International Business Department           Liu Bojia           January 08, 2023

  Uncertainty is a constant in life, and we often need to make trade-offs between a wide range of possibilities, with some options having high rewards but also high risks, and others being safer but also having low returns. Risk-dependent decision-making is critical not only in economic activities such as investing, but also in many everyday scenarios. When undecided, some would figuratively say that there seems to be a tug-of-war between two little people in their heads, one favouring stability and the other more willing to take a chance.

  Interestingly, a recent paper published in the leading academic journal Science has found that there really are two such "little people" in the brain: two neighbouring brain regions compete to influence an individual's attitude in the face of risk, and the outcome of their competition determines the outcome of the individual's actions.

  In this study, researchers at Kyoto University in Japan used Japanese rhesus monkeys (Macaca fuscata) as subjects in a task designed to make them choose between a high-risk, high-reward (HH) and a low-risk, low-reward (LL) option. After being trained by the researchers, the monkeys learnt to indicate their choice between the two cues using eye movements and were rewarded accordingly - with water.

  In each set of experiments, the expected value of the two options was in fact equivalent, that is, the amount of water multiplied by the probability of getting water was equal, with the cue with the higher amount of water corresponding to the smaller probability of getting water (high risk, high reward), and conversely the cue with the smaller amount of water chosen to get water almost every time as expected (low risk, low reward). Such a design implies that the choice preferences exhibited by the monkeys represent their attitudes towards risk.

  Six monkeys were tested and all showed a preference for high risk-high reward. This is consistent with previous research focusing on primate risk behaviour, where monkeys generally preferred high risk-high reward when choosing water.

  And while the macaques were completing the task and making decisions, the researchers took a deeper look at their cerebral cortex, specifically the orbitofrontal cortex (OFC), the anterior cingulate gyrus (ACC), and the ventral aspect of area 6 of Brodmann's subdivisions (BA 6V), as all of these brain regions are likely to influence an individual's attitude toward risk, according to speculation from previous studies.

  The study authors inactivated these subsequent brain regions one by one by injecting the drug muscimol, and were surprised to find that only the inactivation of BA 6V in the frontal lobe affected the monkeys' risk-based decision-making, whereas virtually none of the other brain regions affected the monkeys' high-risk, high-reward preferences when they were inactivated.

  After finding the key brain region BA 6V that controls risk attitudes, the researchers further analysed the role of reward feedback on this network. The key entry point was the dopaminergic neurons projecting from the ventral tegmental area (VTA) to BA 6V. Using delicate optogenetic manipulations, the researchers were able to artificially activate dopamine release in this group of neurons through implanted electrodes.

  Interesting results emerged: the tiny BA 6V can also be subdivided into two parts, dorsal and ventral, which, despite a difference in location of only two or three millimetres, have opposite attitudes to risk based on reward-based feedback, one being a gamble-loving and the other risk averse.

  Specifically, in the short time it takes monkeys to make a decision, after the BA 6V ventral pathway receives dopamine from the VTA, they prefer the high-risk, high-reward option, whereas the dorsal side receives input from the VTA with the opposite effect, with monkeys favouring the low-risk, low-reward option. Together, these two neighbouring parts regulate an individual's attitude to risk.

  It is noteworthy that when one of the two neural pathways from VTA to BA 6V is repeatedly stimulated, monkeys undergo a long-term change in their preference for high-risk, high-reward or low-risk, low-reward, and that this cumulative long-term change over time is no longer affected by light-activation-induced dopamine release.

  Professor Tadashi Isa, the paper's corresponding author, speculated that this long-term change might provide an explanation for the mechanism of gambling addiction. And given the many structural and functional similarities between the human brain and primates such as rhesus monkeys, the findings associated with this study may have potential therapeutic implications that could be applied to intervene in pathological forms of risk-taking behaviour such as gambling addiction.