RELATIVE VALUE-GUIDED DECISION-MAKING IN RATS

Optimal decision-making requires organisms to assess the value of available options. Growing evidence suggests that options are not evaluated in isolation and assigned absolute values, but instead are valued relative to the alternatives with which they are compared. Here, we used a touchscreen-based probabilistic reinforcement learning task to assess the extent to which relative value guides choice in rats. The task consisted of an initial learning phase, in which visual stimuli were presented in fixed and stable pairs (choice contexts), followed by a transfer phase in which stimuli were recombined into novel binary choice contexts. During learning, rats reliably chose the option associated with the higher reward probability. However, during the transfer test, choices did not consistently follow reward probability. Notably, when presented with options associated with identical reward probabilities, rats preferentially selected the option that had previously been paired with a lower-value alternative, revealing a robust relative value bias.
To test the generality of this effect across reward dimensions, we developed a second paradigm based on sucrose reinforcement, in which options differed by reward quality (sucrose concentration) rather than reward probability. Across both tasks, choices in novel contexts reflected previously learned relative values rather than absolute reward properties.
Together, these findings indicate that relative value representations strongly shape decision-making when animals are required to generalize across contexts. Ongoing work is aimed at identifying the neural systems that support this context-dependent valuation process.