How our brains process inequity in rewards.

This work suggests that the calculation of social standing - as indexed by payment - may be an unconscious and automatic process in the brain. The previous post on monkeys judging inequity in rewards suggests an evolutionary origin in earlier primate behavior. Here we have a very similar experiment done on humans, with fMRI data that we can't get from the monkeys. The results provide neurophysiological evidence for the importance of social comparison on reward processing in the human brain. Several studies show that most of us place as much value on relative remuneration, comparing ourselves with others, as on its absolute level. In the current work, when subjects were given different compensation for solving the same puzzle, this was reflected by different activation levels in the ventral striatum, a brain region known to be involved in the comparison of predicted and actually received rewards (i.e., reward prediction error). Here is the abstract from Fliessbach et al., followed by a figure from the paper:

Whether social comparison affects individual well-being is of central importance for understanding behavior in any social environment. Traditional economic theories focus on the role of absolute rewards, whereas behavioral evidence suggests that social comparisons influence well-being and decisions. We investigated the impact of social comparisons on reward-related brain activity using functional magnetic resonance imaging (fMRI). While being scanned in two adjacent MRI scanners, pairs of subjects had to simultaneously perform a simple estimation task that entailed monetary rewards for correct answers. We show that a variation in the comparison subject's payment affects blood oxygenation level–dependent responses in the ventral striatum. Our results provide neurophysiological evidence for the importance of social comparison on reward processing in the human brain.

Figure - Glassbrain projection of brain regions showing stronger BOLD responses in conditions in which a subject received a reward while the other did not compared with conditions in which a subject did not receive a reward at all.