Neuroscientists at the University of California Los Angeles claim they can can predict your behavior better than you can.
The team picked 20 people who didn't use sunscreen every day. They had their brains scanned using functional magnetic resonance imaging (fMRI) as they saw and heard a series of public service announcements.
They were also asked about their intentions to use sunscreen over the next week and their attitudes about sunscreen.
A week later, they were asked on how many days during the week they had used sunscreen.
The team found that the fMRI data could be used to predict whether people would use sunscreen over a one-week period with more accuracy than the participants themselves.
"There is a very long history within psychology of people not being very good judges of what they will actually do in a future situation," said the study's senior author, Matthew Lieberman, a UCLA professor of psychology and of psychiatry and biobehavioral sciences. "Many people 'decide' to do things but then don't do them."
The team discovered that increased activity in the medial prefrontal cortex among individuals viewing and listening to public service announcement slides about sunscreen strongly indicated that these people were more likely to increase their use of sunscreen the following week.
"From this region of the brain, we can predict for about three-quarters of the people whether they will increase their use of sunscreen beyond what they say they will do," Lieberman said. "If you just go by what people say they will do, you get fewer than half of the people accurately predicted, and using this brain region, we could do significantly better."
"While most people's self-reports are not very accurate, they do not realize their self-reports are wrong so often in predicting future behavior," said co-author Emily Falk.
"It is surprising to find out that some technique might be able to predict my own behavior better than I can. Yet the brain seems to reveal something important that we may not even realize."
The finding could be seized on by the advertising industry, Lieberman and Falk said.
"A problem with standard focus groups is that people are lousy at reporting what they will actually do," said Falk.
"We have not had much to supplement that approach, but in the future it may be possible to create what we are calling 'neural focus groups.' Instead of talking with people about what they think they will do, a public health or advertising agency can study their brains and learn what they are really likely to do and how an advertisement would be likely to affect millions of other people as well."