areas

Repetitive transcranial magnetic stimulation (rTMS) applied over brain regions responsible for language processing is used to curtail potentially auditory hallucinations in schizophrenia patients and to investigate the functional organisation of language-related areas. Variability of effects is, however, marked across studies and between subjects. Furthermore, the mechanisms of action of rTMS are poorly understood.

Here, we reviewed different factors related to the structural and functional organisation of the brain that might influence rTMS-induced effects. Then, by analogy with aphasia studies, and the plastic-adaptive changes in both the left and right hemispheres following aphasia recovery, a hypothesis is proposed about rTMS mechanisms over language-related areas (e.g. Wernicke, Broca). We proposed that the local interference induced by rTMS in language-related areas might be analogous to aphasic stroke and might lead to a functional reorganisation in areas connected to the virtual lesion for language recovery.

Differential Age Effects of Transcranial Direct Current Stimulation on Associative Memory

OBJECTIVES

Older adults experience associative memory deficits relative to younger adults (Old & Naveh-Benjamin, 2008). The aim of this study was to test the effect of transcranial direct current stimulation (tDCS) on face-name associative memory in older and younger adults.

METHOD

Experimenters applied active (1.5 mA) or sham (0.1 mA) stimulation with the anode placed over the left dorsolateral prefrontal cortex (dlPFC) during a face-name encoding task, and measured both cued recall and recognition performance. Participants completed memory tests immediately after stimulation and after a 24-h delay to examine both immediate and delayed stimulation effects on memory.

RESULTS

Results showed improved face-name associative memory performance for both recall and recognition measures, but only for younger adults, whereas there was no difference between active and sham stimulation for older adults. For younger adults, stimulation-induced memory improvements persisted after a 24-h delay, suggesting delayed effects of tDCS after a consolidation period.

DISCUSSION

Although effective in younger adults, these results suggest that older adults may be resistant to this intervention, at least under the stimulation parameters used in the current study. This finding is inconsistent with a commonly seen trend, where tDCS effects on cognition are larger in older than younger adults.

Duality of self-promotion on social networking sites

Purpose

Self-promotion on social networking sites (SNSs) is a controversial issue as it has been attributed to various positive and negative consequences. To better understand the reasons for the mixed consequences and the nature of self-promotion on SNSs, the purpose of this paper is to theorize and empirically investigate the duality of SNS self-promotion and its underlying socio-psychological mechanisms.

Design/methodology/approach

By drawing on the motivational affordance lens and self-determination theory, this study develops a theoretical account of the duality of self-promotion on SNSs. The author places subjective vitality and SNS addiction as the positive and negative consequences of self-promotion. The model was tested using partial least squares technique with data collected from 289 Finnish Facebook users using a survey.

Findings

The results show that self-promotion contributes to both subjective vitality and to SNS addiction. Importantly, exhibitionism attenuates the effect of self-promotion on subjective vitality and amplifies the effect of self-promotion on SNS addiction. The feature-level analysis shows that status updates, adding photos, commenting in others’ posts and profile completeness are the main determinants of self-promotion. Status updates, adding photos and check-ins, in turn, have high exhibitionistic appeal.

Originality/value

To date, the empirical attempts to investigate the duality of SNS use have been rare. In particular, prior research is largely silent in explaining what tilt the outcomes of self-promotion either toward positive or negative direction. The paper fills this theoretical and empirical gap and thus contributes to literature on dualities of SNS use.

Adolescent brain development and depression: A case for the importance of connectivity of the anterior cingulate cortex

We propose that structural and functional connectivity of the anterior cingulate cortex (ACC) represents a critical component of adolescent developmental psychopathology. We hypothesize that connectivity of the ACC, a hub for integrating cognitive, affective, and social information to guide self-regulation across domains, supports adaptive development of self-regulation during adolescence and that, conversely, disrupted maturation of ACC connectivity contributes to the development of depression. To integrate findings on typical development, we report results of a meta-analysis of diffusion imaging findings of typical adolescent development of the cingulum and anterior thalamic radiations, the tracts most relevant to ACC connectivity, and provide a critical review of the literature on ACC functional connectivity. Finally, we review the evidence for altered structural and functional connectivity in adolescents with depression. Although the evidence for our claim is persuasive, a more comprehensive understanding of the ACC's role depends upon future investigations with sophisticated modeling of networks, prospective and longitudinal designs, and examination of structure-function associations.

