Background
Sleep spindles are thought to induce synaptic changes and thereby contribute to memory consolidation during sleep. Patients with schizophrenia show dramatic reductions of both spindles and sleep-dependent memory consolidation, which may be causally related.
Methods
To examine the relations of sleep spindle activity to sleep-dependent consolidation of motor procedural memory, 21 chronic, medicated schizophrenia outpatients and 17 healthy volunteers underwent polysomnography on two consecutive nights. On the second night, participants were trained on the finger tapping Motor Sequence Task (MST) at bedtime and tested the following morning. The number, density, frequency, duration, amplitude, spectral content, and coherence of stage 2 sleep spindles were compared between groups and examined in relation to overnight changes in MST performance.
Results
Patients failed to show overnight improvement on the MST and differed significantly from controls who did improve. Patients also exhibited marked reductions in the density (reduced 38% relative to controls), number (reduced 36%), and coherence (reduced 19%) of sleep spindles, but showed no abnormalities in the morphology of individual spindles or of sleep architecture. In patients, reduced spindle number and density predicted less overnight improvement on the MST. In addition, reduced amplitude and sigma power of individual spindles correlated with greater severity of positive symptoms.
Conclusions
The observed sleep spindle abnormalities implicate thalamocortical network dysfunction in schizophrenia. In addition, our findings suggest that abnormal spindle generation impairs sleep-dependent memory consolidation in schizophrenia, contributes to positive symptoms, and is a promising novel target for the treatment of cognitive deficits in schizophrenia.
Eszopiclone significantly increased sleep spindles, which correlated with overnight motor sequence task improvement. These findings provide partial support for the hypothesis that the spindle deficit in schizophrenia impairs sleep-dependent memory consolidation and may be ameliorated by eszopiclone. Larger samples may be needed to detect a significant effect on memory. Given the general role of sleep spindles in cognition, they offer a promising novel potential target for treating cognitive deficits in schizophrenia.
OBJECTIVES-To determine if sleep benefits motor memory in healthy elderly subjects, and, if so, whether the observed sleep-related benefits are comparable to those observed in healthy young subjects.
DESIGN-Repeated measures cross-over design.SETTING-Boston, Massachusetts (general community) and Harvard University.PARTICIPANTS-Sixteen healthy elderly and 15 healthy young subjects.
MEASUREMENTS-MotorSequence Task (MST) performance was assessed at training and at the beginning and end of the retest session; polysomnographic sleep studies were recorded for the elderly subjects.RESULTS-After 12hrs of daytime wakefulness, elderly subjects showed a dramatic decline in MST performance at the beginning of retest, relative to training, and only a non-significant improvement by the end of retest. In contrast, when the same subjects trained in the morning, but were retested 24hr after training, after a day of wake plus a night of sleep, they maintained their performance at the beginning of retest, and demonstrated a highly significant 17.4% improvement by the end of the retest session, essentially identical to the 17.3% improvement seen in young subjects. These strikingly similar improvements occurred despite the presence of other age-related differences, including overall slower motor speed, a lag in the appearance of sleep-dependent improvement, and an absence of correlations between overnight improvement and either sleep architecture or sleep spindle density in the elderly subjects.CONCLUSION-These findings provide compelling evidence that sleep retains the capacity to optimize motor skill performance across the adult life span.
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