Introduction

Bridging the gap between descriptions of human behaviors and underlying neural events has been a dream of both psychologists and neuroscientists for quite some time. William James, in his monumental two-volume work The Principles of Psychology, devotes two insightful chapters to the brain and its relationship to behavior. The prescience of his remarks is particularly remarkable given the fact that they were written 1890. In a fashion typical of much of his writing, James clearly identifies the challenge: “A science of the mind must reduce … complexities [of behavior] to their elements. A science of the brain must point out the functions of its elements. A science of the relations of mind and brain must show how the elementary ingredients of the former correspond to the elementary functions of the latter” (James, 1890, vol. 1, p. 28).

The importance of meeting this challenge was appreciated at about the same time by no less a neuroscientist than Sir Charles Sherrington, who wrote that “… physiology and psychology, instead of prosecuting their studies, as some now recommend, more strictly apart one from another than at present, will find it serviceable for each to give to the results achieved by the other even closer heed than has been customary hitherto” (Sherrington, 1906, p. 387). While it is clear that progress has been made from the time of James and Sherrington until the present through studies in experimental animals and in patients with various diseases afflicting the brain, the opportunity to relate normal behavior to normal brain function in humans was largely nonexistent until the latter part of the twentieth century.

None other than the great experimental physiologist (some might say biological psychologist) Ivan Pavlov envisioned what was needed: “If we could look through the skull into the brain of a consciously thinking person, and if the place of optimal excitability were luminous, then we should see playing over the cerebral surface, a bright spot with fantastic, waving borders constantly fluctuating in size and form, surrounded by a darkness more or less deep, covering the rest of the hemispheres (1928; for translation, see Brugger, 1997). For many years such a vision seemed mere fantasy.

It was the introduction of modern brain imaging techniques in the 1970s, particularly positron emission tomography (PET) and magnetic resonance imaging (MRI), that permitted us to realize Pavlov's vision of monitoring human brain function in a safe yet increasingly detailed and quantitative way. Using strategies to map local changes in brain circulation and metabolism associated with changes in brain cellular activity, these brain imaging techniques initiated a revolution in the relationship between neuroscience and cognitive science that resulted in the birth of cognitive neuroscience (for a review, see Posner & Raichle, 1994).

Cognitive neuroscience has combined with surprising success the experimental strategies of cognitive psychology with brain imaging techniques to actually examine how brain function supports mental activities. The number of papers reporting the results of such studies is increasing at an exponential rate (Illes et al., 2003), as is the investment in brain imaging centers worldwide (many now in psychology departments) devoted to the study of brain-behavior relationships (Raichle, 2003a). Unheard-of in the late 1980s, when the James S. McDonnell Foundation and the Pew Charitable Trusts initiated their program in cognitive neuroscience, were faculty positions in psychology departments for cognitive neuroscientists. They are now common, and young scientists with combined qualifications in imaging and psychology are eagerly sought. Additionally, the research areas included are rapidly expanding into a domain now increasingly referred to as social neuroscience (Cacioppo et al., 2002).

The recent prominence of functional imaging in the scientific literature as well in as the popular press makes it easy to conclude that much of the work leading to the current state of research has evolved since the mid-1990s. Actually, work relevant to the development of these tools has been evolving for more than a century. In order to place current work in its proper perspective, a brief historical review is presented in this chapter along with a brief look at current trends and future directions.