According to the classical view of emotion, our faces hold the key to assessing emotions objectively and accurately (Darwin, Tomkins, Izard, Ekman)..As it turns out in study after study, facial muscle movements do not reliably indicate when someone is angry, sad, or fearful; they don’t form predictable fingerprints for each emotion…An emotion like “Fear” does not have a single expression but a diverse population of facial movements that vary from one situation to the next…Likewise, happiness, sadness, anger, and every other emotion you know is a diverse category, with widely varying facial movements.
With respect to emotions and the autonomic nervous system (controlling heart rate, blood pressure, skin conductance, etc.) .. None of four significant meta-analyses, the largest of which covered more than 220 physiology studies and nearly 22,000 test subjects, found consistent and specific emotion fingerprints in the body. .. On different occasions, in different contexts, in different studies, within the same individual and across different individuals, the same emotion category involves different bodily responses. Any emotion category has tremendous variety, and variation, not uniformity, is the norm. This requires population thinking. A category such as anger can only be described as a collection of instances with no distinctive fingerprint at their core. There is far more variation than the classical view of emotion predicts or can explain. The category can be described at the group level only in abstract, statistical terms.
If not in facial expressions or autonomic nervous system changes, can fingerprints of emotions such as fear be found in the brain? Brain lesion studies undermine the idea that the amygdala contains the circuit for fear. They point instead to the idea that the brain must have multiple ways of creating fear, and therefore the emotion category “Fear” cannot be necessarily localized to a specific region. Results for other emotion categories have been similarly variable. Brain regions like the amygdala are routinely important to emotion, but they are neither necessary nor sufficient for emotion. Many combinations of neurons can produce the same emotional category - this degeneracy is a humbling reality check.
The brain contains core systems that participate in creating a wide variety of mental states. A single core system can play a role in thinking, remembering, decision-making, seeing, hearing, and experiencing and perceiving diverse emotions. A core system is “one to many”: a single brain area or network contributes to many different mental states. The classical view of emotion, in contrast, considers particular brain areas to have dedicated psychological functions, that is, they are “one to one.” Core systems are therefore the antithesis of neural fingerprints. Most neurons are multipurpose, playing more than one part, much as flour and eggs in your kitchen can participate in many recipes.
A meta-analysis covering every usable published neuroimaging study on anger, disgust, happiness, fear, and sadness, (nearly 100 published studies involving nearly 1,300 test subjects across almost 20 years) found that no brain region contained the fingerprint for any single emotion. Fingerprints are also absent if you consider multiple connected regions at once (a brain network), or stimulate individual neurons with electricity. The same results hold in experiments with other animals that allegedly have emotion circuits, such as monkeys and rats. Emotions arise from firing neurons, but no neurons are exclusively dedicated to emotion. These findings are the final, definitive nail in the coffin for localizing emotions to individual parts of the brain.
Brain circuitry operates by the many-to-one principle of degeneracy: instances of a single emotion category, such as fear, are handled by different brain patterns at different times and in different people. Conversely, the same neurons can participate in creating different mental states (one-to-many). …variation is the norm. Emotion fingerprints are a myth. If we want to truly understand emotions, we must start taking that variation seriously. We must consider that an emotion word, like “anger,” does not refer to a specific response with a unique physical fingerprint but to a group of highly variable instances that are tied to specific situations. What we colloquially call emotions, such as anger, fear, and happiness, are better thought of as emotion categories, because each is a collection of diverse instances. .. instances of “Anger” vary in their physical manifestations (facial movements, heart rate, hormones, vocal acoustics, neural activity, and so on), and this variation might is related to their environment or context.