Summary: Neurons in the orbitofrontal cortex encode subjective values and their activity can directly influence which option is chosen.
Source: WUSTL
When you weigh two choices — for example, ice cream versus chocolate cake — groups of neurons just above the eyes become active as you assess the options. Animal research has shown that each choice triggers a distinct population of brain cells, and the more appealing an option, the more strongly and quickly the corresponding neurons fire.
A new study in rhesus monkeys by researchers at Washington University School of Medicine in St. Louis demonstrates that activity in these neurons not only reflects subjective value but causally influences decisions. In controlled experiments where animals chose between different juice flavors, targeted stimulation of neurons in the orbitofrontal cortex changed how attractive each option appeared, shifting the animals’ choices in predictable ways. The findings were published Nov. 2 in the journal Nature.
Understanding how values are computed and compared in the brain is essential to explaining why decision-making can fail in conditions such as addiction, eating disorders, depression and schizophrenia.
“Patients with various mental and neuropsychiatric conditions often make poor choices, and we still don’t fully understand why,” said senior author Camillo Padoa-Schioppa, PhD, professor of neuroscience, economics and biomedical engineering. “This work identifies a key part of the neural circuitry that produces choices. By clarifying how value signals lead to decisions, we can better understand the breakdowns that occur in these disorders.”
The idea that people compute subjective values to compare options dates back to 18th-century thinkers such as Daniel Bernoulli, Adam Smith and Jeremy Bentham, who proposed that choices depend on weighing factors like quantity, quality, cost and probability. It took nearly 300 years to find persuasive neural evidence of such value computations. In 2006, Padoa-Schioppa and John Assad described neurons in the orbitofrontal cortex (OFC) that encode the subjective value of offered and chosen goods. Those neurons suggested a neural basis for valuation, but until now it remained unclear whether these signals directly cause a choice.
To test causality, the research team ran two complementary experiments. The work was carried out by first authors Sébastien Ballesta, PhD (then a postdoctoral researcher), and Weikang Shi (then a graduate student), with contributions from Katherine Conen, PhD, who designed one of the experiments. Ballesta is now an associate professor at the University of Strasbourg and Conen is at Brown University.
In the primary experiment, monkeys were repeatedly offered two different drinks in varying amounts and made selections by glancing toward their choice. Available flavors included lemonade, grape, cherry, peach, fruit punch, apple, cranberry, peppermint tea, kiwi punch, watermelon and, as a control, salted water. The animals often preferred one flavor over another but also valued larger quantities, so their decisions required trade-offs between flavor preference and amount.
Tiny electrodes were placed in each monkey’s orbitofrontal cortex to stimulate neurons that represent the subjective value of each offer. Low-level electrical stimulation increased the firing rate of neurons tied to both options, making both choices seem more attractive overall. Because of how values are encoded, however, one option’s perceived value rose more than the other’s, and this predictable imbalance biased the animals’ selections toward that option.
A second experiment presented the two offers sequentially. When researchers applied higher-current stimulation while the animal evaluated one option, they disrupted the ongoing value computation for that offer. As a result, the disrupted option was less likely to be chosen, indicating that intact value signals in the OFC are necessary for normal choice behavior. Higher-current stimulation also increased variability in choices, consistent with impairing the comparison process that leads to a decision.
“For these types of preference-based choices, monkey and human brains appear to rely on very similar mechanisms,” Padoa-Schioppa said. “We believe this same neural circuit underlies many everyday decisions — from selecting a meal at a restaurant to weighing investments or candidates in an election. Even major life choices, such as careers or partners, are likely to engage the same valuation and comparison processes. Whenever a decision rests on subjective preferences, orbitofrontal circuits play a central role.”
About this neuroscience research news
Source: WUSTL
Contact: Judy Martin Finch – WUSTL
Image: The image is credited to Mike Worful
Original Research: Closed access. “Values encoded in orbitofrontal cortex are causally related to economic choices” by Sébastien Ballesta, Weikang Shi, Katherine E. Conen & Camillo Padoa-Schioppa. Nature.
Abstract
Values encoded in orbitofrontal cortex are causally related to economic choices
The eighteenth-century proposal that economic choices depend on computing and comparing subjective values remains central to modern economic and behavioral research. Behavioral data alone, however, cannot prove that neural value signals are the causal drivers of choice. Prior work showed that neurons in the orbitofrontal cortex encode the subjective value of offered and chosen goods, and that the activity of these neurons correlates with choice variability and decision dynamics. To establish causality, this study used electrical stimulation in rhesus monkeys. Low-current stimulation raised the subjective value of individual offers, producing predictable biases in choice, while high-current stimulation disrupted both value computation and comparison, increasing choice variability. These results demonstrate a causal link between value signals in the OFC and economic decision-making.