The brain science behind ’A beautiful mind’

Experiment at NYU find neurological underpinnings of economic game theory

In article in today’s issue of the journal Neuron, two neuroscientists – Paul Glimcher of New York University and Michael Dorris, a former NYU colleague currently at Queens University, Canada – offer evidence for the neurological basis for the theories of John Nash, the Nobel-winning economist who pioneered game theory. The findings in the Neuron article are a major advancement in the increasingly prominent field of neuroeconomics, which attempts to discover the basis within the brain for the sort of economic decision-making predicted by game theory.

To develop their findings, Glimcher and Dorris used rhesus monkeys to participate in a strategic conflict game known as the “the inspection game” (the game was first developed by the RAND corporation to evaluate the likelihood of Soviet compliance with arms control agreements). In the human version of the game, there are two players, an “employer” and an “employee.” The employee’s goal is to “shirk” as much as possible (for which he receives his wage plus free time), while the employer – who can use an “inspector” to catch the employee – has the goal of spending as little as possible on inspectors while maximizing the employee’s appearances at work.

John Nash, whose life and work was detailed in the movie and book, “A Beautiful Mind,” developed a theory that predicts outcomes in this kind of strategic setting. Dorris and Glimcher sought to test those predictions with experiments on both humans and rhesus monkeys, and to examine in the monkeys whether there was evidence that decision-making became encoded within the posterior parietal cortex of the primate brain.

In their research, a computer played the role of the employer, and the human and monkey participants played the employee. Overall, humans played the game hundreds of times, and the rhesus monkeys played it thousands of times; humans were rewarded with money, and the monkeys were rewarded with fruit juice each time they “won” a round of the game.

Dorris and Glimcher found that with human players, the outcomes predicted by the Nash equilibrium computations were largely correct and surprisingly, that the behavior of the monkeys in this game was essentially identical to that of the humans. This was an important finding, because it permitted the researchers to examine the role of the posterior parietal cortex of the monkeys in a setting in which the monkeys seemed to employ similar, if not identical, strategies as humans in game playing.

Another element of Nash’s theory opened the door for Glimcher’s and Dorris’ neurological findings. In Nash’s theory applied to the inspection game, the “desirability” of the employee’s two options, working or shirking, must be equivalent regardless of the level at which the equilibrium is achieved. That is, from the employee’s perspective, whether the balance of working and shirking requires the employee to work a lot or permits him to shirk a lot (based on how often the employer uses the inspector), the desirability of the two choices should be rendered equal by the actions of his opponent. Glimcher and Dorris reasoned that if the economic theory was sound in terms of producing behavior, then there should be corresponding neurological findings in the posterior parietal cortex.

In fact, when Glimcher and Dorris examined the activities of those neurons while the monkeys played the inspection game, they found that the posterior parietal cortex carried a signal essentially identical to the one expected. When the monkeys’ behavior was well predicted by Nash’s theory, the neural activity corresponded.

Glimcher said, “The field of game theory has till now largely been viewed as purely mathematical and theoretical, with some room for behavioral experimentation. These findings lie at the beginning of a new era in which we will be able to pose and explore economic and decision-making questions with empirical data from brain measurements. These new measurements will give us insights from the biological perspective that will improve both the explanatory and predictive of existing economic approaches. This work really brings into the realm of neurobiological inquiry the kinds of decision-making that we usually call voluntary, and it strengthens the argument that we are beginning to understand where and how the process of making a decision is executed by the human brain.”

Paul Glimcher is an associate professor of neuroscience at New York University. He is a leading scholar in the field of neuroeconomics; he recently published a book on neuroeconomics, Decisions, Uncertainty, and the Brain: The Science of Neuroeconomics (MIT Press/Bradford Press). Michael Dorris was a post-doctoral fellow in Professor Glimcher’s lab when the work described in the Neuron article was conducted; he is currently an assistant professor of physiology at Queen’s University in Ontario, Canada.