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EEC 2022 | Detecting scalp high frequency oscillations in patients with epilepsy

Maeike Zijlmans, PhD, UMC Utrecht, Utrecht, Netherlands, says that approximately a decade ago several centers recorded high frequency oscillations (HFOs) in the brain of patients with epilepsy for the first time. Originally this was observed in animals via microelectrodes but now macroelectrodes are regularly used. This has brought about the possibility of identifying the epileptogenic tissue in patients based on areas showing HFOs. Another improvement of the field is moving away from the idea that it is impossible to record these events non-invasively. In fact, electroencephalography (EEG) and magnetoencephalography (MEG) can detect these HFOs from outside the skull, although weaker. The future challenge is to improve recording and signal analysis in order to better diagnosis and evaluation of treatment. This interview took place at the 14th European Epilepsy Congress (EEC) 2022 in Geneva, Switzerland.

Transcript (edited for clarity)

About 10 years ago in, well, several centers, it was found that high frequency oscillations, so HFOs, can be found in the brain. And first this was found especially in animals with microelectrodes, but soon it was found out that you can also record them with macroelectrodes. Normal, regularly used, invasive electrodes in the brain. And that you can record them in patients, people with epilepsy.

And that the area that shows high frequency oscillations may be pretty informative about really where the epileptogenic tissue can be found...

About 10 years ago in, well, several centers, it was found that high frequency oscillations, so HFOs, can be found in the brain. And first this was found especially in animals with microelectrodes, but soon it was found out that you can also record them with macroelectrodes. Normal, regularly used, invasive electrodes in the brain. And that you can record them in patients, people with epilepsy.

And that the area that shows high frequency oscillations may be pretty informative about really where the epileptogenic tissue can be found. And so this was found first, and then we always thought that it would be impossible to find these events noninvasively, because there is this way of thinking that small signals can’t be found outside of the brain. And then there’s one thing that’s actually in the textbook saying that the skull is a filter for the signal, so you can’t see the signal outside.

Well, we found out that’s not true because actually, with EEG, but also with MEG, which is magnetoencephalography, you can find these little vibrations that you can find in the inside of the brain, you can also find on the outside. They are less strong because you’re further away, but it’s not true that it’s impossible to find them.

And then, the challenge is to improve your recording and your signal analysis in that way, yeah, that you can find them the best you can. If you compare it to all the signals people try to catch from space, I mean, it’s just a matter of improving the way you record to find tiny signals. And then, if you can find them noninvasively, you can also better use them for instance, for the diagnosis, for evaluation of treatments, et cetera.

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