This is well written and informative I think. This was interesting:
"The neurology behind the functions
To repeat, every person goes through life having to process both tangible ("concrete") and conceptual ("abstract") information, and then make both technical (impersonal, logical) and humane (personal, value) judgments. Where our type theory begins; and the whole key to it, is in the way this processing affects us emotionally.
From a neurological standpoint, the "limbic system"; the basic emotional part of the brain that deals with natural reactions such as "fight or flight", is to be distinguished from the frontal cortex, which gives us our distinctively human abilities of awareness, and our cognitive faculties. The functions can be seen as representing different ways of building neurological connections from the frontal cortex back to the limbic area, whose motives reach awareness as images freighted with emotion. (Which are generally forms of "archetypes", as was just discussed). An example of this is when something happens, and we use a metaphor to convey how we feel. These images are filled out by personal experience. The functions translate this limbic motivation into cognitive data, allowing us to redirect the instinctual "energies" the limbic system mobilizes to activities that have individual meaning for us.
The way this works, is that we're faced with a situation. We take in data from what is happening. If it is a negative situation, then our instinctual reactions and emotions such as fear kick in, just like they do for animals. The difference is that the animals remain guided by the instincts. Both have "sensation" of what is happening, but the human cortex interprets the data, and if the preference is Sensation itself, then the person will normally be a bit more inclined than others focus more on what is seen, heard, felt, etc. and react to it based on these factors. If the preference is iNtuition, the person will instead be inclined to connect the data to a larger meaning that is not immediately seen, such as the possible or likely outcomes.
If the person prefers Thinking, they will be normally inclined to focus on the cause and effect of the impersonal elements of the situation, both in analyzing why it happened, as well as in deciding on courses of action. If the person prefers Feeling, they will be more inclined to focus on the more "humane" or personal aspects of the situation. How it affects people, especially emotionally. That any courses of action should take into consideration their needs and well being.
The types all went through the same situation, yet the functions interpreted it differently, and this by focusing on different aspects of it.
Each person will generally prefer one of the first two, to take in information, and one of the second two, to make decisions. However, depending on the situation, the person might use the other functions instead.
Most of these links that we've built from the cognitive brain back to the emotional brain belong to the function we've differentiated. This creates an Ego-identity.
The products of undifferentiated functions (i.e. the aforementioned "senses of meaning") can reach consciousness, but only inasmuch as they're serving dominant goals.
What this means, again, is something that is easy to forget in discussions, and that is that all types engage in behavior associated with all functions. What will be different in each type is the goal the function is working towards, which will be determined by the dominant and its perspective. This is key to understanding the common notion of "using" other functions (which often causes people to be uncertain of their or others' type).
Lenore suggests, taking from Jung, functional differentiation is actually a wound on the psyche (Personality Pathways). Without any functions differentiated, nothing would be suppressed either!
For instance, when a loved one dies, the reaction of human "temperament" (as distinct from the four or more "temperaments") is to mourn. (It is not a specific "Feeler" trait, though it can be considered a kind of "feeling"!) However, a person who prefers Thinking might be less likely to openly display the emotion, as opposed, of course, to those who do prefer Feeling, who will display a lot of emotion. The Thinker with his detached "impersonal" focus feels he has less control over emotions (while the humanely focused Feeler does have more control over them, and thus is more willing to display them). Hence, as evidenced by the Thinker in this example, something has actually been lost.
She has also pointed out that the ego will have an emotional investment in whichever its dominant function is. Many people will mistake any "emotion" for a Feeling "use" or preference, when it is not necessarily.
The way this worked for me, is that I actually had an emotional "attachment" for detached analysis! Seems kind of contradictory, and it was hard to determine when reading so many descriptions that associated Thinking strictly with "detachment" and Feeling with [emotional] "attachment", without allowing for undifferentiated functions that determine the ego's dispositions in the first place.
Continuing (Personality Type, p86), she says that when a cell is close to death, it eliminates the biochemical blocks on its genes, and it has the potential to start over.
Likewise, typologcally, we are ready to grow, and receive more influence from other functions. This is individuation, and the true goal of type which has been misconstrued as "developing all the functions". So what we call "developing" the functions is simply different senses of meaning coming into consciousness."