A graphic power spectrum based method to study variations in circadian rhythms

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Abstract
Circadian rhythm patterns can be well characterized by spectral analysis. Alterations in the rhythm are reflected as specific changes in the spectra. When these changes take place throughout a long span of time, detection becomes difficult because of the background noise and the variability of the daily circadian pattern. In this work, a very simple graphic method is proposed to show and study these types of variations. The method is based on the representation of daily spectra in a graphic matrix, where each row is associated to a day and each column to a harmonic. Each element of this matrix consists of a square with a number of horizontal bars, proportional to the power content of the corresponding harmonic. In this way, the main harmonics are distinguished as dark zones in the graph. To emphasize the tendencies of the harmonics and diminish the variation amongst days, a moving average can be used for each harmonic (smoothing the matrix in a vertical direction). This technique strongly increases the visual comprehension of the matrix. To illustrate the proposed method, a continuous record of motor activity of 6 young mice was kept for 18 days.

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