Figure 1.

Method of detection of ultradian rhythms in gene expression, with the 48-h expression profile of Prrc1 used as an example. A, B) An expression pattern is considered potentially ultradian when both the first and second half of the data (A) exhibit similar periodicity in an autocorrelation analysis (B). C, D) The second criterion, that an ultradian rhythm is not an artifact of a low-frequency fundamental signal, is tested by applying a low-pass filter (C), and retesting for ultradian periods using autocorrelation analysis (D). E) Finally, the ultradian waveform must consistently be expressed throughout the dataset, as evidenced by observing a value of R² ≥ 0.6 in the regression of the average ultradian waveform against the actual signal.