That Neuroscience Guy - Trust

Episode Date: September 19, 2021

Season 2 of That Neuroscience Guy is here! We kick off the season by discussing the neuroscience of why and how humans trust each other. 

Hi, my name is Olof Kregolsen, and I'm a neuroscientist at the University of Victoria. And in my spare time, I'm that neuroscience guy. Welcome to the podcast. And welcome to season two. We're back. Almost 20,000 downloads for season one, and we're ready to go with Season 2. So, as usual, we hope you enjoy the podcast and learn something about the neuroscience of everyday life. What do we mean by trust?

You know, we trust our friends, we trust our significant others, and it's a key part of life. If you can't trust someone, it changes the way you interact with them. You're not able to do things the way you might want to do them. And if you trust someone implicitly, that's the opposite end of the spectrum. You might share your bank details with them or allow them to care for your child. On today's episode, we're going to talk about the neuroscience of trust. In animal studies, researchers look at whether an animal feels like it's safe to approach another animal. And that's sort of a basis for studying trust, and that's where

we'll start today. In human research, it's a bit more complicated, but we'll get to that shortly. So with animal models exploring trust, researchers such as Paul Zak have found that a hormone called oxytocin was released in the brain of an animal when it felt like it was safe to approach another animal. So what is oxytocin? Oxytocin is a hormone and it's normally produced in the hypothalamus and released by the posterior pituitary gland. Traditionally, the release of oxytocin is associated with social bonding, interacting with other people and becoming friends. You see release of oxytocin during reproduction, during childbirth and in the period after childbirth. Given when oxytocin is released and the idea of social bonding that I mentioned,

you can see why this hormone might play a key role in our ability to trust. Now, let's talk about this in humans. So, if you think back to Season 1, in a previous episode we talked about the role of economic games in studying human interaction and concepts like trust. And we mentioned specifically the ultimatum game. If you recall, in the ultimatum game, one person has a lot of money and their job is to share that money with another person.

And they only get to play it once. So imagine you had a hundred dollars and I said, okay, do you want to, how much of this do you want to share with that person over there? That's your job in the game. The other person's job is to say yes or no. If they say yes, then the money is shared that way. And if they say no, it isn't. And what you find is that most people share the money 50-50, but you do get people that are a little bit greedy and keep 80% for them and offer 20% to the other person.

And when that happens, sometimes people say no. So in the study I'm about to tell you about, the researchers used a variant of this game. Basically, the participant chose an amount of money to send to a stranger via computer. So they're going to send them the money over the computer, and they know that the amount of money will triple if the person decides to agree to the split or not. So there's the conflict. You can either keep all the cash, so say it's $100, or I can trust that the other person will share it and I might get back $, because the amount of money has tripled.

So that's the trust element. Should I keep the money for myself, or should I share it with this stranger and trust them? So the researchers wanted to measure oxytocin levels during the experiment, and they did this by drawing blood from their arms. They basically drew blood right before the person was about to get the money and right the person receiving the money, of course, and right after the person decided to trust and send the money to the other person. And the researchers did this

properly. They didn't want to influence behavior or anything. So they didn't even tell people what the study was about. They just told them, this is what we're going to do and we'll fill you in at the end. And they did this because they didn't want the levels of oxytocin to, you know, sort of be manipulated by people playing the game or thinking about how the game is played. And what they found was really cool. They found that people that trusted and were willing to send the money away had more oxytocin than people that decided to keep the money. So that's the same as the animal studies that were done. The amount of oxytocin that was present predicted the degree of trustworthiness. Now, the researchers doing this, Dr. Zak and colleagues, wanted to take this a bit further.

So they actually started giving synthetic oxytocin into actual humans. They do that through a nasal spray. And they basically wanted to see, well, if we give someone oxytocin, can we induce trust? And that's what they found. They found that when they gave oxytocin artificially to people, they were more trustworthy. They were more willing to share money in these kind of economic games. And the researchers, like I said, did this well. They did a whole variety of psychological tests to make sure that no other brain function was really changed. They brought it right back to trust.

