Sleep deprivation induces fragmented memory loss

Abstract

Sleep deprivation increases rates of forgetting in episodic memory. Yet, whether an extended lack of sleep alters the qualitative nature of forgetting is unknown. We compared forgetting of episodic memories across intervals of overnight sleep, daytime wakefulness, and overnight sleep deprivation. Item-level forgetting was amplified across daytime wakefulness and overnight sleep deprivation, as compared to sleep. Importantly, however, overnight sleep deprivation led to a further deficit in associative memory that was not observed after daytime wakefulness. These findings suggest that sleep deprivation induces fragmentation among item memories and their associations, altering the qualitative nature of episodic forgetting.

Figure 1.

Experimental procedures, tasks, and example images. (A) The delay between test 1 (T1) and test 2 (T2) contained daytime wakefulness versus overnight sleep (Experiment 1) or overnight sleep deprivation versus overnight sleep (Experiment 2). A follow-up test (T3) occurred 2 d later. E = encoding. (B) One-hundred and twenty adjective-image pairs were presented at encoding. For each pair, participants were instructed to visualize the adjective and image interacting. They then reported whether the resultant mental image was realistic or bizarre, and indicated whether the presented image was an object or a scene. The same 120 adjectives from encoding were intermixed with 60 foil adjectives at retrieval. Participants first indicated if they recognized the adjective (“old”) or not (“new”), or were uncertain (“?”). For adjectives identified as “old,” participants also indicated whether the associated image was an object or scene (or “?”) and, if applicable, briefly described the image. (C) Example object and scene images (left side = negative; right side = neutral).

Figure 2.

Item forgetting. (A) Experiment 1: Item forgetting was greater after a day of wakefulness relative to a night of sleep. (B) Experiment 2: Item forgetting was also greater after overnight sleep deprivation relative to sleep. Data points represent individual participants. Data are shown as mean ± SEM. (★) P < 0.05; (★★★) P < 0.001.

Figure 3.

Memory fragmentation. (A) Experiment 1: Memory fragmentation was comparable after a day of wakefulness and a night of sleep. (B) Experiment 2: Memory fragmentation was greater after overnight sleep deprivation relative to sleep. Data points represent individual participants. Data are shown as mean ± SEM. (ns) not significant; (★★) P < 0.01.