Awareness of your surroundings occurs only when sensory inputs violate expectations. When the world is successfully predicted away, awareness is not needed because the brain is doing its job well.
David EaglemanIt turns out that dopamine is a chemical on double duty in the brain. Along with its role in motor commands, it also serves as the main messenger in the reward systems, guiding a person toward food, drink, mates, and all things useful for survival. Because of its role in the reward system, imbalances in dopamine can trigger gambling, overeating, and drug addiction - behaviors that result from a reward system gone awry.
David Eagleman