False memories formation after a retention period spent asleep or awake in individuals with insomnia and good sleepers: a polysomnographic study

False memories are a possible by-product of sleep-related memory consolidation processes when delayed testing is performed after a retention interval spent asleep. To date, the effect of a retention period spent asleep or awake on false memories formation has been addressed only in healthy subjects, while neglecting sleep-disordered populations. In the present study, we investigated this effect in 17 insomniacs and 15 good sleepers through the Deese–Roediger–McDermott paradigm. In both groups, the encoding phase was followed by an 8-h retention period spent in polysomnography monitored sleep (S-condition) or wake (WK-condition). We observed that, at free recall, insomniacs produced more false recalls in the WK-condition compared to the S-condition, whereas the good sleepers showed more false recalls in S-condition than in the WK-condition. Moreover, false recalls were higher in good sleepers than in insomniacs in the S-condition. Both groups produced more veridical recalls in the S-condition than in the WK-condition. For recognition, hits (correctly recognised words) were more numerous in the S-condition than in the WK-condition. Our results confirm previous data on sleep-related false memories production in good sleepers. Additionally, they show that, in insomniacs, false memories production is reduced after a sleep relative to remaining awake. These data suggest that false memories formation, reflecting adaptive memory reshaping processes going on during sleep, could occur at awakening as long as the sleep episode is efficient enough. A notable methodological issue was also identified, in that the Deese–Roediger–McDermott paradigm can be useful to investigate sleep-dependent memory processes for false memories only when a more cognitively demanding task is employed (i.e., free-recall instead of recognition tasks).