Transcranial Magnetic Stimulation of Left Dorsolateral Prefrontal Cortex Induces Brain Morphological Changes in Regions Associated with a Treatment Resistant Major Depressive Episode: An Exploratory Analysis

BACKGROUND

Repetitive transcranial magnetic stimulation (TMS) is an FDA-approved antidepressant treatment but little is known of its mechanism of action. Specifically, downstream effects of TMS remain to be elucidated.

OBJECTIVE/HYPOTHESIS

This study aims to identify brain structural changes from TMS treatment of a treatment resistant depressive episode through an exploratory analysis.

METHODS

Twenty-seven subjects in a DSM-IV current major depressive episode and on a stable medication regimen had a 3T magnetic resonance T1 structural scan before and after five weeks of standard TMS treatment to the left dorsolateral prefrontal cortex. Twenty-seven healthy volunteer (HVs) subjects had the same brain MRI acquisition. Voxel-based morphometry was performed using high dimensional non-linear diffusomorphic anatomical registration (DARTEL).

RESULTS

Six clusters of gray matter volume (GMV) that were lower in pre-treatment MRIs of depressed subjects than in HVs. GMV in four of these regions increased in MDD after TMS treatment by 3.5-11.2%. The four brain regions that changed with treatment were centered in the left anterior cingulate cortex, the left insula, the left superior temporal gyrus and the right angular gyrus. Increases in the anterior cingulate GMV with TMS correlated with improvement in depression severity.

CONCLUSIONS

To our knowledge, this is the first study of brain structural changes during TMS treatment of depression. The affected brain areas are involved in cognitive appraisal, decision-making and subjective experience of emotion. These effects may have potential relevance for the antidepressant action of TMS.

Use of repetitive transcranial magnetic stimulation for treatment in psychiatry

The potential of noninvasive neurostimulation by repetitive transcranial magnetic stimulation (rTMS) for improving psychiatric disorders has been studied increasingly over the past two decades. This is especially the case for major depression and for auditory-verbal hallucinations in schizophrenia. The present review briefly describes the background of this novel treatment modality and summarizes evidence from clinical trials into the efficacy of rTMS for depression and hallucinations. Evidence for efficacy in depression is stronger than for hallucinations, although a number of studies have reported clinically relevant improvements for hallucinations too. Different stimulation parameters (frequency, duration, location of stimulation) are discussed. There is a paucity of research into other psychiatric disorders, but initial evidence suggests that rTMS may also hold promise for the treatment of negative symptoms in schizophrenia, obsessive compulsive disorder and post-traumatic stress disorder. It can be concluded that rTMS induces alterations in neural networks relevant for psychiatric disorders and that more research is needed to elucidate efficacy and underlying mechanisms of action.

Somatic therapies for treatment-resistant depression: ECT, TMS, VNS, DBS

The field of non-pharmacological therapies for treatment resistant depression (TRD) is rapidly evolving and new somatic therapies are valuable options for patients who have failed numerous other treatments. A major challenge for clinicians (and patients alike) is how to integrate the results from published clinical trials in the clinical decision-making process.

We reviewed the literature for articles reporting results for clinical trials in particular efficacy data, contraindications and side effects of somatic therapies including electroconvulsive therapy (ECT), transcranial magnetic stimulation (TMS), vagal nerve stimulation (VNS) and deep brain stimulation (DBS). Each of these devices has an indication for patients with different level of treatment resistance, based on acuteness of illness, likelihood of response, costs and associated risks. ECT is widely available and its effects are relatively rapid in severe TRD, but its cognitive adverse effects may be cumbersome. TMS is safe and well tolerated, and it has been approved by FDA for adults who have failed to respond to one antidepressant, but its use in TRD is still controversial as it is not supported by rigorous double-blind randomized clinical trials. The options requiring surgical approach are VNS and DBS. VNS has been FDA-approved for TRD, however it is not indicated for management of acute illness. DBS for TRD is still an experimental area of investigation and double-blind clinical trials are underway.

Impact of one HF-rTMS session on fine motor function in right-handed healthy female subjects: a comparison of stimulation over the left versus the right dorsolateral prefrontal cortex

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive tool to investigate neural conduction in motor processes. Most rTMS research has been conducted by targeting the primary motor cortex. Several studies have also found increased psychomotor speed after rTMS of the dorsolateral prefrontal cortex (DLPFC). However, these studies were mainly performed in psychiatric patients, only targeting the left DLPFC, and often without sham control. Moreover, psychomotor speed is mostly measured based on tasks that also require higher executive functions.

