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We would like to comment on the article by Gottschalk et al,¹ which presented evidence for a low-dimensional chaotic process in mood rating of patients with bipolar disorder. If correct, this is an important result for psychiatric research and treatment, because it implies that one could predict and control mood in bipolar patients using models with few variables. The authors' conclusion of low-dimensional chaotic behavior is, however, inconsistent with the results of their power spectral analysis. The following brief discussion may be helpful for those continuing to analyze psychiatric data using nonlinear dynamics.

A key observation of Gottschalk et al was that their time series had power spectra (a representation of the amount of energy present in the signal at each frequency [f] as computed with Fourier analysis) that decreased at high frequencies as a power-law function (1/f), where the exponent is a positive constant. Such . . . [Full Text of this Article]

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ABSTRACT | FULL TEXT