An Introduction to Social Neuroscience
Abstract and Keywords
Social neuroscience is the interdisciplinary field devoted to the study of neural, hormonal, cellular, and genetic mechanisms, and to the study of the associations and influences between social and biological levels of organization. The current Handbook represents the first comprehensive review of contemporary research in the field. This introductory chapter begins with a brief background on studies of the mind in the 20th century. It then discusses the mechanisms underlying complex behavior and the three principles of social neuroscience (i.e., multiple determinism, nonadditive determinism, and reciprocal determinism). An overview of the eight sections of this Handbook is presented.
Social species, by definition, create emergent organizations beyond the individual—structures ranging from dyads and families to groups and cultures. These emergent social structures evolved hand in hand with neural, hormonal, cellular, and genetic mechanisms to support them because the consequent social behaviors helped these organisms survive, reproduce, and care for offspring sufficiently long that they too reproduced, thereby ensuring their genetic legacy. Social neuroscience is the interdisciplinary field devoted to the study of these neural, hormonal, cellular, and genetic mechanisms, and to the study of the associations and influences between social and biological levels of organization. Humans are fundamentally a social species whose social environment has shaped our genes, brains, and bodies, and our biology has fundamentally shaped the social environments we have created. Social neuroscience, therefore, provides an overarching paradigm in which to investigate human behavior and biology, and to determine where we as a species fit within a broader biological context. The current Handbook represents the first comprehensive review of contemporary research in the field.
During much of the 20th century, the individual was treated as the fundamental unit of analysis, and the brain was treated as a solitary information-processing organ. This is an entirely understandable starting point. The brain, the organ of the mind, is housed deep within the cranial vault, where it is protected and isolated from others, as are the neural, hormonal, and genetic processes of interest to most biological scientists. Even cognition, emotion, and behavior can be thought of as beginning with the neurobiological events within individual organisms, events that can be isolated and examined. It should be no surprise, therefore, that the study of the mind by biological, behavioral, and cognitive scientists (p. 4) in the 20th century tended to focus on single organisms, organs, cells, intracellular processes, and genes.
Further contributing to this backdrop is the well-tested premise that investigation of the mechanisms upon which psychological operations and behavior are based is best addressed at as small a scale as possible. As Llinás (1989) noted:
… the brain, as complex as it is, can only be understood from a cellular perspective. This perspective has been the cornerstone of neurosciences over the past 100 years (p. vii).
An implication drawn from this perspective is that the contributions of the social world to behavior and biology are largely irrelevant with respect to the basic development, structure, or processes of the brain and behavior, and, therefore, they are of little interest. To the extent that social factors were suspected of being relevant, their consideration was thought to be so complicated that they should be considered at some later date, if at all, once the basic mechanisms underlying human biology and behavior had been determined.
The approach of social scientists throughout most of the 20th century was no less focused than that of biologists. World wars, a great depression, and civil injustices made it amply clear that social and cultural forces were too important to address to await the full explication of cellular and molecular mechanisms. Moreover, from the perspective of the social sciences, social factors ranging from mother-infant attachment to culture defined and shaped who we were as a species. As a consequence, biological events and processes were routinely ignored in the social sciences.
Mechanisms Underlying Complex Behavior Exist at Multiple Levels of Organization
It is now recognized that cognitive, affective, and behavioral processes occur unconsciously, with only a subset of the end products reaching awareness (e.g., Wilson & Bar-Anan, 2008). Theoretical models have been developed that specify structures and processes of the mind, as have behavioral paradigms that permit the isolation of posited structures and processes for empirical analysis. These theoretical specifications and paradigms are critically important for understanding the biological basis of mental and behavioral processes because the brain and genes are too complex to identify their functions without theory to guide the process of empirical exploration and discovery. For instance, any given behavior can be ambiguous as to its origins. One may eat because one is hungry, out of habit because it is mealtime, or as a social occasion in which the consumption of food is the norm. The identification of which genes, gene transcripts, proteins, cells, cell assemblies, brain regions, and neural networks are relevant to a given behavior is advanced by the empirical isolation of the underlying psychological component processes. The classic work on the neural substrates of classical conditioning, which proved so productive because behavioral paradigms for isolating specific forms of learning were so well specified, is a case in point.
