The effect of sleep deprivation on the encoding of contextual and non-contextual aspects of emotional memory

Sleep loss affects emotional memory, but the specific effects on its contextual and non-contextual aspects are unknown. In this study we investigated the possible differential influence of one night of sleep deprivation on the encoding and subsequent recall of these two aspects of emotional information. Forty-eight healthy subjects, divided in a sleep deprivation (SD) and a well-rested group (WR), completed two testing sessions: the encoding session took place after one night of sleep for the WR and after one night of sleep deprivation for the SD group; the recall session after two nights of recovery sleep for both groups. During the encoding session, 6 clips of films of different valence (2 positive, 2 neutral and 2 negative) were presented to the participants. During the recall session, the non-contextual emotional memory was assessed by a recognition task, while the contextual emotional memory was evaluated by a temporal order task. The SD group showed a worst non-contextual recognition of positive and neutral events compared to WR subjects, while recognition of negative items was similar in the two groups. Instead, the encoding of the temporal order resulted deteriorated in the SD participants, independent of the emotional valence of the items. These results indicate that sleep deprivation severely impairs the encoding of both contextual and non-contextual aspects of memory, resulting in significantly worse retention two days later. However, the preserved recognition of negative non-contextual events in sleep deprived subjects suggests that the encoding of negative stimuli is more "resistant" to the disruptive effects of sleep deprivation.