doi:10.1016/S0925-2312(00)00281-2
Copyright © 2000 Elsevier Science B.V. All rights reserved.
Symbolic time-series analysis of neural data*1
S. Lesher1,
,
, Li Guan and A. H. Cohen
Department of Biology, Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742, USA
Accepted 13 January 2000.
Available online 13 June 2000.
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Abstract
The symbolic representation of experimental data offers a potentially powerful tool for studying dynamic behavior and for model fitting. We show how experimental time-series data from lamprey locomotion can be mapped onto symbols. Spike time-series from bursting oscillators in the spinal cord are visualized as Poincare sections that slice through the initiation of the fast (spike) oscillations represented in a higher-dimensional phase space. This Poincare map is systematically converted to a string of symbols that capture the dynamics in the plane of slicing. The patterns in these symbol strings can be used to search for repeating behaviors, or, potentially, to fit models.
Author Keywords: Timeseries; Biological oscillators; Symbolic dynamics
Fig. 1. Trace–determinant plane representing the behavior of systems of two-dimensional maps. We make our system two-dimensional by setting Ui+1=Ti; i≠n and substituting so that we have a pair of equations
for which we can find the Jacobean and descriptors derived from it (trace, determinant, discriminant, eigenvalues). We have arbitrarily assigned symbols: *, +,

, ◊, □, ○, →, to represent different regions of the trace–determinant plane.
Fig. 2. Diagram representing how a window of interspike intervals is slid through a time series of such intervals. Using the equations in the text (see also Fig. 1), the behavior of this window of intervals is mapped onto an area of the trace–determinant plane, and hence a symbol. The sequence of windows of interspike intervals thus becomes a sequence of symbols representing a sequence of local dynamics as captured in the interspike intervals.
Table 1. Two symbols

Table 2. Three symbols
