[DIYbio] Re: transcranial magnetic stimulation (TMS) circuit model

No, look. TMS and tDCS are different things. Transcranial magnetic stimulation (TMS) is strong, spatially focused magnetism applied to superficial brain tissue through the skull; this isn't usually DIY'd, as it requires expensive and powerful equipment and is considered safe only when used with some expertise. Transcranial direct current stimulation (tDCS) is running a weak current through the skull, which diffuses across the total path of least resistance between the electrodes, passing through some obvious/predictable and a lot of non-obvious/poorly-predictable brain tissue in so doing; this one is often DIY'd, since the equipment is extremely affordable to put together, and when you stick within certain protocol parameters it is pretty generally safe-ish. ECT isn't generally considered part of the tDCS spectrum.

A fair bit is known about their mechanisms, but they're not so easily explained. The brief summary is that neurons are electrical signalling nodes that decide whether or not they fire based on currents passing through their membranes, and changing electrical or magnetic fields across the susceptible parts of these membranes will therefore change their firing behavior. When you have a lot of neurons that are aligned in the same direction, as in the important projecting neurons of the neocortex, changing a magnetic or electric field across all of them can have predictable effects. So when you can aim the current or magnetism at a piece of neocortex of which you (partially) know what it does, and that happens to be aligned so that you can hit it in the right direction with electrodes placed on the skull, you can make educated guesses at what the effects are going to be.

Mostly, these stimulation methods are used as research tools, and in this they are pretty well established, especially TMS. There are large literatures about their use in figuring out brain activity-behavior relationships. You use them to show causally that brain area X is involved in cognitive process Y, and provide some puzzle pieces as to in what way. Knowing that they do change neuronal behavior - and this has really been established beyond reasonable doubt - the theoretical probability of their usefulness in achieving desired cognitive effects when you find the right protocol is pretty good. However, this is a far less developed field, although quite a few protocol-disease pairings have gained noteworthy traction. I'm not certain about any being FDA-approved as of yet, although I think some might be? Here's a grab with a clinical theme, TMS for depression and tDCS for schizophrenia:

https://scholar.google.nl/scholar?q=TMS+depression&hl=en&as_sdt=0%2C5&as_ylo=2010&as_yhi=
https://scholar.google.nl/scholar?q=tDCS+schizophrenia&btnG=&hl=en&as_sdt=0%2C5&as_ylo=2010

However, if you want to get more confident about their fundamental effectiveness, you might be better off taking a step back to more fundamental research:
https://scholar.google.nl/scholar?q=transcranial+magnetic+stimulation+mechanism&btnG=&hl=en&as_sdt=0%2C5&as_ylo=2000