I mean that an error in prediction will cause a rapid drop in dopamine levels, which motivates a desire to correct one's understanding. There's a limbic structu

I mean that an error in prediction will cause a rapid drop in dopamine levels, which motivates a desire to correct one's understanding. There's a limbic structure, the anterior cingulate cortex, that seems likely to be the origin of this. As for those well-known dopamine stimuli like alcohol, sugar &c, I believe the worst case scenario is that you reinforce an incipient dependency on those things, thus contributing to addiction. I'll hold back on having an opinion about whether the reward sensitization itself directly harms learning. When it comes to sugar overuse, I'd worry more about insulin resistance having an effect on glucose uptake throughout the brain rather than specifically harming the limbic structures.