A neuroeconomic study discovers a mechanism for decision-making.

Call it a first step to dissecting free will—Harvard researchers have found a two-tiered system of neurons that allows us to make judgment calls on the relative worth of items. The finding could play an important role in understanding the seemingly irrational way in which people make decisions.

“Of all the fields of research, human nature has always been the most puzzling,” said Camillo Padoa-Schioppa, a research fellow at Harvard, who published his findings in the April 27th issue of Nature along with neurobiology professor John Assad. “Understanding the mechanism behind how we assess the outside world is important if we are ever to understand why we act the way we do.”

Behavioral economists have long struggled with the puzzling way that humans choose one activity or object over another. This is because the heart of economic theory presumes knee-jerk decision-making that follows strictly logical reasoning, said NYU neuroscientist Paul Glimcher, author of Decisions, Uncertainty, and the Brain: The Science of Neuroeconomics. Instead, he said, there is a sublime mechanistic process ticking away in the brain, which allows each individual to assign personal values that don’t necessarily make sense.

“For example, why don’t the vast majority of people invest enough in their 401K?” Glimcher said. “It’s the perfectly logical decision; but on a wide-spread scale it’s an example of economic theory being slain by what goes on in the human head.”

Padoa-Schioppa’s research focused on a slightly less complicated economic choice: the beverage preferences of two macaque monkeys.

When choosing between a drop of grape juice and a drop of apple juice, for example, the monkeys chose grape every time. However, 10 drops of apple juice proved to be just as desirable as three drops of grape.

The researchers used tiny electrodes inserted into the orbitofrontal cortex at the anterior part of the macaques’ brain to find individual neurons that were excited when the monkeys were each presented with 25 different beverages. They discovered that each beverage triggered the firing of a specific neuron, and that the number of times the neuron fired rose with the number of drops offered.

After quantitative appraisal, each of these different neurons then triggered a set of secondary neurons, which appear to translate the specific values given by the primary neurons into universal values that can be compared across the board. Ten drops of apple juice, for example, caused this second line of neurons to fire roughly as much as three drops of grape.

This system could be the mechanism behind that elusive jump between someone’s ability to make a real-world estimation of worth, and their ability to reason how much a commodity really means to them. So far, comparisons have only been made between food stuffs, but Padoa-Schioppa believes this mechanism translates a value used to weigh everything—from toys to sexual opportunities. 

Validating Padoa-Schioppa’s hypothesis will take time. Scientists must then determine how these values are set, and what the larger overall structure is that uses them in decision-making.

Yet, according to Paul Glimcher, in the coming 20 years, this research might have a wide range of medical applications.

“Most mental illnesses revolve around how we evaluate our environment,” he said. “Addiction, depression and even psychopathic tendencies could just be a result of certain processes gone wrong.”

And in the long term, understanding decision-making could create a better-run society.

“All policy is based on economics, and economics is based on theory that is wrong,” Glimcher said. “Once we figure out the mechanisms that underlie the theory, then maybe we can come up with a 401k that people will actually use.”

Originally published April 24, 2006

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