JOHN T. CACIOPPO, LOUIS G. TASSINARY, AND GARY G. BERNTSON
Psychophysiology is an old idea but a new science. It is a likely assumption that ever since man began to experience himself as an object of his own awareness he has had some intuitive notion that bodily changes were, in some measure, related to his moods, his sentiments, his frustrations, his elations. How to relate these dual aspects of human functioning has been a concern of philosopher-scientists throughout the course of intellectual history. (Greenfield & Sternbach, 1972, p. v)
The first Handbook of Psychophysiology was published more than three decades ago (Greenfield & Sternbach, 1972). Coverage in that Handbook emphasized the peripheral nervous system, an emphasis that many still identify with the term psychophysiology in accord with the history of psychophysiology. As is the case for physiological and other scientific fields, however, psychophysiology has changed dramatically since the appearance of its first Handbook. With the advent of new and powerful probes of the central nervous system (e.g., brain imaging techniques), there is an increased emphasis in the field on investigating the brain and central nervous system as they relate to behavior. Investigations of elementary physiological events in normal thinking, feeling, and interacting individuals are commonplace, and new techniques are providing additional windows through which the neural events underlying psychological processes can be viewed unobtrusively. Instrumentation now makes it possible for investigators to explore the selective activation of discrete parts of the brain during particular psychological operations in normal individuals and patients. Transcranial magnetic stimulation has made it possible to stimulate or temporarily disable a region of the brain to study its role in cognitive operations, and studies of patients with lesions are becoming more precise both in their definition of the lesion and in their specification of behavior.
Preparation of this chapter was supported by National Institute of Aging Program Project Grant No. P01 AG18911. Address correspondence to John T. Cacioppo, Center for Cognitive and Social Neuroscience, 5848 S. University Avenue, Chicago, IL 60637, or by email to [email protected].
Developments in tissue and blood assays, ambulatory recording devices, non-contact recording instruments, and powerful and mobile computing devices make it possible to measure physiological, endocrinological, and immuno-logical responses in naturalistic as well as laboratory settings. New, powerful assays, including DNA genotyping, are now possible using minimally invasive or noninvasive procedures. With recent developments in molecular biology, behavioral genetics is becoming an important new player in the field. However, the views from these windows are clear only because of the deliberate efforts of knowledgeable investigators. Knowledge and principles of physiological mechanisms, biometric and psychometric properties of the measures, statistical representation and analysis of multivariate data, and the structure of scientific inference are important if veridical information is to be extracted from psychophysiological data. These are among the topics covered in depth in this Handbook.
The field of psychophysiology has changed dramatically in other ways as well. Psychophysiology used to be divided into distinct territories, typically defined by organ systems (e.g., the heart, eye blinks), with relatively little integration across these systems. The concept of arousal - the peripheral equivalent of the early notions of the reticular activating system in the brain - dominated the field for the better part of the twentieth century and made the selection of measure a matter of preference rather than a theoretical choice because the responses presumably reflected modulations of arousal regardless of the system one was measuring. Although low correlations among such measures were well recognized, the differences across measures were viewed as less interesting and informative at the time than the confluence of these measures.
Advances in our understanding of the neurophysio-logical basis of these measures have underscored the importance of the unique patterns of peripheral responses that typically emerge across situations and individuals, and the peripheral and central mechanisms that orchestrate these patterns are active areas of inquiry. As part of these inquiries, animal research, molecular studies, and computational modeling are being embraced in the field despite the original definition of psychophysiology in terms of the study of humans rather than nonhuman animals. Moreover, the larger social, cultural, and interpersonal contexts are now recognized as powerful determinants of brain and behavior. Monism has replaced any lingering notions of dualism, as psychological states are more likely to be conceived as represented in and acting through cortical, limbic, and brain stem regions, with influences on autonomic, neuroendocrine, and immune activity, which in turn serve to modulate crucial cellular and molecular processes. Afferent information, in turn, travels from the peripheral to the central nervous system to influence the brain and behavior in social contexts. For instance, interleukin-1^ (IL-1^) in the periphery increases in response to the introduction of antigens, and this increase is reflected in the information carried along the vagal afferent nerve to the brain. As a result of these signals from the periphery, IL-1^ levels in the brain are increased, producing feelings of illness and fatigue. The notion of embodied cognition has been alive and well in psychophysiology for decades (see review by Cacioppo & Petty, 1981), and the identification of canonical and mirror neurons has renewed interest in this area (Garbarini & Adenzato, 2004).
Rose (2005) noted that there are at least two voluminous scientific literatures on psychological states and physiological events that have not been effectively related to one another: the literature on the CNS mechanisms underlying a variety of psychological processes, and the literature on psychological factors and peripheral biological activities including physical health. These literatures have tended to focus on different psychological processes, but there is an increasing recognition that these two areas of study have much in common. For instance, studies of the brain during exposure to potentially stressful stimuli can be an important tool in studying stress biology and evaluating its impact in various systems (Rose, 2005). Both of these literatures are covered in this Handbook and, although much needs to be done to integrate these distinct lines of research, it should be apparent from the chapters in this Handbook that this work has begun.
With the dawning of the twenty-first century, recording standards, procedures for signal representation, and powerful techniques for multivariate statistical analyses have been established. Investigators are now as likely to be studying the interrelationships among brain, autonomic, somatic, endocrinologic, immunologic, and/or genetic processes as they are to be studying any of these systems in isolation. Moreover, given that there are many things going on in the brain at any moment in time, only a few of which are relevant to any particular peripheral organ or effect, it is now recognized that the identification of psychological and brain mechanisms that are related to peripheral changes can be advanced significantly by working from the peripheral effects back to central, psychological, and social conditions, just as it can be advanced by the more traditional, complementary approach of manip ulating psychological states and observing the subsequent changes in CNS and PNS processes.
Finally, psychophysiology has always had a special appeal in scientific investigations of the mind because it offers tools for mining information about nonconscious and nonreportable states, processes, and events. Psycho-physiological studies of attention and cognitive development in neonates, early sensory and attentional processes in schizophrenics, the cognitive operations underlying psychological states, and the study of sleep and dreams in older adults have helped lift the veil from these otherwise difficult-to-gauge behavioral processes.
In sum, psychophysiological research has provided insights into almost every facet of human nature, from the attention and behavior of the neonate to memory and emotions in the elderly. This book is about these insights and advances - what they are, the methods by which they came about, and the conceptualizations that are guiding progress toward future advances in the discipline. Historically, the study of psychophysiological phenomena has been susceptible to "easy generalizations, philosophical pitfalls, and influences from extrascientific quarters" (Harrington, 1987, p. 5). Our objectives in this chapter are to define psychophysiology, briefly review major historical events in the evolution of psychophysiological inference, outline a taxonomy of logical relationships between psychological constructs and physiological events, and specify a scheme for strong inference within each of the specified classes of psychophysiological relationships.
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