Figure 5. Representative traces of intrahippocampal depth electrode EEGs from MSO-treated rats.

Continuous EEG traces recorded from a depth electrode in either the left or right hippocampus are shown in A–C and from an epidural screw electrode are shown in D. Thirty seconds of EEG is displayed in each trace. The light gray vertical lines demarcate 1-second time intervals, and the Y axis in each figure corresponds to 5 mV (±2.5 mV). The seizures in A – D were recorded from different animals. Seizure onset and offset are marked with arrows with the first arrow marking seizure onset and the second arrow marking seizure offset. Two main types of ictal EEG patterns were observed: Type I Seizures (A and B) and Type II Seizures (C and D). Both types of seizures could begin with high-frequency EEG activity, though this was not always observed. Then the EEG frequency decreased, while the amplitude slowly built up and the activity became more regular. A seizure with lack of high-frequency onset signal is seen in A. The high-amplitude, low-frequency EEG discharges usually lasted 30 to 60 seconds, though longer-duration Type I Seizures could also be observed (B); then the seizure stopped and the EEG became quiet. Very low-amplitude rhythmic delta activity, which continued for several seconds, was occasionally present after the seizure (A). Higher-amplitude postictal delta activity was occasionally seen as well (B). The Type II Seizure (C and D) was characterized by a third phase of ictal activity that followed a quiet period, which typically lasted 10 to 30 seconds. This third phase of the seizure was characterized by high-amplitude spike discharges that lasted 5 to 20 seconds.