Neuroscientists Reveal Anna Karenina Principle in Brain's Response to Persuasion

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A team of researchers at HSE University investigated the neural mechanisms involved in how the brain processes persuasive messages. Using functional MRI, the researchers recorded how the participants' brains reacted to expert arguments about the harmful health effects of sugar consumption. The findings revealed that all unpersuaded individuals' brains responded to the messages in a similar manner, whereas each persuaded individual produced a unique neural response. This suggests that successful persuasive messages influence opinions in a highly individual manner, appearing to find a unique key to each person's brain. The study findings have been published in PNAS.

Persuading people to adopt a healthier lifestyle can be accomplished through effective argumentation. For several years, researchers at the HSE Institute for Cognitive Neuroscience have been investigating how expert arguments about healthy eating can influence a person's willingness to purchase sugar-free foods, and, most importantly, which areas of the brain are involved. 

In a recent study, neuroscientists at HSE University compare the brain responses of individuals who are likely to be persuaded by expert arguments with those who resist persuasion. Unlike traditional research approaches, where participants are exposed to isolated words or phrases, the researchers presented the subjects with an expert's talk on the health risks of sugar consumption. This approach supports a more realistic laboratory simulation of persuasive communication. To obtain a comprehensive and detailed picture of neural activity in different groups of participants, the researchers employed functional magnetic resonance imaging (fMRI). Using the mathematical method of intersubject correlation analysis, the researchers then examined whether the neural responses to the healthy eating call were similar or varied across participants.

Figure 1. A illustrates the experimental procedure; B shows an example of a product evaluation task

Source © Ioannis Ntoumanis et al. Deciphering the neural responses to a naturalistic persuasive message (2024)

The experiment involved 50 participants and consisted of two parts. First, participants were asked to rate three types of products—sugar-containing, sugar-free, and non-edible—and to place bids on each by indicating how much they would be willing to pay. Next, the participants listened to a 7-minute lecture by an expert on the health risks of sugar consumption, after which they were asked to bid on the same products once again. Throughout the experiment, the researchers monitored the participants' brain activity using fMRI.

As a result of the healthy eating message, some participants changed their minds in favour of a healthier diet. The persuaded group also displayed highly varied patterns of brain activity, in particular a greater diversity of activity in the lower regions of the frontal cortex, an area crucial for decision-making and social cognition. 

In contrast, the brains of participants who were sceptical and unpersuaded by the expert's arguments processed the information all in a similar manner. They showed high synchronisation of activity in brain regions linked to self-reflection and critical assessment of information.

Vasily Klyucharev

'We used an unconventional method to study brain activity: we examined the similarity of neural activity across a group of individuals. In scientific terms, this is referred to as "intersubject correlation of brain activity." Our findings can be described as a type of Anna Karenina effect, where the responses of those who are indifferent and immune to arguments are alike, while each persuaded individual responds in their own unique way. Apparently, an effective persuasive message can adapt to individuals' unique characteristics, targeting aspects that are particularly relevant to each listener,' explains Vasily Klyucharev, Head of the International Laboratory of Social Neurobiology and of this research project.  

Interestingly, participants influenced by the expert's talk were willing to pay more for healthy food, but the value they placed on sugar-containing food did not decrease. According to the researchers, this may be due to the structure of the audio message: towards the end, the expert emphasised the benefits of healthy eating rather than the negative effects of sugar consumption. Information that concludes a message is typically remembered best.

Ioannis Ntoumanis

'In the future, we hope to continue studying this "Anna Karenina effect" to identify the reasons behind the differences in neuronal activity among those who are persuaded. Does the effectiveness of persuasive messages depend on the chosen arguments, and what factors exactly influence people? All of this can improve the perception of public health messages, making them more personalised and, as a result, more effective,' according to Ioannis Ntoumanis, Junior Research Fellow at the International Laboratory of Social Neurobiology and co-author of the study. 

The study was conducted within the framework of the strategic project 'Human Brain Resilience: Neurocognitive Technologies for Adaptation, Learning, Development and Rehabilitation in a Changing Environment' ('Priority 2030').