A cadre of scientists at University College
London are not only studying the complex neurobiology of how the brain
perceives and determines something of value, they have suggested regions in the
brain that they believe are involved in how choices about value and reward are
made.
Their research is far from frivolous and can
be defined as the quest to document the biological basis of economic behavior,
a pursuit for which they didn't even turn to fellow humankind as test subjects.
Instead, they chose a highly intelligent but distant cousin: rhesus monkeys.
Relying on simian kin allowed the researchers
ample opportunity to explore visual fixation patterns, which they say lie at
the core of economic decision-making.
After studying the animals in controlled experiments
the researchers concluded that making a choice about the value of an object is
based on a variety of factors. One key finding involves how the eyes become
fixated on an object in the course of making a decision. Rhesus monkeys choose
not only what they like but they deem to be of value. Objects that attract
their attention and have value—for monkeys, that means being rewarded with
something to eat—are those considered to be of economic importance.
"Where we direct our gaze can have a big
impact on what we choose," wrote Drs. Sean E. Cavanagh and Steven W.
Kennerley of University College London.
Despite their findings, the science
underlying how choices are made is still fraught with unknowns. For example,
"where we choose to gaze during the decision process is not
well-characterized, despite the important role it plays," the scientists
reported in the Proceedings of the National Academy of Sciences.
In the study, the monkeys performed a simple
decision-making experiment where they were free to look around a computer
screen that displayed choice options. They had been trained to perform
decision-making tasks that allowed them to make choices that would produce a
reward. Two monkeys participated in the project. They were described as two
males, Macaca mulatta, Old World rhesus monkeys widely used in scientific
research.
When choice options appeared, the monkeys
rapidly gazed toward more valuable and novel objects. Despite a gaze
"preference" for novel stimuli, subjects did not always prefer to
choose them. This suggests there are mechanisms in the brain that govern
value-guided choices. The animals would indicate their economic choice by
moving a joystick, essentially saying: "That's the one I want."
"We constantly experience a rich
assortment of visual information, some of which is highly relevant to future
decisions. To make decisions efficiently, we must quickly identify relevant
information in our environment—a process often accomplished by orienting our
eyes toward this information.
"These findings suggest the primate
brain contains fast covert valuation mechanisms to bias fixations toward
valuable information," the scientists wrote.
The London-based research isn't the first to
search for the neurobiological basis of value-based choices. Scientists at
Cambridge University in 2016 embarked on a similar search and noted that they,
too, found a physiological basis for economic behavior. That team, led by Dr.
Fabian Grabenhorst, concluded in the journal Nature: "How such valuations
are converted to economic decisions remains unclear." The Cambridge team
reported that their work demonstrated that "the dorsolateral prefrontal cortex
(of the brain) implements a flexible value code based on object-specific
valuations by single neurons." In short, individual neurons are stimulated
in the process of making economic choices.
The London team found evidence that economic
choices have a more complex neurobiological basis. "Evidence suggests that
the prefrontal cortex is critical for value-based decision making and
prefrontal cortex neurons encode the values of choice options," the team
said, but countered that their results have led them to another conclusion.
They contend in their research that other brain regions are stronger candidates. "The subcortical saccadic system—composed of the caudate nucleus, substantia nigra pars reticulata, and superior colliculus —is a strong candidate for several reasons. Neurons within these brain regions rapidly receive cortical input, and have been shown to discriminate the value of stimuli," the team wrote.
Also important in understanding the
neurobiological basis of economic behavior is learning where the animals first
cast their gaze. "Surprisingly, the direction of this first fixation was
not random but was strongly influenced by the value of the stimuli."
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