As with virtually all fields of research, scientists use special terms when studying the relationship between the mind and the body. Here are some of them:

*Blood-brain barrier -- This barrier is generally believed to separate -- and protect -- the brain from many chemicals and other substances circulating in the blood. New evidence, however, published in the last several months, suggests that the blood-brain barrier is penetrated by many previously unrecognized substances, including white blood cells called macrophages and by the chemical messages they secrete in the blood.

*Endocrine system -- This network of glands secretes chemical substances, called hormones, into the blood. Hormones, are chemical messages that cause the cells of body organs to behave in a variety of ways, depending on the chemical. The newest chapter in emotions research suggests that many hormones do double duty as neuropeptides, capable of affecting the immune system and brain cells.

*Glial cells -- Constituting the majority of cells in the brain, both the origin and duties of glial cells remain a mystery, although they generally are thought to nourish the nerve cells which carry out the brain's activities. Recent research suggests that at least some glial cells are transformed macrophages -- white blood cells produced by the bone marrow. Like white blood cells, glial cells secrete chemical messages called neuropeptides and may help regulate sleep and body temperature.

*Macrophages -- These specialized white blood cells, which originate in the bone marrow, play an important role in healing and protecting the body from viruses and bacteria. Macrophages also appear to be implicated in a form of lung cancer and AIDS.

*Neuroimmunodulation -- The new field of research that combines the study of the brain, the immune system and behavior.

*Neuropeptides -- Some 40 to 50 substances have been identified as chemical messengers in the brain that carry out a number of functions, including pain control, thirst, appetite, pleasure and emotion.

*Receptors -- A specifically shaped protein on the surface of all cells. Receptors act as a kind of microscopic lock. When opened with the right key -- another specially shaped protein circulating in the blood, such as hormones -- receptors help turn on a cell function, such as producing a neuropeptide or firing an electrical impulse along a nerve or contracting a muscle.

*White blood cells -- Several types of white blood cells form the main part of the immune system, the body's defense against disease and other foreign invaders.