METHODS

Here, we examined the lateralized effect of one sham-controlled high-frequency rTMS session applied to the left or right DLPFC on fine motor function in 36 healthy right-handed females, using the Fitts' paradigm.

RESULTS

We found a significant improvement in psychomotor speed only after actively stimulating the right DLPFC.

CONCLUSION

Our results support the assumption of a right prefrontal neural network implicated in visuomotor behavior and performance processes, and that the improvement in psychomotor speed is not a secondary effect of decreased mood.

Translational application of neuromodulation of decision-making

Recent cognitive neuroscience studies indicate that noninvasive brain stimulation can modulate a wide spectrum of behaviors in healthy individuals. Such modulation of behaviors provides novel insights into the fundamentals and neurobiology of cognitive functions in the healthy brain, but also suggests promising prospects for translational applications into clinical populations. One type of behavior that can be modulated with noninvasive brain stimulation is decision-making. For instance, brain stimulation can induce more cautious or riskier behaviors. The capacity of influencing processes involved in decision-making is of particular interest because such processes are at the core of human social and emotional functioning (or dysfunctioning). We review cognitive neuroscience studies that have successfully modulated processes involved in decision-making with transcranial direct current stimulation (tDCS) or transcranial magnetic stimulation (TMS), including risk taking, reward seeking, impulsivity, and fairness consideration. We also discuss potential clinical relevance of these findings for patients who have still unmet therapeutic need and whose alterations in decision-making represent hallmarks of their clinical symptomatology, such as individuals with addictive disorders.

Impact of tDCS on performance and learning of target detection: interaction with stimulus characteristics and experimental design

We have previously found that transcranial direct current stimulation (tDCS) over right inferior frontal cortex (RIFC) enhances performance during learning of a difficult visual target detection task (Clark et al., 2012). In order to examine the cognitive mechanisms of tDCS that lead to enhanced performance, here we analyzed its differential effects on responses to stimuli that varied by repetition and target presence, differences related to expectancy by comparing performance in single- and double-blind task designs, and individual differences in skin stimulation and mood. Participants were trained for 1h to detect target objects hidden in a complex virtual environment, while anodal tDCS was applied over RIFC at 0.1 mA or 2.0 mA for the first 30 min. Participants were tested immediately before and after training and again 1h later. Higher tDCS current was associated with increased performance for all test stimuli, but was greatest for repeated test stimuli with the presence of hidden-targets. This finding was replicated in a second set of subjects using a double-blind task design. Accuracy for target detection discrimination sensitivity (d'; Z(hits)-Z(false alarms)) was greater for 2.0 mA current (1.77) compared with 0.1 mA (0.95), with no differences in response bias (β). Taken together, these findings indicate that the enhancement of performance with tDCS is sensitive to stimulus repetition and target presence, but not to changes in expectancy, mood, or type of blinded task design. The implications of these findings for understanding the cognitive mechanisms of tDCS are discussed.

Baseline brain metabolism in resistant depression and response to transcranial magnetic stimulation

Neuroimaging studies of patients with treatment-resistant depression (TRD) have reported abnormalities in the frontal and temporal regions. We sought to determine whether metabolism in these regions might be related to response to repetitive transcranial magnetic stimulation (TMS) in patients with TRD. Magnetic resonance images and baseline resting-state cerebral glucose uptake index (gluMI) obtained using (18)F-fluorodeoxyglucose positron emission tomography were analyzed in TRD patients who had participated in a double-blind, randomized, sham-controlled trial of prefrontal 10 Hz TMS. Among the patients randomized to active TMS, 17 responders, defined as having 50% depression score decrease, and 14 nonresponders were investigated for prestimulation glucose metabolism and compared with 39 healthy subjects using a voxel-based analysis. In nonresponders relative to responders, gluMI was lower in left lateral orbitofrontal cortex (OFC), and higher in left amygdala and uncinate fasciculus. OFC and amygdala gluMI negatively correlated in nonresponders, positively correlated in responders, and did not correlate in healthy subjects. Relative to healthy subjects, both responders and nonresponders displayed lower gluMI in right dorsolateral prefrontal (DLPFC), right anterior cingulate (ACC), and left ventrolateral prefrontal cortices. Additionally, nonresponders had lower gluMI in left DLPFC, ACC, left and right insula, and higher gluMI in left amygdala and uncus. Hypometabolisms were partly explained by gray matter reductions, whereas hypermetabolisms were unrelated to structural changes. The findings suggest that different patterns of frontal-temporal-limbic abnormalities may distinguish responders and nonresponders to prefrontal magnetic stimulation. Both preserved OFC volume and amygdala metabolism might precondition response to TMS.

