The Disordered Mind: What Unusual Brains Tell Us About Ourselves

by Eric R. Kandel

Wolfram Schultz, a neuroscientist at the University of Cambridge, has studied the role of rewards in learning.2 Schultz’s experiments with monkeys drew on Pavlov’s early experiments with conditioned learning in dogs. Schultz would play a loud tone to monkeys, wait for a few seconds, and then squirt some drops of apple juice into their mouths. While the experiment was unfolding, Schultz monitored the electrical activity inside individual dopamine-producing neurons in the animals’ brains. At first, the neurons didn’t fire until the juice was delivered. However, once the animals learned that the tone predicted the arrival of juice, the same neurons began firing at the sound of the tone—that is, at the prediction of reward instead of the reward itself. To Schultz, the interesting feature about this dopamine learning system was that it is all about expectation.