As talented as our brains are, they are still completely dependent on what happens in the body as a whole.

Signals from within the body influence behavior just as powerfully as influences from the environment. Heart, lung and endocrine problems all have cognitive side effects. Your brain produces substances that can improve your health. These substances include endorphins, which are natural painkillers, and gamma globulin, which strengthens your immune system. Negative thoughts and emotions can keep your brain from producing some of the chemicals that help your body heal. But this doesn’t mean you should blame yourself for getting sick or feeling down about a health problem. Some illnesses are beyond your control. But your thoughts and state of mind are resources you can use to get better.