Credit: Slug Signorino

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Why is it that when you concentrate a lot on one subject or are very angry, your temperature rises? Would thinking very hard about something work when you’re in a dangerously cold situation and need to get warm? —Margarita

Wait—you heat up when you think really hard? You might be on your own with that one, Margarita. Hot because you’re mad, though? Here there’s plenty to say.

And I mean plenty. The nature of emotions such as anger, and how they play out in the body, remain vigorously debated by psychologists and neuroscientists, who stole the topic out from under the philosophers in the 19th century. According to the strictest definition, emotions are simply the body’s automatic reactions to certain stimuli. You see a bear, your pulse spikes: Congratulations, you’ve experienced the emotion fear. A more expansive characterization might consider your conscious reckoning of this cascade of stimulus and bodily reaction—apprehension of bear plus acceleration of heart rate plus utterance of “Oh, shit”—but some neuroscientists differentiate these, using “feeling” to refer to the thing that happens when the brain becomes aware that emotion is in progress.

We should stipulate that we’re talking here about the so-called basic emotions, like anger and fear, which happen automatically, versus complex emotions like envy, which require self-consciousness. Basic emotions happen in the autonomic nervous system, the one we don’t have voluntary control over. The accelerated heartbeat, for instance, gets you ready to outrun the bear. (The bear is the canonical example of a fearful stimulus in much of the discourse, presumably because early scientists hadn’t yet learned about supply-side economics.) Maybe you see the bear stealing your food, thus threatening your survival—you get angry. So basically here’s your answer: You’re hot because, perceiving something that riles you, your body automatically raises its heart rate and blood pressure in preparation for some sort of fight-or-flight outcome.

Beyond the basics, though, agreement breaks down, with contention around a couple key questions. First, which comes first—autonomic response or conscious recognition? And what, if any, is the causal connection? The opening volley came in 1884 from the psychologist William James, who wrote, “The bodily changes follow directly the PERCEPTION of the exciting fact, and that our feeling of the same changes as they occur IS the emotion.” (The very 1880s-style emphasis is James’.) In other words, you take in a stimulus, your body reacts, and your subsequent awareness of stimulus and reaction creates what you feel. There must be a causal link, James thought, because it’s hard to imagine an emotion like fear without an increased heart rate; emotion without bodily manifestation is but “a cold and neutral state of intellectual perception,” and that isn’t too many people’s idea of a good time.

The physiologist Walter Cannon challenged this theory in the early 1900s by means of a charming experiment: He severed the sympathetic-branch nerves of a cat, thus disabling the adrenaline surge that’s central to the standard stress response. When he then scared the creature, it still hissed and its hair stood on end—suggesting that the brain and the autonomic nervous system experience emotion independently, rather than in some causal relationship. Yet another theory, popular in the groovy psychology of the ’60s and ’70s, suggested that a person first perceives a stimulus and exhibits a response, and only then searches her immediate environment for clues about how to label the emotion. Your heart could be racing because a bear is chasing you or because you’re in love—it’s up to you to figure out which.

Which brings us to a second point of contention: Are there distinct, consistent bodily response patterns that can be detected relative to specific emotions? Citing her analysis of some 200 prior studies, Lisa Feldman Barrett, director of an affective-science lab at Northeastern University, wrote last year that no, possible emotional responses are numerous, and vary with the situation. “Even a rat facing a threat,” she pointed out, “will flee, freeze, or fight depending on its surrounding context.”

On the other hand, a 2013 study by Finnish researchers endeavored to create a map of emotions, exposing subjects to certain stimuli—the names of emotions, and movies and stories with emotional content—and asking them to indicate where on their bodies any corresponding sensations were felt. Controlling for cultural differences, the researchers found distinctive locales for individual emotions—fear was in the chest, anger activated the arms, depression muted feeling in the extremities. The implications of this are obviously important: identifying patterns in emotional response is one step toward controlling it, and thus theoretically toward advances in (for instance) how we treat mood disorders. And who knows? Maybe someday you’ll even be able to emote your way out of a snowbank. —Cecil Adams