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Cognition is made possible by the complex interaction of neural assemblies at widely different spatial
and temporal scales (Fries, 2015). So far, the spatio-temporal dynamics of brain networks have been
studied separately at different scales, either at a microscopic level in animals with unit recordings or
at a large scale in humans using non-invasive measures (functional MRI, fMRI,
electroencephalography, EEG, or magnetoencephalography, MEG). Invasive recordings performed
during presurgical evaluation, using the Stereotaxic EEG method (SEEG), provide a unique
opportunity for investigating an intermediate (mesoscopic scale) in humans, particularly to
investigate cognition (Barbeau et al. , 2008, Lachaux et al. , 2012, Llorens et al. , 2016). They also
allow validating surface measure by providing a '"ground truth" to which surface recordings can be
compared to (Malinowska et al. , 2014). In a few studies, microscopic contacts or wires have been
added to the classical SEEG electrodes in order to record neuronal activity at the micro scale (single
unit, multi-unit or micro LFP) (Quiroga et al. , 2005).

The implantation scheme of SEEG electrodes is performed on purely clinical motivations. It allows the
characterization of cognitive networks (functional mapping) with unmatched spatial and temporal
specificity for clinical or neuroscience purposes. Still, a limitation of intracerebal recordings is that
they are local, and remain limited in spatial coverage. An ideal combination is to use both SEEG and
MEG/EEG data in the same protocol. The field of view of SEEG can be expanded by recording it
simultaneously with surface measures (EEG and/or MEG), and combining their analysis. Crucially,
simultaneous recordings ensure that the exact same activity is captured both at the surface and
directly within the cortex - thus controlling for the fluctuations of brain states (vigilance, attention,
motivation, re-test, level of medication...) that are inevitable across recording sessions.

Our main objective is to explore the spatio-temporal dynamics of cognitive brain networks
thanks to simultaneous surface and depth recordings. Specifically, depth recordings will be used to
inform the exploration of functional task networks, either by guiding the analysis at the level of single
trials or by providing high resolution seeds for connectivity measures. We will track medication level,
which could be a confound effect, and set the emphasis on single-subject/single-trial analysis.
Part of the project will be dedicated to methodological issues that arise when analyzing such complex
data. We will validate results of surface analysis with the SEEG ground truth, which will constitute a
technological progress in analysis of non-invasive measures, and we will develop a pipeline for
extracting brain networks based on a joint analysis of EEG, MEG and SEEG. The other part of the
project will focus on the application of this unique technique to unravelling multi-scale cognitive
networks. We thus expect to gain insight on brain networks thanks to our multi-scale approach.

There will be several outcomes of the SCALES project. The first outcome will be methodological,
namely a pipeline of dedicated analysis tools, including a validation of surface network measures
thanks to SEEG that will be useful for regular non-invasive MEG-EEG analyses. The second outcome
will be a characterization of functional brain networks thanks to joint analysis of multi-scale
recordings. The third outcome will be a public database of simultaneous recordings, which will be
useful to the signal analysis, computational modelling and cognitive neuroscience communities.
The consortium gathers experts from different fields: neuroscientists, neurologists, engineers, who
are all specialists in SEEG, and have experience in simultaneous recordings. Ethical issues have been
firstly addressed by declarations to the local committees and will be strictly monitored by an ethics
rapporteur, and a consortium agreement will be signed between partners.