VTA

Meaning: The ventral tegmental area (VTA) is a cluster of dopamine-producing neurons in the midbrain. Its axons project to the nucleus accumbens in the limbic system (mesolimbic pathway) and to the prefrontal cortex (mesocortical pathway). Together with the nucleus accumbens it forms the brain's reward pathway. When a rewarding stimulus occurs, such as food, sex, or a drug, VTA neurons release dopamine in the nucleus accumbens, producing pleasure and reinforcing the behavior that led to it.

On the MCAT: Expect questions on addiction and motivation. Drugs such as cocaine and amphetamines raise dopamine in the nucleus accumbens (cocaine by blocking dopamine reuptake, amphetamines by increasing its release), and the passage may ask you to predict what happens to reward-seeking if VTA activity rises or is blocked. Increased dopamine activity strengthens reinforcement, which fits operant conditioning and positive reinforcement. Over time, repeated drug use can lead to tolerance and dependence. You may also be asked to match VTA to dopamine, or to tell the reward pathway apart from other brain regions in a figure.

Common confusion: Students mix up the VTA with the nucleus accumbens. The VTA is the source that makes and sends dopamine; the nucleus accumbens is a main target that receives it. Another mix-up is with the substantia nigra, a different dopamine region whose neurons project to the striatum and are tied to movement and Parkinson's disease, not reward.