Comparison of clinical outcomes with two Transcranial Magnetic Stimulation treatment protocols for major depressive disorder

Personalized and Circuit-Based Transcranial Magnetic Stimulation: Evidence, Controversies, and Opportunities

The development of neuroimaging methodologies to map brain connectivity has transformed our understanding of psychiatric disorders, the distributed effects of brain stimulation, and how transcranial magnetic stimulation can be best employed to target and ameliorate psychiatric symptoms. In parallel, neuroimaging research has revealed that higher-order brain regions such as the prefrontal cortex, which represent the most common therapeutic brain stimulation targets for psychiatric disorders, show some of the highest levels of interindividual variation in brain connectivity. These findings provide the rationale for personalized target site selection based on person-specific brain network architecture. Recent advances have made it possible to determine reproducible personalized targets with millimeter precision in clinically tractable acquisition times. These advances enable the potential advantages of spatially personalized transcranial magnetic stimulation targeting to be evaluated and translated to basic and clinical applications. In this review, we outline the motivation for target site personalization, preliminary support (mostly in depression), convergent evidence from other brain stimulation modalities, and generalizability beyond depression and the prefrontal cortex. We end by detailing methodological recommendations, controversies, and notable alternatives. Overall, while this research area appears highly promising, the value of personalized targeting remains unclear, and dedicated large prospective randomized clinical trials using validated methodology are critical.

When to hold and when to fold: Early prediction of nonresponse to transcranial magnetic stimulation in major depressive disorder

BACKGROUND

Determining when to recommend a change in treatment regimen due to insufficient improvement is a common challenge in therapeutics.

METHODS

In a sample of 7215 patients with major depressive disorder treated with transcranial magnetic stimulation (TMS) and with PHQ-9 scores before, during and after the course, 3 groups were identified based on number of acute course sessions: exactly 36 sessions (N = 3591), more than 36 sessions (N = 975), and less than 36 sessions (N = 2649). Two techniques were used to determine thresholds for percentage change in PHQ-9 scores at assessments after 10, 20, and 30 sessions that optimized prediction of endpoint response status: the Youden index and fixing the false positive rate at 10%. Positive and negative predictive values were calculated to assess the accuracy of identifying final nonresponders and responders, respectively.

RESULTS

There was greater accuracy in predicting final response than nonresponse, especially in the groups that had at least 36 sessions. Substantial proportions of patients with low levels of early improvement were classified as responders at the end of treatment.

LIMITATIONS

The findings should be validated with clinician ratings using a more comprehensive depression severity scale.

CONCLUSIONS

Manifesting clinical improvement early in the TMS course is strongly predictive of final status as a responder, while lack of early improvement is a relatively poor indicator of final nonresponse status. The predictive value of lack of early symptomatic improvement is too low to make reliable recommendations regarding changes in treatment regimen.

Accelerated TMS - moving quickly into the future of depression treatment

Accelerated TMS is an emerging application of Transcranial Magnetic Stimulation (TMS) aimed to reduce treatment length and improve response time. Extant literature generally shows similar efficacy and safety profiles compared to the FDA-cleared protocols for TMS to treat major depressive disorder (MDD), yet accelerated TMS research remains at a very early stage in development. The few applied protocols have not been standardized and vary significantly across a set of core elements. In this review, we consider nine elements that include treatment parameters (i.e., frequency and inter-stimulation interval), cumulative exposure (i.e., number of treatment days, sessions per day, and pulses per session), individualized parameters (i.e., treatment target and dose), and brain state (i.e., context and concurrent treatments). Precisely which of these elements is critical and what parameters are most optimal for the treatment of MDD remains unclear. Other important considerations for accelerated TMS include durability of effect, safety profiles as doses increase over time, the possibility and advantage of individualized functional neuronavigation, use of biological readouts, and accessibility for patients most in need of the treatment. Overall, accelerated TMS appears to hold promise to reduce treatment time and achieve rapid reduction in depressive symptoms, but at this time significant work remains to be done. Rigorous clinical trials combining clinical outcomes and neuroscientific measures such as electroencephalogram, magnetic resonance imaging and e-field modeling are needed to define the future of accelerated TMS for MDD.

