What can animals' survival instincts tell us about understanding human emotion?

In his essay, which appears in the journal Neuron, LeDoux proposes shifting scientific focus "from questions about whether emotions that humans consciously feel are also present in other animals and towards questions about the extent to which circuits and corresponding functions that are present in other animals are also present in humans."

The neurological common ground between humans and animals includes brain functions used for survival. It is here, LeDoux contends, that researchers may gain new insights into both humans' and animals' emotions.

"Survival circuit functions are not causally related to emotional feelings, but obviously contribute to these, at least indirectly," he writes. "The survival circuit concept integrates ideas about emotion, motivation, reinforcement, and arousal in the effort to understand how organisms survive and thrive by detecting and responding to challenges and opportunities in daily life. Included are circuits responsible for defense, energy and nutrition management, fluid balance, thermoregulation, and procreation, among others."

LeDoux acknowledges that research on feelings is "complicated because feelings cannot be measured directly. We rely on the outward expression of emotional responses, or on verbal declarations by the person experiencing the feeling, as ways of assessing what that person is feeling. This is true both when scientists do research on emotions and when people judge emotions in their social interactions with one another."

We are even more limited in interpreting animals' emotions.

"When a deer freezes to the sound of a shotgun we say it is afraid, and when a kitten purrs or a dog wags its tail, we say it is happy," writes LeDoux, who is also director of the Emotional Brain Institute, part of the Nathan S. Kline Institute for Psychiatric Research. "We use words that refer to human subjective feelings to describe our interpretation of what is going on in the animal's mind when it acts in way that has some similarity to the way we act when we have those feelings."

But while he concedes that "we will never know what an animal feels," the basis for our interpretations of their emotions could eventually become more informed.

"If we can find neural correlates of conscious feelings in humans -- and distinguish them from correlates of unconscious emotional computations in survival circuits -- and show that similar correlates exists in homologous brain regions in animals, then some basis for speculating about animal feelings and their nature would exist," LeDoux posits.