A comprehensive study on electroencephalography and magnetoencephalography sensitivity to cortical and subcortical sources

Abstract

Signal‐to‐noise ratio (SNR) maps are a good way to visualize electroencephalography (EEG) and magnetoencephalography (MEG) sensitivity. SNR maps extend the knowledge about the modulation of EEG and MEG signals by source locations and orientations and can therefore help to better understand and interpret measured signals as well as source reconstruction results thereof. Our work has two main objectives. First, we investigated the accuracy and reliability of EEG and MEG finite element method (FEM)‐based sensitivity maps for three different head models, namely an isotropic three and four‐compartment and an anisotropic six‐compartment head model. As a result, we found that ignoring the cerebrospinal fluid leads to an overestimation of EEG SNR values. Second, we examined and compared EEG and MEG SNR mappings for both cortical and subcortical sources and their modulation by source location and orientation. Our results for cortical sources show that EEG sensitivity is higher for radial and deep sources and MEG for tangential ones, which are the majority of sources. As to the subcortical sources, we found that deep sources with sufficient tangential source orientation are recordable by the MEG. Our work, which represents the first comprehensive study where cortical and subcortical sources are considered in highly detailed FEM‐based EEG and MEG SNR mappings, sheds a new light on the sensitivity of EEG and MEG and might influence the decision of brain researchers or clinicians in their choice of the best modality for their experiment or diagnostics, respectively.

Modality-specific tracking of attention and sensory statistics in the human electrophysiological spectral exponent

“…Occipital electrodes, however, are sensitive to visual cortex activity and are directly positioned above it (Hagler et al, 2009). Further exaggerated by the scaling of volume conduction with distance, this likely results in a reduced signal to noise ratio for auditory compared to visual cortex activity (Piastra et al, 2020). Despite these differences in the sensitivity of EEG signals, our results provide clear evidence for a modality-specific flattening of EEG spectra through the selective allocation of attentional resources.…”

“…Occipital electrodes, however, are sensitive to visual cortex activity and are directly positioned above it ( Hagler et al, 2009 ). Further exaggerated by the scaling of volume conduction with distance, this likely results in a reduced signal to noise ratio for auditory compared to visual cortex activity ( Piastra et al, 2020 ).…”

Modality-specific tracking of attention and sensory statistics in the human electrophysiological spectral exponent

“…While central electrodes capture auditory cortical activity 45,46 and hence are positioned far away from their dominant source, occipital electrodes are sensitive to visual cortex activity and are directly positioned above it 47 . This topographical difference in sensitivity is further exaggerated by the scaling of volume conduction with distance, together resulting in a reduced signal to noise ratio for auditory compared to visual cortex activity 48 .…”

Odor Identity Can Be Extracted From the Reciprocal Connectivity Between Olfactory Bulb and Piriform Cortex in Humans

“…Source reconstruction from human surface EEG is spatially less specific than, for example, surgically placed intracranial electrodes; although, EEG as a method was recently demonstrated to be a reliable method for extracting radial and deep sources (Piastra et al 2021). That said, we have previously shown and extensively validated in several experiments that the EBG signal can be effectively extracted and that it reliably originates from the OB (Iravani et al 2020).…”