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October 2023
Katrin Chunkovsky
Neuroscience has often relied on experiments involving mice to gain insights into memory, behavior, and disease treatments. In a groundbreaking study conducted by MIT researchers, scientists delved into the behavior of mice during learning.
The experiment involved a seemingly simple task for mice: turning a wheel left or right to receive a reward and recognizing when the reward direction switches. Neurotypical humans quickly grasp the concept of "reversal learning" games, where the optimal strategy is to stick with the winning direction until it fails and then switch promptly. Individuals with schizophrenia struggle with this task. Mice, in this study, surprised scientists by demonstrating that although they could learn the "win-stay, lose-shift" strategy, they did not adopt it.
The research revealed that mice, rather than persisting with a specific strategy, deviated occasionally, even when they knew the reward was guaranteed on one side. This behavior puzzled scientists, leading to various hypotheses. One possibility suggested that mice might not trust the stability of their circumstances, prompting them to test different options to ensure the rules had not changed.
Lead author Nhat Le, a graduate student in the Sur Lab, noted the complexity of mouse behavior, suggesting that mice might be smarter than previously believed. The study emphasized the significance of understanding the shifting strategies of mice during lab tasks. Unlike the common belief, mice do not adopt a stationary strategy, and researchers must consider this when interpreting neural activity recordings. The research team utilized a sophisticated analytical framework called a Hidden Markov Model (HMM), adapted to explain choice transitions over entire blocks of the game. This modified model, referred to as blockHMM, enabled scientists to decipher the blending of multiple strategies employed by mice. The mice exhibited a combination of low, medium, and high-performance behavior modes, indicating the coexistence of different cognitive processes.
Moving forward, the researchers plan to delve deeper into the mouse brain to identify the specific brain regions and circuits involved in these shifting strategies. By monitoring brain cell activity during tasks, they hope to unravel the underlying mechanisms guiding the mice's decisions to switch strategies. Moreover, the study's insights might offer valuable clues about neurological disorders such as schizophrenia and autism spectrum disorders, where individuals exhibit altered reversal learning behaviors.
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