Susan Courtney, associate professor of psychological and brain sciences at the Zanvyl Krieger School of Arts and Sciences, has found that it is the prefrontal cortex, the very front area of the brain beneath the forehead, that enables people to hand complex sets of "if-then" rules governing the web of relationships between the items they want to buy, their driving route, their relationships with their spouses and employers, etc.
"This discovery may eventually lead to enhanced understanding of psychiatric diseases such as schizophrenia, obsessive-compulsive disorder and attention deficit disorder, all conditions in which a person's ability to remember and change such rules is impaired," said Courtney, lead author of a paper in a recent issue of Neuron.
The researchers used mental math tasks and functional magnetic resonance imaging to investigate which areas of the brain are used for different functions.
Before beginning the study, participants memorized the numbers 47 and 53, and the operations (rules) "add" and "subtract".
The researchers have revealed that only one of the two numbers, and one of the two operations were relevant to any given trial.
The participants would begin by remembering either 47 or 53 and the instructions to either "add" or "subtract.", and then would be given a second number that they would add to or subtract from the first until instructed to make a change.
That change could involve keeping the add or subtract "rule" and switching the number, keeping the number and switching the rule, or switching both the beginning number and the "rule".
If both rules and numbers were held in the memory in the same way, said Courtney, there would be no difference in the pattern of activity when people were asked to switch up the rules compared to when they changed numbers, because both rules and numbers would be in the same place in memory.
However, the study showed that the prefrontal cortex became more active when participants had to switch rules, and a different part of the brain called the parietal cortex, which is near the back of the head, became more active when the participants were asked to switch numbers.
"This indicates that different parts of our brains store different kinds of memories and information," Courtney said.
"(That) provides clues about how the human brain accomplishes complex, goal-directed behaviours that require remembering and changing abstract rules, an ability that is disrupted in many mental illnesses," she added.