Heads or tails? Random fluctuations in the brain determine how we make decisions when faced with two equally appealing options, scientists say.
An emerging field of study known as neuroeconomics is combining the economists' insights with scientific study of the brain to learn more about decision-making processes and how they can go awry.
"Neuroeconomics is not only helpful for the development of better economic theory, it is also relevant from a clinical point of view," said author Camillo Padoa-Schioppa, from Washington University School of Medicine in St Louis.
"There are a number of conditions that involve impaired economic decision-making, including drug addiction, brain injury, some forms of dementia, schizophrenia and obsessive-compulsive disorder," said Padoa-Schioppa.
To study the roles brain cells play in decision-making, Padoa-Schioppa 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.
Analysing data from the original experiment, Padoa-Schioppa showed that different groups of cells in the orbito frontal cortex reflect different stages of the decision-making process.
"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," he said.
"Yet other neurons encode the value of the chosen option," said Padoa-Schioppa.
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.
"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," Padoa-Schioppa said. The study was published in the journal Neuron.