Population coding and neural rhythmicity in the orbitofrontal cortex.

The orbitofrontal cortex has been implicated in the prediction of valuable outcomes based on environmental stimuli. However, it remains unknown how it represents outcome-predictive information at the population level, and how it provides temporal structure to such representations. Here, we pay attention especially to the population coding of probabilistic reward, and to the importance of orbitofrontal theta- and gamma-band rhythmicity in relation to target areas. When rats learned to associate odors to food outcome with variable likelihood, we found single-cell and population coding of reward probability, but not uncertainty. In related experiments, reward anticipation correlated to firing activity locking to theta-band oscillations. In contrast, gamma-band activity was associated with a firing-rate suppression of neurons that was most active during goal-directed movement. Orbitofrontal coding of outcome-relevant parameters appears bound to all relevant temporal phases of behavioral tasks, has a distributed nature, and is temporally structured according to multiple modes of rhythmicity.