A probabilistic model for the ultradian timing of REM sleep in mice
Fig 3
(A) (Left) Scatter plot of REMpre vs. ln(|N|) with color-coded single and sequential cycles. The threshold optimally separating sequential from single cycles is shown in black. (Right) Illustration of how the threshold was determined for REMpre = 30 s. The probability density functions (PDFs) for the two distributions of the GMM (for REMpre = 30 s) are plotted along the y-axis. The red asterisk indicates the value of ln(|N|) at which the two Gaussians intersect. Values of ln(|N|) below the intersection point are more likely to be drawn from the short distribution and are consequently labeled as sequential cycles. Gray points correspond to cycles with REMpre < 7.5 s for which the conditional GMM is not defined (S1B Fig and Methods). (B) Pie chart indicating the percentage of single and sequential cycles. (C) Box plot comparing REMpre for single and sequential cycles. For sequential cycles, REMpre was shorter than for single cycles (Welch’s t-test, t = -35.13, p = 2.59e-228, nsequential = 947, nsingle = 3961). (D) Histogram of |N| for sequential cycles. The vertical dashed line indicates the mean (85.46 s ± 40.92 s; mean ± s.d.). (E) Bar plot showing the percentage of the number of cycles within a REM sleep sequence. Over half of REM sleep sequences contain only one cycle (i.e. comprise two REM periods). (F) Spectral density of parietal (nsequential = 947, nsingle, = 3961) and prefrontal (nsequential = 936, nsingle = 3919) EEG during REM and NREM sleep for both sequential and single cycles. Horizontal lines indicate frequencies at which the spectral density of sequential and single cycles are statistically different at various ɑ levels; (Welch’s t-test, * p<0.05; ** p<0.01; *** p<0.001). One recording did not contain a prefrontal EEG channel. Shadings, 99% confidence interval (CI).