Cortical and Subcortical Correlates of Electroencephalographic Alpha Rhythm Modulation

Abstract

Neural correlates of electroencephalographic (EEG) alpha rhythm are poorly understood. Here, we related EEG alpha rhythm in awake humans to blood-oxygen-level-dependent (BOLD) signal change determined by functional magnetic resonance imaging (fMRI). Topographical EEG was recorded simultaneously with fMRI during an open versus closed eyes and an auditory stimulation versus silence condition. EEG was separated into spatial components of maximal temporal independence using independent component analysis. Alpha component amplitudes and stimulus conditions served as general linear model regressors of the fMRI signal time course. In both paradigms, EEG alpha component amplitudes were associated with BOLD signal decreases in occipital areas, but not in thalamus, when a standard BOLD response curve (maximum effect at approximately 6 s) was assumed. The part of the alpha regressor independent of the protocol condition, however, revealed significant positive thalamic and mesencephalic correlations with a mean time delay of approximately 2.5 s between EEG and BOLD signals. The inverse relationship between EEG alpha amplitude and BOLD signals in primary and secondary visual areas suggests that widespread thalamocortical synchronization is associated with decreased brain metabolism. While the temporal relationship of this association is consistent with metabolic changes occurring simultaneously with changes in the alpha rhythm, sites in the medial thalamus and in the anterior midbrain were found to correlate with short time lag. Assuming a canonical hemodynamic response function, this finding is indicative of activity preceding the actual EEG change by some seconds.

Neurophysiologic correlates of fMRI in human motor cortex

“…Low frequency sensorimotor rhythms have been associated with reciprocal thalamic and basal ganglia projections to cortex [Brown, 2003;Feige et al, 2005;Pfurtscheller and Lopes da Silva, 1999;Schnitzler et al, 2006]. Assuming that these low frequency rhythms reflect inhibition of a cortical region [Mazaheri et al, 2009], the decrease in power that we measure in a and b1 may reflect a disinhibition or preparation of cortical structures.…”

“…Power decreases in low frequency sensorimotor rhythms are distributed over larger areas of cortex [Crone et al, 1998b;Miller et al, 2007]. These spectral changes are associated with different processes: broadband power change is associated with local neuronal processing [Manning et al, 2009;Miller et al, 2009a], whereas low frequency oscillations reflect an aspect of subcortical-cortical interaction [Brown, 2003;Feige et al, 2005;Pfurtscheller and Lopes da Silva, 1999;Schnitzler et al, 2006]. Functional MRI BOLD change has also been compared with electrocortial stimulation mapping, and has been shown to be adequately sensitive but less specific in predicting electrocortical stimulation sites [Pouratian et al, 2002;Rutten et al, 2002].…”

Frontal theta EEG activity correlates negatively with the default mode network in resting state

“…More recently, simultaneous EEG/ fMRI has been successfully applied to investigate cognitive phenomena such as performance monitoring (Debener et al, 2005) and sustained attention (Eichele et al, 2005). Apart from epilepsy research most studies have focused on the BOLD correlates of ongoing oscillatory activity during resting state (i.e., recorded while the subject was quietly lying in the scanner, with no explicit task), focusing on the posterior alpha rhythm and, to a lesser extent, the beta rhythm (Feige et al, 2005;Goldman et al, 2002;Goncalves et al, 2006;Laufs et al, 2006Laufs et al, , 2003aMoosmann et al, 2003). In these studies, the general idea has been that spontaneous fluctuations in the amplitude of a given oscillatory signal can be correlated with spontaneous fluctuations in the BOLD signal.…”

“…Studies investigating the BOLD correlates of spontaneous fluctuations in alpha activity (Feige et al, 2005;Goldman et al, 2002;Goncalves et al, 2006;Laufs et al, 2006Laufs et al, , 2003aMoosmann et al, 2003) have shown that the expected posterior visual regions and also other regions across the cortex are negatively correlated with posterior alpha fluctuations. Recent findings suggest that there is considerable individual variation in areas that correlate with the alpha fluctuations and that these can be linked to differences in the total power spectrum of an individual (Goncalves et al, 2006;Laufs et al, 2006).…”

An EEG (electroencephalogram) recording system with carbon wire electrodes for simultaneous EEG-fMRI (functional magnetic resonance imaging) recording

“…EEGfMRI recording has been used for localizing epileptic spikes (Warach et al, 1996;Seeck et al, 1998;Krakow et al, 1999;Goldman et al, 2000;Baudewig et al, 2001;Lemieux et al, 2001;Salek-Haddadi et al, 2002;Sommer et al, 2003), determining sources of event related potentials (Bonmassar et al, 1999;Kruggel et al, 2000;Liebenthal et al, 2003;Sommer et al, 2003), or correlating brain rhythms with hemodynamic activities (Goldman et al 2002, Laufs et al 2003, Moosmann et al 2003, Feige et al 2005, de Munck et al 2007). …”