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Detecting and localizing the foci in human epileptic seizures
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View: Figures


Image of FIG. 1.
FIG. 1.

(Color) Subdural ECoG grid of electrodes placed on the surface of the brain for chronic evaluation of epileptic patients before surgical resection.

Image of FIG. 2.
FIG. 2.

(Color) The computed tomography (CT) image with marked electrodes (a) and the electrode scheme (b), projected on the plane, for patient B. The arrays of electrodes are labeled according to their position: F, frontal; P, parietal; AT, anterior temporal; ST, subtemporal; PT, posterior-temporal. The same naming convention is used for all patients. For a description of other marks, see the discussion after Eq. (4) .

Image of FIG. 3.
FIG. 3.

Voltage traces of ECoG signals. Three portions of voltage traces of seven electrodes, taken from a multielectrode recording of 96 electrodes of patient B, cf. Fig. 2 . The seizure onset is marked by a vertical line. The analysis below indicates that the signals coming from electrodes F6, F14, F15, and P50 belong to the epileptic foci, whereas the F13, P29, and AT5 do not. The voltage scale of and the time scale of 1 s are shown below the figure.

Image of FIG. 4.
FIG. 4.

Panels (a), (c), and (e): Synchrograms for three neighboring pairs of electrodes along [F13–F14 (a), F15–F14 (c)] and across the grid [F6–F14 (e)], calculated for the reference electrode F14 (the signals for F6, F13, F14, and F15 are shown in Fig. 3 ). Since the synchronization line appears at , a small phase offset of was added to the phase for clarity. Panels (b), (d), and (f) show the histograms of the phase points distribution within the corresponding synchrogram. Clearly, only one strong line is present in each synchrogram, at the position of the offset phase . This corresponds to the 1:1 synchronization without visible phase difference.

Image of FIG. 5.
FIG. 5.

Histograms for synchrograms of orders , and calculated for the pair of electrodes F14–F15 (cf. Fig. 4 , panels c and d). The dashed lines mark offset positions , and . The same bin size was used in all histograms. The number of strong lines is equal to the order of the synchrogram, confirming the 1:1 synchronization. The position of the synchronization lines coincide with the value of the offset phase within .

Image of FIG. 6.
FIG. 6.

The vicinity of the 1:1 synchronization line for the synchrogram of electrodes F14 and F15, with the phase offset . Note that the synchronization line is clearly isolated.

Image of FIG. 7.
FIG. 7.

(Color) A typical SSD for a focal electrode [here, F14 ( )]. The electrodes here are numbered and correspond to: 1–8 (AT1-AT8), 9–12 (ST1-ST4), 13–58 (P13-P58), 59–64 (PT3-PT8), 65–96 (F1-F32). The time span of the diagram is 1 h 30 min.

Image of FIG. 8.
FIG. 8.

(Color) A typical SSD for a nonfocal electrode [here, AT5 ( )]. Electrodes are numbered as in Fig. 7 . The time span of the diagram is 1 h 30 min.

Image of FIG. 9.
FIG. 9.

(Color) A typical mean pairwise synchronization matrix , computed from the same as shown in Figs. 7 and 8 , for the time interval (2000–2600) s.

Image of FIG. 10.
FIG. 10.

(Color online) The geometric spread of the electrodes, for patient A. The viewing angle was chosen to best present the resected area. Only relevant electrodes are labeled. The electrodes with synchronization strength exceeding the threshold value are marked by a rectangle. The electrodes chosen for resection are highlighted.

Image of FIG. 11.
FIG. 11.

(Color online) The electrodes scheme for patient C. The viewing angle was chosen to best present the resected areas. Only relevant electrodes are labeled for clarity. The electrodes are marked as in Fig. 10 .


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Detecting and localizing the foci in human epileptic seizures