Have you ever cooked on an induction stove? It uses the principles of electromagnetics to transmit electrical energy wirelessly using magnets. Every electrical field is accompanied by a perpendicular magnetic field and vice versa. You can actually put a towel or a slab of wood in between an induction stove and a pot, and it'll go straight through the wood and heat the metal. That's because a magnetic field is transmitting electrical energy into the pot. Which immediately turns the electricity into heat through resistance. A wireless phone charger works the same way, it transmits electricity through magnets.

A TMS machine is basically a magnetic coil that costs thousands of dollars, and a capacitor kinda device that can store a shit ton of energy and send it into the magnetic coil all at once. The result is a really powerful magnetic field that only turns on for a split second. It's powerful enough to go straight through your skull and creature an electrical impulse in your cortical neurons. It can't do the subcortical (inside brain) parts, though. Only the surface.

You can use TMS for a lot. If you stimulate the motor cortex, you can cause muscle twitches all over the body. If you stimulate the prefrontal cortex, you can induce plasticity and aid learning. That's good for treating depression, because you can do cognitive behavioural therapy while having your prefrontal cortex zapped, and you learn healthy thought patterns faster. I haven't read about stimulating the parietal or occipital lobes, but I bet you can make people see things. Nothing complex, just flashes of light probably.

TMS is more like a hammer than a scalpel, since the brain is so complex and it's just sending a burst of electrical energy into a few million neurons. You've got 86 billion neurons in your brain, so if it hits 0.01% of your neurons, that's still 8 million. You can't achieve much precision with that. The motor cortex is the easiest place to do precise things, because it's so well organised and you get immediate visible feedback. You can find the part of the brain that controls the hands or the feet and stimulate that if you've got a steady grip. It's actually really fun. But good luck getting reliable results stimulating the prefrontal cortex.

The placebo effect is super strong in that chair, because as a participant you have no idea what to expect. You know this machine can make your involuntarily move your body, and that wows you so hard, you get super suggestible. You're thinking "if this machine can do that, and I just felt it do that, and I couldn't stop it if I tried, then what else can it do!" And so people get lots of random side effects from TMS even if you turn the machine off ten minutes in. You can pretend to stimulate non motor regions and the participant gets symptoms.

I'm not saying it's pseudoscience at all, I'm just saying, the random bullshit effects are pretty big compared to most forms of science. So you've got to have a control group to filter out the random bullshit effects. And with control group comparisons, you don't know what's happening in the moment, so you can't really correct for stuff as well. Double blind experiments are possible with TMS.