Theory of mind, or how we think about what’s going on in other people’s heads, continues to be one of the hottest topics in cognitive science today. A debate continues to rage over whether we reason about other people’s thoughts by means of theory-like propositional knowledge, or through simulation (i.e., putting yourself in their shoes… in your head). Since psychologists are unlikely to solve this debate by themselves, they’ve called in the artillery – cognitive neuroscientists. And those buggers have come up with some interesting ways to figure out where mentalizing (another name for theory of mind; there are about 50 names for it now) takes place in the brain. A common experimental design in their experiments involves having people perform some task in which they believe they’re interacting either with another human or with a computer. You then compare the brain activity during human-human interactions with that of human-computer interactions, the assumption being that when interacting with another human, people will utilize whatever brain areas are involved in mentalizing in order to figure out what that person is thinking, but that we won’t feel the need to figure out what the computer is thinking. In a paper in press at NeuroImage, Fukui and a half a dozen other people1 (seriously, does it really take that many people to stick someone in an fMRI machine? Why do neuroscience papers always have so many authors?) report one of the more creative versions of this task: a game of chicken.
If you don’t know what chicken is (are you from this planet?), it involves two people in cars driving at each other at high speeds. The first person to get the hell out of the way is the chicken. Unfortunately, it’s impossible to fit a car, much less two, into an fMRI machine, so Fukui et al. came up with a “game theoretical” version. They chose chicken over the more well-known game theoretical game, thePrisoner’s Dilemma, because in Prisoner’s Dilemma tasks, people don’t always behave the way game theory says they should, which leads to empirical and theoretical problems. Chicken is different, largely in that there’s no reward for trying to make the same choice as the other participant. In chicken, you want to make the opposite choice of your opponent. I’ll let them describe their version of chicken (p. 3; figure from p. 2):
In this game, 2 players choose whether or not to aggress against each other; each is rewarded with a sum of money that depends upon the interaction of both players’ choices. There are 4 possible outcomes: player A (subject) and player B reconcile (RR), player A reconciles and player B aggresses (RA), player A aggresses and player B reconciles (AR), or both player A and player B aggress (AA). The payoffs for the outcomes are arranged such that AR > RR > RA > AA and AR + AA = RA + RR = 0. Each cell of the payoff matrix [See Payoff Matrix Below – Chris] corresponds to a different outcome of the social interaction. In contrast to the Prisoner’s Dilemma, the best strategy under this model is to make the opposite move. The task goal is to maximize the final amount of play money.
In case that’s not clear, the biggest payoff is for driving straight while your opponent swerves, and the biggest punishment is for driving straight when your opponent drives straight (crash!). In between those, turning off when your opponent turns off gives a small reward, and turning off when your opponent drives straight a small punishment. The large reward and the large punishment were of equal size, as were the small reward and small punishment. So, if you chose randomly across a large number of trials, your average reward would be 0.
Participants, 16 males, each completed 96 games of chicken. For half of the games, they were told they were playing against the experimenter (they saw a picture of a person), and for the other half, a computer (a picture of a computer). They were also told that the computer would choose to aggress (go straight) 50% of the time. In reality, both the human and computer trials used the same algorithm to choose the opponent’s behavior, so the participants were really playing against a computer all along. While they played their games of chicken, they were strapped into an fMRI machine, and people were taking pictures of their brains.
The average number of games in which participants aggressed was about the same for both the computer (22 out of 48) and human trials (23.9 out of 48). Regardless of whether they believed they were playing against a human or a computer, they aggressed about half of the time. If I were a skeptic, I’d say it looks a lot like they were choosing randomly, but hey, I’m not a reviewer at NeuroImage, so nobody cares what I think. Anyway, the behavioral data isn’t the interesting stuff. The purpose of the study was to contrast the brain activity observed during human-human trials with that during human-computer trials. In that data, there were statistically significant differences. Specifically, increased activation was observed in the supramarginal gyrus, near the rear (posterior) end of the superior temporal sulcus during all human-human trials, regardless of whether they regressed or aggressed. Increased activation was also observed in the anterior paracingulate cortex.
Both of these areas have been implicated in mentalizing in the past, but the supramarginal gyrus is more interesting (to me at least). Fukui et al. interpret the activation of the anterior paracingulate cortex as being involved in risk assessment. They even argue that this area is involved in risk assessment regardless of whether mentalizing is involved. How this fits with their data showing selective activation in this region during human-human trials, I don’t know, but I don’t really care either. Sure, I’d argue that this area serves the more cognitive, perhaps theory-like parts of mentalizing, which are more important when making risky social decisions, but that’s just me. What makes the activation in the supramarginal gyrus (pictured above, from here) interesting is that it fits nicely with the simulation theory of theory of mind. That area, and much of the area surrounding the superior temporal sulcus (the red line surrounded by the peach and yellow in the picture below, from here) is involved in, among other things, movement, orientation, and motion planning. This is exactly what you would expect if we were simulating the physical behavior of another person. Furthermore, in monkeys and humans, the famed mirror neurons have been found in areas around the superior temporal sulcus. If you’re not familiar with mirror neurons, they’re brain cells that fire both when we perform an action, and when we see conspecifics performing that same action. Simulation theorists have latched onto these poorly understood cells, and argued that their existence provides evidence for the simulation theory. So, finding activation in this area helps their case a great deal.
Now, if I was a theory-theory theorist (I just like typing that), I’d argue that the activation of the anterior paracingulate cortex on aggression trials indicates that something other than simulation – something more cognitive – was going on. It might even be evidence that we use both simulation and theory-like knowledge in mentalizing, a revelation that should be greeted with a big “Well duh!” but which, given the heated nature of the debate between the two theories, and the tendency of people to take sides, would be quite a shock to some. Regardless of the theoretical implications, though, it’s just cool to think that someone actually conducted a study on the neural correlates of playing chicken, even if they weren’t playing in cars.