Researchers at the HSE Institute for Cognitive Neuroscience have shown experimentally that magnetic stimulation of the prefrontal cortex of the brain causes test subjects to act less rationally, changing how they assess possible outcomes at the moment they make risky decisions. The scientists believe that the discovery will provide a better understanding of the mechanisms that give rise to gaming addiction. The results of the study were published in the journal Scientific Reports.
In everyday life, we often have to make decisions in conditions of uncertainty and risk. This requires that we process a significant amount of information. For example, if a person is considering whether to buy a lottery ticket costing 100 rubles, they need to evaluate the attractiveness of the potential winnings and whether the probability of winning is high enough to justify the specified price.
The classic way to study how the brain works when making decisions is to conduct behavioural experiments using functional magnetic resonance imaging (fMRI). The subject is placed in an fMRI scanner and asked to choose among different lotteries. Researchers then observe which areas of the brain are more active if the person chooses a riskier option or, conversely, one of lower risk.
However, this research method has two drawbacks. First, it does not prove a causal relationship between the activity of a certain area of the brain and the decision that is made. Second, people tend to perceive the value of the reward and the likelihood of receiving it in a distorted way. For example, it is difficult to gauge the difference between a 1 in a million chance of winning and a 1 in 100,000 chance of winning.
We also determine monetary values in non-linear fashion: for example, we might place greater importance on the difference between 1,000 and 1,100 rubles than on the difference between 10,000 and 10,100 rubles. All of this leads to the question of which areas of the brain are directly involved in generating this distorted perception and how the brain integrates this information to make each individual decision.
A study by the Institute for Cognitive Neurosciences at HSE University managed to answer both questions. Researchers focused their experiments on the dorsolateral prefrontal cortex of the brain because the literature indicates that this area plays an important role in making risky decisions. They used transcranial magnetic stimulation to temporarily suppress the excitability of this region of the brain and then asked subjects to answer a series of questions and choose between lotteries of greater or lesser risk.
Each test subject visited the laboratory three times. On two visits, researchers applied magnetic stimulation to either the right or left dorsolateral prefrontal cortex, and on one they applied no stimulation at all (although the subject was unaware of this).
The transcranial magnetic stimulation method is based on the principle of electromagnetic induction. A magnetic field generator or ‘coil’ is placed near the subject’s head, generating magnetic fields of a specific frequency and intensity. The fields pass easily through the skull and meninges, reaching nearby neurons (at a depth of up to 5 cm) and activating them or, conversely, temporarily ‘turning them off’.
Researchers found that test subjects’ decisions differed after actual brain stimulation versus ‘placebo stimulation’. A temporary decrease in the excitability of the left dorsolateral prefrontal cortex caused subjects to behave less rationally: they focused less on the average winnings that could be obtained in each of the lotteries.
Mathematical analysis showed that this change was due to the fact that magnetic stimulation of the brain caused the perception of winning probabilities to become even more distorted. For example, subjects perceived a 97% probability of winning as a 100% probability, and, conversely, a 1% probability as a 0% probability. At the same time, the subjective value of monetary reward remained unchanged for them.
The prefrontal cortex of the brain plays a leading role in the perception of such abstract information as the probability of possible outcomes. We have shown that there is a causal relationship between the activity of the dorsolateral prefrontal cortex and which lottery a person chooses. The cortex might also combine this information with other aspects of the choice, such as the size of the potential winnings, to make the final decision. The study of such neuronal mechanisms might in the future lead to a better understanding of pathological behaviour, such as gambling, in which a person systematically prefers risky decisions, even to the detriment of their own well-being.
Senior Research Fellow, Center for Cognition & Decision Making, Institute for Cognitive Neuroscience, HSE University