## Biological Basis of the Computational Model The provided code snippet appears to be part of a computational model aimed at studying decision-making processes under uncertainty, likely related to reinforcement learning. This model specifically targets how lesions in different brain regions might affect behavior in a two-step task paradigm. Key biological concepts and regions modeled in the code include: ### Brain Regions 1. **Hippocampus (HPC):** - The hippocampus is primarily associated with memory formation, spatial navigation, and the contextual representation of experiences. In decision-making tasks, it plays a significant role in forming associations between actions and contextual states. 2. **Dorsolateral Striatum (DLS):** - The dorsolateral striatum is implicated in habitual decision-making and procedural learning. It is part of the basal ganglia, a group of nuclei crucial for motor control and associative learning processes. ### Behavioral Paradigm - **Two-Step Task:** - This type of task is commonly used to study model-free versus model-based reinforcement learning. It requires an agent to make a series of decisions that lead to rewards, depending on transitional contingencies (common versus rare outcomes). Such tasks help in differentiating between habitual and goal-directed actions. ### Key Biological Concepts - **Decision-Making Strategy:** - The code analyzes how agents decide to "stay" with their previous action or switch, based on the previous outcome (common or rare) and past rewards. This reflects the biological processes of prediction and error correction typically involved in reinforcement learning. - **Transition Recognition:** - The code classifies outcomes of actions as "common" or "rare," indicating the probability of reaching a certain state from a given action. This is analogous to the brain’s ability to predict outcomes based on learned experiences and adjust behaviors accordingly. ### Lesion Studies The code suggests lesion studies where specific brain regions (HPC, DLS) are affected: - **Lesioning the HPC:** - This might impact an agent's ability to form complex contextual representations, potentially leading to impaired decision-making, especially in situations requiring memory of previous states. - **Lesioning the DLS:** - This might affect habitual learning mechanisms, possibly enhancing or diminishing the tendency to repeat previous actions regardless of outcomes, due to the impairment of procedural learning systems. ### Summary This model investigates how distinct brain structures contribute to the mechanism of decision-making under uncertainty in a structured task environment. By examining lesions, the study likely aims to dissect the contributions of the hippocampus and dorsolateral striatum in different learning strategies—be it model-based, reliant on mnemonic components, or model-free, based on habit and procedural knowledge. These insights could inform our understanding of how these neural circuits function in normal and pathological conditions.