A new Yale study analyzing monkey brains during competitive activity may help scientists better understand strategic and social reasoning in human beings.
In a September study published in the journal Science Express, Yale School of Medicine researchers analyzed the single-neuron activity of three rhesus monkeys engaged in competitive behavior. The researchers monitored several regions of the monkeys’ brains while they played a game against a computer program. By using brain monitoring equipment, researchers identified the region of neurons that is responsible for complex cognitive strategy in the monkey.
“The unique thing about our study was that we found that the activity of single neurons in a region of the brain … was responsible for the switch between complex and simple cognitive strategy in the monkeys,” the study’s lead author Daeyeol Lee said.
Researchers had the monkeys play a simple, reward-based game against a computer program. While the monkeys performed token-based tasks that required them to choose between two identical objects on the computer screen, researchers monitored several different regions of the animals’ brains.
Every time the monkey selected the same object as the computer, the animal won a token. After accumulating six tokens, the monkey received juice as a reward. When the monkey chose a different target than the computer, it lost a token.
According to researcher Hyojung Seo, the monkeys’ object choices were first informed by “operant conditioning,” in which a subject’s behavior is modified by the consequences of its actions.
However, the researchers programmed the computer to exploit the reinforcement and punishment learning processes of the monkey, which disrupted the success of the monkey’s heuristic algorithms.
In a competitive environment, operant conditioning is not the best approach, Lee said.
But to the surprise of several of the researchers, the monkeys were still able to increase their payoffs over time by deviating from their simple operant learning reactions and countering the computer’s own strategy. The monkeys began to employ more complex decision-making by trying to understand the computer’s own actions. This ability to understand the thought processes and motives of others is called “theory of mind.”
“There is a controversy as to whether monkeys actually have full blown theory of mind or they only have very primitive precursors,” Lee said. “But it is clear from this particular experiment that they have at least some primitive form of theory of mind if not the equivalent of human theory of mind.”
The monkey’s deviation from simple learning strategy was specifically reflected by neurological activity in the dorsomedial prefrontal cortex. The researchers found that neurons in the dmPFC region allowed for the switch between heuristic learning algorithms to a more complex strategy. Seo said that, in the future, the team might consider conducting similar research with two monkeys instead of a monkey and a computer. But Yale psychology professor Steve Chang — who reviewed the paper and has studied social cognition in monkeys — said he recognizes the scientific advantages of using a computer opponent.
Through the study of monkeys’ strategic reasoning and decision-making, the researchers hope to learn more about social cognition of humans.
“The part of the monkey brain that is responsible for switch signals between simple and more complex strategy is probably analogous to the part of the human brain that is also involved in social computation,” Lee explained.
The study may give the scientific community insight into the human cognitive processes responsible for complex decision-making strategies, researchers interviewed said. Future research on the dorsomedial prefrontal cortex may also be central to the treatment of psychiatric disorders in humans, Seo said.
The research was conducted over the course of almost a decade.