July 10, 2006 To give your child an incentive to take out the garbage, you might offer to buy her a treat, or you might threaten to withhold her regular allowance. Does the child respond the same way to reward as it does to avoiding punishment? Psychologists have evidence from certain kinds of behavioral experiments to believe that avoiding punishment is itself a reward.
In a new study published online in the open-access journal PLoS Biology , Hackjin Kim, Shinsuke Shimojo, and John O'Doherty investigated this question by scanning the brains of humans performing a simple instrumental conditioning task. A brain area called the medial orbitofrontal cortex (OFC) has been linked to reward-related stimuli, particularly when the reward involves money. The researchers found that the OFC is also activated for avoidance learning, supporting the hypothesis that these cognitive processes share neural mechanisms.
Sixteen people participated in the study, during which they could either lose or win one dollar in an instrumental choice task. During the experimental trials, participants selected one of two fractal images presented on a screen. After a fractal was chosen, it became brighter, and four seconds later the participant got one of four types of feedback: reward (a picture of a dollar bill and the message, You win!), negative outcome (same image, with the text, You lost!), neutral (a scrambled bill with the text, No change), or nothing (a blank screen). During reward trials, the choice led to a high or low probability of reward (earning a dollar); during avoidance trials, the choice led to a high or low probability of avoiding a negative outcome (losing a dollar).
Over time, participants learned to choose fractals associated with a greater probability of reward and a lower probability of a negative outcome. And, as predicted, the medial OFC showed a higher response when participants chose an option that resulted in not losing the dollar or in winning it. Conversely, when participants' choices resulted in negative outcomes and when there was no reward offered OFC activity declined. Compared to neutral trials, reward and avoidance events produced significantly greater brain activity, while negative outcomes and neutral events linked to no chance of reward resulted in significantly decreased activity. Kim et al. argue that these functional magnetic resonance imaging (fMRI) results provide direct evidence that avoiding bad outcomes and receiving a reward provoke a similar response in the medial OFC.
Avoiding negative outcomes and receiving rewards amount to the same thing for the brain: achieving a goal. Reward serves as an external signal that reinforces behavior associated with a positive outcome, Kim et al. explain, and punishment amounts to an intrinsic reward signal that reinforces actions linked to avoiding bad outcomes. With fMRI evidence connecting avoidance and reward circuits, researchers can now determine which neuron populations within the OFC contribute to the avoidance "reward response"and perhaps shed light on the neurobiological roots of pathological risk-seeking behavior.
Citation: Kim H, Shimojo S, O'Doherty JP (2006) Is avoiding an aversive outcome rewarding? Neural substrates of avoidance learning in the human brain. PLoS Biol 4(8): e233. DOI: 10.1371/journal.pbio.0040233.
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