Efficacy of Using Intermittent Theta Burst Stimulation to Treat Negative Symptoms in Patients with Schizophrenia-A Systematic Review and Meta-Analysis

Negative symptoms in schizophrenia impose a significant burden with limited effective pharmacological treatment options. Recent trials have shown preliminary evidence for the efficacy of using intermittent theta burst stimulation (iTBS) in treating negative symptoms in schizophrenia. We aim to systematically review the current evidence of iTBS in the treatment of the negative symptoms of schizophrenia as an augmentation therapy. The study protocol was developed and registered on Prospero (registration ID: 323381). MEDLINE, EMBASE, Web of Science (Scopus), PsycINFO and Wan Fang databases were searched for sham-controlled, randomized trials of iTBS among patients with schizophrenia. The mean difference in major outcome assessments for negative symptoms was calculated. The quality of evidence was assessed using the Cochrane Risk of Bias Tool (version 1) and the GRADE system. Moreover, 12 studies including a total of 637 participants were included. Compared to sham treatment, the pooled analysis was in favor of iTBS treatment for negative symptoms (mean weight effect size: 0.59, p = 0.03) but not for positive symptoms (mean weight effect size: 0.01, p = 0.91) and depressive symptoms (mean weight effect size: 0.35, p = 0.16). A significant treatment effect was also observed on the iTBS target site left dorsal prefrontal cortex (mean weight effect size: 0.86, p = 0.007) and for stimulation with 80% motor threshold (mean weight effect size: 0.86, p = 0.02). Thus, our synthesized data support iTBS as a potential treatment for negative symptoms among patients with schizophrenia. However, the long-term efficacy and safety issues of iTBS in a larger population have yet to be examined.

Pretreatment pupillary reactivity is associated with differential early response to 10 Hz and intermittent theta-burst repetitive transcranial magnetic stimulation (rTMS) treatment of major depressive disorder (MDD)

BACKGROUND

Repetitive Transcranial Magnetic Stimulation (rTMS) is an effective treatment for Major Depressive Disorder (MDD). Two common rTMS protocols, 10 Hz and intermittent theta burst stimulation (iTBS), have comparable rates of efficacy in groups of patients. Recent evidence suggests that some individuals may be more likely to benefit from one form of stimulation than the other. The pretreatment pupillary light reflex (PLR) is significantly associated with response to a full course of rTMS using heterogeneous stimulation protocols.

OBJECTIVE

To test whether the relationship between pretreatment PLR and early symptom improvement differed between subjects treated with iTBS or 10 Hz stimulation.

METHODS

PLR was measured in 52 subjects who received solely 10 Hz (n = 35) or iTBS (n = 17) to left dorsolateral prefrontal cortex (DLPFC) for the first ten sessions of their treatment course. Primary outcome measure was the percent change of Inventory of Depressive Symptomatology - Self Report (IDS-SR) from session 1 to session 10.

RESULTS

There was a positive association between normalized maximum constriction velocity (nMCV) and early improvement in subjects receiving 10 Hz stimulation (R = 0.48, p = 0.004) and a negative association in subjects receiving iTBS (R = -0.52, p = 0.03). ANOVA revealed a significant interaction between nMCV and the type of initial stimulation (p = 0.001). Among subjects with low nMCV, those initially treated with iTBS showed 2.6 times greater improvement after 10 sessions (p = 0.01) than subjects initially receiving 10 Hz stimulation.

CONCLUSION

nMCV may detect physiologic differences between those likely to benefit from 10 Hz or iTBS treatment. Future studies should examine whether PLR could guide prospective treatment selection.

Transcranial Magnetic Stimulation-Induced Heart-Brain Coupling: Implications for Site Selection and Frontal Thresholding-Preliminary Findings

Background

Neurocardiac-guided transcranial magnetic stimulation (TMS) uses repetitive TMS (rTMS)-induced heart rate deceleration to confirm activation of the frontal-vagal pathway. Here, we test a novel neurocardiac-guided TMS method that utilizes heart-brain coupling (HBC) to quantify rTMS-induced entrainment of the interbeat interval as a function of TMS cycle time. Because prior neurocardiac-guided TMS studies indicated no association between motor and frontal excitability threshold, we also introduce the approach of using HBC to establish individualized frontal excitability thresholds for optimally dosing frontal TMS.

