When you are faced with a choice — say, whether to have ice cream or chocolate cake for dessert — sets of brain cells just above your eyes fire as you weigh your options. Animal studies have shown that each option activates a distinct set of neurons in the brain. The more enticing the offer, the faster the corresponding neurons fire.
Now, a study in monkeys by researchers at Washington University School of Medicine in St. Louis has shown that the activity of these neurons encodes the value of the options and determines the final decision. In the experiments, researchers let animals choose between different juice flavors. By changing the neurons’ activity, the researchers changed how appealing the monkeys found each option, leading the animals to make different choices. The study is published Nov. 2 in the journal Nature.
A detailed understanding of how options are valued and choices are made in the brain will help us understand how decision-making goes wrong in people with conditions such as addiction, eating disorders, depression and schizophrenia.
“In a number of mental and neuropsychiatric disorders, patients consistently make poor choices, but we don’t understand exactly why,” said senior author Camillo Padoa-Schioppa, PhD, a professor of neuroscience, of economics and of biomedical engineering. “Now we have located one critical piece of this puzzle. As we shed light on the neural mechanisms underlying choices, we’ll gain a deeper understanding of these disorders.”
In the 18th century, economists Daniel Bernoulli, Adam Smith and Jeremy Bentham suggested that people choose among options by computing the subjective value of each offer, taking into consideration factors such as quantity, quality, cost and the probability of actually receiving the promised offer. Once computed, values would be compared to make a decision. It took nearly three centuries to find the first concrete evidence of such calculations and comparisons in the brain. In 2006, Padoa-Schioppa and John Assad, PhD, a professor of neurobiology at Harvard Medical School, published a groundbreaking paper in Nature describing the discovery of neurons that encode the subjective value offered and chosen goods. The neurons were found in the orbitofrontal cortex, an area of the brain just above the eyes involved in goal-directed behavior.
At the time, though, they were unable to demonstrate that the values encoded in the brain led directly to choosing one option over another.
“We found neurons encoding subjective values, but value signals can guide all sorts of behaviors, not just choice,” Padoa-Schioppa said. “They can guide learning, emotion, perceptual attention, and aspects of motor control. We needed to show that value signals in a particular brain region guide choices.”
To examine the connection between values encoded by neurons and choice behavior,…