Intracranial recordings (stereo-EEG) are revolutionizing the diagnosis and treatment of some persistent neuropathologies, such as epilepsy and Parkinson’s disease. In combination with MRI, it allows precise localization of the electrodes, unattainable by other methods, a precision that is essential to apply very localized solutions that avoid altering other functions. However, the electrical potentials produced by neuronal currents propagate inside the brain and reach distant electrodes, where they mix with those of many other neuronal populations. The high conductivity of the brain therefore means that the advantage of electrode localization is lost. In this work published in The Journal of Neuroscience (1), we have used biomathematical techniques, previously optimized in animal models by Dr. Herreras’ group (2,3), which allow to separate the activities of neuronal populations and, now, to locate their origin thanks to the voltage gradients characteristic of each one. We have been able to determine that customary stereo-EEG recordings are contributed by mixtures of 3 to 5 neuronal populations, so their separation is necessary to correctly evaluate each one and determine their normal or pathological state.

In a group of epileptic patients implanted with exploratory multi-electrodes (Epilepsy Unit, Ruber International) we have achieved a successful separation of 50 to 70 field potential generators per patient, distributed in large areas of the brain and whose activity can be followed with optimal temporal resolution for days. We have been able to discriminate which activities are in the recording area (local) and which come from remote populations, and whether they are epileptic or not. Surprisingly, up to 20% of the recordings of seizures were false positives: epileptic activity comes from regions far away from the recording, and should therefore be excluded from local treatments.

This pioneering application in human intracranial recordings will help to plan clinical intervention to interrupt epileptic networks in a personalized way for each patient and decrease possible sequelae.

Additional information in: https://www.jneurosci.org/content/jneuro/early/2024/10/29/JNEUROSCI.0695-24.2024.full.pdf

(1)          Makarova J, Toledano R, Blázquez L, Sánchez-Herráez E, Gil-Nagel A, de Felipe J, Herreras O. (2024) Intracranial voltage profiles from untangled human deep sources reveal multisource composition and source allocation bias. Journal of Neuroscience doi: 10.1523/JNEUROSCI.0695-24.2024

(2)          Nasretdinov A, Vinokurova D, Lemale C, Burkhanova-Zakirova G, Chernova K,Makarova J, Herreras O, Dreier JP,  Khazipov R. (2023) Diversity of cortical activity changes beyond depression during Spreading Depolarizations. Nature Comm, 14(1):7729. doi:10.1038/s41467-023-43509-3

(3)          Herreras O. (2016) Local Field Potentials: Myths and Misunderstandings. Frontiers in Neural Circuits 10:101 (pp16), DOI: 10.3389/fncir.2016.00101