Short Sleep Makes Declarative Memories Vulnerable to Stress in Humans

Study Objective: This study sought to investigate the role of nocturnal sleep duration for the retrieval of oversleep consolidated memories, both prior to and after being cognitively stressed for similar to 30 minutes the next morning. Design: Participants learned object locations (declarative memory task comprising 15 card pairs) and a finger tapping sequence (procedural memory task comprising 5 digits) in the evening. After learning, participants either had a sleep opportunity of 8 hours (between similar to 23:00 and similar to 07:00, full sleep condition) or they could sleep between similar to 03:00 and similar to 07:00 (short sleep condition). Retrieval of both memory tasks was tested in the morning after each sleep condition, both before (similar to 08:30) and after being stressed (similar to 09:50). Setting: Sleep laboratory. Participants: 15 healthy young men. Results: The analyses demonstrated that oversleep memory changes did not differ between sleep conditions. However, in their short sleep condition, following stress hallmarked by increased subjective stress feelings, the men were unable to maintain their pre-stress performance on the declarative memory task, whereas their performance on the procedural memory task remained unchanged. While men felt comparably subjectively stressed by the stress intervention, overall no differences between pre- and post-stress recalls were observed following a full night of sleep. Conclusions: The findings suggest that 8-h sleep duration, within the range recommended by the US National Sleep Foundation, may not only help consolidate newly learned procedural and declarative memories, but also ensure full access to both during periods of subjective stress.