Surprised to not see my personal metaphors for the suits and trumps: the four alchemical elements and the steps in the Hero's Journey, respectively. Probably goes to show how open to interpretation it is, and how it can be used to channel meaning when you can ascribe whatever meaning fits.
The idea behind ascribing meaning to the tarot is one of reinforcing symbols.
Think of the Tarot as a programming language for the mind.
The more one uses it, the more the rich symbols become grounded to one's individual psyche.
In the Western esoteric tradition (Hermetism), the human mind is viewed as a collection of disparate, autonomous, intelligences. What one considers to be his "Ego", his personality, can be modeled as an emergent illusion that arises out of the interplay of these underlying intelligences that are buried in the unconscious mind. What the alchemists called the King and Queen, the Eagle and the Lion, Mercury and Sulfur, what Carl Jung described as Anima, Animus and Shadow, what the Jewish Kabbalists describe as Sephirot, are all essentially these different aspects of the unconscious mind.
Using the Tarot in this fashion is an essential technique for bridging the gap between the conscious and the unconscious, as through repeated symbol reinforcement the unconscious obtains a way to "talk" to the conscious mind. Initially, through abstract "impressions" and "daydreams" and, if the process continues, through further crystallization and rigidity -- one may start seeing visions or hearing voices in his mind -- till the dissolution of the conscious ego and full-blown mystical experiences. One of the axioms of Alchemy -- Solve et Coagula -- refers to the practice of taking the human mind apart and reintegrating it. In the Hermetic tradition this is called Initiation. Carl Jung calls it Individuation.
The Tarot has been used in this fashion for hundreds of years, but this practical knowledge kept occult whilst different explanations ("divination") allowed to propagate in the popular sphere.
While Jungian archetypes describe compelling characters in terms of mythology, I don't believe they represent fundamental dimensions of the unconscious mind. Our neural wiring is unique enough that I don't think it can be reduced that way. If you look at brain activation in response to stimuli, it's remarkably inconsistent between individuals.
I do like the idea that Tarot cards let people more easily assume alternate positions with conviction. If this is accompanied by a mystical experience all the better - as long as it doesn't lead to doing something stupid.
Yet the brain still relies on hierarchies of models (or archetypes) to make any sense of the world at all. I mean, surely there is little variation in what people consider a nose or the sensation from touching a bumpy surface and how they would describe it. (I'm speculating here, of course.)
Thee difference you're referring to in activation in response to stimuli, as I understand it, is a result of the way and timeline that the models were learned, but it doesn't change the fact that the cortex relies on hierarchies of models to form a representation that we understand to be reality.
That is, if I understand you correctly and am not too outdated here.
the four suits are explicitly tied to the classical elements (swords = air, wands = fire, pentacles = earth, cups = water) and the source material for the cards is drawn directly from Western esoteric traditions, especially Hermeticism and Alchemy.
The Hero's Journey is Campbell's analysis of archetypal themes present in most mythologies, and especially in Ancient Near Eastern and medieval Eureopean hero stories. It maps well to the Major Arcana because they are both archetype maps of the same underlying cultural milieu.
