The reward circuit: reinforcement and dopamine
Explains the biomedical model's core idea: addiction hijacks the brain's reinforcement system — dopamine from the VTA to the nucleus accumbens — and how different drugs raise that dopamine directly or indirectly.
Where this fitsConnects to 3 · Unlocks 1
- Connects to
- Dopamine: receptor families, clearance and pathways — The mesolimbic pathway is one of the three dopamine pathways.
- Where drugs act: the brain's regions — VTA, nucleus accumbens, hippocampus and amygdala all appear here.
- Indirect agonists: reuptake inhibitors, enzyme inhibitors and releasers — Cocaine and amphetamine raise dopamine by reuptake block and release.
- Unlocks
- Why drugs keep reinforcing: prediction, tonic vs phasic, and speed — Why drugs keep reinforcing when natural rewards stop doing so.
Walk through
Reinforcement learning
An animal does something, gets a reward, and the action is reinforced — next time it does the action to get the reward. Two key points: the reward is relevant to survival, and once the behavior is learned the reinforcement can stop (keeping behavior flexible, not compulsive).
Analogy and worked example
Analogy: The reward circuit is a teacher who hands out gold stars for things that keep you alive — eating, bonding, staying safe. Drugs are a counterfeit gold-star printer. The brain can't tell counterfeit stars from real ones, and the printer never runs out.
Heroin doesn't act on dopamine receptors or transporters. How can it raise dopamine in the nucleus accumbens?
- VTA dopamine neurons are normally held in check by GABA interneurons.
Tip: the ← and → keys move through the lesson.
Full lesson: Dopamine families and pathways