Fig. 1.

Schematic of experimental setup. A, The sensorimotor cortex was electrically stimulated with a 5-s train of 100 Hz biphasic square-wave pulses to induce seizures. Pulses were 1 ms in duration per phase and had current amplitude x (A(i)), defined as the threshold for ictal spike-and-wave ECoG activity. During post-acquisition signal processing, the ECoG trace recorded from the ictal focus (A(ii)) was used to set event markers at each peak of the spike component of ictal SWDs (A(iii)); these markers were used as triggers to construct averaged ECoG and impedance waveforms of a single SWD per seizure. B, A 57-electrode epicortical array was placed on the exposed cortical surface of an anaesthetised rat: two electrode pairs on the array were stimulated to induce seizures and obtain EIT measurements simultaneously (B(i)). Transfer impedances were recorded with injection of current through different electrode pairs for 30 seizures; locations of and the distance between EIT electrodes were varied to ensure adequate sampling of cortical tissue (B(ii)). A 7-min rest period between stimulation series prevented neocortical kindling effects during imaging protocols.