Methods

In studies 1A and 1B, we validated intermittent theta burst stimulation (iTBS)-induced HBC (2 seconds iTBS on; 8 seconds off: HBC = 0.1 Hz) in 15 (1A) and 22 (1B) patients with major depressive disorder from 2 double-blind placebo-controlled studies. In study 2, HBC was measured in 10 healthy subjects during the 10-Hz "Dash" protocol (5 seconds 10-Hz on; 11 seconds off: HBC = 0.0625 Hz) applied with 15 increasing intensities to 4 evidence-based TMS locations.

Results

Using blinded electrocardiogram-based HBC analysis, we successfully identified sham from real iTBS sessions (accuracy: study 1A = 83%, study 1B = 89.5%) and found a significantly stronger HBC at 0.1 Hz in active compared with sham iTBS (d = 1.37) (study 1A). In study 2, clear dose-dependent entrainment (p = .002) was observed at 0.0625 Hz in a site-specific manner.

Conclusions

We demonstrated rTMS-induced HBC as a function of TMS cycle time for 2 commonly used clinical protocols (iTBS and 10-Hz Dash). These preliminary results supported individual site specificity and dose-response effects, indicating that this is a potentially valuable method for clinical rTMS site stratification and frontal thresholding. Further research should control for TMS side effects, such as pain of stimulation, to confirm these findings.

Template MRI scans reliably approximate individual and group-level tES and TMS electric fields induced in motor and prefrontal circuits

Background

Electric field (E-field) modeling is a valuable method of elucidating the cortical target engagement from transcranial magnetic stimulation (TMS) and transcranial electrical stimulation (tES), but it is typically dependent on individual MRI scans. In this study, we systematically tested whether E-field models in template MNI-152 and Ernie scans can reliably approximate group-level E-fields induced in N = 195 individuals across 5 diagnoses (healthy, alcohol use disorder, tobacco use disorder, anxiety, depression).

Methods

We computed 788 E-field models using the CHARM-SimNIBS 4.0.0 pipeline with 4 E-field models per participant (motor and prefrontal targets for TMS and tES). We additionally calculated permutation analyses to determine the point of stability of E-fields to assess whether the 152 brains represented in the MNI-152 template is sufficient.

Results

Group-level E-fields did not significantly differ between the individual vs. MNI-152 template and Ernie scans for any stimulation modality or location (p > 0.05). However, TMS-induced E-field magnitudes significantly varied by diagnosis; individuals with generalized anxiety had significantly higher prefrontal and motor E-field magnitudes than healthy controls and those with alcohol use disorder and depression (p < 0.001). The point of stability for group-level E-field magnitudes ranged from 42 (motor tES) to 52 participants (prefrontal TMS).

Conclusion

MNI-152 and Ernie models reliably estimate group-average TMS and tES-induced E-fields transdiagnostically. The MNI-152 template includes sufficient scans to control for interindividual anatomical differences (i.e., above the point of stability). Taken together, using the MNI-152 and Ernie brains to approximate group-level E-fields is a valid and reliable approach.

Dosing transcranial magnetic stimulation in major depressive disorder: Relations between number of treatment sessions and effectiveness in a large patient registry

BACKGROUND

The number of sessions in an acute TMS course for major depressive disorder (MDD) is greater than in the earlier randomized controlled trials.

OBJECTIVE

To compare clinical outcomes in groups that received differing numbers of TMS sessions.

METHODS

From a registry sample (N = 13,732), data were extracted for 7215 patients treated for MDD with PHQ-9 assessments before and after their TMS course. Groups were defined by number of acute course treatment sessions: 1-19 (N = 658), 20-29 (N = 616), 30-35 (N = 1375), 36 (N = 3591), 37-41 (N = 626), or >41 (N = 349) and compared in clinical outcomes at endpoint and at fixed intervals (after 10, 20, 30, and 36 sessions). The impact of additional treatments beyond 36 sessions was also examined.

RESULTS

Groups that received fewer than 30 sessions had inferior endpoint outcomes than all other groups. PHQ-9 symptom reduction was greatest in the group that ended treatment at 36 sessions. The extended treatment groups (>36 sessions) differed from all other groups by manifesting less antidepressant response early in the course and had a slower but steady rate of improvement over time. Extending treatment beyond 36 sessions was associated with further improvement without evidence of a plateau.

