Chronic caffeine consumption curbs rTMS-induced plasticity

Embracing Internal States: A Review of Optimization of Repetitive Transcranial Magnetic Stimulation for Treating Depression

Repetitive transcranial magnetic stimulation (rTMS) is a rapid and effective therapy for major depressive disorder; however, there is significant variability in therapeutic outcomes both within and across individuals, with approximately 50% of patients showing no response to rTMS treatment. Many studies have personalized the stimulation parameters of rTMS (e.g., location and intensity of stimulation) according to the anatomical and functional structure of the brain. In addition to these parameters, the internal states of the individual, such as circadian rhythm, behavior/cognition, neural oscillation, and neuroplasticity, also contribute to the variation in rTMS effects. In this review, we summarize the current literature on the interaction between rTMS and internal states. We propose two possible methods, multimodal treatment, and adaptive closed-loop treatment, to integrate patients' internal states to achieve better rTMS treatment for depression.

The Role of Brain Derived Neurotrophic Factor Polymorphism in Transcranial Magnetic Stimulation Response for Major Depressive Disorder

OBJECTIVES

Repetitive transcranial magnetic stimulation (rTMS) is a safe and effective therapy for treatment-resistant depression (TRD). A crucial next step in improving rTMS therapy is to identify response predictors to inform patient selection criteria. Brain-derived neurotrophic factor (BDNF) exerts influence over TRD treatment modalities. BDNF polymorphism, Val66Met, has shown altered cortical plasticity after single-session rTMS in healthy subjects and clinical response in noninvasive brain stimulation methods in major depressive disorder, stroke, Alzheimer's, and cerebral palsy. We sought to evaluate the effect of this BDNF polymorphism on clinical response in a standard course of rTMS therapy for TRD.

METHODS

In this naturalistic study, 75 patients with TRD completed a standard course of rTMS with weekly clinical assessments via the Inventory of Depressive Symptomatology Self-Report (IDS-SR). BDNF polymorphisms were retrospectively compared in respect to treatment response and remission, baseline and final scores, percent change scores, and scores across the 6-week treatment course.

RESULTS

As expected, rTMS significantly decreased depressive symptoms as measured by IDS-SR scores. No difference was found in baseline, final, or percent change IDS-SR scores between polymorphism types. There was no difference between polymorphisms in IDS-SR scores across the treatment course. Response and remission rates did not differ between genotypes.

CONCLUSIONS

In contrast to previous research highlighting differential response between BDNF polymorphisms to motor plasticity and clinical rTMS outcomes, our data suggest that BDNF polymorphism status may not influence the response to a standard course of 10-Hz rTMS for major depressive disorder. Differences in TMS protocol, target, or BDNF serum levels may underlie our results.

Critically Assessing the Unanswered Questions of How, Where, and When to Induce Plasticity in the Posttraumatic Stress Disorder Network With Transcranial Magnetic Stimulation

Extinction of traumatic memory, a primary treatment approach (termed exposure therapy) in posttraumatic stress disorder (PTSD), occurs through relearning and may be subserved at the molecular level by long-term potentiation of relevant circuits. In parallel, repetitive transcranial magnetic stimulation (TMS) is thought to work through long-term potentiation-like mechanisms and may provide a novel, safe, and effective treatment for PTSD. In a recent failed randomized controlled trial we emphasized the necessity of correctly identifying cortical targets, the directionality of TMS protocols, and the role of memory activation. Here, we provide a systematic review of TMS for PTSD to further identify how, where, and when TMS treatment should be delivered to alleviate PTSD symptoms. We conducted a systematic review of the literature by searching for repetitive TMS clinical trials involving patients with PTSD and outcomes. We searched MEDLINE through October 25, 2023, for "TMS and PTSD" and "transcranial magnetic stimulation and posttraumatic stress disorder." Thirty-one publications met our inclusion criteria (k = 17 randomized controlled trials, k = 14 open label). Randomized controlled trial protocols were varied in terms of TMS protocols, cortical TMS targets, and memory activation protocols. There was no clear superiority of low-frequency (k = 5) versus high-frequency (k = 6) protocols or by stimulation location. Memory provocation or exposure protocols (k = 7) appear to enhance response. Overall, TMS appears to be effective in treating PTSD symptoms across a variety of TMS frequencies, hemispheric target differences, and exposure protocols. Disparate protocols may be conceptually harmonized when viewed as potentiating proposed anxiolytic networks or suppressing anxiogenic networks.

