Essays in Social Neuroscience, edited by John T. Cacioppo and Gary G. Berntson, is a slim collection of highly engaging and—for the overextended neuropsychologist—enjoyably brief essays surveying current research and theory in the emerging field of social neuroscience. Each contributor attests to the variety of examples of research bridging the historic divide between neuroscience and social psychology. For neuropsychologists, this volume offers enlightening demonstrations of the potential for traditional methods in neuroscience to speak to the complex and reciprocal interplay between neural systems and the social world. From Sue Carter's essay “Oxytocin and the Prairie Vole: A Love Story” to Shelley E. Taylor's contribution “The Accidental Neuroscientist: Positive Resources, Stress Responses, and Course of Illness,” these essays speak to such diverse issues as interpersonal attraction, loyalty, emotional reactivity, and environmental contributions to autoimmune disease. Some essays speak more to the potential for bridging the gap than to demonstrated success in this effort, but those essays remain pleasurable, rewarding reads. The large majority of essays, four of which are described in more detail below, beautifully exemplify the fruitfulness of this area of inquiry.

Among the most impressive examples of efforts to bridge the divide between social neuroscience and social psychology is the opening essay by Michael J. Meaney. His research focuses on consequences of maternal behavior in rats to illustrate a behavioral transmission of parental traits to offspring (nongenomic inheritance). The extent to which a mother licks her pups is a stable, individual difference trait that is associated with stable differences in hypothalamic-pituitary-axis (HPA) responses to stress in her offspring. Mothers who are high-frequency lickers have offspring that show lower stress reactivity as measured in both behavioral and endocrine markers. A first attempt at explaining this might be genomic inheritance, likely focusing on a mechanism grounded in the HPA axis. However, studies of cross-fostering (basic science equivalents of foster families) show that the offspring of low-lick mothers who are raised by high-lick mothers will show the same resiliency to stress as the offspring of high-lick mothers. This behaviorally transmitted resiliency appears to be mediated through tissue-specific effects on gene expression. The mechanism of this resiliency has been mapped to the level of DNA methylation, in particular the exon 1₇ glucocorticoid receptor promoter. Cross-fostering offspring of low-lick mothers with high-lick mothers reverses the pattern of methylation in this promoter and protects the offspring of low-lick mothers from over-reactivity to stress. This is a particularly impressive example of success mapping the broad concept of social influences on stress responsivity onto genetic mechanisms.

Child-rearing patterns also influence propensity for aggressive behaviors through effects on the serotonergic system. In an essay dedicated to his colleague, the late Markku Linnoila, Steven Suomi describes his research on rhesus monkeys and the influence of serotonin and patterns of child rearing on aggression, tendency toward alcoholism, and impulsivity. This research demonstrates that serotonin expression interacts with child rearing patterns to influence the propensity for these antisocial behaviors and provides an intriguing parallel to human behavior. Particularly interesting was the report of an interaction between a candidate gene, serotonin transporter gene 5-HTT and mother rearing: animals with a heterozygous short allele (LS) who were raised apart from mothers became aggressive and impulsive later in life whereas those raised with mothers did not exhibit those behaviors. Moreover, because female rhesus monkeys adopt the child rearing practices of their mothers, this interaction suggests a generational transference of the factors leading to this trait. It also raises the intriguing possibility that inheriting the LS allele can lead to psychopathy, but competent mothering can mitigate this unfavorable outcome.\.

In his essay “Protecting and Damaging Effects of Stress Mediators” Bruce McEwen revisits and redefines the stress response originally described by Hans Selye. Here he presents his well-known work expanding the concept of homeostasis and extending it to the concept of allostasis, allostatic states and allostatic load/overload. Allostasis refers to how the systems that maintain homeostasis are themselves kept in balance and adapted to ensure homeostasis. Allostatic states such as hypertension refer to altered and sustained levels of the mediators of allostasis—stress hormones, cortisol, adrenaline, other components of the sympathetic and parasympathetic nervous system, oxytocin, vassopressin, neurotransmitters, neuromodulators, and the immune system—beyond what is adaptive for homeostasis. Allostatic overload refers to the consequences of an imbalance in these mediators when maintained for an extended period of time and includes, for example, abdominal obesity. The clinical relevance of this overarching reconceptualization of the stress response is immediately apparent. Allostatic states and overload contribute to leading health problems in the United States that are less prevalent in other cultures, including obesity and atherosclerosis. Allostatic overload is manifest in the neural systems that underlie memory. When an organism is acutely threatened, say with a pink slip from the NIH—cortisol secretion results in an adaptive response—improved memory for the comments so that the individual can learn to write better grants in the future. However, if stressors are repeated over several weeks, the normally adaptive cortisol response results in neuronal atrophy and heightened responsivity of neural systems mediating the fear response. The conditions under which stressors are experienced play a large role in determining the health consequences of stress mediators.

In a particularly illustrative example of social behaviors regulating neural systems Martha McClintock presents a chapter on “Pheromones, Vasanas, Social Odors and the Unconscious.” We learn that “vasanas” is a term coined from Sanskrit philosophy meaning “to perfume … an unconscious impression left on the mind.” McClintock shows how vasanas modulate—without conscious detection—a woman's behavioral and sympathetic response to the presence of a man. An example of this is androstadienone, a natural steroid secreted in body fluids. Women respond differentially to this social chemosignal depending on whether a man or a woman is running an experiment. If a man is running the experiment, women experience a change in mood and sympathetic tone. If a female experimenter is running the experiment, no change is evident. Men respond in the reverse manner to this vasana by decreasing positive mood and increasing sympathetic activity. Neuroimaging studies show how the presence of this vasana alters patterns of brain activation during visuomotor tasks despite the fact that the signal is undetectable. These chemosignals appear to modulate our emotional responses to varying social encounters.

These four essays, as well as the other seven essays, challenge the external validity of our purposefully simplified and controlled studies to the broader social world. Each essay presents an opportunity to understand the factors in the organism—not just genetic and systemic but social—that can alter what takes place at a cellular and molecular level. Take for example a challenge to basic neuroscientists—the fact that drugs often work differently in isolated cell cultures than they do in organisms. This example, raised by Esther Sternberg, eloquently describes the challenge to researchers attempting to reconcile phenomena that take place on a human time scale in the larger social world to phenomena that take place at the cellular and molecular level within potentially much more rapid time frames. Overall, the collection of essays is a gratifying read for the busy undergraduate or graduate student seeking knowledge and the seasoned researcher seeking continued inspiration.