Reduced Sleep Spindles and Spindle Coherence in Schizophrenia: Mechanisms of Impaired Memory Consolidation?

Abstract

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.

Sleep spindles in midday naps enhance learning in preschool children

“…Spindle onsets and offsets were subsequently verified by a second trained physiologist. Measurements of peak amplitude and peak frequency of the visually identified spindles were determined with an in-house MATLAB (r2009b) routine based on the method and definitions described by Wamsley et al (47). Specifically, EEG data were filtered from 0.5 to 35 Hz.…”

The effect of sex and menstrual phase on memory formation during a nap

“…Stage 2 sleep epochs were exported for further analysis in Matlab 2011b (MathWorks, Natick MA). Sleep spindles were automatically detected using a wavelet-based algorithm developed by Wamsley et al, (2012). Slow oscillations were detected using an algorithm based on methods previously reported (see Molle et al 2002, Massimini et al 2004, Molle et al 2011.…”

Coordination of Slow Waves With Sleep Spindles Predicts Sleep-Dependent Memory Consolidation in Schizophrenia

“…Recent work places deficient sleep-dependent memory consolidation among the cognitive deficits of schizophrenia and implicates reduced sleep spindles, a defining electroencephalographic (EEG) feature of Stage 2 non-rapid eye movement sleep (N2), as a potentially treatable mechanism 4 . Schizophrenia patients have deficient sleep-dependent consolidation of both procedural [5][6][7][8][9][10] and declarative 11 memory that, in some studies, correlates with reduced sleep spindle density (spindles per minute) and number 10,11 . These relations are consistent with a large basic literature showing that spindle activity correlates with measures of intelligence and sleep-dependent memory consolidation 12 .…”