Look up Wada Test, where we shut down each hemisphere (one at a time) of the brain, while the patient is awake, to see how their personality changes without 1/2 their brain. Also stereo EEG. 200+ sensors placed in/on/around the brain, patient stays in bed for a week measuring brain activity. Here's the kicker... neurologists can plug into the brain and send teeny bits of electricity to each of the 200+ sensors individually to see what happens (typically this is for identifying seizure spots). Wish I didn't have to know this, but my partner is very epileptic, and has an RNS device implanted in her head. We upload her brain activity daily!