There’s quite a nice little study by John O’Doherty and his group in the August issue of PLoS Biology pertaining to one of the most fascinating stuctures of the brain, the orbitofrontal cortex. They had subjects play a simple economic game with four different possible outcomes while being scanned in an MR-scanner: (1) receipt of a reward; (2) a missed reward; (3) avoidance of an aversive outcome (i.e., a monetary loss); and (4) receipt of an aversive outcome. The results showed that the medial part of the OFC exhibited increased activity not only when the subjects received a reward, but also when they avoided an aversive outcome. This indicates that to avoid an aversive outcome actually act as a reward, or as the authors write in the paper:
In avoidance learning, an animal or human learns to perform a response in order to avoid an aversive outcome. Here we provide evidence with fMRI that during such learning a part of the human brain previously implicated in responding to reward outcomes, the medial OFC, increases in activity following successful avoidance of the aversive outcome. These results are compatible with the possibility that activity in the medial OFC during avoidance reflects an intrinsic reward signal that serves to reinforce avoidance behavior.
Moreover, when the subjects, conversely, failed to obtain a reward or received an aversive outcome activity in the medial OFC decreased. O’Doherty and his colleagues suggest that this interesting finding can be explained by Solomon’s opponent-theory of motivation which hypothesizes that the termination of an affective process of some valence (positive or negative) is associated with the onset of a complimentary affective response of the opposite valence. In their discussion they offer the following interpretation of the medial OFC’s opponent response profile in regard to rewarding and aversive outcomes and their omission:
These OFC responses cannot be explained as PE [prediction error; MS], because activity does not decrease to rewarding outcomes
nor increase to aversive outcomes even as these outcomes become better predicted over the course of learning. Rather, responses to rewarding and aversive outcomes in this region likely reflect a positive affective state arising from the successful attainment of reward and a negative affective state from failing to avoid aversive outcome. Similarly, differential activity in this region to avoiding an aversive outcome and missing reward may reflect a positive affective response to successfully avoiding an aversive outcome and a negative affective state arising from failure to obtain a reward. Thus, our findings indicate that medial OFC activity at the time of outcome reflects the affective (or reinforcing) properties of goal attainment.
Furthermore, they relate their finding to the current on-going discussion of what possible functional roles the medial and lateral parts of the OFC play:
The findings reported here also help to address previous discrepancies in the reward neuroimaging literature as to thedifferential role of the medial versus lateral OFC in processing rewarding and aversive outcomes [29,44,45]. In the present study we show that the medial OFC responds to reward outcomes (as well as following successful avoidance of aversive outcomes), whereas both medial and lateral OFC responds during anticipation of reward. Indeed, when we tested for regions showing increases in activity to receipt of aversive outcome or omission of reward, we found a region of the lateral prefrontal cortex extending down to the lateral orbital surface with this response profile, implicating this region in responding to monetary an aversive outcomes . These findings suggest the possibility that dissociable activity within the medial versus lateral OFC may be evident during receipt of rewarding and punishing events, but not during their anticipation.
I would like to see Paul Bloom replicate this result using just some reaction-time paradigm! (Sorry to all the non-fMRI hating psychologists about that last snide comment!)
Kim, H, Shimojo, S. & O’Doherty, J. (2006): Is avoding an aversive outcome rewarding? Neural substrates of avoidance learning in the human brain. PLoS Biology 4(8): e233.