## 3 Brain Stimulation Techniques
### Exploring tMS as a Treatment Option for Depression  
Repetitive transcranial magnetic stimulation (rTMS) has been approved for the treatment of major depression for both mild and treatment-resistant forms since 2008 in the US and since 2015 in the UK. Although its effectiveness has been demonstrated in clinical trials worldwide, the accessibility of rTMS varies significantly between countries. While this therapy is more widespread in North America, in other regions, such as Europe, its uptake is slower and uneven, influenced by factors such as resource availability and national clinical guidelines [63].  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Therapeutic Approach** & **Type of Depression** & **Depression Rating Scales** & **Outcome** & **References** \\ \hline
12 sessions; & & Depression scores \(\backslash\)\(\backslash\)\(\backslash\)\(\backslash\) & \\
2 mA for 30 min & Unipolar depression & MADRS & (6 th and 8 th week) & [55] \\ (anode F3; cathode F4) & Bipolar depression & & Cognitive performance (e.g., paired association and social cognition) / & \\ \hline
10 sessions; & & Depression scores \(\backslash\)\(\backslash\)\(\backslash\)\(\backslash\) & \\
2 mA, 20 min & Unipolar danger depression & HDRS, BDI & (t1, immediately after treatment; t2, 15 d \\ (anode F3, cathode Fp2) & H & & after the end of treatment) & [53] \\ \hline
15 sessions; & & Unipolar depression & \\
2 mA for 20 min & Bipolar depression & HDRS, MADRS, BDI & Depression scores \(\backslash\)\(\backslash\)\(\backslash\)\(\backslash\) & \\ (anode F3, cathode F4) & Bipolar depression & & (10 sessions and 1 month) & [57] \\ \hline
10 sessions; & & & & \\
2 mA for 20 min & Unipolar major Depression & BDI & Depression scores \(\backslash\)\(\backslash\)\(\backslash\)\(\backslash\) & \\ (anode F3; cathode F4) & & & (2 nd, 4 th and 8 th week) & [58] \\ \hline
36 sessions (5 \(\times\) 3 \(\times\) 3 \(\times\) 7) & & & & \\
2 mA for 30 min & Major depressive Disorder & HDRS, MADRS & Depression scores \(\backslash\)\(\backslash\)\(\backslash\)\(\backslash\) & \\ (anode F3; cathode F4) & & & (10-week mean \(-\)4.01) & [59] \\ \hline \end{tabular}
\end{table}
Table 1: tDCS in patients with depression.  
Studies have demonstrated excellent tolerability of tMS at a dosage of 6000 stimuli daily and 30,000 weekly, with a motor-evoked potential of approximately 120% without eliciting adverse events. The primary concern is the risk of epileptic seizures, which have been shown to occur more commonly within the motor cortex stimulation site [16].  
In addition to pharmacotherapy, tMS treatment of depression is becoming a promising alternative for patients suffering from treatment-resistant depression. The neuroplasticity induced by tMS acts on both excitatory and inhibitory synapses. Several studies have shown an imbalance between excessive excitability and reduced cortical inhibition in patients with MDD, in addition to a reduced level of neuroplasticity in the PFC compared to healthy subjects [64].  
The two most commonly used rTMS protocols in the literature are high-frequency left PFC stimulation and low-frequency right PFC stimulation. Both are effective in treating depression with comparable effects, but the low-frequency one is better tolerated and has a lower risk of seizures [65].  
Although various studies and even meta-analyses reporting the clinical efficacy of rTMS in treating depression are often contradictory, rapid left frontal rTMS is generally supported as being effective, especially at higher doses and a greater number of sessions [66].