Making good decisions on the fly is critical for many activities, from navigating freeway traffic to trading stocks on the Internet. Now scientists have linked a key component of this type of decision-making--the split-second evaluation of how well things are going--to a distinct pattern of brain activity. Researchers say this brain activity could reflect an immediate emotional reaction that influences how people make decisions.
The anterior cingulate cortex (ACC) is a brain region tucked into the crease between the two cerebral hemispheres. When the ACC is damaged, people tend to make bad judgments. Earlier studies suggested that the ACC reacts when people make mistakes. But the new study suggests that the ACC may be doing something even more fundamental--making subjective judgements about whether outcomes of behaviors are good or bad, even before people are consciously aware of the results of what they've done.
Psychologists William Gehring and Adrian Willoughby of the University of Michigan, Ann Arbor, used electroencephalogram (EEG) electrodes to monitor brain activity in volunteers playing a gambling game in the lab. The gamblers chose one of two boxes that appeared on the screen of a computer monitor. One box indicated a 5-cent bet; the other a 25-cent bet. After a short delay, the boxes changed color. If the chosen box turned green, the amount bet was added to the person's stash; if it turned red, money was taken away. Win or lose, the EEG trace showed a distinctive dip arising from the medial frontal cortex--a response Gehring and Willoughby call the medial-frontal negativity (MFN). The MFN was more pronounced on loss trials--a difference that was evident just 200 to 300 milliseconds after the outcome of each bet was revealed, the team reports in the 22 March issue of Science. The researchers don't see the MFN as simply a reflection of detecting mistakes, because the stronger response showed up even when the lab gamblers made a correct choice, such as taking a 5-cent loss when the alternative was a 25-cent loss.
"This starts to shed light on how subconscious processes can affect our decision-making and starts to provide a bit of the neural basis for that," says George Bush, a research psychiatrist at Harvard Medical School in Boston. The study also represents a step toward the scientific study of human subjectivity, according to experimental psychologist Brian Knutson of Stanford University. "A basic feature of subjectivity is deciding whether things are good or bad. For a long time scientists have considered that unstudiable."