Fig. 6

OFF period detection rationale. Top row depicts data from cortical layer 4, bottom row from layer 6. A MUA and LFP signal from different cortical layers from the same NREM sleep interval. OFF periods can be distinguished by a reduced MUA amplitude and often by the presence of LFP slow waves. The appearance of OFF periods, in terms of amplitude and duration, differs between and within layers. B 1D Histogram of NREM MUA amplitudes after Gaussian smoothing. L = length of smoothing window in ms, width factor = 2.5. The histogram of layer 6 has a bimodal distribution with a narrow low amplitude peak (blue arrow), which we call low amplitude (LA) data points, and a broad high amplitude peak (green arrow), which we interpret as non-LA period data points. The histogram of layer 4 is also bimodal but the peaks are closer together and have similar heights. In both cases, no obvious threshold exists at which to separate the peaks. C 2D histogram of MUA amplitude after Gaussian smoothing with two different window lengths. The histogram is unimodal with only the low amplitude peak retained (blue arrow). Rather than setting an amplitude threshold, LA data points can now be detected by finding points belonging to this high density region