How the Brain Makes Decisions

Study with monkeys identifies region linked to reward judgment

FRIDAY, Dec. 5, 2003 (HealthDayNews) -- An area of the brain that judges the value of rewards and adjusts that value under changing circumstances has been identified by Duke University and Carnegie Mellon University researchers.

They report their findings in the Dec. 4 issue of Neurobiology.

This discovery about the posterior cingulate cortex helps scientists better understand how the brain is wired to make judgments, perhaps even moral decisions. It may also offer more information about some neurological disorders such as Alzheimer's disease, schizophrenia, spatial disorientation, obsessive-compulsive disorder and stroke.

The cognitive decline seen in people with those disorders has been linked to damage in the posterior cingulate cortex.

"Even though the posterior cingulate cortex is a large structure in the brain that is easily identifiable in all mammals, including humans, almost nothing was known about what it might do," lead researcher Dr. Michael Platt, an assistant professor of neurobiology at Duke, says in a prepared statement.

"Anatomical studies show that it is kind of a nexus of brain circuitry involved in motivational or emotional inputs from the limbic system. And it is strongly connected to structures involved in making decisions and generating responses. So, we theorized that it seemed to be important for someone putting together the costs and benefits associated with different options in an animal's environment," Platt says.

He and his colleagues identified the role of the posterior cingulate cortex in judging the value of rewards by studying how monkeys choose to look at lighted targets for fruit juice rewards.

"We manipulated how much fruit juice a monkey got for making particular eye movements, and we found a direct linear relationship between how strongly these neurons (in the posterior cingulate cortex) fired and the amount of fruit juice that was delivered," Platt says.

More information

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SOURCE: Duke University, news release, Dec. 4, 2003
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