For most of the 20th century, investigations of the brain mechanisms underlying these psychological processes were limited in animals to methods such as brain lesions, electrophysiological recording, and neurochemistry, and in humans to post-mortem examinations, observations of the occasional unfortunate individual who suffered trauma to or disorders of the brain, electroencephalography, and event-related brain potential recording in response to specific cognitive or behavioral tasks (Raichle, 2000; Sarter, Berntson, & Cacioppo, 1996). Developments in multimodal structural, hemodynamic, and electrophysiological brain imaging acquisition and analysis techniques; more sophisticated specifications and analyses of focal brain lesions; focused experimental manipulations of brain activity using transcranial magnetic stimulation and pharmacological agents; the integration of neuroimaging, psychophysiological, neuroendocrine, and genetic assessments; and emerging visualization and quantitative techniques that integrate anatomical and functional connectivity—in addition to information about neural processes at different scales of organization—are creating new opportunities for scientific investigations of the working human brain. Despite the increased sophistication and data yield from recent advances that make it possible to observe at various levels of analysis the operation of the working brain, an atheoretical exploration alone is not likely to yield many major discoveries of the working mind and behavior. It is simply too complex to understand the neural basis of specific mental processes without well-designed tasks that isolate those processes:
… the task of functional brain imaging becomes clear: identify regions and their temporal relationships associated with the performance of a well-designed task. The brain instantiation of the task will emerge from an understanding of the elementary (p. 5) operations performed within such a network (Raichle, 2000, p. 34).
Moreover, the emergent structures that characterize social species are not simply late irrelevant add-ons, but rather they were shaped by and shaped basic neural, hormonal, cellular, and genetic mechanisms, and they are important for normal mental and physical development and functioning. Across social species, individual members do not fare well when living solitary lives. Social isolation decreases the lifespan of the fruit fly; promotes the development of obesity and type 2 diabetes in mice; delays the positive effects of running on adult neurogenesis and increases the activation of the sympatho-adrenomedullary response to acute stressors in rats; decreases the expression of genes regulating glucocorticoid response in the frontal cortex of piglets; decreases open field activity, increases basal cortisol concentrations, and decreases lymphocyte proliferation to mitogens in pigs; increases the 24-hour urinary catecholamines levels and evidence of oxidative stress in the aortic arch of the rabbit; increases the morning rise in cortisol in squirrel monkeys; and profoundly disrupts social development in rhesus monkeys. Humans, born to the longest period of total dependency of any species and dependent on conspecifics across the lifespan to survive and prosper, fare poorly both mentally and physically, especially when they perceive they are socially isolated. The mechanism suggested initially for the finding in humans was that isolated individuals engage in poorer health behaviors. This hypothesis is not generally supported by the data in humans and does not account for the effects of isolation in nonhuman social species (cf. Cacioppo & Hawkley, 2009).
It is estimated that hominids have walked the earth for the past 7 million years. Homo sapiens have evolved within approximately the last 1% of that period, and only the last 5% to 10% of this brief span has brought an array of human achievements that we now take for granted. Humans were not the first bipedal creatures or the first to use tools, but humans, apparently uniquely, contemplate the history of the earth, the reach of the universe, the origin of the species, the genetic blueprint of life, and the physical basis of their own unique mental existence. The attributes of Homo sapiens responsible for our success as a species are debatable, but the number of genes and the size of the human brain are themselves insufficient explanations (Cacioppo et al., 2007). Estimates among biologists a decade ago were that 100,000 genes were needed for the cellular processes responsible for human social behavior, but humans have only about a quarter that number of genes. The prefrontal cortex is thought to be particularly important for critical behaviors such as executive function and working memory, yet the ratio of prefrontal to total cortical gray matter is no greater in humans than it is in nonhuman primates. Although humans may have more cortical neurons than most mammals, they have barely more than whales and elephants. The specialized capacities of humans may result from the increased number and processing capacity of synapses in the brain, greater cell-packing density, greater connectivity, and higher neural-conduction velocities, raising the brain’s overall information-processing capacity. Other specialized capacities of humans range from hands with fingers and thumbs to theory of mind and language. Together, these properties support complex and coordinated collective enterprises.
