The mesolimbic reward system, consisting, at its core, of the ventral tegmental area and its downstream targeting brain areas, has historically been investigated for its role in drug addiction and neuropsychological disorders. Award and aversion stimuli are two widely-used measurements in these pathological processes in animal studies. Huge divergence does exist in the responses of this system to award or aversive stimuli, and more and more studies tend to agree that the midbrain reward system, especially the dopaminergic neurons within the ventral tegmental area has great heterogenicity. Focusing on the identification criteria, anatomical location and projection-specification of dopaminergic neuron, this review summarized the heterogeneous responses to reward/aversion, and looked into the directions of future studies.