I recently went through a round of rTMS and participated in a study that used EEG to attempt to find biomarkers for responders vs non-responders. This was largely based on previous findings that altered functional network activity in the brain (namely the default mode network) is correlated with depression in some people, and that EEG could relatively inexpensively detect functional network changes over the course of treatment. This study seems to follow a similar vein and I suspect we'll see more like it in the near future. I'm really glad to see more research being done with TMS - the particular protocol mentioned in this study (SAINT protocol) has had truly amazing success with 80-90% remission rate in already treatment-resistant individuals in a couple of studies. Even ECT, which is currently considered the most effective treatment for treatment-resistant depression, has only a 70-80% response/60% remission ("regular" rTMS is about 60% response/30% remission). The only problem is that SAINT requires fMRI which is expensive and complicated, on top of already expensive rTMS treatment. Hopefully as more research is done it'll become more accessible, personally it was very helpful for me in overcoming many years of intractable depression.