Why drugs keep reinforcing: prediction, tonic vs phasic, and speed
Explains why natural rewards stop producing dopamine once learned but drugs don't, how tonic and phasic dopamine differ, and why faster-acting drugs are more addictive.
Where this fitsConnects to 3 · Unlocks 1
- Connects to
- The reward circuit: reinforcement and dopamine — Builds on the reward circuit and dopamine.
- Absorption and routes of administration — Route of administration sets how fast a drug acts — and so how addictive it is.
- Receptor types: autoreceptors, heteroreceptors and location — Tonic dopamine is regulated through autoreceptors.
- Unlocks
- From use to addiction: receptor loss, hypofrontality, craving and relapse — Repeated over-reinforcement leads to lasting changes in the brain.
Orient
Once behavior has been learned, DA release diminishes upon presentation of natural rewards; it is still released in novel situations, based on predictability of reward. Hacking the system with electrical stimulation or drugs skips this, so behavior keeps getting strongly reinforced → compulsive use. Tonic activity – “background” activity; phasic (burst) activity – bursts and spikes of release. And the quicker the onset of effects, the more addictive the drug will be.
Course terms
Your professor's wording, word for word from the slides. Learn the term and this definition — the explanation underneath is only there to help it make sense.
- Regulating learning
“Once behavior has been learned, DA release diminishes upon presentation of natural rewards”Slides 06, p. 4
Dopamine shifts to reward cues (Schultz et al., 1997).
- Novelty
“Still released in novel situations; based on predictability of reward”Slides 06, p. 4
Unexpected rewards produce dopamine.
- Tonic activity
““Background” activity due to baseline levels of neurotransmitter release”Slides 06, p. 5
Regulated through regular autoreceptor binding over time.
- Phasic activity
“Bursts and spikes of neurotransmitter release in response to stimulus”Slides 06, p. 5
Necessary for reinforcement and reward learning; reaches lower-affinity receptors.
- Onset and addiction
“General principle of drug addiction – quicker the onset of effects, the more addictive the drug will be”Slides 06, p. 5
e.g., crack vs. cocaine vs. coca; IV heroin vs. oral oxycontin.
From your course: Course slides 06, pp. 12–15
Tip: the ← and → keys move through the lesson.