So, in summary, oxytocin, this hormone that's released in the brain, appeared to do just one thing. It reduced the fear of trusting a stranger. Imagine everyday life if we could somehow inject oxytocin at those that we wanted to have trust us. It'd be kind of a cool thing to do. Maybe one day it'll happen. a cool thing to do. Maybe one day it'll happen. Now, this research was taken even further. They started looking at stress and when people are stressed, and they realized that stress actually inhibits the release of oxytocin. So if you're experiencing high stress, your brain is less able to release oxytocin. And we know that when people are stressed out, they trust less. So they were able to discover that link, that the oxytocin basically

controls a person's empathy. And when you're stressed, you're less likely to trust. And that's because oxytocin is inhibited. And Dr. Zak hit home runs with this. He did it really well. He even went to other countries like Papua New Guinea, and they did the same experiment in indigenous people there. And yes, they found a relationship between oxytocin and trust, not just in New Guinea, but in other parts of the world. So this is a universal thing.

The hormone oxytocin really governs how much we trust. Now that's a lot about oxytocin, but what about the brain regions involved in trust? Because the release of the hormone is also controlled by cortical parts of the brain, areas that we've talked about in the past. controlled by cortical parts of the brain, areas that we've talked about in the past. For example, research by Dr. Anne Catherine Fett basically used similar sorts of games, but in this case, people were playing with a partner, and that partner was either trustworthy, so someone that they had faith would act in an appropriate manner, or the partner was unfair. And they wanted to do this to explore the underlying brain mechanisms in cooperation and trust. And when the researchers looked at their behavioral data,

just what was going on, they found that people playing with the trustworthy partner trusted them more by the end of the experiment. And there was a strong decline in trust during interactions with the unfair partner. But what's interesting is this change in trust was paralleled by changes in mentalizing regions of the brain. Now, what's a mentalizing region? These are regions that are active when we're trying to understand the actions of others. We're trying to process what another person is doing. And those regions include the temporal parietal junction, the posterior cingulate cortex, and the precuneus. And the activity in these brain regions

paralleled with the degree of trust. Now, unfortunately, these researchers didn't measure oxytocin, but the obvious conclusion is that these are the brain regions that help govern the release of oxytocin, but the obvious conclusion is that these are the brain regions that help govern the release of oxytocin. Dr. Fett and colleagues found some other cool results as well. They found that age was associated with reduced activation in reward parts of the brain. And they also found reduced activity in the CAU-8 nucleus during interactions with a trustworthy partner. So in that case, it's like the CAU-8 nucleus decreases activity as trust increases,

and it increases activity when someone's untrustworthy. So this could also be tied to the release of oxytocin. trustworthy. So this could also be tied to the release of oxytocin. And a cool result that ties into some stuff that we talked about last season was that during unfair interactions, the researchers saw an increase in activity in the anterior cingulate cortex, our old friend from when we talked about human learning. And the anterior cingulate cortex basically plays a role in inhibition amongst other things. And in this case, the researchers hypothesized that the anterior cingulate cortex is actually inhibiting pro-social tendencies. So in other words, you kind of want to trust the person and the anterior cingulate cortex says, no, I really think trusting this person is a really bad idea.

And like I said, we've talked about the ACC a lot. Previously, we've talked about its role in learning, processing, punishments, and rewards. Well, in this case, the ACC, we're adding sort of another piece to it, which is this role in what's called response inhibition. Your brain's going along, and in this case, just to recap, is saying, all right, let's share some money with this person. And if you come to not trust the person, the ACC is going to put the brakes on that. It's going to inhibit the response and say, no, we're not going to do that. We don't want to share money with this person because we've come to believe they're untrustworthy.

So in summary, the neuroscience of trust. At the lowest level, trust is based on the release of oxytocin. When we trust someone, there's an increased release of oxytocin. And when we don't trust someone, there's a decreased release of oxytocin. Now, what governs that? Well, mentalizing regions of the brain, like the temporal parietal junction, reward processing and planning regions of the brain, like the orbital frontal cortex. And finally, over top of all this is our friend, the anterior cingulate cortex, that's basically allowing things to happen until it feels like it has to put the brakes on.

And together, these brain regions form a neural system responsible for us trusting others. All right, that's all I have for you on this episode. Thanks forever like listening. Remember, you can follow me on Twitter at that neuroscience guy, where I post cool updates about the science that's going on in my lab and other things that I find interesting. I've also started developing a YouTube channel, That Neuroscience Guy. There's some videos that talk about stuff not on the show. It's just little tidbits about how science actually works. And if you haven't done it yet, check out my TEDx talk. Back in March, I gave a cool TEDx talk about how mobile EEG is going to change the world, mobile brainwave technology.

And it relates to some research I was involved with in hospitals measuring brainwaves in doctors. And it also ties into some work I've done with the Mars Habitat in Hawaii. That's also on YouTube. Thanks so much for listening. Welcome back and enjoy season two.