According to the text, chronic drug use can alter higher-order neuronal circuits, causing executive functioning to primarily respond to drug-related stimuli. The mesolimbic dopaminergic system is believed to play a role in drug addiction and the effects of drugs of abuse. Natural rewards activate the reward circuit until the behavior is learned, while drugs of abuse continue to stimulate it upon repeated use. Classical medications used to treat physical withdrawal in drug abusers often target the α-adrenergic system. Addiction and the reinforcing value of drugs involve different areas and neurotransmitter systems. The mesolimbic pathway is activated by addictive drugs and may also play a role in positive symptoms of schizophrenia. Addictive drugs increase dopamine levels in the brain, and cues related to drugs of abuse can trigger brain activation. Drugs of abuse, psychostimulants, and natural rewards can cause modifications to the mesolimbic dopaminergic system.