For many years it was thought the various systems of the body were somewhat separate and functioned autonomously. Scientists have known the brain produced chemicals called neurotransmitters that triggered responses in parts of the body for a long time. But they tell us that not only do various parts of the body respond to neurotransmitters from the brain and but that these chemicals are produced in various organs away from the brain and the brain responds to them. So communication between mind and body is a two way street, down to the cellular level.
Cells communicate with cells.
We've had begun to appreciate more fully how our thinking changes our chemistry. We really become what we think about as thoughts create chemicals that change us all the way down to the cellular level. In more complicated language, the limbic-hypothalamic system of the brain modulates the autonomic, endocrine and immune system and responds to suggestions coming from cognitions. Essentially, we are learning more about the power of belief and have come to appreciate the potency or power of belief as a healing power. Placebos offer us an excellent example of how belief works.