Practice makes plasticity: 10-Hz rTMS enhances LTP-like plasticity in musicians and athletes

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.

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 post-traumatic stress disorder (PTSD), occurs through relearning and may be subserved at the molecular level by long-term potentiation (LTP) of relevant circuits. In parallel, repetitive transcranial magnetic stimulation (rTMS) is thought to work through LTP-like mechanisms and may provide a novel, safe, and effective treatment for PTSD. Our recent failed randomized controlled trial (1) emphasizes the necessity of correctly identifying cortical targets, directionality of TMS protocol, and 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 searching for rTMS clinical trials involving PTSD patients and outcomes. We searched MEDLINE through October 25th, 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 (RCTs), k=14 open label). RCT protocols were varied in TMS protocols, cortical TMS targets, and memory activation protocols. There was no clear superiority across protocols of low-frequency (k=5) vs. high-frequency protocols (k=6), 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.

Repetitive transcranial magnetic stimulation (rTMS) as a tool for cognitive enhancement in healthy adults: a review study

As human beings, we have always sought to expand on our abilities, including our cognitive and motor skills. One of the still-underrated tools employed to this end is repetitive transcranial magnetic stimulation (rTMS). Until recently, rTMS was almost exclusively used in studies with rehabilitation purposes. Only a small strand of literature has focused on the application of rTMS on healthy people with the aim of enhancing cognitive abilities such as decision-making, working memory, attention, source memory, cognitive control, learning, computational speed, risk-taking, and impulsive behaviors. It, therefore, seems that the findings in this particular field are the indirect results of rehabilitation research. In this review paper, we have set to investigate such studies and evaluate the rTMS effectuality in terms of how it improves the cognitive skills in healthy subjects. Furthermore, since the most common brain site used for rTMS protocols is the dorsolateral prefrontal cortex (DLPFC), we have added theta burst stimulation (TBS) wave patterns that are similar to brain patterns to increase the effectiveness of this method. The results of this study can help people who have high-risk jobs including firefighters, surgeons, and military officers with their job performance.

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.

Anti-neuroinflammatory microRNA-146a-5p as a potential biomarker for neuronavigation-guided rTMS therapy success in medication resistant depression disorder

Treatment-resistant depression (TRD) is a challenging issue to address. Repetitive transcranial magnetic stimulation (rTMS) is commonly used but shows varying efficacy, necessitating a deeper understanding of depression physiology and rTMS mechanisms. Notably, an increasing amount of recent data has displayed the connection of TRD and its clinical outcome with chronic inflammatory processes. The current study included 19 TRD patients undergoing rTMS and 11 depressed patients responding to medication as a comparison group. We assessed therapeutic efficacy using MADRS, HAM-D-17, GAD-7, and PHQ-9 tests. Inflammatory markers, neurotrophins, and associated miRNAs were measured in patients blood serum before and during treatment. A control group of 18 healthy individuals provided baseline data. The results of our study showed significantly higher levels of pro-inflammatory interleukins-6 and - 8 in TRD patients compared to drug-responders, which also related to more severe symptoms before treatment. In addition, TRD patients, both before and during treatment, exhibited higher average blood serum concentrations of pro-inflammatory interleukin-18 and lower levels of anti-neuroinflammatory miR-146a-5p compared to healthy controls. We also observed that the expression of miR-16-5p, miR-93-5p, and especially miR-146a-5p correlated with clinical changes following rTMS. Our study confirmed that TRD patients possess a higher inflammatory status, while the anti-neuroinflammatory miR-146a-5p was demonstrated to have a considerable potential for predicting their rTMS treatment success.

Intermittent theta burst stimulation to the left dorsolateral prefrontal cortex improves cognitive function in polydrug use disorder patients: a randomized controlled trial

Background

Polydrug abuse is common among opioid users. Individuals who use both heroin and methamphetamine (MA) have been shown to experience a wide range of cognitive deficits. Previous research shows that repetitive transcranial magnetic stimulation (rTMS) can change cerebral cortical excitability and regulate neurotransmitter concentration, which could improve cognitive function in drug addiction. However, the stimulation time, location, and possible mechanisms of rTMS are uncertain.

Methods

56 patients with polydrug use disorder were randomized to receive 20 sessions of 10 Hz rTMS (n = 19), iTBS (n = 19), or sham iTBS (n = 18) to the left DLPFC. All patients used MA and heroin concurrently. Cognitive function was assessed and several related proteins including EPI, GABA-Aα5, IL-10, etc. were quantified by ELISA before and after the treatment.

Results

Baseline RBANS scores were lower than normal for age (77.25; IQR 71.5-85.5). After 20 treatment sessions, in the iTBS group, the RBANS score increased by 11.95 (95% CI 0.02-13.90, p = 0.05). In particular, there were improvements in memory and attention as well as social cognition. Following treatment, serum EPI and GABA-Aα5 were reduced and IL-10 was elevated. The improvement of immediate memory was negatively correlated with GABA-Aα5 (r = -0.646, p = 0.017), and attention was positively correlated with IL-10 (r = 0.610, p = 0.027). In the 10 Hz rTMS group, the improvement of the RBANS total score (80.21 ± 14.08 before vs.84.32 ± 13.80 after) and immediate memory (74.53 ± 16.65 before vs.77.53 ± 17.78 after) was statistically significant compared with the baseline (p < 0.05). However, compared with the iTBS group, the improvement was small and the difference was statistically significant. There was no statistically significant change in the sham group (78.00 ± 12.91 before vs.79.89 ± 10.92 after; p > 0.05).

Conclusion

Intermittent theta burst stimulation to the left DLPFC may improve cognitive function in polydrug use disorder patients. Its efficacy appears to be better than that of 10 Hz rTMS. The improvement of cognitive function may be related to GABA-Aα5 and IL-10. Our findings preliminarily demonstrate the clinical value of iTBS to the DLPFC to augment neurocognitive recovery in polydrug use disorders.