The ventral tegmental area — abbreviated VTA — sits in the midbrain just medial to the substantia nigra. They are anatomical neighbors. They are functional cousins. Both produce dopamine. Both project upward. But where the substantia nigra projects to the motor system, the VTA projects to the motivational and reward system.
Two major pathways originate in the VTA. The mesolimbic pathway projects from the VTA forward and slightly downward to the nucleus accumbens, the brain's reward center. We will visit the nucleus accumbens in Stage 5. The mesocortical pathway projects from the VTA upward to the prefrontal cortex, supplying the dopamine that the executive office needs for working memory and cognitive control. We will visit the prefrontal cortex in Stage 8.
Now, here is the fact that ties the whole reward system together. Every drug of abuse you have ever heard of — cocaine, amphetamine, opioids, nicotine, alcohol, cannabis — converges on the VTA. They each reach it by different molecular routes. Cocaine blocks dopamine reuptake at presynaptic terminals. Opioids inhibit GABAergic interneurons that normally restrain VTA neurons. Nicotine directly activates nicotinic receptors on VTA dopamine cells. But they all end up making the VTA fire dopamine into the nucleus accumbens.
This is why addiction is sometimes described as a single disease with many doors. The substances are pharmacologically distinct, but the final common pathway is the same: VTA dopamine flooding the accumbens, generating the felt experience of reward and craving and learning.
The mesocortical pathway matters in a different way. In schizophrenia, the working model is that mesolimbic dopamine is hyperactive (driving the positive symptoms — hallucinations, delusions, aberrant salience) while mesocortical dopamine is hypoactive (contributing to negative and cognitive symptoms — flat affect, avolition, working memory failure). Antipsychotics that block D2 receptors globally reduce mesolimbic firing but worsen the already-low mesocortical signal, which is part of why first-generation antipsychotics often blunt cognition.
Hold the geography. Substantia nigra below for movement; VTA beside it for reward and cognition. Two clusters of pigmented cells, a few millimeters apart, controlling everything from your tremor to your motivation to whether a stimulus feels meaningful.