Impairment of executive performance after transcranial magnetic modulation of the left dorsal frontal-striatal circuit

The dorsal frontal-striatal circuit is implicated in executive functions, such as planning. The Tower of London task, a planning task, in combination with off-line low-frequency repetitive transcranial magnetic stimulation (rTMS), was used to investigate whether interfering with dorsolateral prefrontal function would modulate executive performance, mimicking dorsal frontal-striatal dysfunction as found in neuropsychiatric disorders. Eleven healthy controls (seven females; mean age 25.5 years) were entered in a cross-over design: two single-session treatments of low-frequency (1 Hz) rTMS (vs. sham rTMS) for 20 min on the left dorsolateral prefrontal cortex (DLPFC). Directly following the off-line rTMS treatment, the Tower of London task was performed during MRI measurements. The low-frequency rTMS treatment impaired performance, but only when the subjects had not performed the task before: we found a TMS condition-by-order effect, such that real TMS treatment in the first session led to significantly more errors (P = 0.032), whereas this TMS effect was not present in subjects who received real TMS in the second session. At the neural level, rTMS resulted in decreased activation during the rTMS versus sham condition in prefrontal brain regions (i.e., premotor, dorsolateral prefrontal and anterior prefrontal cortices) and visuospatial brain regions (i.e., precuneus/cuneus and inferior parietal cortex). The results show that low-frequency off-line rTMS on the DLPFC resulted in decreased task-related activations in the frontal and visuospatial regions during the performance of the Tower of London task, with a behavioral effect only when task experience is limited.

Interhemispheric Connectivity Influences the Degree of Modulation of TMS-Induced Effects during Auditory Processing

Repetitive transcranial magnetic stimulation (rTMS) has been shown to interfere with many components of language processing, including semantic, syntactic, and phonologic. However, not much is known about its effects on nonlinguistic auditory processing, especially its action on Heschl's gyrus (HG). We aimed to investigate the behavioral and neural basis of rTMS during a melody processing task, while targeting the left HG, the right HG, and the Vertex as a control site. Response times (RT) were normalized relative to the baseline-rTMS (Vertex) and expressed as percentage change from baseline (%RT change). We also looked at sex differences in rTMS-induced response as well as in functional connectivity during melody processing using rTMS and functional magnetic resonance imaging (fMRI). fMRI results showed an increase in the right HG compared with the left HG during the melody task, as well as sex differences in functional connectivity indicating a greater interhemispheric connectivity between left and right HG in females compared with males. TMS results showed that 10 Hz-rTMS targeting the right HG induced differential effects according to sex, with a facilitation of performance in females and an impairment of performance in males. We also found a differential correlation between the %RT change after 10 Hz-rTMS targeting the right HG and the interhemispheric functional connectivity between right and left HG, indicating that an increase in interhemispheric functional connectivity was associated with a facilitation of performance. This is the first study to report a differential rTMS-induced interference with melody processing depending on sex. In addition, we showed a relationship between the interference induced by rTMS on behavioral performance and the neural activity in the network connecting left and right HG, suggesting that the interhemispheric functional connectivity could determine the degree of modulation of behavioral performance.

Assessment of standard coil positioning in transcranial magnetic stimulation in depression

Transcranial magnetic stimulation (TMS) is a non-invasive technique used in the treatment of major depression. Meta-analyses have shown that it is more efficient than a placebo and that its efficacy is enhanced by the optimum tuning of stimulation parameters. However, the stimulation target, the dorsolateral prefrontal cortex (DLPFC), is still located using an inaccurate method. In this study, a neuronavigation system was used to perform a comprehensive quantification of target localization errors. We identified and quantified 3 sources of error in the standard method: cap repositioning, interexpert variability in coil positioning and distance between the stimulated point and the expected target. For cap repositioning, the standard deviation was lower than 5mm in the 3 axes. For interexpert variability in coil positioning, the spatial dispersion of the points was higher than 10mm in 2 of the 3 axes. For interindividual anatomical variability, the distance between the actual "reference" DLPFC and its standard determination was greater than 20mm for 54% of the subjects, while one subject out of eleven was correctly targeted which means 10mm or less from the reference. Results showed that interindividual anatomical variability and interexpert variability were the two main sources of error using the standard method. Results demonstrate that a neuronavigation system is mandatory to conduct reproducible and reliable studies.

