Suppressing the morning cortisol rise after memory reactivation at 4 a.m. enhances episodic memory reconsolidation in humans

Evidence from animal and human research shows that established memories can undergo changes after reactivation through a process called reconsolidation. Alterations of the level of the stress hormone cortisol may be one way of manipulating reconsolidation. Here, in a double-blind, within-subject design, we reactivated a 3-day-old memory at 3:55 a.m., immediately followed by oral administration of metyrapone vs. placebo, to examine whether metyrapone-induced suppression of the morning cortisol rise may influence reconsolidation processes during and after early morning sleep. Crucially, reactivation followed by cortisol suppression vs. placebo resulted in enhanced memory for the reactivated episode (tested four days after reactivation). This enhancement after cortisol suppression was specific for the reactivated episode vs. a non-reactivated episode. These findings suggest that when reactivation of memories is immediately followed by suppression of cortisol levels during early morning sleep, reconsolidation processes change in a way that leads to the strengthening of episodic memory traces.