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A THEORY OF THE MIND/BRAIN DICHOTOMY WITH SPECIAL REFERENCE TO THE CONTRIBUTION OF POSITRON EMISSION TOMOGRAPHY LAURENCE R. TANCREDI* and NORA D. VOLKOWt Introduction Throughout history, human beings have found it difficult to understand their conscious, free, and rational qualities in light of biological developments that continue to present the human condition as constituted chiefly of "mindless, meaningless, physical particles." This seeming inconsistency or paradox led to theories (most particularly the Cartesian perspective) that split these processes into two zones or truly separable realms: "mental" phenomena, which usually included thoughts and feelings, and "physical" phenomena, which consist of mass, weight, texture, and motion of objects in the world [2]. Over the centuries, attempts have been made to deemphasize one portion of this dichotomy over the other. In the current century, biophysiologists and philosophers have mustered strong arguments against the intrinsic character of mental things [3]. Of particular importance in this area have been the contributions of the neurosciences. Advances have related biological processes to phenomena such as the transmission of sensation and information over neurons, and have disclosed specific locations in the brain that deal with perception, emotion, cognition, and speech [4, 5]. However, these arguments have not been completely successful in refuting the existence of a separate "mental" entity [6]. This failure can be attributed to biological as well as philosophical reasons. The biological reasons have to do with the way neuroscientific knowledge has been obtained. Until recently, most of the studies were conducted either on *Health Law Program, School of Public Health, University of Texas, Houston, Texas 77030. fMedical Department, Brookhaven National Laboratory, Upton, New York 11973.© 1992 by The University of Chicago. AU rights reserved. 003 1-5982/92/3504-0798$0 1 .00 Perspectives in Biology and Medicine, 35, 4 ¦ Summer 1992 549 animals, in patients suffering from brain disorders, or on pieces of brain tissue [7]. Philosophical reasons for the lack of a convincing argument against an independent "mental" entity rest in large part on the inadequacy of models that construct a direct interaction between specific biophysiological processes and mental functions. Such models have been largely unsuccessful because they fail to consider the multiplicity of biological phenomena that have to occur simultaneously to generate a specific behavior or mental activity [8]; in large part, such models of mind/ brain tend to create one-to-one relationships between the physical and the mental [9]. Basic theories of dualism generally have depended on a close association between the physical and the mental. For example, one of the most common forms of dualism, epiphenomenalism, is predicated on a causative relationship between physical events, states and processes, and mental events, thereby seeing mind events as essentially echoes of processes occurring in the brain [10]. Alternative dualist models, such as "two-way interactionism," are similarly predicated on a close nexus between what occurs neurophysiologically and what occurs in mental processes [10, H]. Both of these thories, epiphenomenalism and two-way interactionism, seem generally compatible with developments in neurophysiology and clinical neurology [H]. The introduction of imaging technologies, such as positron emission tomography (PET), single photon emission tomography (SPECT), computerized electroencephalography (CEEG) and magnetoencephalography (MNE), in the neurosciences has resulted in discoveries that may shift our perceptions ofthe relationship between the biological processes of the brain and processes of the mind. These imaging technologies have breached the biological limitations imposed by the inaccessibility of the functioning brain to direct observation and investigation, since they allow direct assessment of brain function in the normal living human being. In this article we examine a series of questions about our growing understanding of brain function, incorporating into our discussion some of the knowledge brought about by the use of one of these new imaging technologies, positron emission tomography, and how this knowledge can guide the development of models that better describe the relationship between biological processes and mental phenomena. Even though we emphasize the relevance of direct investigation of the human brain, we recognize that many of the concepts derived from imaging techniques mainly replicate findings that had already been disclosed using electrophysiological, neurochemical, and anatomical techniques [12]. We also are aware that molecular biology is expanding the knowledge we have about the...


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