Researchers have pinpointed an area of the brain that serves as an arbitrator between our two decision-making systems, one devoted to habitual behaviors and the other devoted to actions we take only after careful consideration.
Scientists at the California Institute of Technology (CalTech) say the inferior lateral prefrontal cortex and frontopolar cortex is the arbitrator, weighing the reliability of the predictions each of the decision-making systems makes and then allocating control accordingly.
“Understanding where the arbitrator is located and how it works is a first step towards finding better treatments for brain disorders, such as drug addiction, and psychiatric disorders, such as obsessive-compulsive disorder,” according to John O’Doherty, Ph.D., the study’s principal investigator and director of the Caltech Brain Imaging Center.
“Now that we have worked out where the arbitrator is located, if we can find a way of altering activity in this area, we might be able to push an individual back toward goal-directed control and away from habitual control,” said O’Doherty, who is also a professor of psychology at Caltech.
He added that researchers are a long way from developing actual treatments based on this discovery for disorders that involve supercharging the brain’s habit system, but it has opened up a highly promising avenue for further research.
For the study, researchers recruited volunteers who played a decision-making game on a computer while connected to a functional magnetic resonance imaging (fMRI) scanner that monitored their brain activity.
The participants were told by the researchers to try to make optimal choices in order to gather coins of a certain color, which were redeemable for money.
During a pre-training period, the volunteers familiarized themselves with the game, moving through a series of on-screen rooms, each of which held different numbers of red, yellow, or blue coins.
During the actual game, they were told which coins would be redeemable each round and given a choice to navigate right or left at two stages, knowing that they would collect only the coins in their final room. Sometimes all of the coins were redeemable, making the task more habitual than goal-directed, according to the researchers.
By altering the probability of getting from one room to another, the researchers said they were able to test the extent of the volunteers’ habitual and goal-directed behavior while monitoring corresponding changes in their brain activity.
The researchers also were able to compare the fMRI data and choices made by the volunteers against several computational models they constructed to account for behavior. The model that most accurately matched the experimental data involved the two brain systems making separate predictions about which action to take in a given situation, the researchers reported.
“Receiving signals from those systems, the arbitrator kept track of the reliability of the predictions by measuring the difference between the predicted and actual outcomes for each system. It then used those reliability estimates to determine how much control each system should exert over the individual’s behavior,” the researchers explained.
In this model, the arbitrator ensures that the system making the most reliable predictions at any given moment exerts the greatest degree of control over behavior.
“What we’re showing is the existence of higher-level control in the human brain,” said Sang Wan Lee, Ph.D., lead author of the new study and a postdoctoral scholar in neuroscience at Caltech. “The arbitrator is basically making decisions about decisions.”
Confirming previous findings, the researchers saw in the brain scans that an area known as the posterior putamen was active at times when the model predicted that the habitual system should be calculating prediction values.
Going a step further, they examined the connection between the posterior putamen and the arbitrator. They say what they found might explain how the arbitrator sets the weight for the two learning systems: The connection between the arbitrator area and the posterior putamen changed according to whether the goal-directed or habitual system was deemed to be more reliable.
“However, no such connection was found between the arbitrator and brain regions involved in goal-directed learning. This suggests that the arbitrator may work mainly by modulating the activity of the habitual system,” the researchers speculate.
“One intriguing possibility arising from these findings, which we will need to test in future work, is that being in a habitual mode of behavior may be the default state,” said O’Doherty. “So when the arbitrator determines you need to be more goal-directed in your behavior, it accomplishes this by inhibiting the activity of the habitual system, almost like pressing the brakes on your car when you are in drive.”
The study was published in the journal Neuron.