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Michael Campos, Kari Koppitch, Richard A. Andersen, Shinsuke Shimojo; Overlapping representation of juice and video rewards in primate OFC. Journal of Vision 2008;8(6):546. doi: 10.1167/8.6.546.
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Vision can be inherently rewarding. The reward circuitry in the brain supports an animal in identifying and obtaining rewards from its environment. The orbitofrontal cortex (OFC) is known to encode the subjective value of different juice reward options, and therefore supports decisions based on preferences in the context of appetitive rewards. It is unclear, however, whether the brain circuitry supporting the appetitive rewards is the same, distinct, or overlapping with that supporting non-appetitive rewards, which are important to modern human life. To investigate this issue we used a self-initiated free-choice paradigm in which a monkey pressed buttons to receive either the presentation of a 5 sec video clip in the video-watching period (“leisure”), or a drop of juice in a separate period (“work”). The leisure and work periods were run in separate blocks of 20 minutes each, while we simultaneously recorded 2–10 single OFC neurons.
Neural activity was analyzed with respect to the button press. We first identified significant modulations in firing rate activity in any of five intervals defined with respect to the button press when compared to baseline. We found that two-thirds of the OFC neurons we encountered (394/585) were modulated in at least one interval in either the leisure or work period. Of these, approximately 40% were modulated in both periods, 40% were modulated in the work period exclusively, and 20% in the leisure period exclusively. The neurons that responded in only one period suggest that OFC contains at least two internal representations of distinct reward categories. The neurons that participated in both periods suggest that OFC also represents abstract commonalities between rewards of different kinds. These results are consistent with our intuition that perceptual experience itself is rewarding, and indicate that the neural correlates overlap with that for appetitive rewards.
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