Spatial and temporal resolutions of EEG: Is it really black and white? A scalp current density view

Abstract

Among the different brain imaging techniques, electroencephalography (EEG) is classically considered as having an excellent temporal resolution, but a poor spatial one. Here, we argue that the actual temporal resolution of conventional (scalp potentials) EEG is overestimated, and that volume conduction, the main cause of the poor spatial resolution of EEG, also distorts the recovered time course of the underlying sources at scalp level, and hence degrades the actual temporal resolution of EEG. While Current Source Density (CSD) estimates, through the Surface Laplacian (SL) computation, are well known to dramatically reduce volume conduction effects and hence improve EEG spatial resolution, its positive impact on EEG temporal resolution is much less recognized. In two simulation studies, we first show how volume conduction and reference electrodes distort the scalp potential time course, and how SL transform provides a much better spatio-temporal description. We then exemplify similar effects on two empirical datasets. We show how the time courses of the scalp potentials mis-estimate the latencies of the relevant brain events and that CSD provides a much richer, and much more accurate, view of the spatio-temporal dynamics of brain activity.

Four-dimensional maps of the human somatosensory system

“…Nineteen clustering procedures were performed imposing increasing numbers of clusters (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) and computing silhouette values (75) to evaluate clustering validity. The optimal clustering was defined by the maximal average silhouette value, and leads with negative silhouette values were not considered in the evaluation of the optimal clustering using a repeated-measurement ANOVA with time and cluster as factors.…”

“…It is not sufficient, however, to know which nodes are active; information is also needed about the local dynamics of the nodes, as well as the relative timing of their activity, to fully understand human brain functions (2,3). Even if the temporal resolution of electroencephalography (EEG) and magnetoencephalography (MEG) allowed one to observe the intra-and interareal dynamics, to date such recordings remain too poor in localization power (1-2 cm) (3,4). Combining EEG and fMRI has been suggested as a solution, using EEG to determine the temporal dynamics within and between the areas identified with fMRI (5).…”

Feasibility of imaging evoked activity throughout the rat brain using electrical impedance tomography

“…EEG inverse source localisation can image direct neural activity over large regions of the brain. However, it has a low spatial resolution (Burle et al, 2015;Nunez et al, 1994) and is blind to dipole sources oriented tangentially to recording electrodes (Ahlfors et al, 2010;Hunold et al, 2016). Currently no satisfactory method exists to record direct neural activity occurring over large regions of the brain.…”

Pain & attention

“…Therefore the recorded EEG activity always reflects the summation of the synchronous activity of thousands or millions of neurons that have similar spatial orientation (Speckmann & Elger, 1999). EEG has a high (millisecond) temporal resolution (Sharon, Hämäläinen, Tootell, Halgren, & Belliveau, 2007), but the spatial resolution of EEG is low (2-3cm, see Burle, Spieser, Roger, Casini, Hasbroucq, & Vidala, 2015). However, current analysing techniques and increasing number of electrodes (128 or 256 electrodes) make it possible to perform source analyses on EEG data (< 1cm, see Im, Gururajan, Zhang, Chen, & He, 2007).…”