Brains scans of the animals playing a game, based on televisiom show The Price Is Right, found they register missed opportunities and think about how they can be avoided in the future.
Scientists watched cells in a region of the brain called the anterior cingulate cortex (ACC) that monitors the consequences of actions and mediates resulting changes in behaviour.
They offered monkeys choices from an array of hidden rewards and during each trial they chose from one of eight identical white squares arranged in a circle.
A colour beneath the white square was revealed and the monkey received the corresponding reward which came in different amounts of juice.
"This is the first evidence that monkeys, like people, have 'would-have, could-have, should-have' thoughts," said researcher Ben Hayden, of the Duke University Medical Centre in North Carolina.
Over many weeks the monkeys were trained to associate a high-value reward with the colour green and the low-value rewards with other colours. After receiving a reward the monkey was also shown the prizes he missed.
The findings, published in the journal Science, showed neurons in the ACC responded in proportion to the reward – a greater reward caused a higher response.
The researchers also found these same neurons responded when monkeys saw what they missed. Most of these ACC neurons responded the same way to a real or imagined reward.
To measure how these responses might help the monkey to learn, the researchers kept the high reward in the same position 60 per cent of the time, or moved it one position clockwise, so that a monkey could possibly notice and adapt to that pattern.
The monkeys chose targets next to potential high-value targets more often than those next to low-value targets – 37.7 per cent to 16.7 per cent – which suggested they understood the relationship between the high value target on the current trial and its likely location on the next trial.
The monkeys learned the pattern and chose the high value more often than by a chance.
Neurobiologist Professor Michael Platt, the study's co-author, said: "It is significant to learn that the neurons have a dual role, because the monkey can only adapt his behaviour when he gets information on both of those events, real and missed."
People are much more likely to gamble if they see they could have won big by gambling in the past.
So the researchers hypothesised the monkeys would also select the target if it had offered a large reward on the previous trial and the monkey had missed it, and indeed, they observed this pattern.
The effect may have reflected an increased willingness to switch to a new target, because the likelihood of switching increased with larger missed rewards, they said.
Prof Platt said: "This was not merely a function of the high-value targets holding a positive association for the monkey."
The monkeys' ACC neurons signalled missed reward information, and used a coding scheme in the brain that was similar to the coding used to signal real outcomes, said Prof Platt.
The researchers suspect these neurons actually helped the monkeys to make better choices in the future.
