How brain makes toss-up decisions
Washington: A new study has revealed that random fluctuations in brain cell activity may determine how we make decisions when given choices.
To study the roles brain cells play in decision-making, Camillo Padoa-Schioppa, PhD, assistant professor of neurobiology, economics and of biomedical engineering at Washington University School of Medicine in St. Louis, developed a system for presenting primates a choice between two drinks, such as grape juice or apple juice. The type and amount of the drink varies, and researchers record the activity of individual brain neurons as the primates choose.
Based on the decisions of a single animal over multiple trials, scientists infer the subjective value the animal assigns to each drink and then look for ways this value is encoded in brain cells.
"For example, if we offer a larger amount of apple juice versus a smaller amount of grape juice, and the primate chooses each option equally often, we infer that this primate likes the grape juice better than the apple juice," he explained. "The primate could be getting more juice by choosing the cup with apple juice, but it doesn't always do so. That implies that the primate values grape juice more than apple juice."
Padoa-Schioppa showed that different groups of cells in the orbito frontal cortex reflect different stages of the decision-making process.
He explained that some neurons encode the value of individual drinks; other neurons encode the choice outcome in a binary way these cells are either firing or silent depending on the chosen drink. Yet other neurons encode the value of the chosen option.
Padoa-Schioppa then examined how different groups of cells determine decisions between options of equal value. He showed that toss-up decisions seemed to depend on changes in the initial state of the network of neurons in the orbitofrontal cortex.
Padoa-Schioppa said the fluctuations in the network took place before the primates were even offered a choice of juices, but they seem to somehow bias the decision.
He also found that decisions on choices of equal value were linked to the ease or difficulty with which nerve cells in parts of the orbitofrontal cortex communicate with each other. This property, known as synaptic efficacy, can be adjusted by the brain as part of the process of encoding information.
The study is published in journal Neuron.
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