CONCLUSIONS

In real-world practice, there are strong relations between the number of TMS sessions in a course and the magnitude of symptom reduction. Courses with less than 30 sessions are associated with diminished benefit. Patients with longer than standard courses typically show less initial improvement and a more gradual trajectory, but meaningful benefit accrues with treatment beyond 36 sessions.

Association between daily dose and efficacy of rTMS over the left dorsolateral prefrontal cortex in depression: A meta-analysis

Repetitive transcranial magnetic stimulation (rTMS) is a well-established, safe, and effective brain stimulation technique for depression; however, uniform parameters have not been used in clinical practice. The aim of this study was to identify the parameters that affect rTMS effectiveness and ascertain the range in which that parameter has optimal efficacy. A meta-analysis of sham-controlled trials using rTMS delivered over the left dorsolateral prefrontal cortex (DLPFC) in depression was conducted. In the meta-regression and subgroup analyses, all rTMS stimulation parameters were extracted and their association with efficacy was investigated. Of the 17,800 references, 52 sham-controlled trials were included. Compared to sham controls, our results demonstrated a significant improvement in depressive symptoms at the end of treatment. According to the results of meta-regression, the number of pulses and sessions per day correlated with rTMS efficacy; however, the positioning method, stimulation intensity, frequency, number of treatment days, and total pulses did not. Furthermore, subgroup analysis revealed that the efficacy was correspondingly better in the group with higher daily pulses. In clinical practice, increasing the number of daily pulses and sessions may improve the effectiveness of rTMS.

The timing of transcranial magnetic stimulation relative to the phase of prefrontal alpha EEG modulates downstream target engagement

BACKGROUND

The communication through coherence model posits that brain rhythms are synchronized across different frequency bands and that effective connectivity strength between interacting regions depends on their phase relation. Evidence to support the model comes mostly from electrophysiological recordings in animals while evidence from human data is limited.

METHODS

Here, an fMRI-EEG-TMS (fET) instrument capable of acquiring simultaneous fMRI and EEG during noninvasive single pulse TMS applied to dorsolateral prefrontal cortex (DLPFC) was used to test whether prefrontal EEG alpha phase moderates TMS-evoked top-down influences on subgenual, rostral and dorsal anterior cingulate cortex (ACC). Six runs (276 total trials) were acquired in each participant. Phase at each TMS pulse was determined post-hoc using single-trial sorting. Results were examined in two independent datasets: healthy volunteers (HV) (n = 11) and patients with major depressive disorder (MDD) (n = 17) collected as part of an ongoing clinical trial.

RESULTS

In both groups, TMS-evoked functional connectivity between DLPFC and subgenual ACC (sgACC) depended on the EEG alpha phase. TMS-evoked DLPFC to sgACC fMRI-derived effective connectivity (EC) was modulated by EEG alpha phase in healthy volunteers, but not in the MDD patients. Top-down EC was inhibitory for TMS pulses during the upward slope of the alpha wave relative to TMS timed to the downward slope of the alpha wave. Prefrontal EEG alpha phase dependent effects on TMS-evoked fMRI BOLD activation of the rostral anterior cingulate cortex were detected in the MDD patient group, but not in the healthy volunteer group.

DISCUSSION

Results demonstrate that TMS-evoked top-down influences vary as a function of the prefrontal alpha rhythm, and suggest potential clinical applications whereby TMS is synchronized to the brain's internal rhythms in order to more efficiently engage deep therapeutic targets.

Neurostimulation as a treatment for mood disorders in patients: recent findings

PURPOSE OF REVIEW

The use of neurostimulation to treat mood disorders dates back to the 1930s. Recent studies have explored various neurostimulation methods aimed at both restoring a healthy brain and reducing adverse effects in patients. The purpose of this review is to explore the most recent hypotheses and clinical studies investigating the effects of stimulating the brain on mood disorders.

RECENT FINDINGS

Recent work on brain stimulation and mood disorders has focused mainly on three aspects: enhancing efficacy and safety by developing new approaches and protocols, reducing treatment duration and chances of relapse, and investigating the physiological and pathological mechanisms behind treatment outcomes and possible adverse effects.This review includes some of the latest studies on both noninvasive techniques, such as transcranial magnetic stimulation, magnetic seizure therapy, transcranial direct current stimulation, transcranial alternating current stimulation, electroconvulsive treatment, and invasive techniques, such as deep brain stimulation and vagus nerve stimulation.

