In the previous edition of this book we noted that the neuroscientific study of emotion was flourishing, and this led scientists to recognize that other hot aspects of cognition—namely, the social aspects of cognition—were equally due for attention. In the past five years the field of social neuroscience has exploded, as evidenced by the launching of new journals and major initiatives from many federal funding agencies. At the core of this emphasis on social cognition is the importance of emotional processing. The social and emotional aspects of the brain are inexorably linked, the adaptive significance of emotions being closely linked to their social value, and nearly all social interaction produces affective responses. It is clear from the chapters in this section that the study of emotion and social cognition remains at the forefront of cognitive neuroscience.

The interdisciplinary field of cognitive neuroscience has provided ample evidence of the benefits of examining psychological constructs across multiple levels of analysis, from the molecular to the cultural. The chapters in this section cross many levels, from the role of systems, cellular and molecular mechanisms in learning and memory in adult animals (LeDoux, Schiller, and Cain) and during early development (Sullivan and colleagues), to human studies of emotion (Vuilleumier and Brosch, Whalen and Davis) and emotion regulation (Beer) using functional imaging, including imaging genomics (Hariri), and studies of brain regions that support social cognition (Mitchell and Heatherton), sensitivity to others (Singer and Leiberg), and moral transgressions (Greene), many of the chapters emphasizing how these systems interact. It is clear that research that uses multiple approaches is moving the field toward the ultimate goal of developing coherent models of how the brain makes emotion and performs its social function.

In the last edition there was remarkable convergence of evidence highlighting the important role of the amygdala across animal species and paradigms. The importance of the amygdala continues to hold center stage in the neuroscience of emotion, as is evident in many of the chapters. LeDoux, Schiller, and Cain provide a timely review of the importance of the amygdala in normal and pathological fear, especially the cellular molecular mechanisms that underlie learning and memory. For instance, they update research demonstrating the important role of gene expression in long-term potentiation, which is perhaps the most likely candidate for the physiological basis of fear conditioning and other forms of memory. The chapter by Sullivan and colleagues demonstrates that the role of the amygdala in fear learning depends on its developmental maturity. During the sensitive period associated with a rat pup's attachment to its mother (about 10 days postnatal), fear learning is attenuated due to a lack of amygdala functioning. This process allows the pup to attach to its mother irrespective of whether the mother is treating it harshly or gently. Vuilleumier and Brosch present exciting new evidence that attention and emotion can influence basic visual processing. That is, the emotional significance of stimuli, not just the strictly visual properties of the retinal image, influences basic perceptual processing. They provide compelling evidence that the amygdala plays an important role in the modulation of sensory information. Whalen and Davis address how context influences amygdala activity and subsequent interpretations of emotional stimuli; that is, they describe how amygdala activity is strongly affected by the context in which biologically relevant cues are encountered. Hariri provides examples of how imaging genetics can lead to insights about the biological mechanisms underlying individual differences in complex behavioral traits, such as how abnormal gene expression in the serotonin system can affect how the amygdala responds to facial expressions. Taken together, these chapters not only reinforce the important role of the amygdala in emotional processing but also demonstrate how new techniques and approaches are continuing to provide important insights.

The last four chapters in this section focus more on the social basis of emotional processing. These chapters demonstrate that there continues to be growing interest among social psychologists and cognitive neuroscientists in using brain imaging to study social aspects of cognition, such as recognition of faces and emotional expressions, theory of mind, social emotions such as empathy, judging trustworthiness and attractiveness, and cooperation. Mitchell and Heatherton outline the basic components necessary for a social brain, including a sense of self, mentalizing ability, capacity for self-regulation, and threat detectors for ingroup and outgroup threats, and they discuss the discrete neural signatures of these basic components. Beer describes research on how people are able to regulate their emotions so that they can function in their social groups. She outlines evidence that damage to areas of frontal cortex interferes with emotion regulation. Singer and Leiberg describe fascinating new research on the neural basis of empathy and how it is influenced by both dispositional and contextual factors. Finally, Greene describes research on how human brains make moral judgments. The ethical brain reflects perhaps the greatest achievement of human evolution, and researchers are just beginning to identify how people make these types of important decisions.

Considering the section as a whole, it is clear that the study of emotion continues to be a strong growth area in cognitive neuroscience. Moreover, it has expanded to include the closely connected social brain. As an organ that has evolved to solve adaptive problems, the brain relies on emotional processes to solve challenges to successful adaptation. For humans, many of the most pernicious adaptive problems involve other humans, such as selecting mates, cooperating in hunting and gathering, forming alliances, competing over scarce resources, and even warring with neighboring groups. Interacting with other humans produces emotion, and these emotions serve as guidelines for successful group living. For example, behaviors such as lying, cheating, and stealing are discouraged by social norms in all societies because they decrease survival and reproduction for other group members. They also elicit vigorous emotional responses. Hence any true understanding of human nature will require a full consideration of both the emotional brain and the social brain. We expect that research on this topic will continue to be on the cutting edge of cognitive neuroscience in the next decade.