From Epilepsy Surgery

It’s not what it looks like: High Frequency Oscillations

Following on from the last post on baseline shifts, this is the second post on a few things we don’t normally consider when talking about standard EEG measurements. I had the idea for this one after a few excellent talks by Liset Menendez de la Prida at ISWP7 earlier this year.

Fast and furious (or is it)

Fast stuff on the EEG is difficult to see for a number of reasons: i) We usually filter raw EEG signal to make it look neater and often exclude high-gamma range signal. ii) The signal we measure on the scalp itself is already attenuated by passing through different tissues, making fast activity appear less sharp and prominent. This is true even for ECOG when compared to direct LFP recordings (which is becoming more relevant now that microelectrodes are being used more and more in patients with epilepsy). iii) Higher frequencies have a lower power – usually fast fluctuations are a lot smaller than bigger shifts on the EEG and seem to pale in comparison, when visually analysing the EEG.

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