Background: Sleep spindles are defining oscillations of NREM stage 2 (N2) sleep. Spindles mediate sleep-dependent memory consolidation, but are also thought to protect against sleep disruption. Schizophrenia (SZ) patients show reduced spindle activity that correlates with a deficit in sleep-dependent memory consolidation. We investigate whether this relation reflects the direct effects of reduced spindles on memory, or if reduced spindles lead to more disrupted sleep and consequently to memory consolidation deficits. We examined if SZ patients show increased sleep disruption (measured as arousals and fragmentation) during N2 that correlates with spindle density and sleep-dependent memory consolidation.
Methods: 47 SZ patients and 46 demographically matched healthy controls (HC) completed one night of polysomnography. Participants were trained on the motor sequence task (MST) at bedtime and tested the following morning. Spindles were identified using an automated detector, while sleep disruption was measured using hand-scored arousals and an algorithmically calculated sleep fragmentation index (SFI). MST sleep-dependent improvement was calculated as the percent increase in correct sequences from the last 3 training trials to the first 3 test trials.
Results: 26 SZ and 29 HC had both hand-scored arousals and SFI during N2 sleep. In this subgroup, SZ showed significantly decreased SFI but comparable arousals to HC. Sleep-dependent memory consolidation in SZ significantly correlated with spindles but not with either arousals or SFI. In another dataset, we replicated the finding that SZ patients (n = 22) do not have more fragmented sleep than HC (n = 17), and that SFI does not correlate with sleep-dependent memory consolidation.
Conclusions: SZ patients did not show increased arousals or SFI. In the combined samples, SZ showed lower SFI than HC perhaps reflecting the sedating effects of their medications. Our findings support the hypothesis that spindles rather than sleep disruption account for deficits in sleep-dependent memory consolidation. Moreover, spindles did not correlate with either arousals or SFI which is inconsistent with a role in preserving sleep.
Live Zoom Session – March 9th
Rudra Patel, BS, Dimitris Mylonas, PhD, Olivia Larson, BS, Lin Zhu, PhD, Robert Stickgold, PhD, Bryan Baxter, PhD, Dara S. Manoach, PhD
Dara S. Manoach, PhD