Information processing during NREM sleep and sleep quality in insomnia

Insomnia sufferers (INS) are cortically hyperaroused during sleep, which seems to translate into altered information processing during nighttime. While information processing, as measured by event-related potentials (ERPs), during wake appears to be associated with sleep quality of the preceding night, the existence of such an association during nighttime has never been investigated. This study aims to investigate nighttime information processing among good sleepers (GS) and INS while considering concomitant sleep quality. Following a multistep clinical evaluation, INS and GS participants underwent 4 consecutive nights of PSG recordings in the sleep laboratory. Thirty nine GS (mean age 34.56 ± 9.02) and twenty nine INS (mean age 43.03 ± 9.12) were included in the study. ERPs (N1, P2, N350) were recorded all night on Night 4 (oddball paradigm) during NREM sleep. Regardless of sleep quality, INS presented a larger N350 amplitude during SWS (p = 0.042) while GS showed a larger N350 amplitude during late-night stage 2 sleep (p = 0.004). Regardless of diagnosis, those who slept objectively well showed a smaller N350 amplitude (p = 0.020) while those who slept subjectively well showed a smaller P2 (p < 0.001) and N350 amplitude (p = 0.006). Also, those who reported an objectively bad night as good showed smaller P2 (p < 0.001) and N350 (p = 0.010) amplitudes. Information processing seems to be associated with concomitant subjective and objective sleep quality for both GS and INS. However, INS show an alteration in information processing during sleep, especially for inhibition processes, regardless of their sleep quality.