Certain neural structures, called the reward system, are critically involved in mediating the effects of reinforcement. A reward is an appetitive stimulus given to a human or some other animal to alter its behavior.

Reward system
Stress, eating and the reward system
Reward system and addiction: what dopamine does and doesn’t do
Amphetamine and the reward system: Evidence for tolerance and post-drug depression
Mesolimbic Dopamine Reward System Hypersensitivity in Individuals with Psychopathic Traits
The Vertebrate mesolimbic reward system and social behavior network: A comparative synthesis
Variation in Dopamine Genes Influences Responsivity of the Human Reward System
Scientific Output and Recognition: A Study in the Operation of the Reward System in Science
Orexin/Hypocretin: A Neuropeptide at the Interface of Sleep, Energy Homeostasis, and Reward System
Possible etiology of schizophrenia: progressive damage to the noradrenergic reward system by 6-hydroxydopamine