Carbon dioxide reactivity predicts fear expression after extinction and retrieval-extinction in rats

Cues present during a traumatic event may result in maladaptive fear responses. These responses can be attenuated through extinction learning, which is a core component of exposure therapy. Exposure/extinction is effective for some, but not all. We recently demonstrated that carbon dioxide (CO2) reactivity predicts fear extinction memory and orexin activation, and that orexin activation predicts fear extinction memory, suggesting that a CO2 challenge may enable identifying whether an individual is a good candidate for an extinction-based approach. Another method to attenuate conditioned responses, retrieval-extinction, modifies the original associative memory via distinct neural mechanisms. The purpose of the present study was to examine whether we could replicate previous findings that retrieval-extinction is more effective than extinction at preventing the return of fear and that CO2 reactivity predicts fear memory after extinction. We also examined whether CO2 reactivity predicts fear memory after retrieval-extinction.