Resting state cortical electroencephalographic rhythms are related to gray matter volume in subjects with mild cognitive impairment and Alzheimer's disease

Abstract

Cortical gray matter volume and resting state cortical electroencephalographic rhythms are typically abnormal in subjects with amnesic mild cognitive impairment (MCI) and Alzheimer's disease (AD). Here we tested the hypothesis that in amnesic MCI and AD subjects, abnormalities of EEG rhythms are a functional reflection of cortical atrophy across the disease. Eyes-closed resting state EEG data were recorded in 57 healthy elderly (Nold), 102 amnesic MCI, and 108 AD patients. Cortical gray matter volume was indexed by magnetic resonance imaging recorded in the MCI and AD subjects according to Alzheimer's disease neuroimaging initiative project (http://www.adni-info.org/). EEG rhythms of interest were delta (2-4 Hz), theta (4-8 Hz), alpha1 (8-10.5 Hz), alpha2 (10.5-13 Hz), beta1 (13-20 Hz), beta2 (20-30 Hz), and gamma (30-40 Hz). These rhythms were indexed by LORETA. Compared with the Nold, the MCI showed a decrease in amplitude of alpha 1 sources. With respect to the Nold and MCI, the AD showed an amplitude increase of delta sources, along with a strong amplitude reduction of alpha 1 sources. In the MCI and AD subjects as a whole group, the lower the cortical gray matter volume, the higher the delta sources, the lower the alpha 1 sources. The better the score to cognitive tests the higher the gray matter volume, the lower the pathological delta sources, and the higher the alpha sources. These results suggest that in amnesic MCI and AD subjects, abnormalities of resting state cortical EEG rhythms are not epiphenomena but are strictly related to neurodegeneration (atrophy of cortical gray matter) and cognition.

Figure 1

Recording sites of the 19 scalp electrodes positioned according to the International 10–20 System (i.e., Fp1, Fp2, F7, F3, Fz, F4, F8, T3, C3, Cz, C4, T4, T5, P3, Pz, P4, T6, O1, and O2).

Figure 2

Grand average of LORETA solutions (i.e., normalized relative current density at the cortical voxels) modeling the distributed EEG sources for delta, theta, alpha 1, alpha 2, beta 1, beta 2, and gamma bands in Nold, MCI, AD groups. The left side of the maps (top view) corresponds to the left hemisphere. Legend: LORETA, low resolution brain electromagnetic tomography. Color scale: all power density estimates were scaled based on the averaged maximum value (i.e., alpha 1 power value of occipital region in Nold).

Figure 3

Statistical ANOVA interaction (F(60,7920) = 9.76; P < 0.0001) among the factors Group (Nold, MCI, AD), Band (delta, theta, alpha 1, alpha 2, beta 1, beta 2, gamma), and ROI (frontal, central, parietal, occipital, temporal, limbic).

Figure 4

Grand average of Global low resolution brain electromagnetic tomography (LORETA) solutions (i.e., relative power current density averaged across all cortical voxels ± standard error, SE) modeling the distributed cortical EEG sources for delta, theta, alpha 1, alpha 2, beta 1, beta 2, and gamma bands in normal elderly (Nold), amnesic mild cognitive impairment (MCI), and Alzheimer's disease (AD) subjects. The LORETA values refer to an ANOVA interaction (F(12,1542) = 13.87; P < 0.00001) between the factors Group (Nold, MCI, AD) and Band (delta, theta, alpha 1, alpha 2, beta 1, beta 2, and gamma). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

Figure 5

Scatterplots of LORETA solutions for the delta or alpha 1 rhythms and cortical gray matter volume values in the amnesic MCI (in red) and AD (in blue) subjects. For each group, the regression line is plotted in color. The regression line of the amnesic MCI and AD subjects considered as a whole group is plotted in black. Statistical values of linear correlation were obtained by Pearson test (P < 0.005). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]