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 (labeled Ch1 - IE, Ch2 - PE and Ch3 -CE, and representing the locations described in Fig. 2) showed that seizure activity was initiated medial to the lesion (i.e., the para-infarct electrode, 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 lower panel 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).