The Frontal Cortex

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.

Comments

  1. #1 EJ
    September 10, 2007

    Explains a little bit about your life? Hmmm. It sounds like you have some new terminology to describe your life (someone’s cingulate sulcus is on and someone’s is off). But even if we just accept that cingulate sulcus activity is the cause of the behaviours in question, I don’t see this as too much of an explanation without knowing what in turn causes the behaviour of the cingulate sulcus. And we don’t know, as you acknowledged.

    (still, interesting post.)

  2. #2 Luna_the_cat
    September 13, 2007

    That is interesting…and I would love for this to be done with me and my husband, just to see if we destroy the trend. When we’ve been out to a social event, my husband is usually the one who hashes over motivations and social consequences, whereas I don’t tend to think about it much unless he brings it up. I had always ascribed this to the fact that (especially recently) I was always fairly confident of my social “reading” of things that I made at the time and on the spot, whereas my husband worries more. But I don’t know.

  3. #3 Jonny
    September 14, 2007

    EJ, you certainly have a valid point on the difference between learning a new descriptor and learning a new explanation. On the other hand, I’m certainly interested upon learning either. ;D

    That said, the sample size was pretty decent (n=48 pairs for the main experiment, as I gathered), although I never saw a p value for the gender difference, so I can’t really speculate on whether that finding can be extended to say that men’s brains work in this way and women’s brains work in that way.

    Still, thanks for an interesting read!

  4. #4 elliott
    September 20, 2007

    Interesting post – and this finding is news to me! (and neuroecon is kindof what I do for a living). Is this sex difference finding buried in one of their many Science papers, or is it in submission/press?

    Love your blog –

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