I don't think anybody has ever shown any studies with animals being extra rewarded for achieving difficult tasks. To speculate, that may relate to our social wiring.
Not even the dopamine system is exactly and entirely a "reward system," there are multiple pieces carrying out various signal-processing tasks without clean alignment to our intuitive categories.
Despite the existence of localization and specialization in the brain, it is not common for any high-level behavior to weigh completely on just one distinct piece of the brain.
Not even the dopamine system is exactly and entirely a "reward system," there are multiple pieces carrying out various signal-processing tasks without clean alignment to our intuitive categories.
Despite the existence of localization and specialization in the brain, it is not common for any high-level behavior to weigh completely on just one distinct piece of the brain.