Brain stimulation affects compliance with social norms

Neuroeconomists at the University of Zurich have identified a specific brain region that controls compliance with social norms. They discovered that norm compliance is independent of knowledge about the norm and can be increased by means of brain stimulation.

How does the human brain control compliance with social norms? The biological mechanisms that underlie norm compliance are still poorly understood. In a new study, Christian Ruff, Giuseppe Ugazio, and Ernst Fehr from the University of Zurich show that the lateral prefrontal cortex plays a central role in norm compliance.

Prefrontal cortex controls norm behavior

For the study, 63 participants took part in an experiment in which they received money and were asked to decide how much of it they wanted to share with an anonymous partner. A prevalent fairness norm in Western cultures dictates that the money should be evenly split between the two players. However, this contrasts with the participants’ self-interest to keep as much money as possible for themselves. In another experiment, the participants were faced with the same decision, but knew in advance that they could be punished by the partner for an unfair proposal.

By means of a technique called “transcranial direct current stimulation,” which sends weak and painless electric currents through the skull, the excitability of specific brain regions can be modulated. During this experiment, the scientists used this technique to increase or decrease neural activity at the front of the brain, in the right lateral prefrontal cortex. Christian Ruff, Professor of Neuroeconomics and Decision Neuroscience at the University of Zurich, said: “We discovered that the decision to follow the fairness norm, whether voluntarily or under threat of sanctions, can be directly influenced by neural stimulation in the prefrontal cortex.”

Brain stimulation affects normative behavior

When neural activity in this part of the brain was increased via stimulation, the participants’ followed the fairness norm more strongly when sanctions were threatened, but their voluntary norm compliance in the absence of possible punishments decreased. Conversely, when the scientists decreased neural activity, participants followed the fairness norm more strongly on a voluntary basis, but complied less with the norm when sanctions were threatened. Moreover, neural stimulation influenced the participants’ behavior, but it did not affect their perception of the fairness norm. It also did not alter their expectations about whether and how much they would be punished for violating the norm.

"We found that the brain mechanism responsible for compliance with social norms is separate from the processes that represent one’s knowledge and beliefs about the social norm," says Ernst Fehr, Chairman of the Department of Economics at the University of Zurich. "This could have important implications for the legal system as the ability to distinguish between right and wrong may not be sufficient for the ability to comply with social norms." Christian Ruff adds: "Our findings show that a socially and evolutionarily important aspect of human behavior depends on a specific neural mechanism that can be both up- and down-regulated with brain stimulation."

Literature:

Christian C. Ruff, Giuseppe Ugazio und Ernst Fehr. Changing Social Norm Compliance With Noninvasive Brain Stimulation. Science. October 3, 2013.

(Image: iStockphoto)

By tracking maggots’ food choices, scientists open significant new window into human learning

The squirming larva of the humble fruit fly, which shares a surprising amount of genetic material with the human being, is helping scientists to understand the way we learn information from one another.

Fruit flies have long served as models for studying behaviour because their cognitive mechanisms are parallel to humans’, but much simpler to study.

Fruit flies exhibit many of the same basic behaviours as humans and share 87 per cent of the material that is responsible for genetically based neurological disorders, making them a potent model for study.

While adult fruit flies have been studied for decades, the new paper reveals that their larvae, which are even simpler organisms, may be more valuable models for behavioral research. A fruit fly larva has only 3,000 neurons, for example, while a human has about 10 billion.

The McMaster researchers were able to prove that the larvae, or maggots, are capable of social learning, which opens the door to many other experiments that could provide valuable insights into human behaviour, end even lead to treatments for human disorders, the scientists say.

“People have been studying adult flies for decades now,” explains the study’s lead author, Zachary Durisko. “The larval stage is much simpler in terms of the brain, but behaviour at the larval stage has been less well studied. Here we have a complex behaviour in this even simpler model.”

Durisko and Reuven Dukas, both of McMaster’s Department of Psychology, Neuroscience and Behaviour, have shown that fruit fly larvae are able to distinguish which food sources have been used by other larvae and utilize the information to benefit themselves by choosing to eat from those same established sources instead of available alternatives.

The maggots’ attraction to food that others have been eating is based on smell, and is roughly equivalent to a person arriving in a new city, seeing two restaurants and choosing a busy one over an empty one, the researchers explain.

“They prefer the social over the non-social like we would do, and they learn to prefer the social over the non-social,” Dukas says.

In fact, the motivations may be similar in each case, and could include accepting the judgment of others as an indication of quality and seeking the company of others for protection from harm.

Durisko, the lead author, recently completed his PhD at McMaster, and Dukas, his co-author, is a professor at the university. Their work is published in the prestigious Proceedings of the Royal Society B, one of the society’s biological journals.

The researchers used several combinations of foods, both completely fresh and previously used, and of varying degrees of nutritional value, to compare the maggots’ preferences.