CHANGES IN EEG POWER-DENSITY DURING SLEEP LABORATORY ADAPTATION

First- and second-night effects on the electroencephalogram (EEG) were investigated by means of polygraphic sleep recordings and all-night s pectral analysis. Eighteen normal subjects were studied for three cons ecutive nights in a hospital sleep laboratory. Visual sleep scoring sh owed that there was a first-night effect in normal subjects similar to that reported previously [increased wakefulness; decreased total slee p time, sleep efficiency, and rapid eye movement (REM) sleep]. Spectra l analysis of the sleep EEG revealed important changes, most of which occurred in REM sleep. Increased delta, theta, and beta1 power densiti es accompanied by decreased mean frequency were seen in REM sleep in t he second night. On the basis of REM sleep deprivation results previou sly published, our data suggest that the second night could be affecte d by partial REM sleep deprivation that occurred in the first night. D elta and theta power density values decreased in the first non-rapid e ye movement episode of nights 1 and 2; this could result from increase d REM sleep pressure. The overall consistency of spectral data in the first and second night with REM sleep findings derived from visual sco ring in the first night lends further support to this hypothesis. The sleep disturbance experienced during the first night in a sleep labora tory may be a useful and valid model of transient insomnia. Therefore, we conclude that data from all nights recorded should be included in assessing a subject's sleep.