High Frequency Oscillations in Epileptic Rodents: Are We Doing It Right?

Publication date: Available online 21 February 2018
Source:Journal of Neuroscience Methods
Author(s): Maxime Lévesque, Siyan Wang, Jean Gotman, Massimo Avoli
BackgroundThe detection of high-frequency oscillations (HFOs, ripples: 80–200 Hz, fast ripples: 250–500 Hz) is often based on considering ripples or fast ripples in isolation; overlapping ripples and fast ripples are excluded from further analysis. Here, we studied overlapping HFOs during spontaneous seizures in pilocarpine-treated animals.New methodSpontaneous seizures (n = 6 animals) presented with either hypersynchronous- (HYP, n = 18) or low-voltage fast-onset (LVF, n = 21) pattern. Ripples and fast ripples overlapping by more than 30% were analysed.ResultsOverlapping HFOs could show a unimodal power spectrum between 80 to 500 Hz (n = 188, 58.9%) or a bimodal power spectrum, with peaks in power between 80–200 Hz and between 250–500 Hz (n = 131, 41.1%,). Overlapping HFOs occurred at higher rates during HYP seizures compared to the pre-ictal period in seizure onset zones (p < 0.001) and regions of secondary spread (p < 0.001). When comparing HYP and LVF seizures, we found that overlapping HFOs occurred at higher rates before LVF seizures (p < 0.05) compared to HYP seizures but, during the ictal period, HYP seizures showed higher rates of overlapping HFOs than LVF seizures (p < 0.001).Comparison with existing methodsWe have analysed overlapping ripples and fast ripples shortly before and during seizures.ConclusionsAlthough overlapping ripples and fast ripples represent a minority of HFOs, they may provide additional information on the excitability of neuronal networks that generate seizures in animal models and patients presenting with mesial temporal lobe epilepsy.



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