Hypnogram & SWA Examples - nsrr/SpectralTrainFig GitHub Wiki
Below is an example of a hypnogram and SWA (slow wave activity) from clean spectral results. Each discrete increase in SWA seen on the density plot lines up with periods on the hypnogram with scored stage 3 sleep and share similar amplitude. The lowest periods of SWA also line up with scored REM sleep and share similar amplitude.
This example of false slow wave activity is easily identifiable for several reasons. While there are obvious increases in SWA none line up with the few epochs scored as stage 3 sleep between epochs 150-250. SWA in this example also occurs at a suspiciously high density >4 uV2/Hz that is almost never physiological and typically attributed to sweat artifact or a loose lead.
This example shows spectral results containing unequivocal slow artifact. Periods of scored stage 3 do not line up with the extremely dense periods of SWA which begin abruptly at epoch 200 during wake. SWA density values >6 uV2/Hz are extremely high, never physiological, and typical of studies where a lead has come completely off. In the example below movement during the transition from REM to wake at epoch 200 pulled the EEG lead off, which continued until epoch 650 when it was reattached.
This example shows how the SWA plot can also be used to identify studies with excessive high frequency artifacts. During a transition from stage 2 to wake at epoch 550 the SWA plot abruptly drops to a suspiciously low density of <1 uV2/Hz. This effect is indicative of spectral results where the signal contains a frequency fast enough to suppress normal physiological SWA from showing up on the SWA plot.
