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The present protocol describes the application of repetitive transcranial magnetic stimulation (rTMS), where a subregion of the dorsolateral prefrontal cortex (DLPFC) with the strongest functional anticorrelation with the subgenual anterior cingulate cortex (sgACC) was located as the stimulation target under the assistance of a fMRI-based neuronavigation system.
To achieve greater clinical efficacy, a revolution in treatment for major depressive disorder (MDD) is highly anticipated. Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive and safe neuromodulation technique that immediately changes brain activity. Despite its wide application in the treatment for MDD, the treatment response remains different among individuals, which may be attributable to the inaccurate positioning of the stimulation target. Our study aims to examine whether the functional magnetic resonance imaging (fMRI)-assisted positioning improves the efficacy of rTMS in treating depression. We intend to identify and stimulate the subregion of dorsolateral prefrontal cortex (DLPFC) in MDD with strongest anti-correlation with the subgenual anterior cingulate cortex (sgACC), and to conduct a comparative investigation of this novel method and the traditional 5-cm rule. To achieve more precise stimulation, both methods were applied under the guidance of neuronavigation system. We expected that the TMS treatment with individualized positioning based on resting state functional connectivity may show better clinical efficacy than the 5-cm method.
Major depressive disorder (MDD) is characterized by significant and persistent depression, and in more severe cases, patients can encounter hallucinations and/or delusions1,2. Compared with the general population, the risk of suicide among MDD patients is approximately 20 times higher3. While medication is currently the most used treatment for MDD, 30% - 50% of the patients lack adequate response to antidepressants4. For the responders, the symptom improvement tends to appear after a relatively long latent period and is accompanied by side effects. Psychotherapy, although effective for some patients, is costly and time-consuming. A safer and more effective treatment for MDD is therefore urgently required.
Repetitive transcranial magnetic stimulation (rTMS)is a non-invasive and safe technique and has been approved for the treatment of various mental disorders5,6,7. Although its therapeutic mechanism remains unclear, rTMS was speculated to work by regulating the activity of the stimulated brain regions and the neural plasticity8,9,10, thus normalizing specific functional networks10,11,12. rTMS also causes network effect, which evokes changes in remote brain areas through connection pathways, leading to an amplified therapeutic effect13. Although rTMS changes brain activity immediately and robustly, its response rate in the treatment of MDD is only about 18%14. The main reason may be the inaccurate location of stimulation targets15.
The subgenual anterior cingulate cortex (sgACC) is mainly responsible for emotional processing and plays a role in regulating the response to stressful events, emotional response to internal and external stimuli, and emotional expression16,17,18. This subregion of ACC shares substantial structural and functional connectivity with the cerebral cortex and the limbic system19,20. Interestingly, studies have shown that the post-stimulation activity of this area is closely related to the clinical efficacy of TMS. For instance, the blood flow of sgACC decreased after a course of TMS targeted on the right dorsolateral prefrontal cortex (DLPFC), which was associated with the alleviation of depressive symptoms21. Vink et al.8 found that stimulation targeted on DLPFC was propagated to sgACC, and suggested that sgACC activity can be a biomarker of the treatment response of TMS. According to previous researches, Fox and colleagues22 proposed that targeting on a subregion of DLPFC that shows strongest functional anti-connectivity with sgACC (MNI coordinate: 6, 16, -10) enhances the antidepressant effect. Here, we demonstrate a study protocol aimed to examine this hypothesis.
Inform all participants about the study and ask them to sign the informed consent form prior to the start of the study. The present protocol was approved by the Research Ethics Committee of the Affiliated Brain Hospital of Guangzhou Medical University.
NOTE: In this double-blind study, patients with depression were randomly divided into two groups. In the experimental group, stimulation targets are located by the DLPFC-sgACC-based individualized location method (Please see 3.3 for detailed description). The targets of the control group are obtained by the average 5-cm method (i.e. (-41, 16, 54))22.
1. Participants' selection
2. Preparation of Magnetic Resonance Imaging (MRI) and TMS
3. Treatment (Figure 1)
4. Clinic data collection (Figure 1b)
ROI-wise FC analysis should show that sgACC is significantly anti-correlated with DLPFC, in which the strongest negative correlation is the stimulus target to be chosen. Significant anti-correlation between the sgACC-DLPFC functional connectivity and the treatment response should be found in the correlation analysis33.
The current protocol is based on an innovative TMS targeting method that no previous studies have applied. Here we present results from an fMRI-guided TM...
The sgACC is responsible for emotional processing and plays an important role in stress regulation16,17,18. A study suggests that targeting on a subregion of DLPFC that shows strongest functional anti-connectivity with sgACC (6, 16, -10) may enhance the antidepressant effect25. Therefore, precisely locating this target is the critical step of this protocol. Before the stimulation, the borders of the brain...
Authors have no disclosures to report.
The study was funded by China Postdoctoral Science Foundation funded project (2019M652854) and Natural Science Foundation of Guangdong, China (Grant No. 2020A1515010077).
Name | Company | Catalog Number | Comments |
3T Philips Achieva MRI scanner | Philips | ||
Harvard/Oxford cortical template | http://www.cma.mgh.harva rd.edu/ | ||
MATLAB | MathWorks | ||
SPM12 | http://www.fil.ion.ucl.ac.uk/spm | ||
The Visor2 system | ANT Neuro | The Visor2 software, the optical tracking system, tracking tools and calibration board are part of the visor2 system. | |
TMS device | Magstim, Carmarthenshire, UK |
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