The Gendered Brain

There are so many stupid studies of the gendered brain that it's easy to conclude that good research into psychological sex differences is impossible. But that would be a mistake. I think one of most interesting recent investigations into the cognitive differences of men and women comes from a clever neuroeconomics experiment, designed by Colin Camerer and Read Montague. It's called the trust game, and it goes like this: at the start of each of 10 rounds, an "investor" is given an imaginary stake of $20. They can keep it all, or "invest" some of it with a "trustee". Any money that gets invested is tripled, and the trustee then has the option of returning some portion of that amount back to the investor. For example, if the investor keeps $10 and invests $10, then the trustee has $30 to divide ($10 x 3). However, if the trustee decides to keep all the money there is nothing the investor can do about it. Since the trust game is typically played for 10 rounds, both players have a selfish incentive to trust each other.

While this simple game was being played, Camerer and Montague imaged the brains of the two players. The neuroeconomists discovered that activity in the caudate nucleus - a region involved in the dopamine-reward pathway - was directly correlated with trustworthy behavior. Furthermore, because activity in the caudate nucleus was apparent at least 10 seconds before the players made a decision, the scientists could effectively predict the outcome of each round before it actually happened. They could see the neural roots of fidelity and betrayal.

What does this have to do with the gendered brain? Well, men and women tend to play the trust game pretty differently. When men were contemplating whether or not to trust a stranger with their "investment," an area called the medial cingulate sulcus became active. Like the caudate, the cingulate sulcus is normally associated with the processing of potential rewards. However, once men made their decision - regardless of what their decision was - both the caudate and the sulcus turned themselves off. Their mind went silent.

Female brains acted very differently. The reward areas of their brain remained extremely active until they knew how the investor reacted to their decision. Camerer believes that this is because women are much more attuned to the social consequences of their decisions. "The difference in brain activity in the two genders is like the kind of behavior you might see after a couple gets home from a potluck dinner and rehashes the event," Camerer writes. "The man wants to turn on the TV and catch some sports scores (his cingulate is turned off). The woman is more likely to rehash the events of the evening, and worry about whether she said the right thing and whether the hostess was happy with the dish she brought, and whether plans for having lunch later in the week are genuine."

Of course, all the usual caveats apply: the sample size was small, and nobody has any clue whether such sex differences are biological or cultural. But I find the experiment interesting because it jives with my personal experience (n of 1, so feel free to ignore everything that follows). After a dinner party, or some other social engagement, I'm pretty much content to stop thinking about how it went. My girlfriend, however, is continually peppering me with questions: Did I talk too much? Was my comment about so and so rude? Was the food OK? etc. etc. Her cingulate sulcus is still on, mulling over the details of the social interactions.

I'm not sure what the larger significance of the finding is, and I certainly wouldn't want to construct some lame Pleistocene story about hunter-gathers and gender, but I find the data interesting, if only because it explains a bit about my life.