Rethinking sleep analysis.

Visual sleep scoring is the obligatory reference for sleep analysis. An essential step in sleep scoring is sleep staging. This technique was first described in 1937 and later adapted 3 times: first, in 1957, after the detection of rapid eye movement (REM) sleep, when electrooculography (EOG) was added; second, in 1968, when sleep staging was standardized and electromyography (EMG) was added; and third, in 2007, to integrate accumulated knowledge from sleep science, adding arousals and respiratory, cardiac, and movement events. In spite of the dramatic changes that have taken place in recording and storing techniques, sleep staging has undergone surprisingly few changes. The argument of the present comment is that sleep staging was appropriate as long as sleep biosignals were recorded in the analog mode as curves on paper, whereas this staging may be insufficient for digitally recorded and stored sleep data. Limitations of sleep staging are critically discussed and alternative strategies of sleep analysis are emphasized.