Acquisition and inhibition of conditioned fear is modulated by individual stimulus fear-relevance

- The startle response is modulated by stimulus fear relevance in the AX+/BX− paradigm.
- Individual fear and stimulus fear-relevance modulate fear acquisition and inhibition.
- Fear relevant stimuli can become safety signals for subjects with elevated fear.
- The Rescorla-Wagner-Model correctly predicts fear acquisition and inhibition.

Inhibitory learning is an important factor for decreasing fear expression. We investigated conditioned inhibition of learned fear responses using conditioned excitors and inhibitors differing in fear-relevance in a sample of 48 healthy female students. To study the effect of stimulus fear-relevance, we used the fear potentiated startle paradigm in an AX+/BX− discrimination learning task with fear-relevant (spider) vs. fear-irrelevant (butterfly) pictures as CS+ (A) and CS− (B), respectively. We found that, during acquisition, participants with elevated fear of spiders showed stronger fear potentiated startle to AX+ compared to BX− when the inhibitor (B) was fear-irrelevant (butterfly) using both median split as well as correlational analyses. In contrast, when the excitor (A) was fear-irrelevant (butterfly), fear potentiated startle to AX+ compared to BX− was reduced for participants with higher fear of spiders. Effects of conditioned inhibition were studied in a summation test, where excitor and inhibitor were presented in compound (AB) and compared to the last four excitor trials during prior acquisition. Conditioned inhibition was stronger for participants with a higher fear of spiders, when the butterfly acted as conditioned inhibitor (B). On the other hand, when the spider served as conditioned inhibitor, effects of conditioned inhibition were weaker for participants with higher fear of spiders. Hence, rather than to a general preparedness our data point to a specific impairment in safety learning for individually fear-relevant stimuli.