Figure 5.

Onset of electrographic seizure activity: unilateral versus bilateral. A1, At 2 months of age, seizure onsets were recorded ipsilateral to the HI lesion. Examination of the three EEG channels (Ch1, IE; Ch2, PE; Ch3, CE) showed that seizure activity was initiated medial to the lesion (i.e., Ch 2, PE) seconds before spiking activity occurred over the ischemic lesion (Ch 1, IE), followed by activity over the contralateral hemisphere (Ch 3). A2 is an expansion of the EEG trace marked by a solid black line in A1. B, A representative tonic–clonic convulsive seizure (i.e., grade 5 on the Racine scale) recorded in a 6–11 month rat. Expansions in the bottom row show onset of seizure heralded by the initial large-amplitude sentinel spike (1), followed by rhythmic spiking activity first seen on Ch2 (2) and then on Ch2 and Ch3 (3). Low-amplitude high-frequency spiking was then seen in all three channels (4). Rhythmic 6–7 Hz large-amplitude synchronous spike-wave activity was seen on all three channels (5). Termination of the seizure occurred with large-amplitude, low-frequency spike-wave activity with intervening silent periods (6).