Q: When would you want to adjust the learning rate in an AI or the brain?
A: There are situations in which the world suddenly changes and everything becomes a lot more uncertain and difficult than usual. For example, when you’ve gone to foreign city. In these situations, your old knowledge—your usual model of the world—is out of date and needs to be sidelined or reworked to adapt to the new situation.
In the lab we can create that sort of situation by teaching a mouse or a person a game with certain rules and then abruptly changing the rules. When that happens, serotonin neurons light up. People think of serotonin as related to happiness, but serotonin neurons appear to send a message that is not good or bad but more “oops” or surprise—my old expectations are not right any more.
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