Mechanisms underlying different onset patterns of focal seizures
(A) Seizure onset amplitude is shown (as the size and saturation of the circle markers) with respect to the parameters surround excitability (Psurround), percentage of minicolumns showing microseizure activity, and number of patches. (B) Amplitude of onset is shown only for different values of the surround excitability Psurround. Essentially, the 3D parameter scan in (A) is shown here as a projection onto the parameter Psurround. The red shading indicates parameter ranges for which the surrounding is bistable (seizure and background states coexist). (C) Two dimensional parameter scans of seizure onset amplitude for the parameters of percentage of minicolumns in microseizure activity, and number of patches. Top scan (green frame) is shown for a constant value of surround excitability (Psurround = −1.5), where the system is in a bistable state. Bottom scan (blue frame) is shown for a constant value of surround excitability (Psurround = −4), where the system is in a monostable background state. Both scans are essentially slices of the parameter space shown in (A), indicated by the green and blue frames. The top two small inset panels illustrate the concept of different number of patches for the same percentage of minicolumns in microseizure activity on the cortical sheet. Black indicates the location of the patches on the cortical sheet. The amplitude of onset is measured in arbitrary units (see Methods). The parameters used can be found in Table 1.