Does sleep fragmentation affect sleep-dependent memory consolidation in schizophrenia?

Rudra Patel, BS

Massachusetts General Hospital
Does sleep fragmentation affect sleep-dependent memory consolidation in schizophrenia?

Scientific Abstract

Background: Sleep spindles are defining oscillations of NREM stage 2 (N2) sleep. While extensive research suggests that spindles mediate sleep-dependent memory consolidation, only a few studies have examined if spindles play a protective role against arousals. In schizophrenia (SZ), reduced spindle activity correlates with reduced sleep-dependent memory consolidation. This correlation could reflect the direct effects of reduced spindles on memory, or that reduced spindles lead to more arousals which disrupt memory consolidation. Here, we examine if SZ patients have increased arousals that correlate with spindle density and sleep-dependent memory consolidation.

Methods: 26 SZ patients and 29 demographically matched healthy controls (HC) completed two nights of polysomnography (PSG) with training on the Motor Sequence Task (MST) on the second night and testing the following morning. Arousals were hand scored according to standard criteria, and spindles during N2 were detected using a validated spindle detector. MST consolidation was calculated as the percent change in correct sequences from the last 3 training trials to the first 3 test trials. Arousal density was compared between groups using mixed effects models that included Group and Night as fixed effects. To evaluate the relations of spindle density and MST consolidation with arousal density, we used linear regression models.

Results: SZ patients showed reduced spindle density (p=.01) and reduced arousal density (p=.01) compared to HC, but overnight MST consolidation did not differ by Group. For the combined groups, increased spindle density correlated with increased arousal density (Non- Learning Night: p=.002; Learning Night: p=.02), and this relationship was stronger in the non- learning night (p=.001). Arousal density did not correlate with MST consolidation.

Conclusions: Our findings do not support the hypothesis that increased arousals explain reduced overnight memory consolidation in SZ since increased spindle density was associated with increased arousal density for both groups. Planned analyses will examine whether spindles are related to subtler measures of sleep fragmentation.

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Rudra Patel, BS, Dimitrios Mylonas, PhD, Olivia Larson, BS, Lin Zhu, PhD, Bryan Baxter, PhD, Dara Manoach, PhD

Principal Investigator

Dara Manoach, PhD

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