Effect of sleep quality on repetitive transcranial magnetic stimulation outcomes in depression

Introduction

While repetitive transcranial magnetic stimulation (rTMS) is effective for 50-60% of those treatment-resistant depression, it is critical to identify predictors of response for optimal patient selection to improve therapy. Insomnia is a known symptom of depression that is both correlated with depression severity and associated with poor antidepressant response. Therefore, understanding this relationship may open new opportunities for the optimization of rTMS treatment. We aimed to explore whether baseline sleep quality, specifically insomnia, is associated with rTMS outcomes in a naturalistic sample of 975 patients (age 18-90; 63.9% F) receiving a standard course of rTMS treatment from two outpatient TMS clinics located within psychiatric hospitals in the United States. One site additionally collected information on concurrent medication use on 350 patients; among these, we examined whether pharmacological treatment of insomnia affected TMS treatment response.

Methods

Depression was measured using the 30-item Inventory of Depressive Symptomology Self Report (IDS-SR) in site one and an abbreviated 16-item Quick Inventory of Depressive Symptomology (QIDS) derived from the IDS-SR in site two. Sleep disturbances were measured using three insomnia-related questions. Multilevel logistic regression was used to determine whether baseline insomnia scores were associated with TMS treatment outcome. Upon dichotomous categorization of the sample by insomnia and sleep-medication use, depression and sleep scores were analyzed across time using mixed repeated measures ANOVA.

Results

We found that sleep quality improves after TMS (p<.001) and correlates with improvement in non-insomnia related depression symptoms (r= .318, p<.001). We found that among those who had significant insomnia at baseline, those not using sleep medications had significantly worse post-treatment IDS-SR scores compared to those using sleep medications (p=. 021) despite no difference in final insomnia score.

Discussion

Together, our results suggest that while baseline insomnia is not associated with TMS effectiveness, treating insomnia may affect the trajectory of TMS therapy. Future prospective studies are needed to examine the effect of insomnia treatment alongside TMS for depression.

Combined effects of pharmacological interventions and intermittent theta-burst stimulation on motor sequence learning

Drugs that modulate N-methyl-D-aspartate (NMDA) or γ-Aminobutyric acid type A (GABA A ) receptors can shed light on their role in synaptic plasticity mechanisms underlying the effects of non-invasive brain stimulation. However, research on the combined effects of these drugs and exogenous stimulation on motor learning is limited. This study aimed to investigate the effects of pharmacological interventions combined with intermittent theta-burst stimulation (iTBS) on human motor learning. Nine right-handed healthy subjects (mean age ± SD: 31.56 ± 12.96 years; 6 females) participated in this double-blind crossover study. All participants were assigned to four drug conditions in a randomized order: (1) D-cycloserine (partial NMDA receptor agonist), (2) D-cycloserine + dextromethorphan (NMDA receptor agonist + antagonist), (3) lorazepam (GABA A receptor agonist), and (4) placebo (identical microcrystalline cellulose capsule). After drug intake, participants practiced the 12-item keyboard sequential task as a baseline measure. Two hours after drug intake, iTBS was administered at the primary motor cortex. Following iTBS, the retention test was performed in the same manner as the baseline measure. Our findings revealed that lorazepam combined with iTBS impaired motor learning during the retention test. Future studies are still needed for a better understanding of the mechanisms through which TMS may influence human motor learning.

