Quest to find the biological fingerprints of emotions

Studies suggest each emotion may not have a distinct pattern in the face, body or brain

Our senses appear to show us the world the way it truly is, but they are easily deceived. For example, if you listen to a recorded symphony through stereo speakers that are placed exactly right, the orchestra will sound like it is inside your head. Obviously that is not the case.

But suppose you completely trusted your senses. You might find yourself asking well-meaning but preposterous scientific questions such as "Where in the brain is the woodwinds section located?" A more reasonable approach is not to ask a "where" question but a "how" question: "How does the brain construct this experience of hearing the orchestra in your head?"

I have just set the stage to dispel a major misconception about emotions. Most people, including many scientists, believe that emotions are distinct entities inside us that can be located- but they are not. Searching for emotions in this form is as misguided as looking for cerebral clarinets and oboes.

We do experience anger, happiness, surprise and other emotions as clear and identifiable states of being.

This seems to imply that each emotion has an underlying property or "essence" in the brain or body. Perhaps an annoying colleague triggers your "anger neurons", so your blood pressure rises; you scowl, yell and feel the heat of fury. Or the loss of a loved one triggers your "sadness neurons", so your stomach aches; you pout, feel despair and cry. Or an alarming news story triggers your "fear neurons" so you freeze and feel a flash of dread.

The most well-known "emotion" region of the brain is the amygdala, a group of nuclei found deep within the temporal lobes. Since 2009, at least 30 articles in the popular press have claimed that fear is caused by neurons firing in the amygdala. Yet only a quarter of the experiments we analysed showed an increase in activity in the amygdala during the experience of fear. It has long been known that certain types of "fear" behaviour, such as fleeing, do not require the amygdala.

Such characteristics are thought to be the unique biological "fingerprints" of each emotion. Scientists and technology companies spend huge amounts of time and money trying to locate these fingerprints. They hope someday to identify your emotions from your facial muscle movements, your body changes and your brain's electrical signals.

Some scientific studies seem to support the claim that such fingerprints exist. But many disagree on what the fingerprints are, and a multitude of other studies indicate there are no such fingerprints.

Let's start with neuroscience.

The Interdisciplinary Affective Science Laboratory (which I direct) collectively analysed brain-imaging studies published from 1990 to 2011 that examined fear, sadness, anger, disgust and happiness. We divided the human brain virtually into tiny cubes, like 3D pixels, and computed the probability that studies of each emotion found an increase in activation in each cube.

Overall, we found that no brain region was dedicated to any single emotion. We also found that every alleged "emotion" region of the brain increased its activity during non-emotional thoughts and perceptions as well.

The most well-known "emotion" region of the brain is the amygdala, a group of nuclei found deep within the temporal lobes. Since 2009, at least 30 articles in the popular press have claimed that fear is caused by neurons firing in the amygdala. Yet only a quarter of the experiments we analysed showed an increase in activity in the amygdala during the experience of fear. It has long been known that certain types of "fear" behaviour, such as fleeing, do not require the amygdala.

Other evidence against the amygdala-fear relationship comes from a pair of identical twins, known in the scientific literature as "BG" and "AM", who both have a genetic disease that obliterates the amygdala. BG has difficulty feeling fear in all but the most extreme situations, but AM leads a normal emotional life.

Brain regions such as the amygdala are certainly important to emotion, but they are not necessary or sufficient for it. The workings of the brain are not one-to-one, whereby a given region has a distinct psychological purpose. Instead, a single brain area like the amygdala participates in many different mental events, and many different brain areas are capable of producing the same outcome. Emotions such as fear and anger, my lab has found, are constructed by multi-purpose brain networks that work together.

If emotions are not distinct neural entities, perhaps they have a distinct bodily pattern - heart rate, respiration, perspiration, temperature and so on?

Again, the answer is no. My lab analysed more than 200 published studies, covering nearly 22,000 test subjects, and found no consistent and specific fingerprints in the body for any emotion. Instead, the body acts in diverse ways that are tied to the situation. Even a rat facing a threat (say, the odour of a cat) will flee, freeze or fight depending on its surrounding context.

The same goes for the human face. Many scientists assume that the face clearly and reliably broadcasts emotion (scowling in anger, pouting in sadness, widening the eyes in fear, wrinkling the nose in disgust). But a growing body of evidence suggests that this is not the case. When we place electrodes on a human face and actually measure muscle movements during anger, for example, we find that people make a wide variety of movements, not just the stereotypical scowl.

Charles Darwin famously vanquished the notion of essences in biology. He observed that a species is not a single type of being with a fixed set of attributes, but rather a population of richly varied individuals, each of which is better or worse suited to its environment.

Analogously, emotion words such as "anger", "happiness" and "fear" name a population of diverse biological states that vary depending on the context. When you are angry with someone, sometimes your heart rate will increase, other times it will decrease and still other times it will stay the same. You might scowl, or you might smile as you plot your revenge. You might shout or be silent. Variation is the norm.

This insight is not just academic. When medical researchers ask "What is the link between anger and cancer?" as if there is a single thing called "anger" in the body, they are in the grip of this error. When airport security officers are trained on the assumption that facial and body movements are reliable indicators of innermost feelings, taxpayers' money is wasted.

The ease with which we experience emotions, and the effortlessness with which we see emotions in others, does not mean that each emotion has a distinct pattern in the face, body or brain. Instead of asking where emotions are or what bodily patterns define them, we would do better to abandon such essentialism and ask the more revealing question, "How does the brain construct these incredible experiences?"

NEW YORK TIMES

A version of this article appeared in the print edition of The Sunday Times on August 09, 2015, with the headline 'Quest to find the biological fingerprints of emotions'. Print Edition | Subscribe