The influence of cross unconditional stimulus reinstatement on electrodermal responding and conditional stimulus valence in differential fear conditioning.

We examined whether the inhibitory Conditional Stimulus (CS)-no Unconditional Stimulus (US) association formed during extinction can be triggered by a novel US during the reinstatement of conditional electrodermal responding and self-reported CS valence in human differential fear conditioning. Participants were trained with either a shock or an aversive scream US before undergoing extinction. Participants then received either the same (i.e., shock_shock or scream_scream) or a different US during reinstatement (i.e., shock_scream, scream_shock). Differential conditioning across all indices was stronger when a shock US was used during acquisition. After reinstatement, electrodermal responding to both the CS+ and the CS- increased regardless of the type of US used during reinstatement (non-differential reinstatement). Differential CS valence evaluations were larger after reinstatement in the groups that received the same US during acquisition and reinstatement (differential reinstatement), but differential evaluations did not increase in the groups receiving a different US at reinstatement. This dissociation suggests that the reinstatement of negative stimulus valence and the reinstatement of expectancy learning may differ.