Retrieval practice prevents stress-induced inference impairment by restoring rapid memory reactivation

A hallmark of human memory is its ability to form novel inferences by linking discrete but related events. We examined whether acute stress impairs memory inference and if retrieval practice can buffer this effect. Participants were trained on image pairs, AB and BC, to establish interconnected triads (ABC) with a shared bridge element B. Twenty-four hours later, we induced acute stress in half of the participants and then tested their capacity to infer the indirect AC associations. Behavioral results indicated that acute stress reduced memory inference accuracy and speed, yet targeted retrieval practice of the AB and BC pairs after encoding prevented the stress-induced impairment in both A-C inference accuracy and speed. Using multivariate decoding analysis of human electroencephalogram (EEG) recordings, we found neural evidence that bridge element B is rapidly reactivated during the inferential process, a neural signature predictive of subsequent successful inference. Importantly, stress disrupts this rapid neural reactivation of the bridge element, but retrieval practice buffers the stress effect and enhances the strength of reactivation signals beyond the non-stress condition. Time-frequency analyses of theta oscillations mirrored these effects of stress and retrieval practice on inference performance and neural reactivation. Collectively, our findings pinpoint rapid reactivation of the bridge element as an essential neural mechanism for memory-based inference. Although susceptible to stress, this mechanism can be enhanced through retrieval practice, suggesting that building robust memory traces renders subsequent inferences resilient to stress.