The brain has long enjoyed a privileged status as psychology’s favorite body organ. This is, of course, unsurprising given that the brain instantiates virtually all mental operations, from understanding language, to learning that fire is dangerous, to recalling the name of one’s kindergarten teacher, to categorizing fruits and vegetables, to predicting the future. Arguing for the importance of the brain in psychology is like arguing for the importance of money in economics.

More surprising, however, is the role of the entire body in psychology and the capacity for body parts inside and out to influence and regulate the most intimate operations of emotional and social life. The stomach’s gastric activity , for example, corresponds to how intensely people experience feelings such as happiness and disgust. The hands’ manipulation of objects that vary in temperature and texture influences judgments of how “warm” or “rough” people are. And the ovaries and testes’ production of progesterone and testosterone shapes behavior ranging from financial risk-taking to shopping preferences.

Psychology’s recognition of the body’s influence on the mind coincides with a recent focus on the role of the heart in our social psychology. It turns out that the heart is not only critical for survival, but also for how people related to one another. In particular, heart rate variability (HRV), variation in the heart’s beat-to-beat interval, plays a key role in social behaviors ranging from decision-making, regulating one’s emotions, coping with stress, and even academic engagement. Decreased HRV appears to be related to depression and autism and may be linked to thinking about information deliberately. Increased HRV, on the other hand, is associated with greater social skills such as recognizing other people’s emotions and helps people cope with socially stressful situations, such as thinking about giving a public speech or being evaluated by someone of another race. This diverse array of findings reflects a burgeoning interest across clinical psychology, neuroscience, social psychology, and developmental psychology in studying the role of the heart in social life.

A key moment for the field came in 1995, when Stephen Porges, currently a professor of psychiatry at the University of Illinois at Chicago, put forth Polyvagal Theory, a theory that emphasized the role of the heart in social behavior. The theory states that the vagus nerve, a nerve likely found only in mammals, provides input to the heart to guide behavior as complex as forming relationships with other people as well as disengaging from others. A distinguishing feature of Polyvagal theory is that it places importance not on heart rate per se, but rather on the variability of the heart rate, previously thought to be an uninteresting variable or mere noise.

Since 1995, a broad spectrum of research emerged in support of Polyvagal theory and has demonstrated the importance of the heart in social functioning. In 2001, Porges and his colleagues monitored infants when they engaged in a social interaction with the experimenter (cooing, talking, and smiling at them) and when they encountered the experimenter simply making a still face—a frozen expression—toward them. Infants’ HRV not only increased during the social interaction, but also increases in HRV predicted positive engagement (greater attention and active participation by the infants) during this interaction. In adults as well, HRV appears to be associated with success in regulating one’s emotions during social interaction, extraversion, and general positive mood.

A number of recent findings converge on the role of heart rate variability in adaptive social functioning as well. One study by Bethany Kok and Barbara Frederickson, psychologists at the University of North Carolina, asked 52 adults to report how often they experienced positive emotions like happiness, awe, and gratitude and how socially connected they felt in their social interactions every day for a period of nine weeks. The researchers also measured the HRV of each individual at the beginning and end of the study by measuring heart rate during a two-minute session of normal breathing. HRV at the beginning of the study predicted how quickly people developed positive feelings and experiences of social connectedness throughout the nine-week period. In addition, experiences of social connectedness predicted increases in HRV at the end of the study, demonstrating a reciprocal relationship between heart rate and having satisfying social experiences.

Although high heart rate variability seems to have largely positive effects on people’s emotional state and their ability to adapt to their social environment, the story may soon become more complicated. For example, in unpublished research, Katrina Koslov and Wendy Berry Mendes at Harvard University have recently found that people’s capacity to alter—and in a sense regulate—HRV predicts theirsocial skills. In three studies, Koslov and Mendes measured this capacity to alter HRV during a task involving tracking the location of shapes on a computer screen (completely unrelated to anything social), and demonstrated that people’s capacity to alter HRV during this task subsequently predicted both their ability to judge others’ emotions accurately and their sensitivity to social feedback (how much they responded positively to positive feedback and negatively to negative feedback). These findings suggest that although high HRV at rest may be adaptive for social engagement, the capacity to modulate HRV also promotes social sensitivity.

Writers from Ovid to Stevie Wonder have used the heart as a convenient metaphor to convey emotional responses toward others. Emerging research suggests, however, that this metaphor is an oversimplification. The heart has complex interactions with how we treat and evaluate others, how we cope with social stress, and how we manage our emotions, and research has only begun to explore the relationship between cardiovascular processes and social life. Although philosopher Blaise Pascal noted, “The heart has reasons that reason cannot know,” it is clear that psychological research is beginning to illuminate this mystery.

Are you a scientist? Have you recently read a peer-reviewed paper that you want to write about? Then contact Mind Matters co-editor Gareth Cook, a Pulitzer prize–winning journalist at the Boston Globe, where he edits the Sunday Ideas section. He can be reached at garethideas AT gmail.com