When you have to make a choice, sets of brain cells located above your eyes flame up as you consider your options. Animal studies have suggested that each option activates a specific set of neurons in the brain – the most tempting the offer, the faster the related neurons fire.
New research by scientists at Washington University School of Medicine in St. Louis have shown that the activity of these neurons encrypts the value of the options and decides the final ruling. By modifying the neurons’ movement in monkeys, the researchers changed how attracting the subjects found each option, getting them to make different choices.
The study has been published on November 2nd in the journal Nature.
Encoding the Value of Options and Making Decisions
An elaborate understanding of how options are appreciated and choices are made in the brain will help us learn more about how decision-making goes wrong in people with various conditions, including addiction, depression, eating disorders, 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, Ph.D., a professor of neuroscience, economics, and 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.”
Back in 2006, Padoa-Schioppa and John Assad, Ph.D., a professor of neurobiology at Harvard Medical School, published research in Nature detailing the discovery of neurons that encrypt the subjective value provided and chosen goods. The neurons were found in the orbitofrontal cortex, a region of the brain just above the eyes included in goal-directed behavior.
“We found neurons encoding subjective values, but value signals can guide all sorts of behaviors, not just choice,” Padoa-Schioppa said then. “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 investigate the association between values encoded by neurons and choice behavior, scientists carried out two experiments.
In one of the studies, the researchers continuously presented the subjects with two drinks and recorded their selections. The drinks were offered in different amounts and included lemonade, grape juice, cherry juice, peach juice, fruit punch, apple juice, cranberry juice, peppermint tea, kiwi punch, watermelon juice, and salted water.
The subjects usually preferred one flavor to another, but they also wanted to get more than less, so their decisions were not easy all the time. Each subject pointed their choice by glancing towards it, and the drink was delivered.
Then, the scientists placed small electrodes in the subjects’ orbitofrontal cortex, which stimulate the neurons that show the value of each option. When the researchers pulsed a low current via the electrodes while a subject was offered two drinks, neurons representing both options began to fire faster.
This meant that both options became more attractive but, because of the way the values are encrypted in the brain, the call of one option enhanced more than that of the other. The result is that low-level stimulation made the subject more prone to choose one particular option in a somewhat predictable way.
“When it comes to this kind of choices, the monkey brain and the human brain appear very similar,” Padoa-Schioppa explained. “We think that this same neural circuit underlies all sorts of choices people make, such as between different dishes on a restaurant menu, financial investments, or candidates in an election. Even major life decisions like which career to choose or whom to marry probably utilize this circuit. Every time a choice is based on subjective preferences, this neural circuit is responsible for it.”