Crossroads are common on the path of life and everyone has different motivations for the direction they choose, but a new study suggests many of our choices are made by random fluctuations in the brain.

Economists are hugely interested in the way people make decisions; what values we assign to opinions, how much of the choosing process is performed consciously, and how much comes from the mysterious recesses of the mind.

The emerging field of ‘neuroeconomics’ combines the latest understanding of the way the brain works with studies of its influence or our lives and on society.

A researcher known as one of the founders of the field has conducted a study reporting new links between brain cell activity and difficult choices, where two options have equal appeal.

Decision-making is linked to the orbitofrontal cortex, a region of the brain just behind and above the eyes. Damage to this part of the brain leave patients with all most no decisive abilities – leading them to make extraordinarily poor decisions.

To study the brain cells in question, researchers presented primates with a choice between two drinks; grape juice or apple juice. The type and amount of the drink was varied, while researchers recorded the activity of individual brain neurons as the primates choose.

Watching a single animal over multiple trials, the team were able to map the subjective value assigned to each drink and look for ways the 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,” explained Camillo Padoa-Schioppa, PhD, assistant professor of neurobiology, economics and of biomedical engineering atWashington University School of Medicine in St. Louis.

“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.”

Different groups of cells were linked with different parts 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,” Professor Padoa-Schioppa said.

“Yet other neurons encode the value of the chosen option.”

The most difficult decisions, i.e. between options of equal value, seem to depend on changes in the initial state of 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.

“Neuronal signals are always noisy. In essence, close-call decisions are partly determined by random noise.”

Padoa-Schioppa and his colleagues hope to use the findings to develop a computer model for decision-making, and will conduct further experiments to see if decisions can be biased by artificially manipulating the brain cells.