Lottery-Loving Rats Reveal How the Brain Handles Uncertainty
A new study details an ingenious task that explores how rats weigh up complex economic decisions.
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Whether we decide to gamble or safely invest our money involves carefully calculating future risks. Studying how the brain weighs up this uncertainty has been a significant challenge. Animal research is needed to dig down into these mechanisms, but designing experiments that involve complicated economic decisions has hitherto required non-human primates as test subjects. With the use of these highly intelligent animals in research becoming more regulated, new ways of exploring the uncertain brain have been required.
Now, a new study details an ingenious task that explores how rats weigh up complex economic decisions.
The research was published in Nature Neuroscience.
The study, led by Jeffrey Erlich, group leader at the Sainsbury Wellcome Centre, offered rats a choice between a small and guaranteed reward called a “surebet” and a lottery, which had a range of rewards with a fixed probability. Over a period of around a month, the team managed to teach the rats what the value of the lottery would be, based on a sound that was played to them.
As expected, the rats quickly learned that a sound indicating a very low or zero lottery reward should make them choose the surebet, while a sound indicating a high reward sent them scampering towards the lottery.
Erlich and team carefully monitored the rodents’ brains while they completed the task, studying their frontal and parietal lobes. In particular, they were focused on two brain areas called the frontal orienting field (FOF) and posterior parietal cortex (PPC). The FOF is the rodent equivalent of a primate brain structure called the frontal eye field. “That part of the primate brain is really important for spatial attention, and planning and orienting movements,” says Erlich in an interview with Technology Networks.
In rodents, the FOF plays a central role in the behavioral task that Erlich’s team designed. The mice, upon hearing the sound cue, would have to move either left or right to get to the lottery or surebet. “If you record from neurons in this brain area, you can predict which movement the animal will make at the time of the sound. It encodes upcoming movement,” explains Erlich. But that wasn’t the whole story.
“We could actually see the quality of the lottery in the activity,” explains Erlich. When the FOF was silenced – an effect achieved using drugs and gene modifications – the rodents seemed to lose their appetite for risk. When a high-reward lottery was on offer, the rodents still picked it but became more reticent to go after an intermediate-level lottery reward, preferring the safety of the surebet. They remained uninterested in a low lottery reward. Importantly, the researchers played the tone continuously until the rats made their choice, meaning that they were not required to use their working memory during the task. This enabled Erlich’s team to disentangle the effects of FOF silencing on decision-making from its impact on memory, which previous study designs had been unable to separate.
Making sense of the mouse brain
Silencing the PPC had a much smaller and more short-lived effect on risk tolerance – something that had previously been seen in primates. While the exact influence of the PPC remains mysterious, Erlich is animated about the possibilities that his team’s findings show: “It's confirming that there are these kinds of similarities across species. In the rodent, we can now actually do many more careful circuit experiments to try and understand why the effect is short-lived. Whereas in the monkey, it would be kind of hopeless to try to really understand this short-lived effect.”
While Erlich reckons those further experiments will be taken up by other groups, his team hopes to further explore the neural basis of choice. The applications of this work are myriad – it could help us understand why people vote for poor political candidates or why they get tricked into buying overpriced TVs.
Reference: Bao C, Zhu X, Mōller-Mara J, Li J,
Dubroqua S, Erlich JC. The rat frontal orienting field dynamically encodes
value for economic decisions under risk. Nat Neurosci. 2023:1-11. doi: 10.1038/s41593-023-01461-x