Models of the seizure activity.

Each column presents an example of a simulated seizure with the different models in the noisy variation. From top to bottom, the panels show the position of the seizure patch and the implanted electrodes, source activity in two points on the patch, snapshots of the source activity (at time points marked in the inset above), and simulated sensor activity on two contacts located close to the seizure patch. (A) One homogeneous source model posits that the seizure activity is generated by one contiguous cortical patch, where any point follows the same dynamics (apart from the stochastic noise) with gradually increasing oscillations. (B) In the two homogeneous sources model, there are two patches recruited with a delay. On each patch any point follows the same dynamics with gradual onset as in the one source model. (C) In the spreading seizure model, the seizure activity start at a single point located on the cortical patch, and the seizure then slowly spreads until the whole patch is recruited (recruitment time is represented by the patch color in top panel). In every cortical unit represented by a vertex of the triangulation the seizure activity starts instantly with no transition period (second panel). Despite this rapid onset on the source level, the onset of the seizure activity at the sensor level is gradual (bottom panel). This is due to the spatial averaging effect of the measured local field potential, which transforms the slow spatial spread of the seizure into gradual onset in a sensor signal. The lowermost panel shows that all models produce SEEG signal resembling the TAA pattern.