Assessing interactions in the brain with exact low-resolution electromagnetic tomography

Abstract

Scalp electric potentials (electroencephalogram; EEG) are contingent to the impressed current density unleashed by cortical pyramidal neurons undergoing post-synaptic processes. EEG neuroimaging consists of estimating the cortical current density from scalp recordings. We report a solution to this inverse problem that attains exact localization: exact low-resolution brain electromagnetic tomography (eLORETA). This non-invasive method yields high time-resolution intracranial signals that can be used for assessing functional dynamic connectivity in the brain, quantified by coherence and phase synchronization. However, these measures are non-physiologically high because of volume conduction and low spatial resolution. We present a new method to solve this problem by decomposing them into instantaneous and lagged components, with the lagged part having almost pure physiological origin.

Reduced functional connectivity between cortical sources in five meditation traditions detected with lagged coherence using EEG tomography

“…Milton and Jung, 2003) while decreased coherence is observed during schizophrenic symptomatology (e.g. Pascual-Marqui et al, 2011).…”

“…The signal at each cortical ROI consisted of the average electric neuronal activities of all voxels belonging to that ROI, as computed with sLORETA. Between the sLORETA current density time series of the 19 ROIs, intracortical 'lagged' coherence (Pascual-Marqui, 2007;Pascual-Marqui et al, 2011) was computed between all possible 171 pairs of the 19 ROIs for each of the eight independent EEG frequency bands (Kubicki et al, 1979;Niedermeyer andLopes da Silva, 2005 p. 1234) of delta (1.5-6 Hz), theta (6.5-8 Hz), alpha-1 (8.5-10 Hz), alpha-2: (10.5-12 Hz), beta-1 (12.5-18 Hz), beta-2 (18.5-21 Hz), beta-3 (21.5-30 Hz), and additionally gamma (35-44 Hz) for each subject and for each condition.…”

“…The analysis applies 'lagged' coherence that partials out the effect of zero phase angle coherence (Pascual-Marqui, 2007;Pascual-Marqui et al, 2011), thereby removing the volume conduction artifact. Further, it applies the method to cortical time series of electric neuronal generator activity estimated via LORETA-based source modeling of the head surface-recorded EEG data (sLORETA, Pascual-Marqui, 2002) which removes the ambiguity of source localization.…”

EEG microstates as a tool for studying the temporal dynamics of whole-brain neuronal networks: A review

“…interactions to assess brain connectivity (Pascual-Marqui et al, 2011), and there is good electrophysiological evidence that these lags exist and play a functional role (van Kerkoerle et al, 2014). However, the microstate model contains a strong and a priori constraint on simultaneity, which excludes the existence of significant lags within a microstate.…”

Association of cerebrospinal fluid tap‐related oscillatory activity and shunt outcome in idiopathic normal‐pressure hydrocephalus

“…18 It allows us to compute the source localization of electric brain activity from scalp EEG data. [19][20][21] The particular weights used in eLORETA endow the tomography with the property of exact localization to test point sources, so that it yields images of current source density (CSD) with exact localization but low spatial resolution. In the current eLORETA package, the solution space is limited to the cortical grey matter, corresponding to 6239 voxels at 7 × 7 × 7-mm spatial resolution.…”