Our brains are not solitary information processing devices any more than the cell phone is a solitary information-processing device. The cell phone has been designed to connect to other cell phones, and its very existence and function depends on connection with other such devices. Our brains have evolved to connect to other minds, and our remarkable accomplishments as a species reflect our collective ability, as instantiated in each individual brain, rather than our individual might.
Social neuroscience emerged in the early 1990s as a new interdisciplinary academic field devoted to understanding how biological systems implement social processes and behavior, capitalizing on biological concepts and methods to inform and refine theories of social processes and behavior, and using social and behavioral concepts and data to inform and refine theories of neural organization and function (Cacioppo & Berntson, 1992). Social neuroscience as an approach has faced skeptics representing two diametric positions in the social and biological sciences.
The first is the view that social neuroscience deals in dualistic reasoning:
Historically, the question of the relation of the body to the mind was, at best, opaque; the mental attributes of humans were only vaguely related to the attributes of the brain. Despite the increase in our knowledge of brain morphology and function at the end of the nineteenth century and the beginning of the twentieth century, there was still a feeling among many scholars that the nature of (p. 6) human reason might be related to some new and wonderful knowledge totally alien to that which is accessible through the scientific method (Llinás, 1989, p. vii).
The scientific study of the brain mechanisms underlying social processes and behavior is premised on the rejection of René Descartes’ contention that because the body existed in time and space and the mind had no spatial dimension, the body and mind were made of completely different stuff. Instead, social neuroscientists have developed theoretical constructs and models to provide a means of understanding highly complex activity without needing to specify each individual action’s simplest components, thereby providing an efficient means of describing the behavior of a complex system. Chemists who work with the periodic table on a daily basis use recipes rather than the periodic table to cook not because food preparation cannot be reduced to chemical expressions but because it is not cognitively efficient to do so. The scientist who uses theoretical constructs is no more a dualist than a chemist who uses both culinary and chemical levels of analysis to understand what it takes to develop fine cuisine.
A second set of skeptics has argued that any reductionist account of mental or behavioral phenomena falls outside the purview of the behavioral and social sciences (e.g., Coltheart, 2006; Kihlstrom, 2006). However, social neuroscience is not a substitute for the behavioral or social sciences, it is an interdisciplinary field that draws on these sciences as well as on the neurosciences to provide a single, integrative paradigm in which to investigate complex human behavior across levels of organization, from the molecular to the molar.
The field of social neuroscience is grounded in three simple principles (Cacioppo & Berntson, 1992). The first, the principle of multiple determinism, specifies that a target event at one level of organization can have multiple antecedents within or across levels of organization. On the biological level, for instance, researchers identified the contribution of individual differences in the endogenous opioid receptor system in drug use, whereas on the social level investigators have noted the important role of social context. Both operate, and our understanding of drug abuse is incomplete if either level is excluded. Similarly, immune functions were once considered to reflect specific and nonspecific physiological responses to pathogens or tissue damage. It is now clear that immune responses are heavily influenced by central nervous processes that are affected by social interactions. It is clear that an understanding of immunocompetence will be inadequate in the absence of considerations of social and behavioral factors. The implication is that major advances in the neurosciences and the social sciences can result from increasing the scope of the analysis to include the contributions of factors and processes from both perspectives.
An important corollary to this principle is that the mapping between elements across levels of organization becomes more complex (e.g., many-to-many) as the number of intervening levels of organization increases. One implication is that the likelihood of complex and potentially obscure mappings increases as one skips levels of organization. This is one reason that going from the genotype to endophenotypes and from endophenotypes to phenotypes has proven to be more productive than going directly from the genotype to phenotype.
The second principle is of nonadditive determinism, which specifies that properties of the whole are not always readily predictable from the properties of the parts. Consider an illustrative study by Haber and Barchas (1984), who investigated the effects of amphetamine on primate behavior. The behavior of nonhuman primates was examined following the administration of amphetamine or placebo. No clear pattern emerged between the drug and placebo conditions until each primate’s position in the social hierarchy was considered. When this social factor was taken into account, amphetamine was found to increase dominant behavior in primates high in the social hierarchy and to increase submissive behavior in primates low in the social hierarchy. The importance of this study derives from its demonstration of how the effects of physiological changes on social behavior can appear unreliable until the analysis is extended across levels of organization. A strictly physiological (or social) analysis, regardless of the sophistication of the measurement technology, may not have revealed the orderly relationship that existed.
