How can dopamine turn a Hebbian rule into learning from reward? · Grey Matter

A pure Hebbian rule strengthens every connection that takes part in firing a cell, whether the result was useful or not.

How can dopamine turn a Hebbian rule into learning from reward?

A pure Hebbian rule strengthens every connection that takes part in firing a cell, whether the result was useful or not. In three-factor models, coincident activity of two cells only leaves a temporary mark on the synapse (an eligibility trace, lasting around a second), and the change becomes lasting only if a third signal arrives while the mark remains. Dopamine bursts after a better-than-expected outcome can play that role, and in the striatum, dopamine acting on D1 receptors shortly after a pre-post pairing has been shown to convert it into potentiation. The rule then strengthens the connections that preceded good outcomes, which is what reinforcement learning needs.