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Depression is characterized by functional insufficiency of the right hemisphere combined with its physiological overactivation. This paradox can be solved in the frame of the general concept of brain laterality. According to the present assumption, the left hemisphere organizes any information in an unambiguous monosemantic context, and this process requires an additional activation of the brain cortex in order to restrict natural relationships between objects and events. On the contrary, the right hemisphere organizes any information in the polysemantic context based on the simultaneous capture of the numerous natural relationships between elements of information. In healthy creative subjects this process does not require additional physiological activation of the cortex. In depression the physiological overactivation of the right hemisphere reflects the unsuccessful effort to overcome its functional insufficiency.

Introduction: REM sleep latency is a clinically significant sleep variable that is found to be decreased in several psychiatric disorders. However, it is not known whether alteration of REM sleep latency is similar across disorders. In order to test whether incorporation of wakefulness in the first sleep cycle has a different outcome on REM sleep latency in different clinical groups, the authors have investigated correlation between sleep variables in the first sleep cycle in 25 patients with major depression, 24 patients with chronic schizophrenia, and in 10 healthy subjects., Results: REM sleep latency correlates with the duration of wakefulness in the first cycle in patients suffering from chronic schizophrenia and in healthy subjects. This correlation does not hold true in patients suffering from major depression., Conclusion: Wakefulness incorporated in the first cycle influences REM sleep latency in healthy subjects and in patients suffering from chronic schizophrenia but not in patients suffering from major depression. This finding further supports the evidence that reduced REM sleep latency is a nonflexible marker of depression.