[Reward value encoded by electrocorticography (ECoG) power spectrum in the prefrontal cortex]

Calculating reward value is a core component in the value-based decision-making process, where the brain guides behavioral choices by evaluating the reward values of different options. The prefrontal cortex (PFC), a central hub for higher-order cognitive functions, has been involved in reward encoding across multiple subregions, as evidenced by numerous experimental studies. However, these studies often focused on the activity of a single or two brain regions within specific experimental paradigms, leading to potential variability in the functional interpretation of the same region across different experimental designs. To simultaneously investigate how multiple subregions of the PFC encode reward values, our study was based on a free-choice reward prediction task in macaques, recording neural signals from the anterior cingulate cortex (ACC), lateral prefrontal cortex (LPFC), medial prefrontal cortex (MPFC), and orbitofrontal cortex (OFC) by a 64-channel electrocorticography (ECoG) electrode array in each area. The task designed five stimulus-reward pairings, so that macaques could associate stimuli with corresponding juice rewards. The preferences and values of each reward were determined by the macaques' choice frequencies. We compared the mean power intensity of ECoG in different frequency bands and reward conditions in the four subregions. On the alpha band of OFC and the theta, alpha, beta bands of LPFC, we found that the mean power not only distinguished the five reward conditions, but also exhibited the consistency between the rankings of mean power intensity and the macaques' preferences of juice rewards. Meanwhile, the mean power on the alpha and beta bands of MPFC and ACC were modulated by the stimuli. Notably, the mean power related with reward value encoding was predominantly concentrated during the delay period, which is between the stimulus period and the reward period. These results suggest that, within the same reward task, the four PFC subregions are differentially involved in reward encoding, highlighting their distinct functional contributions. This finding provides a foundation for further exploration of the interactions among PFC subregions in reward value encoding.