Mahdi Ramadan Thesis Defense: The cognitive and neural basis of complex decision-making in the primate brain

Building 46, 6011

Date/time: Wednesday, May 8th at 10amIn-person location: Simons Center 46-6011On Zoom: https://mit.zoom.us/j/97630915583Title: The cognitive and neural basis of complex decision-making in the primate brainAbstract: A longstanding question at the intersection of comparative psychology, cognitive ethology, and neuroscience is what cognitive strategies primates use to tackle complex multi-step decisions, and what are the neural underpinnings of the strategies. In this thesis, I designed a novel multi-step decision-making task that was sufficiently complex to allow for multiple strategies, ranging from basic heuristics to more optimal strategies. In the first chapter, I present a series of human psychophysical experiments that show that humans rely on a heuristic hierarchical strategy to solve the task sequentially, and when uncertain, flexibly revise their decisions. In chapter two, I train two monkeys on the task, and find that monkeys also adopt a hierarchical and revision strategy to solve the task, like humans. Monkeys were also able to readily generalize their strategy to novel scenarios, and made eye-movements that were indicative of simple forms of counterfactual reasoning. It was difficult from behavior alone to test whether monkeys were actually using multiple strategies to solve the task. To investigate this possibility and the underlying neurobiology of hierarchical and revision strategies, in chapter three we conducted high-density neural recordings from monkeys while they performed the task. Neural recordings revealed that monkeys were not using one strategy to solve the task, but rather showed the initialization and dynamic progression of two distinct cognitive strategies that monkeys adaptively selected for different scenarios. We find that neural population initial conditions and response dynamics were flexibly modulated to implement these distinct decision-making strategy plans. And finally, we use the neurally inferred strategies to build composite psychophysical models that better capture the monkeys’ behavior. These results point to the importance of neural recordings in understanding primate cognition.