Spared and impaired sleep-dependent memory consolidation in schizophrenia

Abstract

Objective: Cognitive deficits in schizophrenia are the strongest predictor of disability and effective treatment is lacking. This reflects our limited mechanistic understanding and consequent lack of treatment targets. In schizophrenia, impaired sleep-dependent memory consolidation correlates with reduced sleep spindle activity, suggesting sleep spindles as a potentially treatable mechanism. In the present study we investigated whether sleep-dependent memory consolidation deficits in schizophrenia are selective. Methods: Schizophrenia patients and healthy individuals performed three tasks that have been shown to undergo sleep-dependent consolidation: the Word Pair Task (verbal declarative memory), the Visual Discrimination Task (visuoperceptual procedural memory), and the Tone Task (statistical learning). Memory consolidation was tested 24 h later, after a night of sleep. Results: Compared with controls, schizophrenia patients showed reduced overnight consolidation of word pair learning. In contrast, both groups showed similar significant overnight consolidation of visuoperceptual procedural memory. Neither group showed overnight consolidation of statistical learning. Conclusion: The present findings extend the known deficits in sleep-dependent memory consolidation in schizophrenia to verbal declarative memory, a core, disabling cognitive deficit. In contrast, visuoperceptual procedural memory was spared. These findings support the hypothesis that sleep-dependent memory consolidation deficits in schizophrenia are selective, possibly limited to tasks that rely on spindles. These findings reinforce the importance of deficient sleep-dependent memory consolidation among the cognitive deficits of schizophrenia and suggest sleep physiology as a potentially treatable mechanism.