For our beliefs to influence our physical functions, there must not only be pathways and channels connecting head to toe but also some system of messengers for the brain to issue directives to the body. An explosion of knowledge in the neurosciences has uncovered dozens of chemical messengers that the brain uses for its far ranging influence in the body and communication between cells. Among these potent compounds are stress hormones and fast acting neurotransmitters that vary in magnitude or kind depending at least, in part on our attitudes, moods and ways of reacting to problems. How we experience something how we define our situations has effects on the very molecules that act as cell receptors for the neuro-chemicals, and this kind of remarkable influence is a concrete example of how the mind/body barrier has evaporated.

But if mental states thoughts, attitudes, moods do, in fact, cause neural events changes in brain cells and their activity how does this effect occur? The answer seems to lie at the fascinating intersection between the new physics and neuroscience, where the intangible (thinking) is now seen as perfectly capable of affecting the tangible (nerve endings that release chemical transmitters), somewhat as the electric field around physical bodies is a nonmaterial force that produces material consequences.

The heady revolution has overthrown a number of myths about the brain. Contrary to the long held belief that the structure of the adult brain does not change, mounting evidence from animal studies shows that the cerebral cortex can actually grow in response to stimulating environments and activity. Rather than losing brain cells as we grow older, we can actually extend our neural connections just as old rats become smarter and run mazes better. Both brain chemistry and structure are affected by the way we experience and perceive the environment.

As neurons change their signals in the brain and to the body as they respond to our perceptions, they seem to make switches in the communication molecules they use to transmit messages. Our brains, then, are distinguished by their dynamic plasticity, making them highly responsive to the environment and our interpretation of it.

Unraveling some of the chemistry of thinking is helping to build the foundation of an exciting new field of molecular psychology, which is devoted to probing the interaction between chemical molecules in the brain and our cognitions and behavior. And what is being found is that just as brain chemicals can change thoughts, so too can thoughts change the chemicals and how well we feel and function.

"Breakthrough" is a word used with caution in science, but the strides made in understanding the chemical machinery of our cognitions our thoughts, feelings, perceptions and experiences are dramatic. Sir John Eccles, a Nobel laureate in neurophysiology, calls "extraordinary" the new knowledge of how the mental can affect the physical at the most basic level. Even color coded pictures of some of the effects of the mental on the physical are increasingly common. Brain scanning is permitting us for the first time to picture what is going on in our heads as we worry, anticipate and change our thoughts and moods or as we get sick and recover. For instance, positron emission tomography (PET) is providing a "window into the brain" as the brain functions or falters from a deficiency or excess of the chemical messengers that largely regulate our mental and physical health. Brain scanners, which are a boon to medical diagnosis and science, have also been described as promising "to do for human psychology what the telescope did for astronomy and the microscope for biology."