The Gambler’s Fallacy and Brain Activity

Betting on the toss is something most of us have done at one time or another, even it is as harmless as deciding who should start first in some game or other. Our logic tells us that heads or tails is a 50:50 chance. Of course, logic sometimes goes out the window.

If we repeatedly toss a coin and we get a run of heads or tails, our logic weakens and we misquote the law of averages and bet against the run, even though in calmer moments we know that the chance of that last coin toss is still 50:50 for heads or tails.

This poor judgment is known as the gambler’s fallacy and is very difficult to resist if the run is a long one. In order to see where in our brains we work so hard to make silly decisions, Xue et al has used fMRI scans with a card choice game and have published their data in the Proceedings of the National Academy of Science (1).

The choice was to guess the color of a black or white card so, like coin tossing, each choice had a 50:50 chance. However, the gambler’s fallacy is alive and well and the subjects made bad decisions when there was a run of one color so over the long run, they did rather worse than the 50% correct that would always be approached with enough turns.

The interesting new bit of information is that there was a rush of oxygenated blood to the heads of the subjects about 10 seconds before letting their instinct over-ride their better judgment. To be precise, the blood oxygen levels in the left lateral prefrontal cortex were elevated.

Now remember that the prefrontal cortex is where our emotional responses are buzzing around and that the dopamine and serotonin receptors are making us feel good so its not surprising that our logic can slip a little. If the region was externally stimulated electrically, the bad decisions on card choice were exacerbated.

Would holding our breath before making decisions help, I wonder or would that be counter productive by subsequently increasing our heart rate? Perhaps it’s better to avoid such excitement altogether.

  1. G. Xue, C-H. Juan, C-F. Chang Z-L. Lu and Q. Dong, Proc. Nat. Academy. Sci., (2012). doi:10.1073/pnas.1111927109

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