Article

High frequency EEG activity associated with ictal events in an animal model of infantile spasms

Department of Neurology Neuroscience, Baylor College of Medicine, Houston, Texas, USA.
Epilepsia (Impact Factor: 4.57). 01/2011; 52(1):53-62. DOI: 10.1111/j.1528-1167.2010.02887.x
Source: PubMed
ABSTRACT
To describe high frequency (HF) electrographic activity accompanying ictal discharges in the tetrodotoxin (TTX) model of infantile spasms. Previous studies of HF oscillations in humans and animals suggest that they arise at sites of seizure onset. We compared HF oscillations at several cortical sites to determine regional differences. Methods:  TTX was infused for 4 weeks into the neocortex of rats beginning on postnatal days 11 or 12. Electroencephalography (EEG) electrodes were implanted 2 weeks later and video-EEG recordings were analyzed between postnatal days 31 and 47. EEG recordings were digitally sampled at 2,048 Hz. HF EEG activity (20-900 Hz) was quantified using compressed spectral arrays and band-pass filtering.
  Multiple seizures were analyzed in 10 rats. Ictal onset was associated with multiple bands of rhythmic HF activity that could extend to 700 Hz. The earliest and most intense discharging typically occurred contralaterally to where TTX was infused. HF activity continued to occur throughout the seizure (even during the electrodecrement that is recorded with more traditional filter settings), although there was a gradual decrease of the intensity of the highest frequency components as the amplitude of lower frequency oscillations increased. Higher frequencies sometimes reappeared in association with spike/sharp-waves at seizure termination.
The findings show that HF EEG activity accompanies ictal events in the TTX model. Results also suggest that the seizures in this model do not originate from the TTX infusion site. Instead HF discharges are usually most intense and occur earliest contralaterally, suggesting that these homologous regions may be involved in seizure generation.

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    • "In contrast to the observations that ictal HFOs associated with focal seizures frequently evolved into another form such as repetitive spike-wave discharges, ictal HFOs associated with spasms frequently terminated without evolving into another form (Nariai et al., 2011). A study of a rat model of epileptic spasms with ECoG also showed that ictal events began with increase of HFOs below 200 Hz, which was followed within 100 ms by increase of activity above 200 Hz and ictal HFOs subsequently slowed down in frequency to below 100 Hz (Frost et al., 2011). These observations are consistent with the hypotheses that spasms are of cortical and not of brainstem origin and that the cortical sites showing initial increase of HFOs during ictal events may be located close to the region responsible for seizure generation. "
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