The body and heart are two distinct substances for sure. But through experience I think you'll agree its necessary to say the two substances interact on such a level that they seem to be one unified (substance.) I believe it is for this reason there is so much misunderstanding and this causes further categorizing of what man is (i.e. heart, mind, soul, spirit, self, etc.) The categorizing attempts to make sense of the complex interaction of body and heart.
The heart and body exist as two parts and yet they are completely unified. To define the two parts as separates is easier to do than to understand them as they interact as one - the interaction is somewhat of a mystery and must be accepted. To seek precise understand or how body and heart interact leads to disappointment.
Speaking of dual and yet unified substances, where in Christianity is this also displayed? Welch gives examples, or rather analogies, from scripture:
- Marriage between man and woman (Ephesians 5:31-32)
- Relationship between Christ and the church (1 Corinthians 12)
- Oneness with Christ through faith (Romans 6)
- Vine and branches (John 15)
- The Trinity (entire Scripture)
"These analogies suggest that although we may not fully understand the simultaneous unity and duality of spirit and body, we should be somewhat comfortable with it because God's word is filled with similar mysteries.Welch, page 47, Blame It on the Brain.
These analogies also remind us to be careful not to emphasize our duality over our unity. Heart and body are both two and one. They are two in that body cannot be reduced to heart or spirit, and heart cannot be reduced to body. But they are mutually interdependent. They need each other. Human life cannot even be imagined without both the inner and outer person."
At the level of the brain, this unity suggests that the heart or spirit will always be represented or expressed in the brain's chemical activity. When we choose good or evil, such decisions will be accompanied by changes in brain activity. When we think about how to disciple our children, there will be unique brain activity. This does not mean that the brain causes these decisions. It simply means the brain renders the desires of the heart in the physical medium. It is as if the heart always leaves its footprints on the brain."
Knowing this I am now more prepared to deal with scientific research that says the brain of an angry person or depressed person or an alchoholic or a person with bi-polar or with any other psyhcological disorder is different form the brain of a normal person. There is no denying or arguing with scientific research on brain chemicals, I should expect most of its findings. The Bible is clear, what goes on in the heart is represented in the body. But, the brain does not cause behaviors, it is the opposite, brain changes are caused by behavior.