The third principle is of reciprocal determinism, which specifies that there can be mutual influences between biological and social factors in determining behavior. For example, not only has the level of testosterone in nonhuman male primates been shown to promote sexual behavior, but the availability of receptive females influences the level of testosterone in nonhuman primates. Accordingly, comprehensive accounts of these behaviors cannot be achieved if the biological or the social level of organization is considered unnecessary or irrelevant.
(p. 7) Mounting evidence for the importance of the relationship between social events and biological events has prompted biological, cognitive, and social scientists to collaborate more systematically, with a common view that the understanding of mind and behavior could be enhanced by an integrative analysis that encompasses levels of organization ranging from culture to genes. Indeed, there has been a dramatic growth in social neuroscience over the past two decades. Subareas within the broad perspective of social neuroscience include computational social neuroscience, social cognitive neuroscience, social affective neuroscience, cultural neuroscience, neuroeconomics, social developmental neuroscience, and comparative social neuroscience. Work in each of these fields is represented in this Handbook.
One can ask whether social constructs, once reduced to their neural, hormonal, and genetic components, will be relegated to the junk pile of excess theoretical baggage. Such a question reflects the conflation of different levels of analysis and what has been called a category error (Ryle, 2000). The job of science is to align adjacent scientific fields to specify the bridging laws that link different levels of analysis (Cacioppo & Tassinary, 1990; Nagel, 1961), not to reduce and eliminate higher levels of analysis. Indeed, the constructs developed by behavioral and social scientists provide a means of understanding highly complex activity without needing to specify each individual action by its simplest components, thereby providing a cognitively efficient approach to describing complex systems. The efficiency of expression is not the only issue: The concepts defining fine cuisine are not part of the discipline of chemistry. The theoretical terms of the behavioral and social sciences are similarly valuable in relation to those of biology, but can be informed and refined through integration with theories and methods from the neurosciences. The field of social neuroscience, therefore, represents a new paradigm that embraces animal as well as human studies, patient as well as nonpatient studies, computational as well as empirical analyses, and neural as well as behavioral research.
Like any new field, social neuroscience faces problems and challenges that must be confronted and addressed. Doing so will make it possible to provide more comprehensive accounts for the basic structures, processes, and behaviors of humans and other complex social species. The purpose of this Handbook of Social Neuroscience is to stimulate just such interactions by providing a review of representative research in the field, acknowledging contemporary problems and challenges, and identifying fertile paradigms and areas of future inquiry.
Our goal in constituting this Handbook is to provide a representative rather than exhaustive coverage of the field. The Handbook nevertheless includes 67 chapters which are partitioned into eight related sections. The first section outlines a brief history and some of the most important foundational principles and methods underlying the field, laying the groundwork for the chapters to follow.
Social and emotional processes are closely intertwined in humans and other social species, and the second section focuses on different aspects of social motivation and emotion. Humans are a highly symbolic, meaning-making species, and our social environment contributed to our development and expansion of our cognitive capacities. The third section, therefore, focuses on processes of social cognition such as self-other distinctions, face perception, and impression formation. The fourth section addresses some of the same issues but moves from a focus on the effects of social stimuli on an individual’s brain and biology—that is, intrapersonal processes—to interpersonal processes. The fifth section continues to scale up the level of organization to focus on group processes, while still focusing on the underlying neural, hormonal, cellular, and genetic mechanisms that influence and are influenced by them.
The final third of the Handbook moves from a focus on processes across levels of organization (intrapersonal to group) to a focus on problems and applications. The sixth section, for instance, deals with social influences on health and clinical syndromes, ranging from the health effects of social isolation to the social underpinnings of various psychopathologies. As complex social behavior comes under the scrutiny of the neurosciences, new insights are provided for addressing applied problems. The seventh section addresses illustrative applications that have benefitted from a social neuroscientific approach. The final section addresses a set of societal implications from the perspective of social neuroscience.
We would like to thank all of our colleagues who contributed to the Handbook. By providing an authoritative reference in the field of social neuroscience, we hope this volume proves useful to scholars and students and facilitates training, developments, and progress in the field.
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