Relative reward processing in primate striatum.

Rewards are often not only valued according to their physical characteristics but also relative to other available rewards. The striatum (caudate nucleus, putamen, ventral striatum including nucleus accumbens) is involved in the organization of movement and the processing of reward information. We studied the activity of single striatal neurons in macaques that were presented with different combinations of two rewards. We found in nearly half of the investigated neurons that the processing for one reward shifted, relative to the other rewards that were available in a given trial block. The relative reward processing concerned all forms of striatal activity related to reward-predicting visual stimuli, arm movements and reception of rewards. The observed changes may provide a neural basis for the known shifts in valuation of rewarding outcomes relative to known references.