If you’re going to open someone’s head, you might as well make the most of it, right? This must be what surgeons at U Penn thought. To control the tremors and rigidity of Parkinson’s, they commonly insert small, batterypowered devices called neuro-stimulators deep within patients’ midbrains. Since patients have to be awake during the surgery, why not also use microelectrodes to measure the firing rates of dopamine-releasing neurons in patients’ substantia nigra during a simulated gambling task?
Here’s what they found:
Neurons turned on dopamine when subjects won simulated money. And the dopamine release was proportionate to the amount of money they won. No surprise. But when winning was unexpected—bang!—dopamine skyrocketed, with “winnings” in the brain disproportionate to the amount of winnings in the gambling task.
In other words, while meeting our expectations has a slightly reinforcing effect on our emotional memory, and thus future behavior, something unexpected makes us drastically adjust our worldview. In the mathematics of evolution, it’s as if an expected result—no matter how large—is just another dot on an existing curve. But even a small, unexpected result forces us to redraw these curves entirely.
And in the substantia nigra of patients undergoing conscious neurosurgery, we can see how.