Social equality in the number of choice options is represented in the ventromedial prefrontal cortex.

Aoki, R., Matsumoto, M., Yomogida, Y., Izuma, K., Murayama, K., Sugiura, A., Camerer, C. F., Adolphs, R., & Matsumoto, K. (2014). Social equality in the number of choice options is represented in the ventromedial prefrontal cortex. Journal of Neuroscience, 34(18), 6413-6421. PDF   Online Article