## 3 Brain Stimulation Techniques
However, rTMS is noninvasive and does not require anesthesia, making it a safer, easier-to-administer alternative with fewer cognitive side effects. It is thus widely accepted and more convenient for outpatient settings, especially for patients averse to ECT's invasiveness. tDCS is the least invasive and least costly of the three, making it accessible in outpatient and even home-based treatments. This portability and its mild side effect profile make tDCS favorable for prolonged treatment regimens and combination therapies [37]. As a limitation, ECT is associated with cognitive side effects, particularly memory loss, which can be both short-term and longer-lasting. Stigma and the need for anesthesia further limit its acceptability despite its efficacy. rTMS requires daily sessions over several weeks  
Figure 2: (**A**) Example of tMS coil placement and electromagnetic flow. (**B**) Example of an Electroconvulsive therapy (ECT) device electrode placement (generated with Biorender). to achieve a clinical response, making it logistically demanding. While it is well-tolerated, its efficacy can be limited, particularly in patients with severe depression. tDCS efficacy in TRD is not consistently established, and results are typically less robust than ECT or rTMS. Its lower intensity of stimulation means slower response rates and its clinical effectiveness is highly dependent on proper application techniques, which vary across studies [37]. Transcranial DCS (tDCS) as a practical depression intervention is mainly due to its portable design, accessibility, and easy-to-use configuration. The method has shown promise in improving neurological conditions, including depression, migraines, and motor deficits, by delivering low-level electrical currents to specific brain regions. Achieving consistent results depends on carefully calibrated factors--electrode placement, current intensity, and session duration--that researchers meticulously manage in clinical studies but can be harder to regulate outside the lab. Despite the popularity of tDCS for both therapeutic and cognitive enhancement purposes, its efficacy outside controlled environments can be inconsistent due to these varying parameters and individual differences in responsiveness to stimulation [38]. The real-world application of tDCS introduces practical challenges, notably patient adherence and the requirement for trained professionals to supervise sessions. Although some patients can independently use home-based tDCS devices, adherence to treatment schedules may decrease without the structured oversight typical of clinical settings. Electrode placement significantly impacts the results of tDCS as a method of treating depression. Inappropriate placement, even with relatively minor differences, can significantly influence the results, decreasing the effectiveness of the intervention or causing patient dissatisfaction. For individuals who do not have regular access to trained professionals, maintaining consistent, high-quality tDCS treatments can be a challenge [39]. The widespread use of tDCS is influenced by safety concerns. Although it is generally considered a safe method, especially compared to more invasive neuromodulation methods, the efficacy and safety of tDCS depend on compliance with specific parameters that may not always be controllable. Scientific research precisely controls various parameters to avoid adverse effects, but in a non-clinical setting, there is a risk of misuse. Not respecting the guidelines regarding session duration, electrode placement, or current intensity can lead to ineffective or even unsafe results, especially if the patient is to use tDCS outside of clinical supervision [38]. Despite these limitations of tDCS, there is a steady improvement in methods to make it more adaptable for unsupervised use. Devices are now easier to use, and misuse can be prevented through features such as preset stimulation parameters and fixed or guided electrode placement. This reduces risks and improves accessibility for non-professional users.