There are a lot of people who want to trace this stuff directly back to brain structures and brain functioning. And all of the stuff that we have seen has been false. So don’t get fooled by people who say they’ve mapped it all out or charted the differences. The actual, physical human brain consists of 100 billion neurons is much more complex than these simple combinations indicate.
So it is false to say that there are distinct ‘types’ of brains. But on the other hand, the types can give some general pointers to the overall brain structure. For example, when the brain gets aroused it produces a chemical called dopamine which is then slowly absorbed and drained out of the brain again. Now, in other psychology studies (where they were not working with this typology, but just in general) they found that people who are very extroverted tended to have larger faculties for draining the dopamine out of their brain again. In other words, these people can stomach far more thrills that other people before they have to withdraw to recuperate. And likewise, because these people are so quick to drain dopamine from the brain, they also tend to need stronger sense impressions to achieve the same level of stimulation as other people do. So for example, a “normal” person might get a thrill by riding a roller coaster. But someone who is not very strongly affected by normal levels of arousal might want to do something even wilder, like skydiving.
So, for example, very loosely concluded, you could say that if a person is an ESP type, he will also have a good chance of having a structure in the brain that is better at breaking down arousal chemicals than other types.
Likewise (although scientists don’t use these four-letter codes) other types of research have shown that if you are what would correspond to an ISJ type, then the area in the brain that deals with the perception of threats will tend to be physically larger. (And then ISJs will tend to react more strongly when shown a picture of something threatening.)
So to sum up there probably are some very general correlations between types and overall brain structures. But there is nothing certain and nothing to the level of detail that some people say. A lot of people love the theory of types and so they really want the types to be physically there, rather than just a nice psychological theory. This sometimes leads people to say dishonest things about the connection between types and brain science. So take care.