Monkeys Think "Coulda, Woulda, Shoulda"

In a new study published in the journal Science, researchers at Duke University Medical Center found that monkeys are able to think “could-have, would-have, should-have.”

The researchers created a “Let’s Make A Deal” style game for their two rhesus monkeys, in which the experimenters offered the monkeys an array of hidden awards.  During each trial, the monkeys choose from one of eight white squares arranged in a circle.  Each square had a color underneath, and each color had a corresponding reward.  In this game, the rewards were different amounts of juice.

After weeks of the game, the monkeys were trained to associate green with a high-value reward, and other colors with a low-value reward.  After receiving a reward, the monkeys were shown the other rewards he missed.

The researchers watched individual neurons in a region of the brain called the anterior cingulate cortex (ACC), which monitors the consequences of actions and mediates resulting changes in behavior.

The researchers saw that the neurons in the ACC responded in proportion to the reward, and a greater reward elicited a greater neural response.  The same neurons responded when the monkeys saw the rewards they missed.

In the second part of the study, the researchers kept the high-value reward in the same position 60 percent of the time, or moved it one position clockwise.  The monkeys began to learn this pattern, choosing targets next to potential high-value targets more often (37.7 percent) than those next to low-value targets (16.7 percent).  People are more likely to gamble if they see the opportunity to win big.  Likewise, the monkeys were willing to take a risk in order to win a greater reward.  The researchers believe that the ACC neurons help the  monkeys make better choices in the future, which may be crucial in complex social environments.

Hayden, B., Pearson, J., & Platt, M. (2009). Fictive Reward Signals in the Anterior Cingulate Cortex Science, 324 (5929), 948-950 DOI: 10.1126/science.1168488