BEHIND THE SCENES OF FUNCTIONAL BRAIN IMAGING - A HISTORICAL AND PHYSIOLOGICAL PERSPECTIVE

At the forefront of cognitive neuroscience research in normal humans a re the new techniques of functional brain imaging: positron emission t omography and magnetic resonance imaging, The signal used by positron emission tomography is based on the fact that changes in the cellular activity of the brain of normal, awake humans and laboratory animals a re accompanied almost invariably by changes in local blood flow, This robust, empirical relationship has fascinated scientists for well over a hundred years, Because the changes in blood flow are accompanied by lesser changes in oxygen consumption, local changes in brain oxygen c ontent occur at the sites of activation and provide the basis for the signal used by magnetic resonance imaging, The biological basis for th ese signals is now an area of intense research stimulated by the inter est in these tools for cognitive neuroscience research.