What does scalp electroencephalogram coherence tell us about long‐range cortical networks?

Abstract

Long-range interactions between cortical areas are undoubtedly a key to the computational power of the brain. For healthy human subjects, the premier method for measuring brain activity on fast timescales is electroencephalography (EEG), and coherence between EEG signals is often used to assay functional connectivity between different brain regions. However, the nature of the underlying brain activity that is reflected in EEG coherence is currently the realm of speculation, because seldom have EEG signals been recorded simultaneously with intracranial recordings near cell bodies in multiple brain areas. Here, we take the early steps towards narrowing this gap in our understanding of EEG coherence by measuring local field potentials with microelectrode arrays in two brain areas (extrastriate visual area V4 and dorsolateral prefrontal cortex) simultaneously with EEG at the nearby scalp in rhesus macaque monkeys. Although we found inter-area coherence at both scales of measurement, we did not find that scalp-level coherence was reliably related to coherence between brain areas measured intracranially on a trial-to-trial basis, despite that scalp-level EEG was related to other important features of neural oscillations, such as trial-to-trial variability in overall amplitudes. This suggests that caution must be exercised when interpreting EEG coherence effects, and new theories devised about what aspects of neural activity long-range coherence in the EEG reflects.

Distinct Sources of Variability Affect Eye Movement Preparation

“…The magnitude of r sc decreased with increasing electrode separation (Pearson's r ϭ Ϫ0.070, p Ͻ 0.0001). This finding is consistent with findings of the distance dependence of r sc in numerous previous studies (Smith and Kohn, 2008;Leavitt et al, 2013;Smith and Sommer, 2013;Zirnsak et al, 2014;Snyder et al, 2018).…”

“…terneuronal distance and increased with tuning similarity, traits that match previous findings in other cortical areas (Kohn and Smith, 2005;Smith and Kohn, 2008;Cohen and Maunsell, 2009;Leavitt et al, 2013;Smith and Sommer, 2013;Ruff and Cohen, 2014a;Snyder et al, 2018). This is consistent with a conserved structure of correlated variability across multiple cortical regions in the visual hierarchy.…”

Monkey EEG links neuronal color and motion information across species and scales

“…High electrode density and methods identical to those used in human M/EEG enabled us to perform source reconstruction and directly relate measures across species. The few available previous studies measuring EEG in nonhuman primates were typically restricted to only a few electrodes (Bimbi et al, 2017;Snyder et al, 2015Snyder et al, , 2018 and used diverging methods such as skull-screw electrodes, or both (Godlove et al, 2011;Musall et al, 2014;Reinhart et al, 2012;Whittingstall and Logothetis, 2009;Woodman et al, 2007). We show how monkey EEG can serve as a missing link to enable the disentangling of species differences from differences in measurement modality.…”

“…Second, invasive and non-invasive electrophysiology are largely separate research fields. Comparable experiments performed on both levels and in the same species are rare, with few recent exceptions (Bimbi et al, 2017;Godlove et al, 2011;Reinhart et al, 2012;Shin et al, 2017;Snyder et al, 2015Snyder et al, , 2018. Third, studies employing invasive and non-invasive methods in parallel suffer from sparse sampling of recording sites.…”

Aversive conditioning in oddball paradigm modulates multisensory integration, attention and emotional processing

“…We ought to say that in our study this analysis was unplanned and thus to express our concern about the reliability of the results. Miltner et al (1999) did not provide a clear rationale for the chosen frequency band, and we also did not have another rationale but simply followed Miltner et al Therefore, we still cannot be sure that these results are not spurious, particularly in the light of the recent data showing no reliable relationship between local field potentials and scalp EEG coherence (Snyder, Issar, & Smith, 2018). On the other hand, almost the same frequency band (36.5-44 Hz) was used in another classical conditioning study, but again without clear justification (Mueller, Panitz, Hermann, & Pizzagalli, 2014).…”