Investigation of sleep spindle activity and morphology as predictors of neurocognitive functioning in medicated patients with schizophrenia.

Neurocognitive impairment is a trait marker of schizophrenia, but no effective treatment has yet been identified. Sleep spindle deficits have been associated with diminished sleep-dependent memory learning. We examined whether this link could be extended into various cognitive domains by investigating the association of a neurocognitive test battery (the Brief Assessment of Cognition in Schizophrenia) with sleep spindle activity and morphology. We examined 37 outpatients diagnosed with schizophrenia and medicated with both antipsychotics and benzodiazepines. Participants underwent 1 night polysomnography and test of neurocognitive functioning. We identified and analysed sleep spindles in all non-rapid eye movement sleep and in non-rapid eye movement sleep stage 2 in a central electroencephalography channel using an automatic sleep spindle detector previously validated. Slow sleep spindle density was computed from a frontal electroencephalography channel as well. We found no association between cognitive functioning and sleep spindle density or sleep spindle morphology for spindles in non-rapid eye movement sleep when controlling for gender, age, symptom severity, and daily dose of antipsychotics and benzodiazepines. For spindles in non-rapid eye movement sleep stage 2, we found that motor speed was associated with frontal slow sleep spindle density. We conclude that frontal slow spindle density might predict motor speed in medicated patients with schizophrenia, but that no other sleep spindle activity or sleep spindle morphology measures were predictors of neurocognitive functioning.