Abstract—Internal state has an impact on individuals’ preferences and their behavioral choices, but it remains unclear how the brain modulates the value of rewards through neural computation. Some research indicates that Dopamine (DA) neurons are involved in encoding Reward Prediction Error (RPE), while internal states such as hunger and social isolation may change the value judgment of different rewards. This study aims to investigate how internal states modify the value encoding of DA neurons located in the Ventral Tegmental Area (VTA), and will further examine how the brain prioritizes a specific need when food reward and social reward compete. In this proposal, we hypothesize that internal states can reweight different reward-relative RPE signals dynamically. This process will therefore influence reward assessment and decision-making. Here, we suggest manipulating hunger and social isolation manually to test how these internal states shift the behavioral value of food and social rewards. Subsequently, a conditioning task is suggested to compare neural signals under different reward conditions. VTA DA neuron activity should be recorded using fiber photometry under expected reward, unexpected reward, and reward omission conditions. This trial will help determine whether internal states modulate the RPE for food and social rewards selectively. Finally, it is suggested to establish a direct competing task between food and social reward, in which the choice of mice and their VTA DA activity is recorded simultaneously, to examine dynamical RPE alternation and verify its relationship with reward priority. This proposal will explore how internal states affect reward perception at three levels, which are behavioral, neurocomputational, and decision-making. Results may help establish a deeper understanding of how the brain modulates reward values and RPE based on current needs, thus contributing to eventual decision-making.
 
Keywords—internal states, reward prediction error, Ventral Tegmental Area (VTA) dopamine neurons, food reward, social reward, reward competition, decision-making

Cite: Jiachen Xu, "Internal-state-dependent Reweighting of Food and Social Reward Prediction Errors in VTA Dopamine Neurons," International Journal of Pharma Medicine and Biological Sciences, Vol. 15, No. 4, pp. 144-150, 2026.

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