Combining Functional Neuroimaging with Off-line Brain Stimulation: Modulation of Task-related Activity in Language Areas

Repetitive TMS (rTMS) provides a noninvasive tool for modulating neural activity in the human brain. In healthy participants, rTMS applied over the language-related areas in the left hemisphere, including the left posterior temporal area of Wernicke (LTMP) and inferior frontal area of Broca, have been shown to affect performance on word recognition tasks. To investigate the neural substrate of these behavioral effects, off-line rTMS was combined with fMRI acquired during the performance of a word recognition task. Twenty right-handed healthy men underwent fMRI scans before and after a session of 10-Hz rTMS applied outside the magnetic resonance scanner. Functional magnetic resonance images were acquired during the performance of a word recognition task that used English or foreign-language words. rTMS was applied over the LTMP in one group of 10 participants (LTMP group), whereas the homologue region in the right hemisphere was stimulated in another group of 10 participants (RTMP group). Changes in task-related fMRI response (English minus foreign languages) and task performances (response time and accuracy) were measured in both groups and compared between pre-rTMS and post-rTMS. Our results showed that rTMS increased task-related fMRI response in the homologue areas contralateral to the stimulated sites. We also found an effect of rTMS on response time for the LTMP group only. These findings provide insights into changes in neural activity in cortical regions connected to the stimulated site and are consistent with a hypothesis raised in a previous review about the role of the homologue areas in the contralateral hemisphere for preserving behavior after neural interference.

Baseline 'state anxiety' influences HPA-axis sensitivity to one sham-controlled HF-rTMS session applied to the right dorsolateral prefrontal cortex

Although negative results have been reported, an important aspect of the physiology of repetitive transcranial magnetic stimulation (rTMS) could be related to the endocrinological response of the hypothalamic-pituitary-adrenal (HPA) axis, such as cortisol secretion. Because endocrinological responses are influenced by anxiety states, this could influence the effect of rTMS in healthy individuals. In this sham-controlled, "single blind" crossover study, we examined whether one session of HF-rTMS could affect the HPA-system, when taking into account individual state anxiety scores based on the State-Trait Anxiety Inventory (STAI). Twenty-four healthy rTMS naïve females received one sham-controlled high frequency (HF)-rTMS session delivered on the right dorsolateral prefrontal cortex (DLPFC). The Profile of Mood States (POMS) questionnaire, together with salivary cortisol samples, was collected before, just after and 30 min post HF-rTMS. To examine whether state anxiety could influence endocrinological outcome measurements, we administered the STAI-state just before each HF-rTMS experiment started. Based on the POMS questionnaire, no mood changes were observed. Without taking individual state anxiety scores into account, one sham-controlled right-sided HF-rTMS session did not influence the HPA-system. When taking into account individual STAI-state scores, we found that healthy women scoring higher on the STAI-state displayed a significantly more sensitive HPA-system, resulting in salivary cortisol concentration increases after real HF-rTMS, compared to those scoring lower on this anxiety scale. Our results indicate that healthy women scoring high on state anxiety display a more sensitive HPA-system when receiving one right-sided HF-rTMS session. Our findings suggest that the incorporation of individual anxiety states in experimental rTMS research could add further information about its neurobiological influences on the HPA-system.

