• Corpus Callosum: The neural network which hard-wires the right hemisphere to the left hemisphere. Or, more specifically, the neural network which hard wires the right frontal lobe to the left frontal lobe and the left posterior cortical convexity to the right posterior cortical convexity.

  In noticing the natural bridges which exist in the cortex (the corpus collosum and the circuits of the communication areas), it is worth observing two facts: 1) the communication between the right and left hemispheres via the bridge formed by the corpus collosum is massive and easy when compared with the communication between each frontal lobe with the posterior cortical convexity, immediately behind it; and 2) both patterns of communication are easier than any diagonal communication as there are no diagonal hard-wires linking the Right Frontal Lobe with the Left Posterior Cortical Convexity or the Left Frontal with the Right Posterior Cortical Convexity.

• Hippocampus: The hippocampus (or rather, "hippocampi" since there are two of them) lies tucked within the basal (temporal) lobes of the cerebral cortex. It appears to have two rather different functions, being responsible for adjusting moods and emotions to incoming information from the environment as well as playing a critical role in the process of memory formation. In this latter role (memory), the hippocampus is responsible for forming a memory of the part of the environment which has already been explored so that it may be distinguished from unexplored areas. Therefore, what activates this memory formation sequence (and turns on the hippocampus) is "novelty" in the environment. In addition, the hippocampus is involved in the laying down and retrieving of long term memories (though the specifics of this process are not, as yet, fully understood) and if the hippocampus and the amygdala are both damaged global anterograde amnesia results and no information can be committed to or retrieved from memory.

  In its other capacity as mood adjuster, the hippocampus is usually inhibited by the neurotransmitter seratonin. When it is deprived of seratonin, which can be caused by temporal lobe epilepsy, hallucinagens, repetitive chanting, meditation, or marathon running among other things, the hippocampus fires wildly and loses its connection to "external reality". The result is the same kind of experience that characterizes right temporal lobe epilepsy: dream states, feelings of deja- and jamais-vu, a sense of "significance" and meaningfulness", cosmic insights, and the re-living of past experiences in vivid sensory detail. If such experiences appeal to you but have eluded you in the past, the solution to your problems may simply be to find ways of depriving your brain of seratonin.

• Limbic System: The middle brain as identified in Paul MacLean's triune model. It is generally believed to be involved with the emotions, body temperature, and sex as well as with memory storage and retrieval. (See Appendix B in The Art of Using Your Whole Brain for a more detailed description.) In MacLean's model, this area of the brain included the amygdala the the hypothalamus.

• Amygdala: The amygdala (of which there are two) are involved in associative memory and, along with the hippocampus, in long-term memory storage and retrieval. Like the hypothalamus, they are part of both the pleasure and pain systems, although the pain component is by far the more significant. The amygdala are connected to aggression, and electrical stimulation of these areas will produce displays of excitement, rage, and fear. Although removal of the amygdala does cause a reduction in aggression, it also produces excessive sexual displaying and a loss of status in the social hierarchy.

• Hypothalamus: The hypothalamus, which lies just below the thalamus, appears to be the master regulator of the autonomic nervous system. It controls body temperature, blood pressure, water levels, sex, appetite/food intake, and endocrine levels (through its control over the pituitary). The hypothalamus is also part of the pleasure and pain systems, depending on which half is stimulated. Lesions in the posterior hypothalamus produce an increase in aggressiveness, and electrical stimulation of this area generates a rage reaction and attack behaviors. Conversely, stimulation of the anterior hypothalamus produces pleasure reactions. Perhaps most importantly when considered in relation to human thinking, the hypothalamus appears to function not only as the central control for the limbic system, but also as the liaison between the limbic system and the cerebral cortex.

From the above overview we have learned that:

1. Jung's four Functions are rooted in four distinct areas of the cortex. Thinking is housed in the Left Frontal Lobe. Intuition is housed in the Right Frontal Lobe. Sensation is housed in the Left Posterior Convexity. Feeling is housed in the Right Posterior Convexity.

2. Jung's assertion that each of us has one Natural Lead Function is the result of a neuro-chemical - physiological fact that each person has one area which is 100 times more efficient than their remaining three areas.

3. Jung's assertion that each person has two natural auxiliaries can be understood to be the natural result of the brain's structure. Factually speaking, neuronal bridges hardwire a person's Natural Lead to their auxiliaries, making communication between their lead and auxiliaries easy, even though each actual auxiliary is relatively speaking highly inefficient.

4. Jung's assertion that once a person's Natural Lead Function has been identified, one can confidently calculate the person's greatest Natural Weakness, is the result of the simply fact that there are no diagonal bridges in the human brain.

5. The difference between the Feeling Function and Emotions can be understood more clearly. The Feeling Function is a cortical capacity to recognize the presence or absence of harmony — between colors, tones, or human beings. By contrast, emotions are a limbic capacity to experience delight, anger, fear, grief.

6. Jung's belief that Falsification of Type was real possibility is understood to be the natural result of anyone developing and using any of their three inefficient, non-preferred Functions more than their highly efficient Natural Lead Function. What's more, Jung's assertion that Falsification of Type can be a serious threat to a person's physical and mental / emotional health has been validated by the work of Dr. Katherine Benziger and Dr. Arlene Taylor, resulting recently in the profound recognition that Falsification of Type leads dependably to a serious results as defined by PASS.

Thus, quite simply, the elements of Jung's Typology related to the existence and relative organization of four specialized functions or ways of "thinking" is explained.