SUMMARY

Brain stimulation is widely used in clinical settings; however, there is a lack of understanding about its neurobiological mechanism. Further studies are needed to understand the neurobiology of brain stimulation and how it can be used to treat mood disorders in their diversity, including comorbidities with other illnesses.

Early Improvement Predicts Clinical Outcomes Similarly in 10 Hz rTMS and iTBS Therapy for Depression

Background

Prior studies have demonstrated that early treatment response with transcranial magnetic stimulation (TMS) can predict overall response, yet none have directly compared that predictive capacity between intermittent theta-burst stimulation (iTBS) and 10 Hz repetitive transcranial magnetic stimulation (rTMS) for depression. Our study sought to test the hypothesis that early clinical improvement could predict ultimate treatment response in both iTBS and 10 Hz rTMS patient groups and that there would not be significant differences between the modalities.

Methods

We retrospectively evaluated response to treatment in 105 participants with depression that received 10 Hz rTMS (n = 68) and iTBS (n = 37) to the dorsolateral prefrontal cortex (DLPFC). Percent changes from baseline to treatment 10 (t10), and to final treatment (tf), were used to calculate confusion matrices including negative predictive value (NPV). Treatment non-response was defined as <50% reduction in PHQ-9 scores according to literature, and population, data-driven non-response was defined as <40% for 10 Hz and <45% for iTBS.

Results

For both modalities, the NPV related to degree of improvement at t10. NPV for 10 Hz was 80%, 63% and 46% at t10 in those who failed to improve >20, >10, and >0% respectively; while iTBS NPV rates were 65, 50, and 35%. There were not significant differences between protocols at any t10 cut-off assessed, whether research defined 50% improvement as response or data driven kernel density estimates (p = 0.22-0.44).

Conclusion

Patients who fail to achieve >20% improvement by t10 with both 10 Hz rTMS and iTBS therapies have ~70% chance of non-response to treatment. With no significant differences between predictive capacities, identifying patients at-risk for non-response affords psychiatrists greater opportunity to adapt treatment strategies.

Corticomotor plasticity as a predictor of response to high frequency transcranial magnetic stimulation treatment for major depressive disorder

BACKGROUND

Many patients with treatment-resistant depression (TRD) respond to repetitive transcranial magnetic stimulation (rTMS) treatment. This study aimed to investigate whether modulation of corticomotor excitability by rTMS predicts response to rTMS treatment for TRD in 10 Hz and intermittent theta-burst stimulation (iTBS) protocols.

METHODS

Thirteen TRD patients underwent two evaluations of corticomotor plasticity-assessed as the post-rTMS (10 Hz, iTBS) percent change (%∆) in motor evoked potential (MEP) amplitude elicited by single-pulse TMS. Following corticomotor plasticity evaluations, patients subsequently underwent a standard 6-week course of 10 Hz rTMS (4 s train, 26 s inter-train interval, 3000 total pulses, 120% of motor threshold) to the left dorsolateral prefrontal cortex. Treatment efficacy was assessed by the Beck Depression Inventory II (BDI-II) and Hamilton Depression Rating Scale (HAM-D). The change in MEPs was compared between 10 Hz and iTBS conditions and related to the change in BDI-II and HAM-D scores.

RESULTS

Analyses of variance revealed that across all time-points, higher post-10 Hz MEP change was a significant predictor of greater improvement on the BDI-II (p < 0.001) and HAM-D (p = 0.022). This relationship was not observed with iTBS (p-values≥0.100). Post-hoc tests revealed the MEP change 20 min post-10 Hz was the strongest predictor of BDI-II improvement.

LIMITATIONS

Cortical excitability was measured from the motor cortex, rather than the dorsolateral prefrontal cortex, where treatment is applied. The 10 Hz and iTBS protocols were performed at different intensities consistent with common practice.

CONCLUSIONS

Modulation of corticomotor excitability by 10 Hz can predict response to rTMS treatment with 10 Hz rTMS.

Similar Outcomes in Treating Major Depressive Disorder With 10 Hz Repetitive Transcranial Magnetic Stimulation (rTMS) Versus Intermittent Theta Burst Stimulation (iTBS): A Naturalistic Observational Study

BACKGROUND

Results reported in the existing literature have shown intermittent theta burst stimulation (iTBS) to be noninferior to 10 Hz repetitive transcranial magnetic stimulation (rTMS) in treating major depressive disorder (MDD) when targeted at the left dorsolateral prefrontal cortex. The goal of this naturalistic observational study was to further explore potential differences between these 2 treatment modalities in treating depression in a real-world cohort.

