We discuss this and also link a great site that discusses this some as well. In some ways, the full mechanism of how exactly transcranial magnetic stimulation (TMS) helps depression is not completely understood. But there are some findings that give us a glimpse. The brain after all is quite complex and in and of itself remains unknown in many ways. In our heads, around 100 billion neurons are housed that connect to thousands of other neurons. They communicate and send information at a rate up to 268 mph according to Stanford University. However, disorders like major depressive disorder (MDD) are in part related to dysfunctional processing.
Now back to how exactly TMS has a role in relieving depression, per Mark George, who directs the Medical University of South Carolina, potentiation plays a role. Longitudinally, exciting these neurons create what is known is potentiation. The brain is being stimulated, trained to be more active and more efficient in the regions where depression affects it the most, the dorsolateral prefrontal cortex. Our brains have something known as synaptic plasticity, meaning that they can be trained. This however, is not just specific to TMS but can be exercised even in evidence based psychotherapy.
Other findings have also been found in the medical literature. In particular, after a course of TMS is completed, even levels of dopamine and serotonin which reached deficient concentrations seem to normalize. How exciting is that?!