Neuropharmacological basis of rTMS-induced analgesia: the role of endogenous opioids

We investigated the role of endogenous opioid systems in the analgesic effects induced by repetitive transcranial magnetic stimulation (rTMS). We compared the analgesic effects of motor cortex (M1) or dorsolateral prefrontal cortex (DLPFC) stimulation before and after naloxone or placebo treatment, in a randomized, double-blind crossover design, in healthy volunteers. Three groups of 12 volunteers were selected at random and given active stimulation (frequency 10Hz, at 80% motor threshold intensity, 1500 pulses per session) of the right M1, active stimulation of the right DLPFC, or sham stimulation, during two experimental sessions 2 weeks apart. Cold pain thresholds and the intensity of pain induced by a series of fixed-temperature cold stimuli (5, 10, and 15°C) were used to evaluate the analgesic effects of rTMS. Measurements were made at the left thenar eminence, before and 1 hour after the intravenous injection of naloxone (bolus of 0.1mg/kg followed by a continuous infusion of 0.1mg/kg/h until the end of rTMS) or placebo (saline). Naloxone injection significantly decreased the analgesic effects of M1 stimulation, but did not change the effects of rTMS of the DLPFC or sham rTMS. This study demonstrates, for the first time, the involvement of endogenous opioid systems in rTMS-induced analgesia. The differential effects of naloxone on M1 and DLPFC stimulation suggest that the analgesic effects induced by the stimulation of these 2 cortical sites are mediated by different mechanisms. Endogenous opioids are shown to be involved in the analgesic effects of repetitive transcranial magnetic stimulation of the motor cortex.

Modulating spontaneous brain activity using repetitive transcranial magnetic stimulation

Background

When no specific stimulus or task is presented, spontaneous fluctuations in brain activity occur. Brain regions showing such coherent fluctuations are thought to form organized networks known as 'resting-state' networks, a main representation of which is the default mode network. Spontaneous brain activity shows abnormalities in several neurological and psychiatric diseases that may reflect disturbances of ongoing thought processes. Information about the degree to which such spontaneous brain activity can be modulated may prove helpful in the development of treatment options. We investigated the effect of offline low-frequency rTMS on spontaneous neural activity, as measured with fMRI, using a sequential independent-component-analysis and regression approach to investigate local changes within the default mode network.

Results

We show that rTMS applied over the left dorsolateral prefrontal cortex results in distal changes of neural activity, relative to the site of stimulation, and that these changes depend on the patterns of brain network activity during 'resting-state'.

Conclusions

Whereas the proximal changes may reflect the off-line effect of direct stimulation of neural elements, the distal changes likely reflect modulation of functional connectivity.

Functional connectivity of the temporo-parietal region in schizophrenia: effects of rTMS treatment of auditory hallucinations

Auditory-verbal hallucinations are a hallmark symptom of schizophrenia. In recent years, repetitive transcranial magnetic stimulation (rTMS) targeting speech perception areas has been advanced as a potential treatment of medication-resistant hallucinations. However, the underlying neural processes remain unclear. This study aimed to assess whether 1 Hz rTMS treatment would affect functional connectivity of the temporo-parietal junction (TPJ). Resting state fMRI scans were obtained from 18 patients with schizophrenia. Patients were assessed before and after a 6 day treatment with 1 Hz rTMS to the left TPJ, or placebo treatment with sham rTMS to the same location. We assessed functional connectivity between a priori defined regions-of-interest (ROIs) comprising the putative AVH network and the bilateral TPJ seed regions, targeted with rTMS. Symptom improvement following rTMS treatment was observed in the left rTMS group, whereas no change at occurred in the placebo group. Although no corresponding changes were observed in the functional connections previously found to be associated with AVH severity, an increase in connectivity between the left TPJ and the right insula was observed in group receiving rTMS to the left TPJ. The placebo group conversely showed a decrease in connectivity between the left TPJ and left anterior cingulate. We conclude that application of 1 Hz rTMS to the left TPJ region may affect functional connectivity of the targeted region. However, the relationship between these functional changes during the resting state and the rate of clinical improvement needs further clarification.

Influence of prefrontal target region on the efficacy of repetitive transcranial magnetic stimulation in patients with medication-resistant depression: a [(18)F]-fluorodeoxyglucose PET and MRI study