METHODS

The participants were 105 patients, 18 years of age or older with a diagnosis of MDD who received standard clinical 10 Hz rTMS or iTBS treatment between 2016 and 2020. Clinical outcomes of depression treatment were assessed on the basis of changes in scores on the Patient Health Questionnaire-9 and on the Montgomery-Asberg Depression Rating Scale.

RESULTS

Reduction in depression symptoms was measured with the Patient Health Questionnaire-9 and Montgomery-Asberg Depression Rating Scale from baseline to end of treatment, and no discernible differences in percent change, response, remission, or minimum clinically important difference were found between the 10 Hz rTMS and iTBS treatment groups.

CONCLUSIONS

Findings in an observational, real-world clinical sample showed no significant differences in outcomes between 10 Hz rTMS and iTBS targeted at the left dorsolateral prefrontal cortex in the treatment of MDD. Because of the shorter treatment time involved, the choice of iTBS may reduce hospital exposure and increase savings and the treatment capacity of clinics without sacrificing effectiveness.

Prefrontal transcranial magnetic stimulation for depression in US military veterans - A naturalistic cohort study in the veterans health administration

BACKGROUND

Repetitive transcranial magnetic stimulation (TMS) is an evidence-based treatment for pharmacoresistant major depressive disorder (MDD), however, the evidence in veterans has been mixed. To this end, VA implemented a nationwide TMS program that included evaluating clinical outcomes within a naturalistic design. TMS was hypothesized to be safe and provide clinically meaningful reductions in MDD and posttraumatic stress disorder (PTSD) symptoms.

METHODS

Inclusion criteria were MDD diagnosis and standard clinical TMS eligibility. Of the 770 patients enrolled between October 2017 and March 2020, 68.4% (n = 521) met threshold-level PTSD symptom criteria. Treatments generally used standard parameters (e.g., left dorsolateral prefrontal cortex, 120% motor threshold, 10 Hz, 3000 pulses/treatment). Adequate dose was operationally defined as 30 sessions. MDD and PTSD symptoms were measured using the 9-item patient health questionnaire (PHQ-9) and PTSD checklist for DSM-5 (PCL-5), respectively.

RESULTS

Of the 770 who received at least one session, TMS was associated with clinically meaningful (Cohen's d>1.0) and statistically significant (all p<.001) reductions in MDD and PTSD. Of the 340 veterans who received an adequate dose, MDD response and remission rates were 41.4% and 20%, respectively. In veterans with comorbid PTSD, 65.3% demonstrated clinically meaningful reduction and 46.1% no longer met PTSD threshold criteria after TMS. Side effects were consistent with the known safety profile of TMS.

LIMITATIONS

Include those inherent to retrospective observational cohort study in Veterans.

CONCLUSIONS

These multisite, large-scale data supports the effectiveness and safety of TMS for veterans with MDD and PTSD using standard clinical approaches.

Targeting the Salience Network: A Mini-Review on a Novel Neuromodulation Approach for Treating Alcohol Use Disorder

Alcohol use disorder (AUD) continues to be challenging to treat despite the best available interventions, with two-thirds of individuals going on to relapse by 1 year after treatment. Recent advances in the brain-based conceptual framework of addiction have allowed the field to pivot into a neuromodulation approach to intervention for these devastative disorders. Small trials of repetitive transcranial magnetic stimulation (rTMS) have used protocols developed for other psychiatric conditions and applied them to those with addiction with modest efficacy. Recent evidence suggests that a TMS approach focused on modulating the salience network (SN), a circuit at the crossroads of large-scale networks associated with AUD, may be a fruitful therapeutic strategy. The anterior insula or dorsal anterior cingulate cortex may be particularly effective stimulation sites given emerging evidence of their roles in processes associated with relapse.

