A visual aid for computer-based analysis of sleep-wake state in rats

Computer-based sleep scoring systems are often calibrated by reference to a conventional visual analysis of electroencephalographic (EEG) and electromyographic (EMG) traces. However, these types of data place high demands on digital storage capacity which may limit the duration or feasibility of some studies. The present paper describes an approach to visual analysis that involves reconstruction of a waveform (termed a "pseudopolygram" (PPG)) from conditioned data derived from the EEG and EMG. The PPG is the sum of three sine waves, each of which has a distinct frequency (non-REM sleep (NREM), 3 Hz; rapid eye movement sleep (REM), 7 Hz and wakefulness (WAKE), 60 Hz) and amplitude proportional to the value of a state-specific scoring variable. Thus, in NREM sleep the wave depicting the NREM quantifier has high amplitude and produces a PPG with dominant 3 Hz frequency. In REM sleep, the wave depicting the REM quantifier has high amplitude and produces a PPG with a dominant 7 Hz frequency, and in WAKE the PPG is dominated by 60 Hz. Thus, the PPG provides a means for visual discrimination of the three behavioural states. Validation studies found an overall reliability of 94% compared with conventional visual analysis of EEG and EMG. The PPG was also found to remain accurate in rats after 24 h of sleep deprivation.