Time course of relative slow wave activity (SWA) across non-rapid eye movement (NREM) sleep periods. Individual SWA values per NREM sleep period (expressed as a percentage of all night SWA) are plotted at period midpoint relative to sleep onset for MDD and healthy controls A) unstratified and B) stratified by sex. All data from the first four NREM periods were included to maximize fit of the exponential function. Lines represent exponential functions that were fitted to the data using the equation SWAt = (SWA0 * e-rt) + SWA∞, in which SWAt is the SWA value at a given time point t, SWA0 represents the hypothetical SWA value at time 0, t indicates time (min) from sleep onset, r is the rate (min-1) of exponential decay, and SWA∞ indicates the SWA value of the decay function’s asymptote.
Plante et al. BMC Psychiatry 2012 12:146 doi:10.1186/1471-244X-12-146