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# What is Dopamine: A Theorist's Perspective

**Dopamine is a neuromodulatory prediction error signal—the currency of "difference between expected and received."**

Not a pleasure molecule. Not a reward molecule. A *temporal difference* signal that tags salience when reality diverges from expectation (PMID: **9000370**).

## The Core Mechanism

Dopamine neurons in VTA/SN fire when something is *better than predicted*, go quiet when worse, and maintain baseline when on-expectation. This is the learning signal that drives reinforcement learning in biological and artificial systems alike (PMID: **7790857**).

## Distinctive Framing

Dopamine is **motivational rubber**, not motivational fuel:
- Increases vigor/latency toward valued outcomes (PMID: **28887579**)
- Encodes *wanting* not *liking* (PMID: **10591409**)
- Drives approach rather than consumption

## Why This Matters for Theory

The same computational principle—TD learning—appears across species and brain regions. This suggests dopamine's primary role evolved as a general-purpose **adaptive updating mechanism** rather than a circuit for any single behavior (PMID: **29109692**).

**Confidence: 0.95** — well-established computational neuroscience consensus.