RESUMO
Sleep spindles are believed to mediate sleep-dependent memory consolidation, particularly when coupled to neocortical slow oscillations. Schizophrenia is characterized by a deficit in sleep spindles that correlates with reduced overnight memory consolidation. Here, we examined sleep spindle activity, slow oscillation-spindle coupling, and both motor procedural and verbal declarative memory consolidation in early course, minimally medicated psychosis patients and non-psychotic first-degree relatives. Using a four-night experimental procedure, we observed significant deficits in spindle density and amplitude in patients relative to controls that were driven by individuals with schizophrenia. Schizophrenia patients also showed reduced sleep-dependent consolidation of motor procedural memory, which correlated with spindle density. Contrary to expectations, there were no group differences in the consolidation of declarative memory on a word pairs task. Nor did the relatives of patients differ in spindle activity or memory consolidation compared with controls, however increased consistency in the timing of SO-spindle coupling were seen in both patient and relatives. Our results extend prior work by demonstrating correlated deficits in sleep spindles and sleep-dependent motor procedural memory consolidation in early course, minimally medicated patients with schizophrenia, but not in first-degree relatives. This is consistent with other work in suggesting that impaired sleep-dependent memory consolidation has some specificity for schizophrenia and is a core feature rather than reflecting the effects of medication or chronicity.
RESUMO
Sleep spindles, defining oscillations of non-rapid eye movement stage 2 sleep (N2), mediate memory consolidation. Spindle density (spindles/minute) is a stable, heritable feature of the sleep electroencephalogram. In schizophrenia, reduced spindle density correlates with impaired sleep-dependent memory consolidation and is a promising treatment target. Measuring sleep spindles is also important for basic studies of memory. However, overnight sleep studies are expensive, time consuming and require considerable infrastructure. Here we investigated whether afternoon naps can reliably and accurately estimate nocturnal spindle density in health and schizophrenia. Fourteen schizophrenia patients and eight healthy controls had polysomnography during two overnights and three afternoon naps. Although spindle density was lower during naps than nights, the two measures were highly correlated. For both groups, naps and nights provided highly reliable estimates of spindle density. We conclude that naps provide an accurate, reliable and more scalable alternative to measuring spindle density overnight.
