Delta power in sleep in relation to neuropsychological performance in healthy subjects and schizophrenia patients.

Delta power in sleep is of increasing interest because of its association with waking performance in neuropsychological tests. In schizophrenia, this link might be impaired because of a decrease in delta power in sleep and pronounced cognitive deficits. The authors analyzed delta power in sleep and neuropsychological performance in 16 patients with schizophrenia on stable medication with amisulpride and 17 healthy subjects. In healthy subjects, the authors found significant positive correlations between morning performance in declarative memory, procedural learning, and attention and delta power, especially in frontal channels. The authors interpret these results in terms of dysfunctions of thalamocortical and prefrontal networks in schizophrenia.

Impairment of visuospatial memory is associated with decreased slow wave sleep in schizophrenia.

Cognitive impairments such as memory deficits and sleep disturbances are common clinical features of schizophrenia. Since sleep plays an important role in consolidation of memory, we hypothesize, that there is an interrelationship between distinct alterations in sleep and memory performance in schizophrenia. We studied 17 patients with schizophrenia on stable antipsychotic medication with amisulpride (age range 22-44 years; 7 women) and 17 healthy controls (matched for age, gender and educational level). Sleep was recorded and scored according to the standard criteria by Rechtschaffen and Kales. Immediately before polysomnography and the morning after we performed neuropsychological tasks including Rey-Osterrieth Complex Figure Test and a test for recall of spatial location for testing aspects of declarative memory and a mirror tracing skill for procedural memory. In comparison to healthy controls, the patients showed a significant increase in sleep onset latency and a significant decrease in sleep efficiency and amount of slow wave sleep (SWS). Furthermore, the patients' performance in recall of the Rey-figure and of spatial location the next morning was significantly impaired. These impairments in the tests for visuospatial memory were positively correlated with reduction in the amount of SWS and in sleep efficiency. These results point to a functional interrelationship between regulation of SWS and performance in visuospatial memory in schizophrenia. If these results of our pilot study hold true, they will allow the development of innovative treatment strategies for neuropsychological deficits in patients with schizophrenia.