Abstract
Depression and schizophrenia are defined only by their clinical features, and diagnostic separation between them can be difficult. Disturbances in motor activity pattern are central features of both types of disorders. We introduce a new method to analyze time series, called the similarity graph algorithm. Time series of motor activity, obtained from actigraph registrations over 12 days in depressed and schizophrenic patients, were mapped into a graph and we then applied techniques from graph theory to characterize these time series, primarily looking for changes in complexity. The most marked finding was that depressed patients were found to be significantly different from both controls and schizophrenic patients, with evidence of less regularity of the time series, when analyzing the recordings with one hour intervals. These findings support the contention that there are important differences in control systems regulating motor behavior in patients with depression and schizophrenia. The similarity graph algorithm we have described can easily be applied to the study of other types of time series.
Highlights
Depression and schizophrenia represent major health problems worldwide [1][2]
In a previous paper on mathematical analyses of motor activity time series, we reported a strong negative correlation between sample entropy values and standard deviation (SD) [10], but we were not able to discriminate between patients with depression or schizophrenia and controls, neither in the 300 min or the 288 hrs time series using the sample entropy method
We have presented a new algorithm to analyze time series of motor activity based on graph theory, which we call the similarity graph algorithm
Summary
Depression and schizophrenia represent major health problems worldwide [1][2]. As is the case with other functional psychiatric disorders, they are defined only by their clinical features, and diagnostic separation between them is not always easy. Depressive symptoms are defining features of depressive disorders, but are common in the course of schizophrenia, and psychotic symptoms are often part of the clinical presentation of depression[3]. It would be an important aid in classification, diagnosis and possibly in prognostic assessment if one could find objective biological, differences between these disorders. Changes in motor activity are seen both in depression and schizophrenia. Changes in motor activity are seen both in unipolar depressive disorder[5]and in the depressive phase of bipolar disorder[6].
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