It is currently unknown whether the antidepressant effect of repetitive transcranial magnetic stimulation (rTMS) depends on specific characteristics of the stimulated frontal area, such as metabolic changes. We investigated the effect of high-frequency rTMS, administered over the most hypometabolic prefrontal area in depressed patients in a two-site, double-blind, randomized placebo-controlled add-on study. Forty-eight patients with medication-resistant major depression underwent magnetic resonance imaging and [(18)F]-fluorodeoxyglucose positron emission tomography (PET) in order to determine a target area for rTMS. After randomization to PET-guided (n = 16), standard (n = 18), or sham rTMS (n = 14) conditions, the patients received 10 sessions of 10-Hz rTMS (1600 pulses/session) at 90% motor threshold. Change from baseline in Montgomery-Asberg Depression Rating Scale (MADRS) scores did not differ between PET-guided, standard and sham groups at 2-wk end-point. Exploratory comparison of left PET-guided (n = 9), right PET-guided, standard, and sham rTMS revealed significant effects. The highest improvement in MADRS scores was observed with left PET-guided (60 + or - 31%), significantly superior to sham (30 + or - 37%, p = 0.01) and right-guided (31 + or - 33%, p = 0.02) stimulation. Comparison between left PET-guided and standard rTMS (49 + or - 28%) was not significant (p = 0.12). Comparison between stimulation over dorsolateral prefrontal cortex (BA 9-46), stimulation of other areas, and sham rTMS was statistically significant. Stimulation over BA 9-46 region (n = 15) was superior to sham rTMS (p = 0.02). The results do not support the general hypothesis of increased antidepressant effects of high-frequency rTMS with prefrontal hypometabolism-related PET guidance. Nonetheless, whether metabolism and anatomy characteristics of left frontal area underneath the coil might account for an increase or speeding up of rTMS effects needs further investigation.

Dual- and triple-acting agents for treating core and co-morbid symptoms of major depression: novel concepts, new drugs

The past decade of efforts to find improved treatment for major depression has been dominated by genome-driven programs of rational drug discovery directed toward highly selective ligands for nonmonoaminergic agents. Selective drugs may prove beneficial for specific symptoms, for certain patient subpopulations, or both. However, network analyses of the brain and its dysfunction suggest that agents with multiple and complementary modes of action are more likely to show broad-based efficacy against core and comorbid symptoms of depression. Strategies for improved multitarget exploitation of monoaminergic mechanisms include triple inhibitors of dopamine, serotonin (5-HT) and noradrenaline reuptake, and drugs interfering with feedback actions of monoamines at inhibitory 5-HT(1A), 5-HT(1B) and possibly 5-HT(5A) and 5-HT(7) receptors. Specific subsets of postsynaptic 5-HT receptors mediating antidepressant actions are under study (e.g., 5-HT(4) and 5-HT(6)). Association of a clinically characterized antidepressant mechanism with a nonmonoaminergic component of activity is an attractive strategy. For example, agomelatine (a melatonin agonist/5-HT(2C) antagonist) has clinically proven activity in major depression. Dual neurokinin(1) antagonists/5-HT reuptake inhibitors (SRIs) and melanocortin(4) antagonists/SRIs should display advantages over their selective counterparts, and histamine H(3) antagonists/SRIs, GABA(B) antagonists/SRIs, glutamatergic/SRIs, and cholinergic agents/SRIs may counter the compromised cognitive function of depression. Finally, drugs that suppress 5-HT reuptake and blunt hypothalamo-pituitary-adrenocorticotrophic axis overdrive, or that act at intracellular proteins such as GSK-3beta, may abrogate the negative effects of chronic stress on mood and neuronal integrity. This review discusses the discovery and development of dual- and triple-acting antidepressants, focusing on novel concepts and new drugs disclosed over the last 2 to 3 years.

Acute prefrontal rTMS increases striatal dopamine to a similar degree as D-amphetamine

Prefrontal repetitive transcranial magnetic stimulation (rTMS) has been shown to increase striatal dopaminergic activity. Here we investigated dopaminergic neurotransmission using single photon emission computed tomography (SPECT) and [(123)I]IBZM to indirectly assess the change in endogenous striatal dopamine concentration upon rTMS as compared with d-amphetamine challenge. SPECT imaging was performed twice each in five patients during rTMS, and in two patients who received 0.3 mg/kg D-amphetamine. Administration of rTMS led to a mean relative decrease in striatal IBZM binding by 9.6+/-6.2%, and d-amphetamine challenge (n=4) induced a mean relative reduction by 8+/-2.95% (difference not statistically significant). Acute rTMS challenge showed similar striatal dopaminergic effects to those associated with the administration of d-amphetamine, a substance known to increase synaptic dopamine.

