Distinct cortisol effects on item and associative memory across memory phases

Our daily lives are filled with stressful situations, which powerfully shape the way we form, consolidate, and retrieve episodic memories. As such, stress hormones affect different memory phases of both individual items and their associations, whether they are neutral or emotional. However, an interplay between all these factors in our memory of stressful events is still poorly understood. To address this conundrum, we employed a within-subject, double-blind, placebo-controlled design with exogenous cortisol administration (10 mg hydrocortisone) to affect different memory phases (pre-encoding, post-encoding, pre-retrieval). Our participants encoded neutral and emotional noun - image pairs. After a 24 h delay, we tested their memory for individual items (nouns) and their associations (nouns - objects). While accounting for baseline (no stress) memory performance, we found divergent cortisol effects on item and associative memory, depending on affected memory phase and on emotionality of memoranda. While post-encoding cortisol administration enhanced item memory, pre-encoding, and pre-retrieval cortisol administration impaired item memory. Similarly, pre-encoding cortisol administration impaired associative memory, but only for neutral stimuli. Moreover, we observed that both salivary cortisol levels and emotionality of memoranda modulated item and associative memory performance. These findings highlight a complex interplay of how stress hormone cortisol, throughout all memory phases, differently modulates item and associative memory of neutral and emotional events.