Most such procedures you mention involve an interventional radiologist, using complex imaging modalities to carefully snake the device through your arteries. It's an extremely common procedure, because it is safe and relatively painless, considering. The article sites a procedure that would have occurred on patients TRIPPING ON LSD that had wires surgically implanted in their brain. IN THE 1950's. I guarantee that this procedure has become less invasive over time. Even so, such procedures are done with reluctance even today. Why? Because it's your brain, it's not a groin, an artery etc. We can tread heavily in certain areas of medicine, because we know the biology better, but the brain is still some very thin ice. Imagine how thin it was in the 1950s.
The brain is strangely robust and fragile at the same time. People with massive trauma to all kinds of shit can eventually regain almost 100% functionality as the brain routes around damaged areas. Or, you can get a microscopic clot in just the right area and die near-instantly. Crazy shit.
Ok that makes sense, and it also leaves me wondering how much of their data corresponds to the particular state of the patient during their trip which I'm just gonna assume would be the worst trip imaginable given the environment and experience. it would be interesting to see if the readings would be different if they were having a good time.