**Core Concept**
Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive neurostimulation technique that uses magnetic fields to stimulate brain activity. It has been explored for various neurological and psychiatric conditions, including depression.

**Why the Correct Answer is Right**
The US FDA has approved rTMS for the treatment of major depressive disorder (MDD). This approval is based on clinical trials that demonstrated the efficacy of rTMS in reducing symptoms of depression in patients who have not responded to other treatments. The exact mechanism of action of rTMS is not fully understood, but it is thought to involve modulation of neural circuits in the brain, particularly those involved in mood regulation.

**Why Each Wrong Option is Incorrect**
**Option A:** rTMS is not typically used for the treatment of anxiety disorders, although it may be used off-label in some cases. **Option B:** While rTMS has been studied in various other conditions, including obsessive-compulsive disorder and post-traumatic stress disorder, it is not FDA-approved for these indications. **Option C:** rTMS is not commonly used for the treatment of schizophrenia.

**Clinical Pearl / High-Yield Fact**
It's worth noting that rTMS is typically used in conjunction with other treatments for depression, such as medications or psychotherapy.

**Correct Answer:** C. Major depressive disorder (MDD).