Science & Technology

The Theory of Moral Neuroscience

Modern brain science is confirming an 18th century philosopher's moral theories


"As we have no immediate experience of what other men feel, we can form no idea of the manner in which they are affected, but by conceiving what we ourselves should feel in the like situation," observed British philosopher and economist Adam Smith in the first chapter of his magisterial The Theory of Moral Sentiments (1759). "Whatever is the passion which arises from any object in the person principally concerned, an analogous emotion springs up, at the thought of his situation, in the breast of every attentive spectator." Smith's argument is that our ability to empathize with others is at the root of our morality.

Recent discoveries in neuroscience are bolstering Smith's insights about the crucial role of empathy in human sociality and morality. For example, in the 1990s, Italian scientists researching motor neurons in macaque monkeys discovered mirror neurons. As the story goes, a monkey's brain had been wired up to detect the firing of his neurons when planning and carrying out a movement such as grasping a peanut. One researcher returned from lunch licking an ice cream cone. As the monkey watched the researcher, some of his neurons fired as though he were eating the ice cream, even though he was not moving. The monkey's neurons were "mirroring" the activity that the monkey was observing.

Neuroscientist Giacomo Rizzolatti and his colleagues at the University of Parma reported their discovery of monkey mirror neurons in 1996. Researchers soon found evidence for mirror neurons in human beings. Just like monkeys, it turns out that when we see someone perform an action—picking up a glass of water or kicking a ball—our mirror neurons simulate that action in our brains. Researchers have suggested that mirror neurons are crucially involved in the distinctive human development of language, morality, and culture.

Research looking at the brains of autistic people highlights the role that some neuroscientists believe that mirror neurons play in empathy. Normal people can implicitly, without thinking, identify the emotions and intentions of others. However, the symptoms of autism often involve a marked lack of awareness of the feelings of others and little or no social interaction or communications with others. In 2005, researchers at the University of California San Diego (UCSD) compared brain wave activity associated with mirror neurons in high functioning individuals with autism spectrum disorders (ASD) and in typical individuals. In normal individuals, mu brain wave activity is suppressed whenever they move their hand, imagine moving their hand, or see someone else move their hand. "The ASD group showed significant mu suppression to self-performed hand movements but not to observed hand movements. These results support the hypothesis of a dysfunctional mirror neuron system in high-functioning individuals with ASD," concluded the study.

Subsequent experiments by Jaime Pineda and his colleagues at UCSD found that individuals with ASD develop compensatory brain mechanisms that allow them to identify correctly the emotions of others and determine their intentions. Mirror neurons are not absent from the brains of ASD people, but they are misfiring. Pineda suggests that neurofeedback retraining might reduce some of the social symptoms of autism.

Up until recently the existence of mirror neurons in humans was largely inferred from the results of functional MRI and electro-encelphalogram (EEGs) studies. At the annual meeting of the Society of Neuroscience earlier this month, Marco Iacoboni and his colleagues at the University of California Los Angeles (UCLA) reported that they had detected human mirror neurons directly. His team inserted electrodes into the frontal lobes of people already undergoing surgery to treat their epileptic seizures. The patients were asked to perform activities and view videos that helped Iacobini and his colleagues identify 34 mirror neurons.

Mirror neurons are not the sole source of our moral sense. After all, ASD individuals are not notably immoral. However, they are an important part of it. Empathy, the ability to feel someone else's joy, pain, and gratitude, helps guide our pre-reflective moral values. So let's consider the limits of empathy for schooling us in morality. Harvard University psychologist Joshua Greene offers the case in which, while driving, you see a bleeding hiker lying by the roadside. You must decide between taking the man to the hospital or refuse to do so because the injured man would bleed all over your expensive upholstery.

Greene correctly observes, "Most people say that it would be seriously wrong to abandon this man out of concern for one's car seats" But what about the case in which you receive a letter from an international charity that promises to lift a poor family in Africa out of abject misery at the cost of a $200 contribution from you? "Most people say that it would not be wrong to refrain from making a donation in this case," writes Greene. What's the difference? In both cases, you can help meet the desperate medical needs of someone else at relatively modest cost to yourself.

Greene conducted fMRI brain scans on people while they considered these personal versus impersonal moral dilemmas. He discovered the first "involved greater activity in brain areas that are associated with emotion and social cognition." Why? Greene proposes an evolutionary answer. He points out that our ancestors evolved in an environment in which they could only choose to save people that they knew personally, not total strangers living continents away.

Greene's findings again buttress Adam Smith's insight from more than two centuries ago that empathy works to prompt us to help our neighbors but attenuates with social distance. "That we should be but little interested, therefore, in the fortune of those whom we can neither serve nor hurt, and who are in every respect so very remote from us, seems wisely ordered by Nature," writes Smith. Wisely ordered or not, modern neuroscience is showing that Nature has so ordered our moral intuitions.

But we do not have to be the slaves of our evolved moral intuitions. By showing us the neural workings of our moral sense, neuroscience is giving us the tools to understand and improve our moral choices. As Greene concludes, "I am confident that the scientific study of human nature will have an increasingly important role in nature's grand experiment with moral animals."

Ronald Bailey is Reason's science correspondent. His most recent book,
Liberation Biology: The Scientific and Moral Case for the Biotech Revolution, is available from Prometheus Books.