An excerpt from the article explaining what TMS is trying to change:
There are cortical and sub-cortical loops, or circuits, and generally with depressed patients, they have a lack of cortical control, or sort of decreased top down functioning, if you will, between these areas of the brain. Generally, when you stimulate or modulate the dorsolateral prefrontal cortex, there’s sort of this window into this cortical control circuit. What you see in time is increased blood flow, increased metabolism, and downward sort of top down control of maybe hyperactive or hyper-functioning circuits.
Read the article, “TMS: A Top Down Process”