Modulation of high-frequency (600 Hz) somatosensory-evoked potentials after rTMS of the primary sensory cortex

Somatosensory inputs to the primary sensory cortex (S1) after median nerve stimulation include temporally overlapping parallel processing, as reflected by standard low-frequency somatosensory-evoked potentials (LF-SEPs) and high-frequency SEPs (HF-SEPs), the latter being more sensitive to arousal and to other rapid adaptive changes. Experimental data suggest that cortical HF-SEPs are formed by two successive pre- and postsynaptic components, respectively, generated in the terminal part of thalamo-cortical radiation (early burst) and in specialized neuronal pools within S1 (later burst). In eight healthy subjects, slow (1 Hz) or rapid (10 Hz) repetitive transcranial magnetic stimulations (rTMS), which are known to induce opposite changes on cortical excitability, applied on S1 did not modify LF-SEPs, while HF-SEPs showed a series of dissociate changes in the early and later high-frequency burst, moreover occurring with a different time-course. Slow rTMS caused an immediate and lasting decrease of the later burst activity, coupled with an immediate increase of the earlier part of the burst, suggesting that inhibition of cortical excitability triggered opposite, compensatory effects at subcortical levels; rapid rTMS induced a delayed increase of later HF-SEPs, leaving unaltered the earlier subcortical burst. Findings causally demonstrate that LF- and HF-SEPs reflect two distinct functional pathways for somatosensory input processing, and that early and late high-frequency burst do actually reflect the activity of different generators, as suggested by experimental data. Possible underlying neurophysiological phenomena are discussed.

Assessing the neural correlates of self-enhancement bias: a transcranial magnetic stimulation study

Considerable research has focused on overly positive self-perceptions (self-enhancement), and yet little is known about the underlying neural mechanisms. The present study sought to assess the neural correlates of self-enhancement by applying Transcranial Magnetic Stimulation (TMS) to three brain regions. Twelve participants rated their best friend, as well as the self on a set of desirable or undesirable traits while TMS pulses were delivered in a virtual lesion manner. During the baseline condition (Sham TMS), participants produced more desirable and fewer undesirable ratings for themselves as compared to their best friend, showing self-enhancement. Compared to Sham TMS, TMS delivered to the Medial Prefrontal Cortex (MPFC) reduced self-enhancement whereas TMS delivered to the Supplementary Motor Area (SMA) and the precuneus did not. Together, these findings suggest that the MPFC may influence self-enhancement.

Induction of a mixed depressive episode during rTMS treatment in a patient with refractory major depression

Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive experimental technique which has mostly been investigated in the treatment of mood disorders with possible efficacy in depression. Among its potential side effects, there have been some reports of rTMS-induced (hypo)mania in the literature but none for rTMS-induced mixed episodes. We report the case of a 39-year-old woman suffering from refractory chronic major depression who developed a depressive mixed episode associated with a mild serotonin syndrome during her second week of rTMS treatment. She was receiving a combination of antidepressants, the doses of which were kept unchanged during rTMS treatment. Mixed as well as manic episodes may be induced by transcranial magnetic stimulation, complications already observed with antidepressants and electroconvulsive therapy. Therefore, caution should be exercised among clinicians using this experimental procedure, particularly in the treatment of bipolar depressed patients.

Lateralized and frequency-dependent effects of prefrontal rTMS on regional cerebral blood flow

Repetitive transcranial magnetic stimulation (rTMS) is a means to study the function and connectivity of brain areas. The present study addressed the question of hemispheric asymmetry of frontal regions and aimed to further understand the acute effects of high- and low-frequency rTMS on regional cerebral blood flow (rCBF). Sixteen healthy right-handed men were imaged using H(2)(15)O positron emission tomography (PET) immediately after stimulation. High (10 Hz)- and low (1 Hz)-frequency suprathreshold short-duration rTMS was applied over either the left or right dorsolateral prefrontal cortex (DLPFC). Slow and fast rTMS applied over the left DLPFC significantly increased CBF in the stimulated area. Compared to baseline, slow rTMS induced a significant increase in CBF contralateral to the stimulation site, in the right caudate body and in the anterior cingulum. Furthermore, slow rTMS decreased CBF in the orbitofrontal cortex (OFC, ipsilateral to stimulation side). Fast rTMS applied over the right DLPFC was associated with increased activity at the stimulation site, in the bilateral orbitofrontal cortex and in the left medial thalamus compared to 1-Hz rTMS. These results show that rCBF changes induced by prefrontal rTMS differ upon hemisphere stimulated and vary with stimulation frequency. These differential neurophysiological effects of short-train rTMS with respect to side and frequency suggest hemisphere-dependent functional circuits of frontal cortico-subcortical areas.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.