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Scientists like to study choice behavior. It's an important area of study for lots of different applications, including things like, say, marketing, but also things including mate choice, nutrition, drug addiction, and well...your life is FULL of choices. When you're at the store facing that huge freaking WALL full of different kinds of cereal? When you decide to hit snooze on your alarm? When you decide to see the dessert menu after dinner? All of these are different kinds of choices, and our brain has different ways of calculating the cost and benefits of each one (or, in the case of mine, going into complete shut down at the sight of that gigantic cereal aisle. I hate that thing).
But when scientists study choice and decision making, they often study it in something of a vacuum. Not a literal vacuum, but in an environment with very few variables. You have a rat with a choice of levers or in a maze with a choice of directions. You have a human in a scanner making a choice of two different objects or how much to wager. This is really great for studying how different kinds of decisions are made, but as we get to know more about choice, we have to begin adding more variables.
And with choice in real life comes something else: competition. A lot of the most important decisions are made in the presence of competition, like decisions for resources. Find a good patch of berries? Someone was probably there before you. Come across a lovely lady or boy vole you'd like to woo? There's probably another suitor knocking at the door. So the question now becomes, how does the brain deal with decision making in the presence of competition?
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Hillman and Bilkey. "Neural encoding of competitive effort in the anterior cingulate cortex" Nature Neuroscience, 2012.
To look at how competition changes the way the brain processes a choice, the authors of this study had to invent a new kind of behavioral study. They set up rats to record neurons from the anterior cingulate cortex, an area involved in determining effort in cost-benefit decision making. Then they allowed the rat to run a maze. In one side of the maze the rats got access to two food pellets, which were next to a partition. On the other side of the partition was another rat, who also got his own two food pellets. On the other side of the maze, the rats got access to TWELVE food pellets, but this time the partition was slightly open, meaning the rat was competing against another rat on the other side for the food.
So the choice is between an uncontested position with a small reward, and a contested position with a large reward.
And while the rat was making this decision, they recorded neuronal activity from the anterior cingulate.
You can see along the bottom of that figure the heat map which shows the total activity in the anterior cingulate. The shape is the maze. The non contested reward is on the left, and the contested reward is on the right. You can see that activity in the anterior cingulate was higher on the right side, when the decision making involved competition, than it was on the left.
The firing differences also varied as a feature of the social dominance of the animal. When the rat faced off against another rat he knew to be subordinate to him, there was more firing in the anterior cingulate cortex than when the rat faced off against a rat which he knew to be dominant.
Upon further analysis, something interesting came out. The activity in the anterior cingulate was not dependent on the OUTCOME of the competition, just the presence of their being a competitor in the cost-benefit equation. So it appears that the changes in firing are changes in the way the rat analyzes the options, knowing that a competitor is present, but are not associated with the final decision that the rat makes. The authors call this "encoding competitive effort", a calculation of how much effort it will take to obtain the reward.
This is the first time that anyone has looked at this using one on one competition between rats, but I wonder if this "competitive effort" firing would also work for other types of effort, if a reward was simply harder to receive and required more work (say, with a lever press). Does "competitive effort" differ from other types of effort? And how?
But the next time you start to jockey for position to get the last donut, think of your options. And think of your anterior cingulate.
Hillman KL, & Bilkey DK (2012). Neural encoding of competitive effort in the anterior cingulate cortex. Nature neuroscience, 15 (9), 1290-7 PMID: 22885851