Psychiatric Applications of Repetitive Transcranial Magnetic Stimulation

Transcranial magnetic stimulation (TMS) is an increasingly popular noninvasive brain stimulation modality. In TMS, a pulsed magnetic field is used to noninvasively stimulate a targeted brain region. Repeated stimulation produces lasting changes in brain activity via mechanisms of synaptic plasticity similar to long-term potentiation. Local application of TMS alters activity in distant, functionally connected brain regions, indicating that TMS modulates activity of cortical networks. TMS has been approved by the U.S. Food and Drug Administration for the treatment of major depressive disorder, obsessive-compulsive disorder, and smoking cessation, and a growing evidence base supports its efficacy in the treatment of other neuropsychiatric conditions. TMS is rapidly becoming part of the standard of care for treatment-resistant depression, where it yields response rates of 40%-60%. TMS is generally safe and well tolerated; its most serious risk is seizure, which occurs very rarely. This review aims to familiarize practicing psychiatrists with basic principles of TMS, including target localization, commonly used treatment protocols and their outcomes, and safety and tolerability. Practical considerations, including evaluation and monitoring of patients undergoing TMS, device selection, treatment setting, and insurance reimbursement, are also reviewed.

The Problem and Potential of TMS' Infinite Parameter Space: A Targeted Review and Road Map Forward

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive, effective, and FDA-approved brain stimulation method. However, rTMS parameter selection remains largely unexplored, with great potential for optimization. In this review, we highlight key studies underlying next generation rTMS therapies, particularly focusing on: (1) rTMS Parameters, (2) rTMS Target Engagement, (3) rTMS Interactions with Endogenous Brain Activity, and (4) Heritable Predisposition to Brain Stimulation Treatments.

METHODS

We performed a targeted review of pre-clinical and clinical rTMS studies.

RESULTS

Current evidence suggests that rTMS pattern, intensity, frequency, train duration, intertrain interval, intersession interval, pulse and session number, pulse width, and pulse shape can alter motor excitability, long term potentiation (LTP)-like facilitation, and clinical antidepressant response. Additionally, an emerging theme is how endogenous brain state impacts rTMS response. Researchers have used resting state functional magnetic resonance imaging (rsfMRI) analyses to identify personalized rTMS targets. Electroencephalography (EEG) may measure endogenous alpha rhythms that preferentially respond to personalized stimulation frequencies, or in closed-loop EEG, may be synchronized with endogenous oscillations and even phase to optimize response. Lastly, neuroimaging and genotyping have identified individual predispositions that may underlie rTMS efficacy.

CONCLUSIONS

We envision next generation rTMS will be delivered using optimized stimulation parameters to rsfMRI-determined targets at intensities determined by energy delivered to the cortex, and frequency personalized and synchronized to endogenous alpha-rhythms. Further research is needed to define the dose-response curve of each parameter on plasticity and clinical response at the group level, to determine how these parameters interact, and to ultimately personalize these parameters.

Accelerated theta burst stimulation for the treatment of depression: A randomised controlled trial

INTRODUCTION

Theta burst pattern repetitive transcranial magnetic stimulation (TBS) is increasingly applied to treat depression. TBS's brevity is well-suited to application in accelerated schedules. Sizeable trials of accelerated TBS are lacking; and optimal TBS parameters such as stimulation intensity are not established.

METHODS

We conducted a three arm, single blind, randomised, controlled, multi-site trial comparing accelerated bilateral TBS applied at 80 % or 120 % of the resting motor threshold and left unilateral 10 Hz rTMS. 300 patients with treatment-resistant depression (TRD) were recruited. TBS arms applied 20 bilateral prefrontal TBS sessions over 10 days, while the rTMS arm applied 20 daily sessions of 10 Hz rTMS to the left prefrontal cortex over 4 weeks. Primary outcome was depression treatment response at week 4.

RESULTS

The overall treatment response rate was 43.7 % and the remission rate was 28.2 %. There were no significant differences for response (p = 0.180) or remission (p = 0.316) across the three groups. Response rates between accelerated bilateral TBS applied at sub- and supra-threshold intensities were not significantly different (p = 0.319). Linear mixed model analysis showed a significant effect of time (p < 0.01), but not rTMS type (p = 0.680).

CONCLUSION

This is the largest accelerated bilateral TBS study to date and provides evidence that it is effective and safe in treating TRD. The accelerated application of TBS was not associated with more rapid antidepressant effects. Bilateral sequential TBS did not have superior antidepressant effect to unilateral 10 Hz rTMS. There was no significant difference in antidepressant efficacy between sub- and supra-threshold accelerated bilateral TBS.