There is an evidence of problem solving process being improved by sleep in the healthy controls. Previous studies show REM sleep enhances creative problem solving and slow wave sleep is also shown to have positive effects for problem solving process. Problem solving as well as sleep has been shown to be impaired in schizophrenia patients. The present study aimed at exploring and investigating relationships between sleep and problem solving in patients with schizophrenia.
A consolidation paradigm was used to investigate the question. Participants were tested a day- and night-time condition following learning, separated by a week, with half of them being allocated to the night or the day condition first in a balanced design. Sleep parameters examined by means of a whole night polysomnography.
The present study shows that patients with schizophrenia suffer from a wide range of cognitive deficits including sustained attention, verbal memory, working memory, long term memory, verbal fluency, problem solving and executive functions. Sustained attention, speed of processing and working memory deficits are more pronounced in patients with schizophrenia. Schizophrenia patients performed generally worse in the Tower of London test compared to the healthy controls. Patients took significantly longer to complete the Tower of London test. In general, sleep had no effect on task performance in contrast to a comparable wakefulness in both groups. Sleep parameters did not substantially differ between schizophrenia patients and healthy controls, except shorter sleep onset latency in the patients. Some performance measures were differently correlated to specific sleep parameters. In the patients, a higher number of K-complexes were associated with a higher number of solved tasks in the Tower of London following sleep. In addition, a less time spent in slow wave sleep was associated with a more time taken to solve the Tower of London tasks. No comparable results were observed for the healthy controls. In the controls, less number of sleep spindles was associated with more total time taken in the Tower of London test.
In sum, the present study revealed that sleep specific parameter the number of K-complexes had a beneficial effect on problem solving in patients with schizophrenia. Although this effect did not enhance total performance of the schizophrenia patients, the result pattern indicate that within the cognitive impairment of patients with schizophrenia, beneficial effects of sleep can be assessed. These promoting effects of sleep were nevertheless too weak to generally enhance the performance measures compared to a time of wakefulness or compared to the healthy controls. Nonetheless, they probably point to schizophrenia specific process during sleep, which may be helpful for the understanding of cognitive disturbances of this disorder. The overall results indicate different modes of problem solving associated to sleep in schizophrenia patients and healthy controls.