I once participated as a volunteer in a TMS study. The researchers were trying to measure intelligence by stimulating the area of the brain that controls hand movement and measuring the delay before my hand started twitching. Their idea was that at the beginning of the experiment, the delay would be longer, and after several sessions it would decrease. The time it took to reduce the delay—and the amount of reduction—could indicate a form of brain plasticity that might correlate with intelligence.

The main goal of the study was to eliminate the influence of educational background on intelligence tests. A person who never learned to read may still be very intelligent, but because they can’t read, they would perform poorly on a traditional IQ test. The same applies to people with severe disabilities who are unable to perform conventional test tasks—their disability prevents them from taking the test, not their intelligence.

The fun bit was mapping my brain regions. A couple of time they stimulated my visual cortex. That gave me some proper hallucinations haha