Disentangling prediction error and value in a formal test of dopamine's role in reinforcement learning.

The discovery that midbrain dopamine (DA) transients can be mapped onto reward prediction errors (RPEs), the critical signal that drives learning, is a landmark in neuroscience. Causal support for the RPE hypothesis comes from studies showing that stimulating DA neurons can drive learning under conditions where it would not otherwise occur. However, such stimulation might also promote learning by adding reward value and indirectly inducing an RPE.

Causal evidence supporting the proposal that dopamine transients function as temporal difference prediction errors.

Reward-evoked dopamine transients are well established as prediction errors. However, the central tenet of temporal difference accounts-that similar transients evoked by reward-predictive cues also function as errors-remains untested. In the present communication we addressed this by showing that optogenetically shunting dopamine activity at the start of a reward-predicting cue prevents second-order conditioning without affecting blocking.

Dissociation of Appetitive Overexpectation and Extinction in the Infralimbic Cortex.

Behavioral change is paramount to adaptive behavior. Two ways to achieve alterations in previously established behavior are extinction and overexpectation. The infralimbic (IL) portion of the medial prefrontal cortex controls the inhibition of previously established aversive behavioral responses in extinction.