The old “monkey see, monkey do” adage may rest on some neuroscientific evidence, a new Yale study finds.
To examine how the primate brain facilitates cooperative behavior among individuals during social interaction, a team of researchers trained pairs of marmoset monkeys to cooperate in a task.
What you need to know
How do primates use visual cues during cooperative decision making?
Primates rely primarily on visual cues to gauge each other’s mindsets during social interactions. Yale scientists have determined that the same canonical computations are involved in the brain whether individuals are making social or non-social decisions.
In a study of marmoset monkeys, the researchers found that the animals use what they call “the social gaze.” Specifically, the monkeys cooperated by continuously gathering and interpreting social information. The animals especially focused on eye gaze and body movements to predict what each other was about to do.
How might these insights better inform medical outcomes?
Understanding how regions of the brain cooperate in processing communication can shed new light into conditions that impact social function, such as autism.
The challenge: If the monkeys pulled separate levers within one second of each other, they’d receive treat rewards. Success required astute mutual observation between both monkeys and the ability to read body language cues so they could gauge each other’s readiness to act.
The result: They pulled it off.
How? By employing what the researchers have dubbed “the social gaze.” Specifically, the monkeys cooperated by continuously gathering and interpreting social information. The animals especially focused on eye gaze and body movements to predict what each other was about to do.
“It’s all about gathering evidence from your partner to figure out, ‘Okay, is this is a great time to work together?’” said Steve Chang, an associate professor of psychology in Yale’s Faculty of Arts and Sciences and associate professor of neuroscience tenure at Yale School of Medicine. In the work, Chang’s lab collaborated with the lab of Monika Jadi, associate professor of psychiatry and neuroscience; and with the lab of Anirvan Nandy, associate professor of neuroscience and psychology. (Weikang Shi, a postdoctoral fellow in the Jadi, Chang & Nandy labs, led this work.)
From left, Anirvan Nandy, Monika Jadi, and Steve Chang.
According to their findings, published in the journal Neuron, the monkeys used a kind of “evidence accumulation” process in a brain region called the dorsomedial prefrontal cortex (dmPFC), which is involved in social thinking and decision-making. During the experiment, the researchers recorded activity in the animals’ dmPFC, finding that neurons in this region showed activity patterns that steadily ramped up as the animals approached a cooperative action.
This can help explain how the primate brain transforms social information into cooperative action, a big part of social behavior in both humans and animals, and an underlying factor in some psychiatric conditions, the researchers say.
In a Q&A, Chang, Jadi, and Nandy discuss nonverbal communication, the role of visual cues, and why primates look (at each other) before they leap.
You’ve all studied various aspects of decision-making, but in the latest work, you brought these different areas of research together?
Anirvan Nandy: The marmosets have given us a golden opportunity to study complex social behaviors in a more natural dynamic, and the three of us bring complementary areas of expertise. Steve’s expertise is in primate social behaviors. Mine has been in dense recordings from primate brains, and Monika’s expertise is in modeling computational aspects of the brain at work.
How was your approach to decision-making different from previous research?
Monika Jadi: Decision-making has been studied extensively. It’s a very robust and vigorous line of research in neuroscience. But most of the neural studies have looked at static decision-making, meaning “How am I making decisions with respect to what is going on in the world around me?” We know a lot about which neural mechanisms are involved in a controlled setting involving a single individual, but we didn’t know if the same neural principles would apply in a social context involving collaborative decisions.
The key finding here is that the animals actively seek out the evidence about their partner’s actions before they act themselves. And we found that when they seek out evidence, their brains seem to be doing very similar things to what has been found in the other individual studies.
What are their brains doing?
Nandy: The marmosets solve the cooperation problem by taking time to gather evidence before taking action, and that is the basis of their successful cooperation. The cool part is that we’re seeing that the brain seems to be using a conserved set of mechanisms to solve very different problems — decisions you make on your own and decisions you collaborate on with others.
Imagine that you start off having to decide whether to choose A or B. As you are gathering evidence about which choice to go for, you are wavering in the middle. Then if you find more evidence towards choice B, you move — let’s say “drift” — towards it. But if the evidence is weak, you wait longer and continue gathering. This is called the “drift diffusion” model of decision-making. And we found that the exact same process is being used in social decision-making when the animals are observing a partner’s actions.
So, the monkeys must be able to read each other?
Jadi: We found that if you want to cooperate well, you want to be in a really closed loop between individuals so you can communicate well and then collaborate. Our study shows that actively gathering information helps close that loop in a way, so that we can work together and synchronize better.
Is this practice widespread in the animal kingdom?
Steve Chang: It’s probably widespread, but the way primates do it is very vision centric. We use our vision, too, to sample the world. You and I could be just sitting in one place and not move an inch but be sampling the world around us. In contrast, if we were to do this study in rodents, for example, they would use other sensory modalities — whisker vibrations, sense of smell perhaps. If you work with preverbal infants, visual cues become very important when you’re trying to communicate and do something together. I think throughout evolution these bodily cues and facial cues became very important in both sending messages and in gathering information.
And what does that say about social bonding? About social cooperation?
Chang: That’s an interesting question. I think to cooperate well, you need to really get to know each other. And at some point, I think when you have a strong bond, you don’t need to always actively gather information. You’ve kind of built a model of your partner that can be predictive.
What’s next in this line of research?
Nandy: In this study, we looked at one brain area, the dorsomedial prefrontal cortex. But there are other parts of the prefrontal cortex that are also involved in cooperation. Next we want to record other brain areas such as the orbitofrontal cortex [an areas that has been associated with reward-related decision-making]. We want to understand how these brain areas are working together. They’re talking to each other. We want to understand the nature of that language. How are these multiple brain areas talking to each other to solve, not just cooperation, but in any other kinds of social interactions.
From a medical perspective, what might this research help shed light on?
Nandy: The most relevant psychiatric conditions that this kind of work can influence are related to social dysfunction. One example is autism spectrum disorder. Even though our work is basic science work, this enables us start making connections to what the brain is doing and how it could influence different disorders.
