Your question is of the same type as: « Does the Freudian triptych id-ego-superego exist physically? » or, « Does the Big Five model of personality exist physically? ». I purposely took an old and a new model because both are… models. Like Jung’s. The answer I propose is for all these questions.
Cognitive functions are invisible at the level of neural excitation. Their organization is not perceptible even with perfect knowledge of the physiology of the neuron. This is not the right model. Just as a physicist, having the standard model to describe with incredible precision the ballet of atomic fields, would be even further from the count. We need a model of patterns formed by neurological signals.
The closest organization of neural excitations is the treatment of elementary sensory signals. The model of a sensorimotor reflex is very simple: sensitive excitation triggering an impulse motor with sometimes very few intermediary relays. Easy to follow anatomically, it does not matter if hundreds of thousands of neurons participate. They are all part of the same organization level. This simple model of treatment of sensory afference has made the success of the multi-centric vision of the brain: visual, auditory, locomotor, visceral, memory, emotional, etc… But what happens next? What becomes of the signals that undertake loops more complicated than the simple sensory-motor reflex?
They integrate with others within neural groups of higher hierarchy. A simple excitation correlated with a sensory impulse then becomes an embryo of concept. The luminous point of a retinal stick integrates, with its neighbors, the abstract concept of « line ».
The first levels of this conceptual assemblage are still fairly anatomically localized. However, as one goes up in the hierarchy, that elaborate concepts integrate information of varied origin, by means of long connections, the localization of the function of the neural schema is distended at the point of reaching many mental areas. At the top, consciousness can claim to occupy the entire brain, while only a minority of neurons participate.
You understand the difficulty of locating consciousness. Its support exists only by the relations of the neurons which constitute it. The problem is almost as difficult for the highest mental functions in the hierarchy, such as self-awareness, imagination, abstraction. Worse, the current psychological models, by ignoring this hierarchy, amalgamate organizational schemes and mental productions, as if the “laws” could be mixed with the “results”. For example, “perception” is the set of signals resulting from the treatment of sensory afference, while “learning” is the way in which neural patterns are modified by these sensory inputs and feedback from higher levels. Locating perception is possible; for learning, it makes no sense. We put the driver and the engineer side by side in the same theory.
Faced with this criticism, the Jungian model is probably better off than newer models because it had the advantage of simplicity. When no mechanic has yet managed to dismantle the engine, the least talkative engineer in his theoretical building is the one who is the least mistaken.
In the end, Jungian cognitive functions exist physically as model representations conceived by our superior neural schemas. It’s a certainty, otherwise you could not talk about it. Your consciousness, where their essence is, is the only level capable of experience them (intuiting for a philosopher). With respect to the other levels of your cognition, they become descriptive models, the mold of a mental functioning that the consciousness can not experience directly. These models have a greater or lesser value depending on their fidelity. Jung’s was remarkable for the time, and is still at the root of contemporary models. They all, however, have the defect of a purely horizontal vision, too focused on the geography of the nervous centers, and dumb on their entangled hierarchy. Relents of the ancient belief in the soul, the divine gnome who would make his market in all these mental productions and dress to form the « I ». If one wishes to free oneself from the mysterious intervention of the soul, one must think carefully about the way in which these schemas organize themselves to become the contents of consciousness. A vision necessarily vertical.
With the help of this integrative vision, the research will eventually be satisfied with a model of the psychological levels of the neural organization, of which the Jungian model will be the ancestor, in the same way that the Copernican astronomy was the ancestor of the Einsteinian cosmogony.