Source Analysis of Alpha Rhythm Reactivity Using LORETA Imaging with 64-Channel EEG and Individual MRI

Abstract

Conventional EEG and quantitative EEG visual stimuli (close-open eyes) reactivity analysis have shown their usefulness in clinical practice; however studies at the level of EEG generators are limited. The focus of the study was visual reactivity of cortical resources in healthy subjects and in a stroke patient. The 64 channel EEG and T1 magnetic resonance imaging (MRI) studies were obtained from 32 healthy subjects and a middle cerebral artery stroke patient. Low Resolution Electromagnetic Tomography (LORETA) was used to estimate EEG sources for both close eyes (CE) vs. open eyes (OE) conditions using individual MRI. The t-test was performed between source spectra of the two conditions. Thresholds for statistically significant t values were estimated by the local false discovery rate (lfdr) method. The Z transform was used to quantify the differences in cortical reactivity between the patient and healthy subjects. Closed-open eyes alpha reactivity sources were found mainly in posterior regions (occipito-parietal zones), extended in some cases to anterior and thalamic regions. Significant cortical reactivity sources were found in frequencies different from alpha (lower t-values). Significant changes at EEG reactivity sources were evident in the damaged brain hemisphere. Reactivity changes were also found in the "healthy" hemisphere when compared with the normal population. In conclusion, our study of brain sources of EEG alpha reactivity provides information that is not evident in the usual topographic analysis.

Intrinsic sensory disinhibition contributes to intrusive re-experiencing in combat veterans

“…Alpha (8-12 Hz) power was normalized by the mean power for the global spectrum (1-50 Hz) within each epoch, and averaged across occipito-parietal electrodes, where alpha is maximally distributed (Foxe & Snyder, 2011;Klimesch, 2012;Palva & Palva, 2007) (Figure 2A). Figure 2A further illustrates the intracranial alpha source, localized to the striate/extrastriate visual cortices (e.g., maximum in the cuneus; x, y, z = -10, -80, 10) based on the exact Low-Resolution Electromagnetic Tomography (eLORETA) (Pascual-Marqui, et al, 2011), in keeping with the literature (Cuspineda, et al, 2009;Neuner, et al, 2014;Pascual-Marqui, et al, 2011).…”

The Default Mode Network and EEG Regional Spectral Power: A Simultaneous fMRI-EEG Study

“…We consider the source localisation approach as adequate due to the fact that there was a clear occipital source of the alpha-band during eyes closed resting state [53], also suggesting that the artefact correction of the EEG data permitted a successful application of LORETA (Figure 2). …”

“…Time courses of EEG activity within these ROIs were exported as mean activity and used as covariants in the analysis of the fMRI data. In order to give more validity to the approach, an additional source localisation analysis of the alpha-band oscillations (7.5–12 Hz) was performed using LORETA in search of an occipital source for these oscillations [53].…”

Persistent Vegetative and Minimally Conscious States

“…In some of them, only the primary cortical components Nl and/or P2 were reliably proven, but more complex cortical responses were also present in their patients. Hence, the results reported by Kotchoubey and other authors indicating a high frequency of responses in association cortical areas in patients with PVS should be taken into consideration for future research, because these neurophysiological techniques are capable of providing earlier and different brain functioning signs compared to fMRI, PET and SPECT 721, 48,163,165,167,168,195,1967. Kotchoubey and his group argued that their results, indicating a high frequency of cortical responses in patients with PVS, might be due to an indication of possible diagnostic errors, or as evidence that isolated thalamo-cortical circuits may be working in patients with PVS, indicating spared function of some specialized processing modules, although this process is unrelated to conscious experience 716, 44,80,118,121-124,128,179,2187. Nonetheless, it is important to consider the time and space resolutions in assessing brain function comparing neurophysiological with other neuroimaging methods.…”