Unexpected holiday rewards in the human brain
Dr Robb Rutledge is a Senior Research Associate at the Wellcome Trust Centre for Neuroimaging at University College London. With Professor Ray Dolan, he studies how the human brain responds to rewards. Could his research help us to pick the perfect gift this Christmas?
Gift-givers will spend billions of pounds in the United Kingdom this holiday season. Many people will be delighted with the gifts they receive, but some gifts will unfortunately go unappreciated. The gift-giver’s dilemma is that they rarely know precisely what the recipient would like. And different tastes are only part of the problem: how a gift is received may depend just as much on what was expected as on the gift itself.
I started investigating how the brain responds to rewards as a graduate student with Professor Paul Glimcher at New York University. In a study published in the Journal of Neuroscience (1), we used MRI to show that an area deep in the brain, called the nucleus accumbens, responds strongly to rewards. The image above shows a cross-section of the human brain as seen from the front, as if you were standing face to face with our subject. Activity in the nucleus accumbens (highlighted in the image) is higher after winning than after losing money.
In my current research, we use monetary gambles in many of our experiments. For example, one of our subjects might choose between getting £10 for sure, or gambling with equal chances of winning £20 or getting nothing. Subjects make decisions, and experience the outcomes, while being scanned in MRI machines – allowing us to measure how the human brain responds to these events.
If we were to monitor her nucleus accumbens, a child unwrapping a present on Christmas may not be that different from a subject waiting to see if she has won £20. Both are hoping to get something good. In an instant, they find out whether their prize is better or worse than expected. Since the gift-giver wants to please the recipient’s brain, perhaps our studies can provide helpful insights. How might a gift-giver maximize the response in the nucleus accumbens of her intended recipient?
When we examined this brain area more carefully, we found that the level of activity was strongly influenced by the expectations of the subject. The highest neural responses occurred when expectations of winning were low. When expectations were high, we observed lower neural activity for exactly the same prize.
The nucleus accumbens may be the most reward-responsive area of the human brain, but this area does not simply respond to how much reward was received. Instead it responds according to what is called a “reward prediction error”: the difference between what you got and what you expected to get. The reward prediction error is positive when you get more than you expected and negative when you get less than you expected. For this brain area, expectations matter just as much as rewards. When you do not get the gift you were hoping for, the feeling of disappointment might be related to the negative reward prediction error represented in this area.
Perhaps it is a little surprising that the most reward-responsive brain area cares so much about expectations. After all, the gift box (almost) always contains an item of some value. On the other hand, maybe your brain is trying to do something more ambitious than just watch you open presents. These reward prediction errors may play an important role that extends into the next holiday season and beyond.
That role is to help you predict the future. Your brain is constantly making predictions about what will happen next. Knowing whether outcomes are better or worse than expected is a good way to figure out what to expect next time. These reward prediction error signals exist so you can make better predictions, and better decisions, in the future.
So as you finish your last-minute shopping, think for a moment about what the people on your list might be expecting. If you must ask someone what they would like, get at least two suggestions and do not tell them which one you have chosen. Try not to raise expectations before the big day: if expectations are too high, your recipient might be disappointed by a gift she would otherwise be delighted by. Above all, try not to tell anyone exactly what he or she will be getting. The brain always likes to get at least a little more than it expected.
(1) Robb B. Rutledge, Mark Dean, Andrew Caplin & Paul W. Glimcher (2010). Testing the reward prediction error hypothesis with an axiomatic model. Journal of Neuroscience (30), 13525-13536 PMID: 20926678