Two monkeys sit opposite each other and take turns touching a stimulus on a horizontal monitor between them (top). Stimulus touch delivers first own reward and then the conspecific's reward, the amount being indicated by the colored rings (middle). The animal's eyes fixate the own stimuli, the conspecific's stimuli, and the conspecific's reward spout (bottom). View the report here (Báez-Mendoza et al. 2013).
Most neurons in the monkey caudate nucleus and putamen are interested in the own reward as opposed the conspecific's reward (77% vs. 23%). Activity in these socially differentiating reward neurons differentiated further between the actors: 68% of neurons responded to own reward only when the animal itself acted, whereas 32% of neurons responded to own reward only when the other animal acted. View the report here (Báez-Mendoza et al. 2013).
Humans and animals usually don't like it when the other individual receives more reward than onself (disadvantageous inequity aversion). Less consistently but also often observed is the opposite: dislike of having more than the other individual (advantageous inequity aversion). Some neurons in the monkey caudate nucleus and putamen reflect these socially induced changes in reward value. View the report here (Báez-Mendoza et al. 2016).