Written by Payel Chatterjee Jan. 19, 2025 Simple choices can arise from diverse brain strategies, shedding light on the origins of individual variability Even rats have distinct personalities when making a decision, suggests a new set of findings from the Princeton Neuroscience Institute. By showing how different parts of the brain respond in a variable way when animals make choices, the results shed light on the nuances behind our own decision-making. Understanding these intricacies could lead to new insights into how and why we make certain choices in varying contexts.“We constantly have to make decisions and very often, these decisions have to take context into consideration,” said Marino Pagan, Ph.D., a former postdoctoral researcher in the lab of Carlos Brody, Ph.D. at the Princeton Neuroscience Institute, and the lead author of the new paper. “So we wanted to understand the mechanism that the brain uses to solve these tasks.”Their work was published in the journal Nature on November 28, 2024.People and animals alike adjust their behavior based on context.Someone trying to read a book in a café, for example, must tune their visual attention to the words on the page and ignore the surrounding chatter. If someone’s feeling nosey instead, they can swap their attention to eavesdropping on the conversation at the next table over. This type of context-based decision-making is pervasive in our daily lives, yet the biology behind how animals evaluate a situation and make a decision is poorly understood.Working in the lab of Carlos Brody, Ph.D., the Wilbur H. Gantz III '59 professor of neuroscience, researchers trained thirsty rats to pass a “hearing test.” In each session, rats listened to tones playing from two different speakers. Sometimes they had to figure out which speaker played tones more frequently, regardless of the pitch of the tones, while other times they had to decide whether there were more higher- versus lower-pitched tones, regardless of which speaker played them. A set of lights in the rat’s testing room tipped them off about the type of test for that session: if all three lights were on, they were looking for the speaker with a greater tone rate; if only one light was on, they were comparing tone pitches instead.Though it might sound simple, it’s really quite a complicated task: a rat must quickly determine whether the test is about rate or frequency, pay close attention to the relevant sound cues, and ignore the rest.All the while, each rat donned a small, surgically implanted cap that allowed scientists to measure brain activity from nearly 3,500 neurons across seven rats in a decision-making region called the frontal orienting field.Surprisingly, both the rats’ behavior and their neural signals showed a lot of variability. The rats did not rely on a single, uniform strategy to make their choices, even if they reached the same correct answer.Interestingly, these findings line up with similar research in monkeys, suggesting that rats and primates may share core brain mechanisms for how they gather and process information before making a decision. Such parallels help scientists better understand how different brains might tackle the same problem in unique but related ways.The researchers then developed a mathematical framework to shed more light on how the brain arrives at decisions. By analyzing the data through a quantitative lens, they found that multiple strategies can lead to the same final choice in these tasks. In other words, changes in the stimulus inputs, or in the brain’s own internal dynamics, could drive variability in how decisions are made. Pagan and Brody’s theoretical modelling also predicted a tight link between behavioral variation and neural activity, a prediction the team confirmed with their experimental data.In short, combining experiments with mathematical modeling helped reveal the remarkable diversity behind our decision-making processes. This study underscores that variability isn’t a bug, but rather a vital feature of how the brain works. Embracing that complexity could ultimately help scientists uncover the roots of cognitive challenges in some individuals, guiding us toward more personalized approaches in both research and treatment. “Our findings open the door to the study of individual variability in higher cognitive functions which so far, has only been studied in terms of what is common across subjects,” Pagan said. “But a big part of the story is what is different across animals.”CITATION: “Individual variability of neural computations underlying flexible decisions,” Marino Pagan, Vincent D. Tang, Mikio C. Aoi, Jonathan W. Pillow, Valerio Mante, David Sussillo, Carlos D. Brody. Nature, November 28, 2024. DOI: 10.1038/s41586-024-08433-6 Related People Carlos Brody Jonathan Pillow