# Recovery sleep after total sleep deprivation preserves neutral and enhances emotional declarative memory

## TL;DR

Napping after a night without sleep helps restore memory, especially for emotional content, to levels seen in well-rested people.

## Contribution

This study is the first to show that recovery sleep after total sleep deprivation preserves neutral memory and enhances emotional memory.

## Key findings

- Total sleep deprivation impaired memory for all components except neutral objects.
- A 90-minute nap after sleep deprivation preserved neutral memory and improved memory for negative objects.
- Participants who napped after sleep deprivation had memory performance equal to those who slept normally.

## Abstract

While recovery sleep can ameliorate the negative impacts of total sleep deprivation (TSD) on cognitive functioning, the effects of post-TSD sleep on different forms of emotional functioning remain unknown. Here, we investigated the effects of TSD and post-TSD recovery sleep on emotional memory processing.

Participants viewed scenes with negative or neutral central objects overlain on neutral backgrounds. The scene components were then presented separately for recognition testing. Participants in the TSD (n = 46) and Sleep (n = 22) conditions encoded the scenes the morning after the sleep manipulation (~10:00) and recognition memory was tested for half of the scene components after a short delay (Recog_1, ~10:45). Twenty of the TSD participants then received a 90-min nap opportunity (TSDNap). All participants then completed a second recognition test on the remaining images (Recog_2, ~14:00).

At Recog_1, all TSD participants showed worse overall memory compared to sleep participants. Specifically, memory was significantly worse for every scene component except neutral objects during Recog_1. At Recog_2, while memory deteriorated further for all scene components in the TSDNoNap group, the TSDNap group showed no memory decline and had improved memory for negative objects, matching the sleep group at Recog_2.

Post-TSD recovery sleep preserves and restores memory functioning to the level seen in typically rested individuals. But extending TSD leads to continued memory deterioration, highlighting the importance of sleep in healthy emotional memory functioning.

This paper is part of the Festschrift in honor of Dr. Robert Stickgold.

Statement of SignificanceNapping after a night of total sleep deprivation (TSD) improves performance on many tasks. However, the impact that “recovery sleep” has on emotional memory has never been investigated prior to this study. As expected, total sleep loss prior to learning had a negative impact on all memory scores after a 10-min delay. TSD participants were then allowed a 90-min nap, or they stayed awake. At a second memory test, 4-h later, memory got worse for all stimuli in TSD participants that stayed awake. Intriguingly, the sleep deprived participants that napped showed no memory decline for neutral information and had improved memory for negative memory elements, resulting in memory abilities equivalent to those that slept normally the previous night.

Napping after a night of total sleep deprivation (TSD) improves performance on many tasks. However, the impact that “recovery sleep” has on emotional memory has never been investigated prior to this study. As expected, total sleep loss prior to learning had a negative impact on all memory scores after a 10-min delay. TSD participants were then allowed a 90-min nap, or they stayed awake. At a second memory test, 4-h later, memory got worse for all stimuli in TSD participants that stayed awake. Intriguingly, the sleep deprived participants that napped showed no memory decline for neutral information and had improved memory for negative memory elements, resulting in memory abilities equivalent to those that slept normally the previous night.