Figure 3: Recurrence Plot of an ECoG epoch selected according to our sampling protocol. | Scientific Reports

Figure 3: Recurrence Plot of an ECoG epoch selected according to our sampling protocol.

From: Following a potential epileptogenic insult, prolonged high rates of nonlinear dynamical regimes of intermittency type is the hallmark of epileptogenesis

Figure 3

The Recurrence Plot (RP) shown in the figure is the graphical representation of the recurrence matrix associated to an ECoG epoch selected according to our sampling protocol, i.e., 12 seconds (4800 data points) every 5 minutes of ECoG (middle trace). In this example, the ECoG was recorded during the period of epileptogenesis of an animal that developed epilepsy following the exposure to ICV infusion of albumin. In the figure, the selected epoch for the construction of the RP is represented by the highlighted portion of the ECoG. In the RP, the occurrence of laminarity states generates dark areas, with different extension, which are made of adjacent points positioned vertically and/or horizontally, sometimes loosely similar to squares and rectangles. The RQA variable LAM is aimed at measuring the percentage of the recurrent points which form vertical lines in the RP. Another important graphical aspect of RPs is the presence of diagonal lines which are associated to the degree of determinism of the time-series. In this case, the RQA variable DET is aimed at measuring the percentage of the recurrent points which form diagonal lines in the RP (see also the Supplementary Discussion). The RPs are graphically symmetric respect to the diagonal representing the line of identity (LOI) of the squared recurrence matrix. The width of the white stripe along the LOI depicts the extension of the Theiler’s window, which usually varies from epoch to epoch. In the context of our analytical protocol it is important to consider that the RP associated to each ECoG epoch does not correlate with the actual amount of laminarity (and determinism) of the time-series, since the range of variation of the RAD is limited by the constrain to vary until the imposed fixed amount of recurrences is reached (1%). See the ‘Methods’ section, paragraph ‘Normalization of the variable LAM’, for details. The lower ECoG trace represents a typical ictal event (seizure) occurring in the animals that developed epilepsy.

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