NMDA and GABA Receptor-Mediated Plasticity Induced by 10-Hz Repetitive Transcranial Magnetic Stimulation

Although 10-Hz repetitive transcranial magnetic stimulation (rTMS) is an FDA-approved treatment for depression, we have yet to fully understand the mechanism through which rTMS induces therapeutic and durable changes in the brain. Two competing theories have emerged suggesting that 10-Hz rTMS induces N-methyl-D-aspartate receptor (NMDAR)-dependent long-term potentiation (LTP), or alternatively, removal of inhibitory gamma-aminobutyric acid receptors (GABARs). We examined these two proposed mechanisms of action in the human motor cortex in a double-blind, randomized, four-arm crossover study in healthy subjects. We tested motor-evoked potentials (MEPs) before and after 10-Hz rTMS in the presence of four drugs separated by 1-week each: placebo, NMDAR partial agonist d-cycloserine (DCS 100mg), DCS 100mg + NMDAR partial antagonist dextromethorphan (DMO 150mg; designed to "knock down" DCS-mediated facilitation), and GABAR agonist lorazepam (LZP 2.5mg). NMDAR agonism by DCS enhanced rTMS-induced cortical excitability more than placebo. This enhancement was blocked by combining DCS with NMDAR antagonist, DMO. If GABARs are removed by rTMS, GABAR agonism via LZP should lack its inhibitory effect yielding higher post/pre MEPs. However, MEPs were reduced after rTMS indicating stability of GABAR numbers. These data suggest that 10-Hz rTMS facilitation in the healthy motor cortex may enact change in the brain through NMDAR-mediated LTP-like mechanisms rather than through GABAergic reduction.

The future of brain circuit-targeted therapeutics

The principle of targeting brain circuits has drawn increasing attention with the growth of brain stimulation treatments such as transcranial magnetic stimulation (TMS), deep brain stimulation (DBS), and focused ultrasound (FUS). Each of these techniques can effectively treat different neuropsychiatric disorders, but treating any given disorder depends on choosing the right treatment target. Here, we propose a three-phase framework for identifying and modulating these targets. There are multiple approaches to identifying a target, including correlative neuroimaging, retrospective optimization based on existing stimulation sites, and lesion localization. These techniques can then be optimized using personalized neuroimaging, physiological monitoring, and engagement of a specific brain state using pharmacological or psychological interventions. Finally, a specific stimulation modality or combination of modalities can be chosen after considering the advantages and tradeoffs of each. While there is preliminary literature to support different components of this framework, there are still many unanswered questions. This presents an opportunity for the future growth of research and clinical care in brain circuit therapeutics.

Pharmacological adjuncts and transcranial magnetic stimulation-induced synaptic plasticity: a systematic review

BACKGROUND

Transcranial magnetic stimulation (TMS) is a noninvasive neurostimulation modality that has been used to study human synaptic plasticity. Leveraging work in ex vivo preparations, mechanistically informed pharmacological adjuncts to TMS have been used to improve our fundamental understanding of TMS-induced synaptic plasticity.

METHODS

We systematically reviewed the literature pairing pharmacological adjuncts with TMS plasticity-induction protocols in humans. We searched MEDLINE, PsycINFO, and Embase from 2013 to Mar. 10, 2023. Studies published before 2013 were extracted from a previous systematic review. We included studies using repetitive TMS, theta-burst stimulation, paired associative stimulation, and quadripulse stimulation paradigms in healthy and clinical populations.

RESULTS

Thirty-six studies met our inclusion criteria (28 in healthy and 8 in clinical populations). Most pharmacological agents have targeted the glutamatergic N-methyl-d-aspartate (NMDA; 15 studies) or dopamine receptors (13 studies). The NMDA receptor is necessary for TMS-induced plasticity; however, sufficiency has not been shown across protocols. Dopaminergic modulation of TMS-induced plasticity appears to be dose-dependent. The GABAergic, cholinergic, noradrenergic, and serotonergic neurotransmitter systems have small evidence bases supporting modulation of TMS-induced plasticity, as do voltage-gated calcium and sodium channels. Studies in clinical populations suggest that pharmacological adjuncts to TMS may rescue motor cortex plasticity, with implications for therapeutic applications of TMS and a promising clinical trial in depression.

LIMITATIONS

This review is limited by the predominance in the literature of studies with small sample sizes and crossover designs.

CONCLUSION

Pharmacologically enhanced TMS largely parallels findings from ex vivo preparations. As this area expands and novel targets are tested, adequately powered samples in healthy and clinical populations will inform the mechanisms of TMS-induced plasticity in health and disease.